There is evidence that the inferotemporal visual cortex in the monkey projects to the amygdala, and evidence that damage to this region impairs the learning of associations between visual stimuli and reward or punishment. In recordings made in the amygdala to determine whether or not visual responses were found, and if so how they were affected by the significance of the visual stimuli, neurons were found in the dorsolateral part of the amygdala with visual responses which in most cases were sustained while the animal looked at effective visual stimuli. The latency of the responses was 100 to 140 ms or more. The majority (85%) of these neurons responded more strongly to some stimuli than to others, but physical factors which accounted for the responses of the neurons, such as shape, size, orientation, color, or texture, could not usually be identified. Although 22 (19.5%) of these neurons responded primarily to food objects, the responses were not uniquely food-related. Furthermore, although some neurons responded in a visual discrimination test to a visual stimulus which indicated reward, and not to a visual stimulus which indicated saline, only minor modifications of the magnitude of the neuronal responses to the stimuli were obtained when the reward-related significance of the stimuli was reversed. The visual responses of these amygdaloid neurons were thus intermediate in some respects between those of neurons in the inferotemporal cortex, which are not affected by the significance of visual stimuli, and those of neurons in a region to which the amygdala projects, the lateral hypothalamus and substantia innominata, where neurons respond to visual stimuli associated with food reward.

This chapter describes activity of neurons in the neostriatum and related structures in the alert animal. Movement-related neuronal activity has been found in the caudate nucleus of the monkey. In recordings made in the caudate nucleus and putamen of the monkey, it was found that the activity of some neurons is related to movements made by the monkey, although it is usually more difficult than with neurons in the globus pallidus to demonstrate a strong relation between neuronal activity and a particular movement. An example of the activity of a caudate neuron with movement-related activity is as follows. The neuron had a slow spontaneous firing rate of 2 spikes/s, and increased its rate when the monkey extended his contralateral arm to depress an illuminated panel. The unit responded during extension of the arm to reach the panel or during pressing the panel with the fingers if the arm was already extended. The response illustrated was related to movement of the contralateral arm and similar, but smaller responses were obtained with movements of the ipsilateral arm and hand.

The inhibition hypothesis advocated by Ekman (1985) states when an emotion is concealed or masked, the true emotion is manifested as a micro-expression (ME) which is a fleeting expression lasting for 40 to 500 ms. However, research about the inhibition hypothesis of ME from the perspective of electrophysiology is lacking. Here, we report the electrophysiological evidence obtained from an electroencephalography (EEG) data analysis method. Specifically, we designed an ME elicitation paradigm to collect data of MEs of positive emotions and EEG from 70 subjects, and proposed a method based on tensor component analysis (TCA) combined with the Physarum network (PN) algorithm to characterize the spatial, temporal, and spectral signatures of dynamic EEG data of MEs. The proposed TCA-PN methods revealed two pathways involving dorsal and ventral streams in functional brain networks of MEs, which reflected the inhibition processing and emotion arousal of MEs. The results provide evidence for the inhibition hypothesis from an electrophysiological standpoint, which allows us to better understand the neural mechanism of MEs.

To investigate whether the responses of neurones in the lateral hypothalamus and substantia innominata associated with the sight of food could control the responses of the hungry monkey to the food, the latency of activation of these neurones by food was measured. It was found that when an electromagnetically operated wide-aperture shutter opened to reveal food or non-food objects, these hypothalamic neurones responded with a latency of 150–200 msec to the food objects, and did not respond to the non-food objects. To measure the latency of the monkey's responses to the food, a visual discrimination task was set in which the monkey could lick a tube to obtain fruit juice if a food-related visual stimulus was shown, but obtained hypertonic saline, which was aversive, if a different visual stimulus was shown. In this situation the typical latencies of the neuronal responses to the food were 150–200 msec, of the lick responses 350–400 msec. and of the EMG activity associated with these lick responses 250–400 msec. Thus the responses of these hypothalamic neurones precede the monkey's responses to the food, and could mediate the feeding and other responses of the animal to the food.