Rolls Edmund T
University of Oxford, Department of Experimental Psychology, South Parks Road, Oxford OX1 3UD, United Kingdom.
Neuropsychologia. 2007 Jan 7;45(1):124-43. doi: 10.1016/j.neuropsychologia.2006.04.019. Epub 2006 Jun 23.
Neurophysiological evidence is described showing that some neurons in the macaque inferior temporal visual cortex have responses that are invariant with respect to the position, size and view of faces and objects, and that these neurons show rapid processing and rapid learning. Which face or object is present is encoded using a distributed representation in which each neuron conveys independent information in its firing rate, with little information evident in the relative time of firing of different neurons. This ensemble encoding has the advantages of maximising the information in the representation useful for discrimination between stimuli using a simple weighted sum of the neuronal firing by the receiving neurons, generalisation and graceful degradation. These invariant representations are ideally suited to provide the inputs to brain regions such as the orbitofrontal cortex and amygdala that learn the reinforcement associations of an individual's face, for then the learning, and the appropriate social and emotional responses, generalise to other views of the same face. A theory is described of how such invariant representations may be produced in a hierarchically organised set of visual cortical areas with convergent connectivity. The theory proposes that neurons in these visual areas use a modified Hebb synaptic modification rule with a short-term memory trace to capture whatever can be captured at each stage that is invariant about objects as the objects change in retinal view, position, size and rotation. Another population of neurons in the cortex in the superior temporal sulcus encodes other aspects of faces such as face expression, eye gaze, face view and whether the head is moving. These neurons thus provide important additional inputs to parts of the brain such as the orbitofrontal cortex and amygdala that are involved in social communication and emotional behaviour. Outputs of these systems reach the amygdala, in which face-selective neurons are found, and also the orbitofrontal cortex, in which some neurons are tuned to face identity and others to face expression. In humans, activation of the orbitofrontal cortex is found when a change of face expression acts as a social signal that behaviour should change; and damage to the orbitofrontal cortex can impair face and voice expression identification, and also the reversal of emotional behaviour that normally occurs when reinforcers are reversed.
文中描述了神经生理学证据，表明猕猴颞下回视觉皮层中的一些神经元对人脸和物体的位置、大小及视角具有不变的反应，并且这些神经元表现出快速处理和快速学习能力。呈现的是哪张脸或哪个物体是通过分布式表征进行编码的，其中每个神经元在其放电率中传达独立信息，不同神经元放电的相对时间中几乎没有明显信息。这种群体编码具有以下优点：通过接收神经元对神经元放电进行简单加权求和，最大化表征中对区分刺激有用的信息、实现泛化以及平稳退化。这些不变表征非常适合为眶额皮质和杏仁核等脑区提供输入，这些脑区学习个体面部的强化关联，这样一来，学习以及适当的社交和情感反应就能推广到同一张脸的其他视角。文中描述了一种理论，说明在具有汇聚连接的分层组织的视觉皮层区域集合中，如何产生这种不变表征。该理论提出，这些视觉区域中的神经元使用带有短期记忆痕迹的修改后的赫布突触修改规则，以捕捉随着物体在视网膜视角、位置、大小和旋转方面发生变化时，每个阶段中物体不变的任何特征。颞上沟皮质中的另一群神经元编码面部的其他方面，如面部表情、目光注视、面部视角以及头部是否在移动。因此，这些神经元为参与社交交流和情感行为的脑区，如眶额皮质和杏仁核的部分区域，提供了重要的额外输入。这些系统的输出到达杏仁核（其中发现了面部选择性神经元）以及眶额皮质（其中一些神经元被调整为对面部身份敏感，另一些对面部表情敏感）。在人类中，当面部表情变化作为行为应改变的社交信号时，会发现眶额皮质被激活；而眶额皮质受损会损害面部和声音表情识别，以及通常在强化物反转时发生的情感行为反转。
