Inguinal hernia repair: MedlinePlus Medical Encyclopedia
You Are Here:
Inguinal hernia repair
URL of this page: //medlineplus.gov/ency/article/007406.htm
To use the sharing features on this page, please enable JavaScript.
Inguinal hernia repair is surgery to repair a
in your groin. A hernia is tissue that bulges out of a weak spot in the abdominal wall. Your intestine may bulge out through this weakened area.
During surgery to repair the hernia, the bulging tissue is pushed back in. Your abdominal wall is strengthened and supported with sutures (stitches), and sometimes mesh. This repair can be done with open or laparoscopic surgery. You and your surgeon can discuss which type of surgery is right for you.Your surgeon will decide which kind of anesthesia you will receive: is medicine that keeps you asleep and pain-free., which numbs you from the waist to your feet..
In open surgery:
Your surgeon makes a cut near the hernia.The hernia is located and separated from the tissues around it. The hernia sac is removed or the hernia is gently pushed back into your abdomen.The surgeon then closes your weakened abdominal muscles with stitches.Often a piece of mesh is also sewn into place to strengthen your abdominal wall. This repairs the weakness in the wall of your abdomen.At the end of the repair, the cut is stitched closed.
In laparoscopic surgery:
The surgeon makes three to five small cuts in your lower belly.A medical device called a laparoscope is inserted through one of the cuts. The scope is a thin, lighted tube with a camera on the end. It lets the surgeon see inside your belly.A harmless gas is pumped into your belly to expand the space. This gives the surgeon more room to see and work.Other tools are inserted through the other cuts. The surgeon uses these tools to repair the hernia.The same repair will be done as the repair in open surgery.At the end of the repair, the scope and other tools are removed. The cuts are stitched closed.
Your doctor may suggest hernia surgery if you have pain or your hernia bothers you during your everyday activities. If the hernia is not causing you problems, you may not need surgery. However, these hernias most often do not go away on their own, and they may get larger.Sometimes the intestine can be trapped inside the hernia. This is called an incarcerated or strangulated hernia. It can cut off blood supply to the intestines. This can be life-threatening. If this happens, you would need emergency surgery.
Risks for anesthesia and surgery in general are:Reactions to medicines, blood clots, or infection Risks for this surgery are:Damage to other blood vessels or organsDamage to the nervesDamage to the testicles if a blood vessel connected to them is harmedLong-term pain in the cut areaReturn of the hernia
Tell your surgeon or nurse if:You are or could be pregnantYou are taking any medicines, including drugs, supplements, or herbs you bought without a prescription During the week before your surgery:You may be asked to stop taking blood thinning medicines. These include aspirin, ibuprofen (Advil, Motrin), clopidogrel (Plavix), warfarin (Coumadin), naprosyn (Aleve, Naproxen), and others.Ask your surgeon which drugs you should still take on the day of surgery. On the day of surgery:Follow instructions about when to stop eating and drinking.Take the medicines your surgeon told you to take with a small sip of water.Arrive at the hospital on time.
Most people are able to get out of bed an hour or so after this surgery. Most can go home the same day, but some may need to stay in the hospital overnight.Some men may have problems passing urine after hernia surgery. If you have problems urinating, you may need a catheter. This is a thin flexible tube that is inserted into your bladder for a short time to drain urine.Following instructions about how active you can be while recovering. This may include:Returning to light activities soon after going home, but avoiding strenuous activities and heavy lifting for a few weeks.Avoiding activities that can increase pressure in the groin and belly. Move slowly from a lying to a seated position. Avoiding sneezing or coughing forcefully.Drinking plenty of fluids and eating lots of fiber to prevent constipation.Follow any other
to help speed your recovery.
Outcome of this surgery is usually very good. In some people, the hernia returns.
H Hernioplasty - inguinal
Kuwada T, Stefanidis D. The management of inguinal hernia. In: Cameron JL, Cameron AM, eds. Current Surgical Therapy. 12th ed. Philadelphia, PA: E .Malangoni MA, Rosen MJ. Hernias. In: Townsend CM Jr, Beauchamp RD, Evers BM, Mattox KL, eds. Sabiston Textbook of Surgery: The Biological Basis of Modern Surgical Practice. 20th ed. Philadelphia, PA: E 2017:chap 44.
Updated by: Debra G. Wechter, MD, FACS, general surgery practice specializing in breast cancer, Virginia Mason Medical Center, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.目的探讨改进新式子宫下段剖宫产术脂肪层和皮肤缝合的优越性和可行性。
Objective To explore the practicality of fat and skin suture at cesarean section.
（治疗结果）差别存在于最小的不同，直到最后的皮肤缝合。
The little details, to the tail of the last skin suture, are what make the difference.
方法 ：用改良式缝皮法对2 00例腹式横切口皮肤缝合。
Methods:Modified skin suture was used in 200 cases of transverse incision of abdominal section.
在这里我们报告两例开放性距骨全脱臼，治疗是以即刻的清创，距骨复位和皮肤缝合，然后用石膏固定。
Herein we report two cases of open total talar dislocation. Immediate debridement, reduction of the talus, and primary skin closure was done followed by cast immobilization.
这种引流管易操作、引流可靠、不需皮肤缝合固定、患者受痛少。
The utility model has the advantages of easy operation, reliable drainage and light pains of patients without need of closure or fixation of skin.
方法：采用横切口，将内眦韧带固定于鼻背筋膜，切除上下方多余皮肤后缝合。
Methods Canthoplasties were performed by cutting canthus in a crosscut and fix the medial cantho-ligament to the nasal dorsal fascia.
方法：假手术组仅切开颈部皮肤后缝合切口。
METHODS: In sham operation group, an incision was made on rats' cervical skin and sutured.
这张电子皮肤正在缝合。
This skin is being stitched together.
最后缝合皮肤。
At last the skin is sutured.
在改良技术中，“结肠切缘直接与皮肤进行缝合，而不与筋膜和壁腹膜进行缝合”。
In their modified technique, "the cut edges of the colon were sutured to the skin…without fascial or peritoneal sutures."
目的探讨妇科微创开腹手术及皮肤美容缝合在附件手术中的优点及临床应用。
Objective To study the advantages and clinic application of gynaecology minimally invasion and skin hairdressing stich in the accessories operation .
腹腔注射4%水合氯醛麻醉下，暴露左侧舌下神经，剪断后缝合皮肤。
The left hypoglossal nerve of the mouse was cut under 4% chloral hydrate anesthesia, and then the skin was sutured.
皮肤皱缩缝合；
Skin wrinkling suture;
最后将皮肤重新缝合到本位。
Finally, the skin is redraped over the new framework.
结论在缝合肥胖者的腹部切口时，贯穿缝合皮肤及浅层皮下脂肪同时加引流条引流的方法是一种有效的预防脂肪液化的缝合方法。
Conclusion The suture of only superficial subcutaneous fat as well as putting rubber drainages in the abdominal incision is a simple and effective way to prevent lipoliquefaction for obese patients.
目的为临床寻找实用、可行的最佳剖宫产皮肤切口缝合方式。
Evaluation of wound healing with different wound closure methods in cesarean. ;
经过数小时的手术后，医生们接好了血管、固定了手臂的骨头、缝合了皮肤和肌肉。
After hours of surgery the doctors reconnected the blood vessels, pinned the arm bone together, and grafted skin and muscle together.
