Showing papers by "Edmund T. Rolls published in 1982"

Visual Neurones Responsive to Faces in the Monkey Temporal Cortex

Abstract: Of 497 single neurones recorded in the cortex in the fundus of the superior temporal sulcus (STS) of three alert rhesus monkeys, a population of at least 48 cells which were selectively responsive to faces had the following response properties: (1) The cells' responses to faces (real or projected, human or rhesus monkey) were two to ten times as large as those to gratings, simple geometrical stimuli or complex 3-D objects. (2) Neuronal responses to faces were excitatory, sustained and were time-locked to the stimulus presentation with a latency of between 80 and 160 ms. (3) The cells were unresponsive to auditory or tactile stimuli and to the sight of arousing or aversive stimuli. (4) The magnitude of the responses of 28 cells tested was relatively constant despite transformations, such as rotation, so that the face was inverted or horizontal, and alterations of colour, size or distance. (5) Rotation to profile substantially reduced the responses of 21 cells (31 tested). (6) Masking out or presenting parts of the face (i.e. eyes, mouth or hair) in isolation revealed that different cells responded to different features or subsets of features. (7) For several cells, responses to the normal organisation of cut-out or line-drawn facial features were significantly larger than to jumbled controls. These findings indicate that explanations in terms of arousal, emotional or motor reactions, simple visual feature sensitivity or receptive fields are insufficient to account for the selective responses to faces and face features observed in this population of STS neurones. It appears that these neurones are part of a system specialised to code for faces or features present in faces, and it is suggested that damage to this system is related to prosopagnosia, or difficulty in face recognition, in man and to the tameness and social disturbances which follow temporal lobe damage and are part of the Kluver-Bucy syndrome in the monkey.

Neuronal responses related to visual recognition

Abstract: To analyse the neural basis of long-term memory, recordings were made from single neurons in monkeys performing a visual recognition task of the type impaired in anterograde amnesia in man. Each visual stimulus was shown twice per day, once as novel, and after 0 to 17 other intervening items in the recognition task, on a second trial, as familiar, when the monkey could lick to obtain fruit juice if he recognized the stimulus correctly. At the anterior border of the thalamus, a population of neurons was found which responded to the stimuli only when they were familiar. The activity of these neurons was not related to lick responses. Further, in a different, visual discrimination, task, a number of these neurons were found to respond both to the familiar rewarded stimulus to which the monkey always licked, and to the familiar aversive stimulus to which he did not lick. This shows that in a reward association task these neurons respond on the basis of familiarity, providing evidence for a dissociation of recognition and associative memories. Analysis of the responses of these neurons in the continuous visual recognition task showed that the responses to familiar stimuli were time-locked to the onset and duration of the visual stimulation (brief exposures producing brief responses). The response latencies were in the range 100 to 200 ms. A 100 ms exposure of the stimulus was sufficient for the stimulus to be encoded, and a 100 ms exposure was also sufficient for a recognition related response. The magnitude of the neuronal response on trials with familiar stimuli decreased as the number of trials between the first (novel) and second (familiar) presentation of the same stimulus increased. The rate of this decay or 'forgetting' varied from cell to cell and was best described by an exponential function. Repeated exposure tended to slow the rate of forgetting, and two or three repeated presentations prolonged some cell 'memories' for more than 100 intervening trials. Although the majority of the neurons did not have such long 'memories', in that they responded as novel to stimuli seen on a preceding day, so that their responses could be related to recency but not to absolute recognition of ever having seen a stimulus before, 2 neurons did respond to stimuli which had not been seen for 24 h. The neurons showed some ability to respond to stimuli as familiar despite changes in viewing conditions and transformations such as 90 deg rotation. These findings indicate that the responses of these neurons at the anterior border of the thalamus are activated during recency or longer term recognition processing, both of which are impaired in anterograde amnesia in man. Measurement of the responses of these neurons, which appear to have access to memory mechanisms, has allowed parameters affecting such memory mechanisms to be investigated.

How flavour and appearance affect human feeding

Abstract: It is the purpose of this paper to consider the ways in which the different sensory aspects of food presentation such as flavour, appearance, portion size and shape influence food intake in human subjects within the range of normal body-weights. One way in which the sensory properties of food influence feeding is by contributing to a form of satiety which is partly specific for the particular food eaten.

Physiological mechanisms for thirst in the nonhuman primate.

Abstract: The relationship between body fluid deficits and drinking has been investigated in a nonhuman primate. Intravenous sodium chloride infusions (0.93-3.25 M) given to rhesus monkeys caused drinking correlated with increases in plasma osmolality and sodium concentrations. Sucrose infusions (0.3 M in 0.15 M NaCl) also caused drinking while equiosmolal urea infusions did not. It was found that the drinking threshold corresponded to a 2.3% increase in plasma osmolality. Water deprivation for 24 h caused significant cellular dehydration, as indicated by a 5.8% elevation in plasma osmolality that exceeded the threshold for thirst, and a significant hypovolemia as indicated by elevated plasma protein and hematocrit values. Intravenous water preloads decreased plasma osmolality and produced a dose-related decrease in subsequent drinking. Infusions that restored plasma osmolality to predeprivation values, reduced intake by 85%. Intravenous isotonic saline preloads which abolished the hypovolemia did not have a consistent effect and reduced mean water intakes by only 3.2%. Thus in the rhesus monkey, cellular dehydration is an effective stimulus for thirst, and it is the primary determinant of drinking after water deprivation, used as an example of a natural thirst stimulus. In contrast to findings in nonprimates, the extracellular deficit contributes very little to drinking after water deprivation.

Neuronal Mechanisms Underlying the Formation and Disconnection of Associations Between Visual Stimuli and Reinforcement in Primates

Abstract: Damage to the temporal lobe neocortex or to the amygdala impairs the ability of primates to perform tasks which require the formation of learned associations between complex visual stimuli and reward or punishment. Analysis of the responses of single neurons in the anatomically connected sequence inferior temporal visual cortex / amygdala / hypothalamus in the monkey showed that neuronal responses to visual stimuli were not related in ‘the inferior temporal cortex to whether the stimuli were associated with reinforcement, were partly related to this in some amygdaloid neurons, and were related to reinforcement in a population of hypothalamic neurons. Damage to the primate orbitofrontal cortex impairs the performance of tasks which require the disconnection of associations between stimuli and reinforcement. Neuronal responses recorded in this region were related for example to whether particular visual stimuli had been reinforced previously, or for different subsets of neurons to whether reward or punishment had been obtained, or reward had been omitted. These findings thus provide evidence on how associations are formed and broken between stimuli normally of importance to primates and reinforcement, and indicate that the formation and disconnection are separable processes.