Disconnection of the amygdala from visual association cortex impairs visual reward-association learning in monkeys

Cynomolgus monkeys (Macaca fascicularis) were trained in a task that assessed their ability to associate visual stimuli with food reward. Acquisition of stimulus-reward associations was measured under 2 conditions, a 2-stimuli acquisition condition and a 1-stimulus acquisition condition. On each trial in the 2-stimuli condition, the positive (correct) and negative (incorrect) stimuli were presented side by side and the animal chose one by touching it; if the choice was correct, a food reward was dispensed. On each trial in the 1-stimulus condition, either the positive or the negative stimulus was presented alone; if the stimulus was the positive, it was followed by reward delivery, regardless of the animal's response to it, and if it was the negative, it was not followed by reward delivery. Thus, reward delivery was contingent upon the animal's response to the stimuli in the 2-stimuli condition but not in the 1-stimulus condition. The effect of acquisition trials under these 2 conditions was measured, in both conditions, by the animal's subsequent choice when presented with the 2 stimuli side by side. Following preoperative training in this task, the animals were first subjected to unilateral ablation of the inferotemporal cortex. This operation had little effect on the animals' learning ability. Then, the amygdala was ablated in the hemisphere contralateral to that in which the unilateral inferotemporal ablation had been carried out. This combination of crossed unilateral lesions of the amygdala and of the inferotemporal cortex, which disconnects the amygdala from the output of visual association cortex, produced a profound impairment in stimulus-reward-associative learning.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activity of neurones in the inferotemporal cortex of the alert monkey.

The activity of neurones in the inferotemporal cortex of the alert rhesus monkey was recorded while the monkey was shown visual stimuli, which included both food and non-food objects for comparison with the activity of neurones in the lateral hypothalamus and substantia innominata. In the anteroventral part of the inferotemporal cortex, neurones were found with visual responses which were sustained while the animal looked at the appropriate visual stimuli. The latency of the responses was 100 msec or more. The majority (96/142 or 68%) of these neurones responded more strongly to some stimuli than to others. These units usually had different responses when objects were shown from different views, and physical factors such as shape, size, orientation, colour and texture appeared to account for the responses of some of these units. Association of visual stimuli with a food reward (glucose solution) or an aversive taste (5% saline solution) did not affect the magnitude of the responses of the neurones to the stimuli either during the learning or after the period of learning. Nor did feeding the monkey to satiety affect the responses of the neurones to their effective stimuli.     

Neuronal responses of the rat amygdala during extinction and reassociation learning in elementary and configural associative tasks

To investigate functional heterogeneity within the amygdala in appetitive conditioned instrumental behaviours, neuronal activity was recorded from the amygdala of behaving rats during learning and discrimination of conditioned sensory stimuli associated with or without reinforcement [sucrose solution, intracranial self-stimulation (ICSS)]. Sensory stimuli included auditory (tone), visual (light) and configural (simultaneous presentation of tone and light) stimuli. The rat was trained to lick a spout protruded close to its mouth just after a conditioned sensory stimulus to obtain a reward. Of the 609 neurons recorded from the amygdala and amygdalostriatal transition area, 154 responded to one or more sensory stimuli. The 62 amygdalar neurons responded strongly to certain conditioned sensory stimuli associated with rewards. Of these 62 neurons, 45 were tested with the extinction trials. Responses of 31 neurons to conditioned stimuli were finally extinguished, and those of the remaining 14 were not extinguished. Furthermore, responses of 26 of these 31 neurons resumed in the relearning trials (plastic neurons), suggesting that these sensory responses were associative rather than just responses to physical properties of the stimuli. These plastic neurons were located mainly in the basolateral nucleus of the amygdala, and responses of the plastic neurons were correlated with behavioural responses. These results suggest that the basolateral nucleus is crucial in associative learning between sensory information and affective significance for behavioural outputs in appetitive conditioned instrumental behaviours.     