把近端2/3的尿道海绵体部缝合到皮肤上，远程的部份切断。
Suture the proximal 2/3rds of the penile urethra to the skin;
目的：观察与评价小切口、皮肤作皮内缝合阑尾切除术的效果；
Objective: To observe and comment on the effect of appendectomy with intradermic suture in a small incision.
方法采用分层对位缝合和“Z”或“W”成形术缝合，皮肤用皮内连续缝合法。
Methods Using lamination oversew and "Z" or "W" plastic surgery and intracutaneous continued suture in skin.
目的：探讨额颞部除皱术治疗额颞部皮肤老化的缝合方法及临床效果。
Objective To study a new method of incision closure in forehead and temporal rhytidectomy.
用钛镍记忆合金组织吻合器（皮内吻合器）缝合非直线状的皮肤伤口与缝合直线状伤口的缝合方法是完全相同的。
How to apply Ni-Ti shape memory alloy tissue anastomat to non-straight incisions?A: There is no difference in applying the anastomat to straight or non-straight incisions.
下睑基底细胞癌。2。菱形皮瓣。3。菱形皮瓣转位缝合遮盖皮肤缺损区。4。术后效果。
Lower eyelid basal cell carcinoma. 2. Rhombic flap. 3. Rhombic flap sutured into the defect. 4. Postoperative result.
形缝合创面皮肤；
Suture the skin in "Z";
一种自我锚定的缝合线被设计用于皮肤组织伤口的缝合。
A new self-anchoring suture is designed for wound closure of dermal tissue.
无需外科手术式的大切口，只需在皮肤开个小切口，术后不须缝合。
No surgical incision is needed—only a small nick in the skin that does not have to be stitched closed.
将120只兔随机分为5组（每组24只）：假手术组：切开左侧面部皮肤，暴露面神经后缝合。
Stochastically divides into 5 groups 120 rabbits (each group of 24) False surgery group: Left side the incision the face skin, after exposes the facial nerve to suture.
股二头肌被缝合后，其他结构将自行回复原位，故仅需缝合皮下组织和皮肤。
After suturing the biceps, close the wound by suturing only the skin and subcutaneous tissue because the other structures fall into position.
股二头肌被缝合后，其他结构将自行回复原位，故仅需缝合皮下组织和皮肤。
After suturing the biceps, close the wound by suturing only the skin and subcutaneous tissue because the other structures fall into position.
$firstVoiceSent
- 来自原声例句
请问您想要如何调整此模块？
感谢您的反馈，我们会尽快进行适当修改！
请问您想要如何调整此模块？
感谢您的反馈，我们会尽快进行适当修改！【龙腾★各国】印度非法狗肉交易令国外网民震惊不已【龙腾网吧】_百度贴吧
&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&&签到排名：今日本吧第个签到，本吧因你更精彩，明天继续来努力！
本吧签到人数：0可签7级以上的吧50个
本月漏签0次！成为超级会员，赠送8张补签卡连续签到：天&&累计签到：天超级会员单次开通12个月以上，赠送连续签到卡3张
关注：17,802贴子：
【龙腾★各国】印度非法狗肉交易令国外网民震惊不已
译者：unknown
译文摘要:比起印度人，他们更像是中国人。他们绝对不是印度教徒译文来源:原文地址：【dailymail.co.uk/news/】正文翻译:Horrifying footage has emerged unveiling the cruel underground dog trade in India where pets' mouths are stitched closed before they are clubbed to death. 恐怖的画面揭示了印度残忍的地下狗交易，这些宠物狗的嘴巴被缝绑住，之后殴打致死。 The chilling video was shot in a dog meat death pit in Kohima where canines were beaten with wooden sticks and killed in front of each other for their meat. 这个令人心寒的视频是在科希马的一个狗肉屠宰场拍到的，狗狗们被木棍活活打死。 It's thought more than 30000 dogs are killed by smugglers - who stitch their lips together to keep them quiet during transport - every year in Nagaland India alone.
人们认为仅在印度的那加拉邦每年就有超过30000只狗被走私者屠杀。这些走私者将狗狗的嘴巴绑起来，以使它们在运输途中能保持安静。 The footage was taken by Humane Society International in India (HSI/India) at local markets in Kohima and Dimapur. 这些画面由印度的国际人道组织在科希马和迪马普尔的当地市场拍到的。 It shows dogs packed in sacks with just their heads poking out their mouth either stitched closed or bound tight with rope to keep them quiet so that they can be illegally smuggles into Nagaland from neighbouring states. 画面显示这些狗被装在麻袋里，只露出脑袋，嘴巴要么被缝上，用么用绳子绑住以保持安静，这样它们就可以从邻国非法走私到那加拉邦。 During transport and display in the markets they are denied movement food or water before finally being clubbed to death.
在狗狗们最终被殴打致死前，无论是在运输过程中，还是在市场展示时，都未给它们提供过任何食物和水。
龙腾持基金销售牌照,专注投资理财11年,超过12000只私募基金,明星基金经理投资分析风险低,收益高,私募基金投资就是好买基金网,
评论翻译:Devongazza
This is so heartbreaking. I hope these people get the same treatment when they die. And I hope it is also a slow painful death. Rot in hell dog killers. 简直令人心碎！我希望这些人在死后也遭受如此待遇。希望他们同样经历一场缓慢而痛苦的死亡。在地狱中腐烂吧这些屠狗者。 FROZEN
Ohhhhh my heart is aching I only scrolled quickly .The look on their little poor faces is heart-rending. 噢噢噢噢我的心太痛了我只好快速下翻。狗狗那小可怜的表情令人心碎。 justjill
Sick behaviour and they don't even know it. 病态行为！可他们甚至不知道！
点亮12星座印记,
JBUSA These disgusting capabilities are in all of us. Would they starve otherwise? 这种恶心的能力我们都有，否则他们要挨饿？ Just So ... We live in a v very sick world... I am deeply ashamed ope（可能是ape what is done to defenceless animals with no voice no care and no hope... Today another nail in an already broken heart!!! I hit for them yet I am ashamed to say this for in my life I will never know this fear!!! I am sorry!!! 我们生活在一个邪恶的世界，对动物做这样的事情，他们不能发声，没能得到照顾，没有希望，让我非常沉重的羞愧。今天的新闻让我破损的心再一次受到伤害。 我感同身受，然而我也羞于这么说，因为这种事情不可能发生在我身上！！！非常抱歉！！！ M3lody Stop this!!!!! its hurts me?? all the sweet dogs&cats all animals deserve to live... with all the love and care?? 住手 ！这伤害了我？所有这些可爱的猫猫狗狗这些动物应该活在这样的关爱下吗？ Dennis Opihory so u think people taking the video would do something? 那么你以为拍这视频的人会有所作为吗？ LordPete Seems like Nagaland is more like &outland.& They obviously want the advantages of being part of India without having to follow Indian law. 那加兰邦[印度邦名]看起来更像外国。他们明显想要作为印度一部分的好处而不去遵守印度法律。
点亮12星座印记,
sp. go and vote on the humane society page. messaging chains are being formed in india by animal lovers and owners. please do your part too and stop this mass slaughtering. 去人道社会网页投票去。由动物主和动物爱好者发送的链接在印度正在形成，请你们也尽一份力同时阻止大屠杀。 ZA Absolutely savage. 简直就是野蛮人。 MrBeanBean We send aid to them why? 为什么我们要给予他们帮助？ orlandofl OK. I am not against people eating whatever animals they choose...To me the eating of a cow or pig or chicken is the same as the eating of a dog or cat or horse...... Although I eat the first three and have only once accidentally eaten horsemeat it is not the eating of the animal that disgust me it is in the way they are treated before being slaughtered and the actual process of slaughtering them that worries me....If people want to kill animals for food fair enough but please do not let them endure both painful and terrifying deaths. orlandofl 好吧，我不反对人们吃任何动物，这是他们的选择(决定)····对于我来说吃牛.猪.鸡和吃狗.猫.马.是一样的，虽然我只吃前三种(指牛.猪.鸡)只有一次不小心吃了马肉恶心到我了，让我厌恶(讨厌)的是他们在屠宰动物前对待它们的方式和屠宰他们的工艺····如果有人想杀死食物，这没问题(公平)，但请不要让它们在承受痛苦中死去(意指虐杀) donna edwards stay away from my dog donna edwards 离我的狗远一点
点亮12星座印记,
MarkRees -& kirsun Oh for goodness sake even INDIA ITSELF has made this illegal INDIA ITSELF! Read the article before screaming paranoia and racial intolerance! 噢看在上帝的面上，印度也将这样的虐狗行为定义为非法的！ 在尖叫偏执狂和种族排外之前赶紧读完这篇文章。 Izzy23 This happens in so many places and we all say we need to stop it now but nothing ever changes. I am appalled by this behaviour and wish I could rescue each and every one. We have to do more and do it now............It is just barbaric and there is no sense of wrongness which is why they will not change their ways. How do we fight this? 在这么多地方发生这种残忍的事， 我们总是说我们需要阻止它，但现在没有任何变化。我对这种行为很震惊，我希望能够拯救出每一只狗狗。我们需要做得更多，并且现在就着手。这种事情是野蛮的，没有意义，完全错误的，为什么他们就不能改变方式呢？我们应当如何对抗？ Sally.S -& Izzy23 You can write to their Embassy and attend protests it's the only way one day we will make them take notice. 你可以写信给他们的大使馆，参加抗议活动，这是唯一的方法，总有一天我们会引起他们注意的。 Dominic Fastbender Second most vile place on earth. 地球上第二恶劣的地方。
点亮12星座印记,
爱狗人士呢？怎么不敢去印度闹了？
。。。。。。
Dominic Fastbender Second most vile place on earth. 地球上第二恶劣的地方。那么第一恶劣的地方是哪儿？
觉得这些西方国家的人简直就是吃饱了没事干
权利和义务是对等的，口口声声说动物和人一样，结果犀牛顶死了人，狒狒挠死了人，大象撞死了人的时候却又拿着他们是动物这种借口来给动物开脱，这时候怎么不谈平等了？当弱势群体变成了弱智群体，还谈什么公平
网页速度,品味,量身定做..我们只做好网站,设计师一对一服务,为您提供优质服务!深圳网络公司欢迎垂询!
看来外国人都不知道南北棒子才是是狗肉大国
(⊙o⊙)…还是猪最可怜……被人类吃了那么久，也没人站出来为他们说过话
中国人貌似躺枪了
贴吧热议榜
使用签名档&&
保存至快速回贴Thank you for visiting nature.com. You are using a browser version with
limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off
compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site
without styles and JavaScript.
AbstractTracking odour trails is a crucial behaviour for many animals, often leading to food, mates or away from danger. It is an excellent example of active sampling, where the animal itself controls how to sense the environment. Here we show that rats can track odour trails accurately with near-optimal sampling. We trained rats to follow odour trails drawn on paper spooled through a treadmill. By recording local field potentials (LFPs) from the olfactory bulb, and sniffing rates, we find that sniffing but not LFPs differ between tracking and non-tracking conditions. Rats can track odours within ~1 cm, and this accuracy is degraded when one nostril is closed. Moreover, they show path prediction on encountering a fork, wide 'casting' sweeps on encountering a gap and detection of reappearance of the trail in 1–2 sniffs. We suggest that rats use a multi-layered strategy, and achieve efficient sampling and high accuracy in this complex task.
