Kendrick K M
The Babraham Institute, Babraham, Cambridge CB2 4AT,UK.
Behav Processes. 1994 Dec;33(1-2):89-111. doi: 10.1016/0376-6357(94)90061-2. Epub 2002 May 31.
This paper describes neurophysiological and behavioural experiments which investigate the ability of sheep to recognise different individuals using visual and olfactory cues. Behavioural experiments using Y-mazes with back-projected images of faces have shown that sheep can distinguish between the faces of sheep and humans when the faces are presented in a frontal view although they have more difficulty in doing so if the faces are presented in profile, upside down or with the eyes obscured. Single-cell electrophysiological recordings made from neurones in the temporal cortex have shown that sheep, like non-human primates, have cells in this region that code preferentially for facial stimuli and that their responses are also diminished or abolished if the faces are presented upside-down, in profile, or with the eyes obscured. Different sub-populations of cells code for faces of similar social and emotional significance. Thus one population of cells codes for faces with horns and their responses are also modulated by the size of the horns, another population codes for faces of animals of the same breed, and particularly familiar animals, and a final population codes for faces of humans and dogs. Visual cues from body shape and posture are also important for recognition of different classes of individual. Field studies have shown that sheep find it difficult to recognise humans approaching them if they change their posture to quadrupedal as opposed to a bipedal one. Electrophysiological studies have also demonstrated the presence of cells in the temporal cortex which respond preferentially to the sight of a human body shape and their activity is influenced by body orientation, posture and direction of movement. In some cases alterations to the human's appearance can also influence their activity. Olfactory recognition studies have used electrophysiological, in vivo sampling and behavioural analyses to establish the mechanisms whereby a maternal ewe develops the ability to selectively recognise the odour signatures of its own lambs within the first few hours of giving birth. Electrophysiological recordings from mitral cells in the olfactory bulb have shown that none of them respond preferentially to lamb odours pre-partum, when the ewes show no interest in lambs, whereas 60% of them do so after ewes have bonded with their lambs. A sub-population of mitral cells also responds differentially to own and alien lamb odours post-partum. Neurochemical studies have shown that lamb odours do not evoke transmitter release within the olfactory bulb pre-partum whereas, post-partum, own lamb odours stimulate release of the intrinsic amino acid transmitters, GABA and glutamate whereas both own and alien lamb odours evoke equivalent increases in the release of the centrifugal pathway transmitters, acetylcholine and nonadrenaline. Overall these experiments provide compelling evidence that the sheep, which is after all a social animal, makes use of sophisticated visual cues from the face and body and of olfactory cues from the body and wool to recognise different individuals. The neural pathways which are involved in both of these recognition processes also show remarkable evidence of plasticity. However, there appears to be a much closer link between recognition and emotional significance demonstrated in the coding strategies employed by the neural circuits involved in individual recognition in the sheep brain compared to that of a primate and, indeed, they seem to be organised more for identifying a small number of different categories of individuals rather than for a large number of individuals per se. It is possible therefore that social evolutionary pressures to specifically identify large numbers of individuals of similar emotional significance has been achieved by weakening the organisational influence of affect on coding strategies of cells in the temporal cortex in favour of a more extensive feature detection system allowing accurate discrimination between a large number of individuals and their expressions under a number of different viewing conditions.
本文描述了神经生理学和行为学实验，这些实验研究了绵羊利用视觉和嗅觉线索识别不同个体的能力。使用带有面部背投图像的Y型迷宫进行的行为实验表明，当面部以正视图呈现时，绵羊能够区分绵羊和人类的面部，尽管当面部以侧视图、倒置或眼睛被遮挡的方式呈现时，它们在区分上会有更多困难。从颞叶皮质神经元进行的单细胞电生理记录表明，绵羊与非人类灵长类动物一样，在该区域有优先对面部刺激进行编码的细胞，并且如果面部以倒置、侧视图或眼睛被遮挡的方式呈现，它们的反应也会减弱或消失。不同亚群的细胞对具有相似社会和情感意义的面部进行编码。因此，一群细胞对面部长有角的面部进行编码，它们的反应也会受到角大小的调节，另一群细胞对同一品种动物的面部，特别是熟悉的动物的面部进行编码，最后一群细胞对人类和狗的面部进行编码。来自身体形状和姿势的视觉线索对于识别不同类别的个体也很重要。实地研究表明，如果人类改变姿势为四足而不是两足，绵羊很难识别接近它们的人类。电生理研究还证明，颞叶皮质中存在优先对人体形状的视觉做出反应的细胞，并且它们的活动会受到身体方向、姿势和运动方向的影响。在某些情况下，人类外貌的改变也会影响它们的活动。嗅觉识别研究使用电生理、体内采样和行为分析来确定母羊在分娩后的头几个小时内如何发展出选择性识别自己羔羊气味特征的能力。嗅球中二尖瓣细胞的电生理记录表明，在产前母羊对羔羊没有兴趣时，没有一个细胞优先对羔羊气味做出反应，而在母羊与羔羊建立联系后，其中60%的细胞会这样做。一群二尖瓣细胞在产后对自己和外来羔羊气味也有不同反应。神经化学研究表明，产前羔羊气味不会在嗅球内引起递质释放，而产后，自己羔羊的气味会刺激内源性氨基酸递质γ-氨基丁酸（GABA）和谷氨酸的释放，而自己和外来羔羊的气味都会引起离心通路递质乙酰胆碱和去甲肾上腺素释放的等量增加。总体而言，这些实验提供了令人信服的证据，即绵羊作为一种群居动物，利用来自面部和身体的复杂视觉线索以及来自身体和羊毛的嗅觉线索来识别不同个体。参与这两种识别过程的神经通路也显示出显著的可塑性证据。然而，与灵长类动物相比，在绵羊大脑中参与个体识别的神经回路所采用的编码策略中，识别与情感意义之间似乎存在更紧密的联系，实际上，它们似乎更多地是为了识别少数不同类别的个体，而不是大量个体本身。因此，有可能通过削弱情感对颞叶皮质细胞编码策略的组织影响，转而支持更广泛的特征检测系统，从而在特定识别大量具有相似情感意义个体的社会进化压力下，实现了在多种不同观察条件下对大量个体及其表情的准确区分。