IntroductionThe ability of animals to track odour trails is well known but sparingly studied,,,,,. Fundamental issues regarding the behavioural and neural mechanisms of this ethologically important behaviour remain poorly understood. These include the possible use of stereo odour sampling, active sampling strategies, and whether neural correlates seen in constrained tasks are present in this more natural behaviour.Rodents are primarily olfactory animals with robust and versatile olfactory learning abilities. However, odour trail tracking in rodents has not been thoroughly studied in the lab. In studies on other animals, a few common themes have emerged. First, as shown clearly by moths, insects often combine zigzagging through an odour plume while approaching its source and wide 'casting' movements to search for the trail whenever they lose it,. The zigzagging approach has been observed in several other animals including bees, cockroaches, dogs and humans,,,. Second, the use of stereo olfaction in efficiently performing this task has been repeatedly suggested. Disrupting bilateral input affects tracking in bees, drosophila larvae, and humans.This behaviour represents a good example of active sensory sampling, where the animal itself modulates when and where it receives sensory input in order to get a better picture of its environment. Here, we describe the development of an experimental system where rats were trained to follow trails of different odours. We show that odour trail tracking employs a multi-layered strategy utilizing near-optimal sampling and path prediction, and develop a model that captures many aspects of this strategy. Further, sniffing and local field potential (LFP) characteristics during this task differ from those seen in more constrained tasks.ResultsRats track various odour trails accuratelyWe trained nine female Wistar rats to track odour trails (see Methods). We built a treadmill that used a 38 cm wide and 3 m long looped sheet of paper as its belt on which the rats ran (). A meandering odour trail was drawn on this paper. The trail was either a pure odourous liquid deposited at a fixed rate on the paper, and was uniformly 3 mm wide (), or a chocolate trail where a piece of chocolate was rubbed manually and uniformly on the paper, and was again about 3 mm wide. The liquid odours were L-carveol (LC, spearmint odour) and phenethyl alcohol (PEA, rose odour). These odours were relatively less volatile and were smelled distinctly by the experimenter only when the nose was directly above the trail. Thus by studying 'surface-borne' odour trail tracking, we have circumvented the difficult problem of studying air-borne odour plumes with animals moving through them.Figure 1: Rats can track odour trails on a treadmill.(a) A schematic of the apparatus. Above, a side view of the treadmill showing camera position. Below, top view showing the trail in blue. (b) An example of a stretch of tracking. The rat's nose trajectory (red) is overlaid on the trail (blue) in this and subsequent figures. The rat always moves from the bottom to the top. Note that the x and y scaling in this and subsequent such plots are not always equal. (c) An example where after pausing to eat a chocolate piece (arrowhead), the rat resumed tracking by making wide casting movements to first find the trail. The trails in b and c were chocolate in light and LC in the dark, respectively. (d) The mean deviation of the nose from the trail compared between 12 and 30 days post initiation of training was significantly reduced, *P & 10-4 (two-tailed t-test, P=2.3×10-5, n=21 stretches from four rats and n=19 stretches from four rats, respectively, chocolate trail in light, 12 cm s-1 speed). (e) Mean deviations across different trail conditions is constant (analysis of variance, P=0.15, mean deviation=13.8, 14.3, 13.9, 12.0 and 14.0 mm, n=36, 30, 29, 28 and 22 stretches, respectively, and all with four rats except chocolate in light, three rats, all 15 cm s-1 speed). (f) Mean deviation at three different treadmill speeds and for two different trails. There was a significant difference only between the 19 cm s-1 case and the other two lower speeds for LC in dark trail (analysis of variance followed by a multiple comparison procedure, P=0.0048).As the treadmill moved, we occasionally placed small pieces of chocolate on the trail. The rats soon learnt to track the odour trail to find the chocolate. All the rats tracked the trail by moving their noses over the trail in a zigzag fashion, similar to the reports for other species,,, ( and ). They were able to track all the different types of trails closely and were capable of following turns, often correcting their path very rapidly. On losing the trail, rats sometimes made wide sweeping movements (), akin to the casting behaviour observed in moths, when they have lost a scent trail. It also appears that the nose zigzagging movement is not generated by only a neck-onwards movement, but by involving the entire body ().In order to characterize the tracking behaviour of rats, we measured the average absolute horizontal distance of the nose from the trail in different stretches of tracking (a 'stretch' and its deviation from the trail are defined in ). This mean deviation, or accuracy of tracking, was compared across different conditions.We first checked if rats displayed learning over time. The mean deviation from the trail decreases significantly from 12 days to 30 days after initiating training (). This suggests that this behaviour has a learning component to it. We next studied different types of odour trails. The three substances used for our trails, LC, PEA and chocolate, are clearly distinct odours. In addition, the chocolate trail is different because it leaves a texture of deposited chocolate behind, as opposed to the textureless LC and PEA trails. Further, we also considered the contribution of visual information, by comparing tracking in the light and dark. We thus studied five different trail conditions. Interestingly, all these conditions showed the same level of accuracy (). As the LC and PEA in dark are purely odour trails, this suggests that the other trails are also tracked primarily using odour cues. Further, rats were unable to track an odourless line drawn by pencil in light (), suggesting that they do not rely on visual cues.Last, we studied different treadmill speeds. There is an increase in the deviation with increasing speeds for both trails studied (). This may be because the trail can veer away from the rat rapidly at higher speeds, and wider nose swings reduce the chance of thus losing the trail. Though deviation consistently increased with speed, there was a significant difference only between the 19 cm s-1 case and the other two lower speeds for the LC in dark trail.Stereo olfaction improves accuracy of trackingRats have been shown to have stereo olfaction, the ability to localize an odour by comparing the signals across nostrils. Similar abilities have been demonstrated in other animals,,,. It is not known if rats use this ability in the context of tracking odour trails. We tested this by stitching closed one nostril in each of three rats to disrupt bilateral odour sampling. These same rats earlier underwent a sham surgery in which the stitch did not close the nostril. We found that the unilaterally sensing rats were still able to follow odour trails, but they needed to make larger movements over the trail compared with sham controls ( and ). The PEA trail was made of approximately double intensity for both sham and stitched cases to compensate for the reduction in the amount of odour reaching the rat when stitched. The deviation from the trail for the stitched rats in both PEA and chocolate trails in dark was significantly higher than sham (). Though the complexity of this behaviour makes it difficult to rule out other effects of closing one nostril, we nevertheless suggest that the loss of stereo sampling is a likely factor in this degradation of performance and that stereo sampling may contribute to efficient performance in natural odour tracking.Figure 2: Nostril stitching reduces tracking accuracy.(a) An example with a sham stitch. (b) An example of the same rat with the right nostril stitched closed (chocolate trail in dark, 19 cm s-1 speed). (c,d) Box plots showing that the median deviation from the trail for the stitched case was significantly higher than sham for both a PEA trail of double intensity (c) and chocolate trail (d), *P & 10-3 . Two-tailed Wilcoxon rank-sum test, P=1.56×10-4, n=25 and 17 stretches for PEA sham and stitched, respectively, P=5.95×10-5, n=34 and 27 stretches for chocolate sham and stitched, respectively, 19 cm s-1 speed, all with three rats. On box plots here and later, the central mark is the median, the edges of the box are the 25th and 75th percentiles, the whiskers extend to the most extreme data points not considered outliers, and outliers are red crosses.Sniffing is modulated during trackingWe next utilized the tracking task in conjunction with two physiological measurements. We implanted a thermocouple (TC) in the rat's nasal cavity to monitor the sniffing (five rats), and a LFP electrode in the olfactory bulb (OB) to monitor neural activity (four rats). Example traces of the voltage signals from both are shown in . An example plot of the sniffing frequency over time shows that the sniffing frequency varied very rapidly from sniff to sniff (). Interestingly, sniffing frequencies were higher and less variable during tracking (black bar in ). This can also be seen in an example trace with the sniffing frequency overlaid on the nose trajectory in colour code (). In
we summarize the sniffing frequencies during different behaviours at 19 cm s-1 treadmill speed. This and subsequent data are pooled data from chocolate and PEA trails in dark, unless specified, as they showed no differences. Sniffing frequencies were significantly higher during tracking (11.1±1.7 Hz,), than non-tracking (10.4±2.3 Hz), and were further significantly lower when the treadmill was stationary (8.6±2.4 Hz; during stationary periods, the rat was typically exploring the walls of the box). Sniffing frequency during tracking at a slower 15 cm s-1 speed (10.9±1.9 Hz) was slightly but significantly lower than that at 19 cm s-1, but still significantly higher than non-tracking periods (). In general, the sniffing behaviour observed here is highly dynamic,. Interestingly, the frequencies observed during odour tracking are much higher than the ~8 Hz observed during odour-based discriminations in more-controlled odour sampling tasks in rats,. This higher 11–12-Hz sniffing has been observed in these previous studies but it occurred only during the period of reward anticipation.Figure 3: Modulation of sniffing during tracking.(a) Example traces of simultaneously recorded sniffing through a thermocouple (TC, black trace) and local field potential signals from the OB (LFP, red trace). (b) Example trace of sniffing frequency over time, calculated at each sniff. Black bar indicates tracking period. (c) An example stretch with the sniffing frequency overlaid on the nose trajectory in colour code. The rat is tracking from about 400 to 1200 mm. Chocolate trail in dark, speed 15 cm s-1. (d) Sniffing frequency histograms of tracking (red) and non-tracking periods (green) at 19 cm s-1 (53 stretches each), and with the treadmill stationary (blue, 11 cases). The three distributions are all significantly different (Kruskal Wallis test and multiple comparison procedure, P&10-7). (e) Scatter plot of the sniffing frequency versus the distance from the trail at the time of that sniff. 57 stretches, Pearson's correlation=-0.04.We tested if the sniffing frequency is modulated by how far the rat's nose is from the trail. We found no such correlation (). The correlation coefficient was -0.04 and was not significantly different from 0 (Pearson's correlation, P=0.098). We also plotted sniffing frequency versus nose oscillation phase, or half of one complete zigzag of the nose across the odour trail. This too showed no significant modulation (). Further, the sniffing frequency was also not correlated with the nose velocity ().LFP oscillations are dynamic and uncorrelated with sniffingWe measured the LFP from the OB simultaneously with sniffing in four rats. The raw LFP traces (, bottom) showed transient oscillations at a range of frequencies. We studied the frequency bands of theta (4–12 Hz), beta (14–44 Hz) and gamma (60–90 Hz) in further detail. shows the power of theta oscillations colour coded on the rat's nose trajectory. Theta oscillations typically varied rapidly over time (). We compared theta power between the stationary treadmill case, the rat tracking case and the case of the rat not tracking but running on the treadmill (, left). There was no significant difference between stationary, tracking and not tracking conditions. We also looked at the gamma and beta oscillations across these three conditions and found no significant difference between them (, ).Figure 4: Modulation of OB LFP during tracking.(a) An example stretch of tracking with the LFP theta (4–12 Hz) power overlaid on the nose trajectory in colour code. Chocolate trail in dark, 19 cm s-1. (b) Box plots showing that there is no significant difference between tracking and not tracking periods and stationary treadmill periods for theta power (left, Kruskal Wallis test, P=0.10) or gamma power (right, Kruskal Wallis test P=0.97, n=47 stretches in both tracking and not tracking, n=9 for stationary condition). (c) Scatter plot of the LFP theta power (calculated at 128 ms intervals) versus the distance of the nose from the trail. 47 stretches, Pearson's correlation=-0.02. (d) The thermocouple signal (black, TC) and LFP signal (red, LFP) show transient high correlations (blue, Corr.). Both TC and LFP are filtered through a 30 Hz low-pass filter. The correlation is calculated in a 200 ms sliding window. The dotted lines show 0 and ±1 correlation. Solid horizontal line shows a period of theta oscillations with high correlation. Dashed horizontal line shows a period of theta but low correlation. (e) Histograms of correlation coefficients of the TC and LFP signals during tracking (red) and non-tracking (green) periods. The two distributions are not significantly different (47 stretches, two-tailed t-test, P=0.84).We tested if the LFP oscillations were modulated by how far the nose was from the trail. Such modulation would be expected if there was a significant odour-driven oscillation when the nose was directly above the trail. To test this, we plotted the LFP theta power versus the distance from the trail (). The correlation was -0.02 and was not significantly different from 0 (Pearson's correlation, P=0.13). This result was the same for the gamma and beta oscillations as well (). Together, these data suggest that the LFP oscillations in the OB are not strongly modulated by the tracking behaviour or the olfactory input during this task.The OB LFP oscillations have been considered to be highly correlated with the animal's respiration or sniffing,,. However, it has been shown in the rat whisker system that though the whisking frequency and hippocampal theta oscillations have the same frequencies, they are not synchronous. We similarly determined the extent of correlation between the TC and LFP signals. We first calculated the correlation between the raw TC and LFP electrode signals in a 200-ms sliding window. The sniffing and LFP signals showed transient periods of high correlations (example trace in , solid horizontal line shows the period of high correlation). However, we could not find any consistent behavioural correlate of these short high-correlation stretches. Further, there were other periods with LFP oscillations of similar frequency as sniffing, which showed no correlation with it (dashed horizontal line).We then calculated the average correlation between the two signals for each stretch of tracking. We did the same for equivalent stretches where the rat was not tracking. The histograms of the values of these correlations are shown in
(47 stretches each). The values were low, with the mean for tracking periods being 0.007 and for non-tracking periods being 0.004. Further, the two distributions were not significantly different. Overall, we find no correlations between sniffing and LFP under any of our behavioural contexts.Rats scan gaps widely and predict bifurcation trail directionIn order to better understand the strategies rats use to follow these trails, we presented them with two variations of the simple trail-tracking task. In the first case there was a gap in the trail. All the six rats tested in this condition showed a strong tendency to increase the width of their nose swings on encountering the gap.
shows three examples of this behaviour (see also ). In 62/77 or 80.5% of the cases, there was at least a doubling of the width of the nose swing on encountering the gap (). As soon as they re-encountered the trail, they resumed tracking with very little overshoot. Of all cases where tracking was resumed, 61% overshot by &15 mm (), which is comparable to the average distance from the trail during normal tracking. Further, in 67% of cases it took &120 ms to reverse the movement of the nose on re-encountering the trail. Given that these rats sniff at ~11 Hz, this suggests that they make this decision in one to two sniffs. Thus, wide casting behaviour is a reliable fallback strategy on losing the trail, and the rat can very rapidly return to on-trail tracking when it finds the trail.Figure 5: Trails with gaps and bifurcations.(a) Examples of encountering a gap in the trail. The rats increased the amplitude of their nose swings. The gap was 23 cm wide on a chocolate trail in dark and speed was 15 cm s-1 in all three. (b) Pie chart showing that in 62/77 or 80.5% of the cases there was at least a doubling in the swing amplitudes on encountering the gap. (c) Histogram of the distance of overshoot on the first pass on the trail on resuming tracking after the gap. Dotted line indicates the 15 mm limit, which included 61% of the cases. (d) Box plots comparing the gap period and an equal duration period just preceding the gap. Plots show the sniffing frequency (19 stretches, four rats), nose velocity (47 stretches, five rats), LFP theta oscillations (14 stretches, three rats) and LFP gamma oscillations (14 stretches, three rats). Only the nose velocity was significantly increased during the gap period (two-tailed Wilcoxon rank-sum test, P=0.002 for nose velocity, P&0.05 for the rest, all with 19 cm s-1 speed). (e) Examples of encountering a bifurcation in the trail. The rat could choose one of the arms of the bifurcation (left, chocolate trail in dark, 15 cm s-1) or neither and go though the centre (centre, chocolate trail, 19 cm s-1). If one of the arms of the bifurcation was going in roughly the same direction as the approaching stretch ('Straight Arm'), the rats preferred that arm (right, chocolate trail, 19 cm s-1). (f) Pie charts show the distribution of behaviours observed for symmetrical bifurcations (above) and asymmetrical bifurcations (below).We also recorded sniffing and LFP while the rats performed the gap task. We calculated the average sniffing frequency, nose velocity, and theta and gamma power in the LFP signal before and during the gap (). Of these, the nose velocity showed a significant increase during the gap due to the casting behaviour, while the remaining measures showed no difference.In another variation, we presented six rats with a bifurcation in the trail (, ). This bifurcation was either symmetrical ( left, centre) or asymmetrical, where one of the two arms continued in approximately the same direction, that is, the straight arm (, right). In each case, the rats either chose one of the two arms or went through the centre. The distributions among these behaviours are shown in . Interestingly, upon encountering an asymmetrical bifurcation, the rats had a strong preference to proceed along the arm that was going straighter (). This, and the tendency to continue straight through the centre in symmetrical bifurcations (), suggests that in our setup the trail-tracking strategy has a predictive component, where the rat expects the trail to continue in the same direction.Rats use a highly efficient gradient measurement strategyWe next asked how a rat might combine nose position and the sniffing times in its sampling strategy. We first checked if the combination of rate of sniffing and nose oscillations was optimized by some mathematical criterion. To do this, we plotted each sniff overlaid on the trajectory of the nose (), designating the time from the valley to the peak of the TC signal as inhalation and peak to next valley as exhalation. This plot shows that the rat typically sniffs multiple times in each cyclic sweep, or nose oscillation, across the odour trail. We took a subset of stretches, which had relatively consistent nose oscillations, and measured the number of sniffs per nose oscillation. The histogram of these values is shown in . The average is 5.7 sniffs per nose oscillation, or 2.85 sniffs each time the nose crosses the trail. This is close to the optimal Shannon–Nyquist sampling criterion of two samples per cycle (the Shannon–Nyquist theorem is a result from information theory that states that the rate of sampling a signal need be only twice its highest frequency in order to completely determine the signal). This number is constant for two different treadmill velocities tested (). Though it is unlikely that the rat is estimating an odour concentration time series in the rigorous sense of information theory, this result is none the less indicative of a highly efficient strategy. In fact, close to two sniffs per trail crossing suggests a comparison across only a pair of samples before making a decision to turn.Figure 6: Sampling strategies.(a) An example stretch of tracking showing each sniff overlaid on the nose trajectory. Black indicates inhalation and yellow exhalation. Multiple sniffs are taken during each nose oscillation. (b) Histogram of the number of sniffs per nose oscillation (33 stretches combining 15 and 19 cm s-1 cases). (c) A schematic of the nose crossing the trail showing the location of a turning point and the locations at which sniffs were taken. (d) Values of the difference in concentration detected on average between two consecutive sniffs (percentage of the maximum concentration, 34 stretches, t-test, *P&0.05). S-1 refers to the Sniff-1 in panel c and so on.This highly efficient tracking behaviour prompted us to look at the sampling strategy in further detail. We asked how many sniffs it takes going down a falling odour gradient before the rat decides to reverse direction. Here, we considered the nose turning point and the sniffs before and after it (). As we know the location of the nose at the time of each sniff, we can estimate the concentration of odour at each sniff if we know the concentration cross-section of the trail. As the rat's nostrils have added 'reach' on each side due to the air flow patterns, we chose the effective trail cross-section to be a Gaussian of s.d. 20 mm. The following results, however, are also valid for narrower and broader trails (7 mm to 50 mm). We calculated the average difference in odour concentration detected by the rat in the two sniffs just before it turned (S-1–S-2) and the two sniffs just before these (S-2 –S-3). These values are plotted in the first two bars in . The average difference detected just before a turn (S-1–S-2) was significantly different from zero (-9.9% of the maximum concentration). Interestingly, the difference between the two sniffs just preceding this (S-2–S-3) is not significantly different from zero (2.1%). Thus, on an average, the rat uses only a pair of sniffs to detect a drop in the concentration that prompts it to reverse its direction.The remaining two bars in
show the differences in concentration detected by later sniffs. The sniffs just before and after a turn do not detect a significant difference (mean difference 1.8%). The sniff pair just after this, however, does encounter a significant difference (mean difference 8.1%). Thus, on average, the rat uses just two sniffs to detect a rise in concentration when it moves towards the trail. Judging from the above results, it appears that rats indeed have a near-optimal sampling strategy.Rats do not favour 'off centre' edge trackingFor an animal tracking an odour trail, the rising and falling odour concentration at the edges of the trail contains more information than the centre of the trail. Using this logic, a recent study has predicted that the zigzagging of a rat's nose should be centred on the edge of the trail and not on its centre, similar to bats directing their ultrasonic clicks on the edges of objects instead of directly at them.We tested this prediction by measuring the mean of the rat's nose trajectory with respect to the trail. With the narrow trails studied so far, we found many stretches where the nose was not centred on the trail, but consistently to one side (). We plotted the mean of the nose and its error for four rats that tracked a trail of LC in the dark (). Interestingly, all four rats showed a significantly rightward-shifted tracking trajectory (t-test, P&0.05). Data from other trails showed similar trends, including the nostril stitched case.Figure 7: Off-centre tracking and wide trails.(a) An example stretch of tracking of a chocolate trail (~3 mm wide) showing the nose trajectory centred to the right of the trail, yet consistently crossing the trail. (b) The average offsets from 3 mm wide trails across 67 stretches for four rats (R1–R4) tracking an LC trail in the dark, all three speeds combined. Positive values indicate a bias to the right of the trail. All rats showed a significant rightward shift of the nose from the trail (t-test, *P&0.05, error bars represent s.e.m.). Similar effects were observed for all trails studied. (c) Two example stretches of rats tracking an extra-wide chocolate trail (45 mm wide). (d) Only 12% of the total tracking duration was classified as edge tracking. The rest of the time the rat appeared to utilize multiple different strategies (22 stretches, four rats, 19 cm s-1 speed).However, this is not proof of edge tracking, as the nose still crosses over to the other side of the trail consistently (). To test for edge tracking, we used a much wider trail (a 45 mm wide chocolate trail, with a step-shaped odour profile, ). Two examples of nose trajectories are shown in . These show a complex strategy that involved not only zigzagging on the trail edge but also zigzagging completely across the entire trail, and to a greater extent, moving inside the trail till hitting the edge and then turning. In fact, the percentage of edge tracking (locking onto and zigzagging across one edge) was only 12% (). Thus, although detecting the edges of a trail is critical to tracking, rats do not appear to do purely edge tracking.Quantitative model of path prediction and error estimatesWe developed a mathematical and computer model to test and refine our understanding of the rat odour tracking strategy. This model involved the rat's nose moving at a constant forward velocity and a constant x-velocity across the trail until deciding to turn. The model rat obtained noisy, discrete samples of the odour concentration and its gradient, akin to sniffing, at 11 Hz. It also maintained an estimate of where the trail was and an error in that estimate. It would turn around if one of the following happened: (a) it detected a large drop in odour concentration (comparing with previous sniff), (b) it detected a large downward gradient of odour (in that sniff) or c) it crossed beyond the trail error estimate. Details of the model are in the .We implemented this model in Matlab. The resulting computer simulations qualitatively resembled observed tracking behaviour well (). Specifically, it replicated the tracking of meandering trails (), an increase in the deviation from the trail when stereo sampling was lost ( inset), the casting behaviour upon encountering a gap () and choosing one arm in a bifurcation ( left), with a preference for the straight branch in asymmetrical bifurcations ( right, inset. Tracking continues down the straight arm in 70% of cases.).Figure 8: Model of tracking.(a) An example trace of a simulated nose trajectory tracking a meandering trail. The black dashed line is the rat's estimate of the position of the trail and the grey region indicates its estimate of the error in the trail position, that is, the limits of where it thinks the trail can be. The trail estimate can veer away from the true trail at turns, as in the real tracking cases. Inset: box plots showing that on removing odour gradient information from the model, similar to stitching one nostril closed, the simulated deviation from the trail increases (median deviation from trail increases significantly from 12.5 mm to 16.2 mm, 24 stretches each, two-tailed Wilcoxon rank-sum test, P=8.04×10-6). (b) An example of the model's behaviour on encountering a gap in the trail. The error estimate starts to grow and the nose makes wider swings until it crosses the error estimates. On re-encountering the trail, the error estimate is reset and the tracking resumes. (c) Left: on encountering a wide bifurcation, the model continues tracking down one of the arms, with equal probability of choosing left or right in symmetrical bifurcations. Right: for narrow bifurcations, the model switches between the two arms in 25% of cases. Inset: In 70% of cases for asymmetrical bifurcations, tracking proceeds along the straight arm. (d) Experimental data showing switching on narrow bifurcations, which happens in 27% of cases. PEA and chocolate trail in dark, respectively, speed 19 cm s-1.The model also made an interesting prediction. On encountering a wide bifurcation, it chose one of the two arms and stuck to it ( left), but for narrow bifurcations (such as the asymmetrical bifurcations), in 25% of cases it went down one arm and then switched to the other ( right). We looked for this pattern in the experimental data and found that indeed in 27% of the narrow bifurcation cases there was switching between the two arms (for example, , ). This was not seen in any wide bifurcations (for example,
left), thus validating the above prediction.DiscussionOur study is among the first to combine behavioural and physiological measurements in an animal tracking an odour trail. We find that rats can rapidly track surface-borne odours with highly efficient, near-optimal sampling, and achieve this high performance using a combination of strategies. Stereo sampling improves tracking precision significantly, and rats employ complementary search strategies such as path prediction and casting to follow trails and recover from errors. We are able to model these strategies and find that path prediction accounts for many details of the observed tracking behaviour. Sniffing rates during tracking are among the highest reported for any olfactory task and are modulated continually and rapidly.Our study provides significant insights into the neuroethology of odour trail tracking. We believe that this behaviour of odour trail tracking on a treadmill is close to a natural and ethologically relevant one. The key 'natural' aspect of behaviour in our task is that the rat controls when and where sensory sampling occurs, and guides its movements accordingly. In addition, this complex behaviour emerged spontaneously, without explicit training. We only placed chocolate pieces on the trail, and the rats quite rapidly discovered that the best strategy was to track the trail to find the chocolate. This basic pattern of movement is seen in moths, dogs and humans tracking unrestrained in the open,,,. Furthermore, we were able to characterize the underlying strategies used by the rats. The rats had the fallback of casting behaviour on losing the trail, an assumption of the trail continuing in a straight direction, a sampling rate that matched their movement pattern to provide efficiency and a stereo nostril comparison to further improve accuracy. Also, they did not track only the edge of a wide trail as had been predicted. Thus it is a repertoire of behaviours connected with rules (in short, a strategy) that the rats bring to this task. This supports the claim that we are studying a naturally relevant behaviour.The salient differences between the current task and natural behaviour are the fact that the rat is on a treadmill instead of a true track, that the speed at which the rat may move forward is governed by the treadmill speed and the finite width of the treadmill box. Further, the speed of the treadmill was much slower than the maximum speed at which a rat runs, which is about 1 m s-1 (unpublished results).The ability of animals to compare across two nostrils or antennae has been shown in various species, including rats, flies, humans and moths,,,. However, it was not known if animals use this ability to track odours. Our study provides evidence for a direct link between stereo olfaction and natural olfactory behaviours.The sniffing data provide useful insights into sampling strategies during tracking. First, the sniffing frequency is on an average at 10–12 Hz, the highest sniffing frequency reported across rats and mice,. This finding clears doubts about the use of this high-frequency sniffing in a relevant context. Second, rats could detect the resumption of the trail after a gap, within just 1–2 sniffs. Third, the sniffing rate combined with the nose movement is optimized for efficiently tracking the trail. Thus, a sniff is not only a snapshot of the olfactory world but a stereo snapshot whose location and timing are dynamically modulated for highly efficient sampling.The LFP oscillations provided us neural correlates of this complex behaviour. Running on the treadmill elicited a small but insignificant increase in the theta power compared with the stationary condition. Previous studies in many animals including rats,, hedgehogs, zebrafish, locusts and mollusks have found an increase in LFP oscillations at various frequency ranges on odour stimulation. Given this background, it is surprising that we found no difference between the conditions of tracking and not tracking for any frequency band. Even when comparing across conditions when the nose was close to or far from the trail, we saw no difference. Another significant finding of the present study was that the LFP theta oscillation is not strongly correlated with sniffing. This correlation has been shown in anaesthetized rats but is prominent only during odour presentation. In awake animals there was some previously reported evidence for correlations. This lack of increased oscillations or correlations with sniffing is interesting, and though largely unexplained at present, may be related to the fact that the rats are constantly running/walking in our experiments.In the present study, we suggest that active sampling is guided by an internal model of the world. By computationally modelling this internal representation, we suggest that, in addition to position and direction of the odour trail, there is likely to be a representation of uncertainty of position. We suggest that the orbitofrontal cortex, in combination with the hippocampus, may be a likely candidate for neuronal activity encoding representations of the odour trail. The hippocampus has been shown to have olfactory, as well as spatial representations. The orbitofrontal cortex has been shown to encode uncertainty. These parameters may be revealed by further studies involving single-unit recordings from these brain regions.MethodsAnimalsAll of the experimental procedures were approved by the National Centre for Biological Sciences institutional animal ethics committee, in accordance with the guidelines of the Government of India and equivalent guidelines of the Society for Neuroscience. Nine female Wistar rats were used for this experiment. The rats were 3 months old at the start of the training. Males could not be used because they soon grew too heavy for the treadmill to pull.Apparatus and odour trailsThe treadmill was constructed using parts from an old dot matrix printer. The basic design is shown in . A stepper motor located at the rear end of the treadmill turned a rod that pulled a sheet of dot matrix paper perforated at the sides. The paper passed through a transparent Perspex box, which had gaps in the bottom of the front and back walls to allow the paper to pass through. The box was 380 mm wide and 500 mm long. The paper was also 380 mm wide. The paper was looped around in most experiments. The length of the loop was usually 3 m and occasionally slightly more. As the treadmill was running with the rat on it, the experimenter placed pieces of chocolate on the paper before it entered the box through the gap and became available to the rat. A cardboard was placed to obscure the rat's view of the chocolate being placed. A camera was used to film this from a top-front angle at 25 frames per second. The camera could film in visible light as well as infrared light in which case the arena was lit with an array of infrared light-emitting diodes.The odours LC and PEA were chosen for the odour trails because they were appropriately volatile (). Also, PEA is known not to excite the trigeminal nerve, which is sensitive to irritant chemicals, even at high concentrations. Thus, this task utilizes only the main olfactory pathway. These trails were made by depositing the chemical at a constant rate on the paper in a meandering line. Chocolate trails were also used and were drawn by rubbing a chocolate piece over the paper.Surgical proceduresFor nostril stitching and sham stitching, rats were placed under surgical plane halothane anaesthesia (Surgivet) for 10 min after which the nose cone providing anaesthetic was removed from the rat. This provided about 1 min before the rat started to recover during which the stitch was made. For the nostril stitch, one stitch was made using cotton suture closing the nostril completely. The closure of the nostril was checked by placing a drop of water on the closed nostril. For the sham stitch, a stitch was made that did not close the nose but just looped through the upper flap of the nostril. First, the sham stitch was done on the left nostril of three rats that were tested 5.5 h later the same day. A week later, the same rats underwent nostril stitching on the right nostril and were again tested 5.5 h later. Stitches were removed the same evening or next morning.For implanting the TC and LFP electrode, surgery was performed under halothane anaesthesia maintained at a surgical plane and regularly monitored by a lack of response to a sharp toe pinch. Halothane was used at 4% for induction and adjusted between 1.25–2% for maintenance. Rectal temperature was measured and maintained by a heating lamp at about 95° F. Five rats were implanted with both TCs and LFP one of them gave no LFP signals. The two wires from the TC, the LFP electrode (and reference if present) and ground wire were connected to a light-weight connector, which was cemented on the rat's skull using 6–8 skull screws.Post surgery, the site was cleaned with iodine solution, neomycin sulphate antibiotic powder was applied and 5 mg kg-1 pentazocine (an analgesic) was injected subcutaneously. The pentazocine was given every 12 h for about 2 days. The rat was allowed to recover for at least 5 days before resuming the behavioural tasks.ElectrophysiologyDuring recording sessions, the TC and LFP signals were first passed through a custom-made head-mounted preamp and then through a tether, and were amplified further in a commercial amplifier (Neuralynx Inc.). The TC signal was differentially amplified from ×10,000 to ×200,000 depending on the signal quality. The LFP was amplified with respect to a skull screw in three rats and with respect to a reference electrode in the OB in one rat. LFP signals were generally amplified from ×2,000 to ×5,000 depending on the signal quality. The LFP signal was filtered in the amplifier from 1–200 Hz. The signals were digitized at 1,000 Hz and stored on a computer (DAP 5200a data acquisition card, Microstar Laboratories).Video analysisThe video of the rat tracking was taken from the front and at an elevated angle at 25 frames per second (Sony Handycam DCR-SR300E, Sony Corporation). We first chose sections of the video through visual inspection where the rat was tracking the trail. The criterion for choosing a section of video was that the rat should be following the trail with its nose on the paper for at least 2 s. As the rat usually moved its nose zigzag when it was on the paper, the criterion was effectively that its nose should be crisscrossing the trail consistently for at least 2 s. Usually short stretches just before and after the tracking were included here. The time spent not tracking was spent in zigzagging its nose on non-trail areas, pausing to eat chocolate crumbs and rearing up against or sniffing the side and front walls, as seen in . We took a video from a side angle and confirmed that the rats were not licking the chocolate trail while they were tracking.The video selections, typically 4–10 s, were then digitized using custom software in Matlab (MathWorks Inc.). We took each frame, and found the position of the trail and the rat's nose. To do this, we first performed a projective transformation of the region described by the four corners of the box. This prevented errors in calculating coordinates owing to the rat being at different distances from the camera. The trail was detected automatically at the front edge, and the user had to click on the tip of the rat's nose for each frame. The error in the manual estimation of the nose by this method was calculated by doing this for the same stretch of ~50 frames ten times. The error (s.d.) was 1 mm in both x and y coordinates.
References1.Vickers, N. J. Winging it: moth flight behavior and responses of olfactory neurons are shaped by pheromone plume dynamics. Chem. Senses 31, 155–166 (2006).2.Gomez-Marin, A., Duistermars, B. J., Frye, M. A. & Louis, M. Mechanisms of odor-tracking: multiple sensors for enhanced perception and behavior. Front Cell Neurosci. 4, 6 (2010).3.Wallace, D. G., Gorny, B. & Whishaw, I. Q. Rats can track odors, other rats, and themselves: implications for the study of spatial behavior. Behav. Brain Res. 131, 185–192 (2002).4.Basil, J. & Atema, J. Lobster orientation in turbulent odor plumes: simultaneous measurement of tracking behavior and temporal odor patterns. Biol. Bull. 187, 272–273 (1994).5.Willis, M. A. & Avondet, J. L. Odor-modulated orientation in walking male cockroaches Periplaneta americana, and the effects of odor plumes of different structure. J. Exp. Biol. 208, 721–735 (2005).6.Gomez-Marin, A., Stephens, G. J. & Louis, M. Active sampling and decision making in Drosophila chemotaxis. Nat. Commun. 2, 441 (2011).7.Beshel, J., Kopell, N. & Kay, L. M. Olfactory bulb gamma oscillations are enhanced with task demands. J. Neurosci. 27,
(2007).8.David, C. T., Kennedy, J. S. & Ludlow, A. R. Finding of a sex pheromone source by gypsy moths released in the field. Nature 303, 804–806 (1983).9.Kennedy, J. S. & Marsh, D. Pheromone-regulated anemotaxis in flying moths. Science 184, 999–).10.Gibbons, B. The intimate sense of smell. Natl Geographic Mag. 170, 324–361 (1986).11.Porter, J. et al. Mechanisms of scent-tracking in humans. Nat. Neurosci. 10, 27–29 (2007).12.Martin, H. Osmotropotaxis in the honey-bee. Nature 208, 59–63 (1965).13.Louis, M., Huber, T., Benton, R., Sakmar, T. P. & Vosshall, L. B. Bilateral olfactory sensory input enhances chemotaxis behavior. Nat. Neurosci. 11, 187–199 (2008).14.Kleinfeld, D., Ahissar, E. & Diamond, M. E. Active sensation: insights from the rodent vibrissa sensorimotor system. Curr. Opin. Neurobiol. 16, 435–444 (2006).15.Rajan, R., Clement, J. P. & Bhalla, U. S. Rats smell in stereo. Science 311, 666–670 (2006).16.Borst, A. & Heisenberg, M. Osmotropotaxis in Drosophila melanogaster. J. Comp. Physiol. A 147, 479–484 (1982).17.Porter, J., Anand, T., Johnson, B., Khan, R. M. & Sobel, N. Brain mechanisms for extracting spatial information from smell. Neuron 47, 581–592 (2005).18.Kepecs, A., Uchida, N. & Mainen, Z. F. Rapid and precise control of sniffing during olfactory discrimination in rats. J. Neurophysiol. 98, 205–213 (2007).19.Wesson, D. W., Donahou, T. N., Johnson, M. O. & Wachowiak, M. Sniffing behavior of mice during performance in odor-guided tasks. Chem. Senses 33, 581–596 (2008).20.Buonviso, N. et al. Rhythm sequence through the olfactory bulb layers during the time window of a respiratory cycle. Eur. J. Neurosci. 17,
(2003).21.Kay, L. M., Lancaster, L. R. & Freeman, W. J. Reafference and attractors in the olfactory system during odor recognition. Int. J. Neural Syst. 7, 489–495 (1996).22.Kay, L. M. & Laurent, G. Odor- and context-dependent modulation of mitral cell activity in behaving rats. Nat. Neurosci. 2,
(1999).23.Berg, R. W., Whitmer, D. & Kleinfeld, D. Exploratory whisking by rat is not phase locked to the hippocampal theta rhythm. J. Neurosci. 26,
(2006).24.Wilson, D. A. & Sullivan, R. M. Respiratory airflow pattern at the rat's snout and an hypothesis regarding its role in olfaction. Physiol. Behav. 66, 41–44 (1999).25.Yovel, Y., Falk, B., Moss, C. F. & Ulanovsky, N. Optimal localization by pointing off axis. Science 327, 701–704 (2010).26.Thesen, A., Steen, J. B. & Doving, K. B. Behaviour of dogs during olfactory tracking. J. Exp. Biol. 180, 247–251 (1993).27.Kepecs, A., Uchida, N. & Mainen, Z. F. The sniff as a unit of olfactory processing. Chem. Senses 31, 167–179 (2006).28.Kay, L. M. Two species of gamma oscillations in the olfactory bulb: dependence on behavioral state and synaptic interactions. J. Integr. Neurosci. 2, 31–44 (2003).29.Adrian, E. D. Olfactory reactions in the brain of the hedgehog. J. Physiol. 100, 459–473 (1942).30.Friedrich, R. W. & Laurent, G. Dynamic optimization of odor representations by slow temporal patterning of mitral cell activity. Science 291, 889–894 (2001).31.Laurent, G. & Davidowitz, H. Encoding of olfactory information with oscillating neural assemblies. Science 265,
(1994).32.Gelperin, A. & Tank, D. W. Odour-modulated collective network oscillations of olfactory interneurons in a terrestrial mollusc. Nature 345, 437–440 (1990).33.Wood, E. R., Dudchenko, P. A. & Eichenbaum, H. The global record of memory in hippocampal neuronal activity. Nature 397, 613–616 (1999).34.Deshmukh, S. S. & Bhalla, U. S. Representation of odor habituation and timing in the hippocampus. J. Neurosci. 23,
(2003).35.O'Keefe, J. & Dostrovsky, J. The hippocampus as a spatial map. Preliminary