Neural correlates to both emotion and cognitive functions in the monkey amygdala

Recent lesion and non-invasive studies identify the medial temporal lobe, including the amygdala, not only with emotion but also with working memory in relation to the prefrontal cortex. In the present study, amygdalar neuronal activity was recorded from monkeys during performance of discrimination tasks that led to presentation of emotion-related (rewarding or aversive) stimuli. The task had three phases: (1) discrimination (visual, auditory), (2) operant response (bar pressing) and (3) ingestion (reward) or avoidance (aversion). These neurons were further analyzed by a short-term memory task, delayed pair comparison (DPC) using colored lamps. Of 585 amygdalar neurons, 107 responded primarily to single sensory stimulation (40 vision related, 26 audition related, 41 ingestion related), 117 to multimodal stimulation (multimodal) and 14 responded selectively to only one item (selective). Of 417 neurons tested by the DPC, 122 responded in one or more phases. Of these 122 neurons, 10.7% responded in the delay period. These delay-responsive neurons also responded to various objects with positive and negative affective significance. These results suggest that amygdalar neurons are not specifically related to working memory, as are those in the inferotemporal and prefrontal cortices, but are related to more general non-specific functions or processes such as arousal or attention during the cognitive tasks. A functional role of the amygdala in working memory is discussed in terms of recent non-invasive studies suggesting a functional coupling between the amygdala and prefrontal cortex.     

Hippocampus and medial temporal cortex: neuronal activity related to behavioural responses during the performance of memory tasks by primates

Neuronal activity was recorded in the hippocampal formation, the parahippocampal gyrus and medial inferotemporal cortex of monkeys performing memory tasks. In a modified delayed matching to sample task in which 2 sequentially presented stimuli were compared on each trial, a match condition required a right panel press, whereas a non-match condition required a left panel press. The activity of 336/736 (45.7%) neurons was related to the behavioural responses (left or right panel presses) in this task. The incidence of response-related activity was 57.4% in cortical areas adjacent to the rhinal sulcus plus medial inferotemporal cortex, and 40.2% for the hippocampal formation. For 58.9% of these response-related neurons, the activity change associated with the behavioural response was greater than that during presentation of the sensory stimuli, though neurons commonly responded (33.2% of all recorded neurons) to both sensory and motor events. The activity of 198 neurons (26.9%) differed between go-left and go-right trials; such neurons were found in all areas but were nearly twice as common in the posterior as in the anterior hippocampal formation. The importance of visual stimuli for the response-related neuronal activity was examined during the performance of a delayed alternation task without visual cues indicating direction of response. The response-related activity of 8 neurons recorded during the delayed alternation and the delayed matching tasks was similar in both tasks, indicating that memory for the behavioural responses influences the activity of the response-related neurons. In order to test the effects of stimulus familiarity and non-spatial responses on medial temporal neurons, recognition memory and visual discrimination tasks requiring lick responses were performed. The activity of 2/375 (0.5%) neurons was related to the lick responses; 3/68 neurons in the inferomedial temporal cortex responded on the basis of stimulus novelty and none reflected their reinforcement value. It is concluded that the hippocampal formation, the parahippocampal gyrus and medial inferotemporal cortex all have a role in the utilisation of sensory, mnemonic and motor information underlying the selection of spatially-directed behavioural responses.     

Amygdaloid neuronal responses to complex visual stimuli in an operant feeding situation in the monkey

In chronically prepared monkeys, 337 neurons were recorded from the anterolateral amygdala during an operant task that required visual discrimination. Twelve percent (39/337) of the neurons responded to one or more of food or non-food visual stimuli. A subset of these responsive neurons was selectively sensitive to the sight of non-food objects with aversive associations. Simultaneous presentation of a food stimulus with the aversive object inhibited the response of these neurons. These response characteristics could not be explained by simple sensory processing of the visual stimuli. It is suggested that the amygdala plays an important role in the elaboration of motivational behavior by using the complex or associative properties of visual stimuli.     

Responses of striatal neurons in the behaving monkey. 1. Head of the caudate nucleus

The activity of 394 neurons in the head of the caudate nucleus and the most anterior part of the putamen was analyzed in 3 behaving rhesus monkeys in order to analyze the functions of this part of the striatum. Of these neurons, 64.2% responded in the tests used in relation to, for example, environmental events, movements made by the monkey, the performance of a visual discrimination, or during feeding. However, only relatively small proportions of these neurons had responses which were unconditionally related to visual (9.6%), auditory (3.5%), or gustatory (0.5%) stimuli, or to movements (4.1%). Instead, the majority of the responsive neurons had activity in relation to stimuli or movements which was conditional, in that the responses occurred in only some test situations, and were often dependent on the performance of a task by the monkeys. Thus, it was found in the visual discrimination task that 14.5% of the neurons responded during a 0.5 sec tone/light cue period which signalled the start of each trial; 31.1% responded in the period in which the discriminative visual stimuli were shown, with 24.3% of these responding more to either the visual stimulus which signified food reward or to that which signified punishment; and 6.2% responded in relation to lick responses. Yet these neurons typically did not respond in relation to the cue stimuli, to the visual stimuli, or to movements, when these occurred independently of the task, or when performance of the task was prevented. Comparably, of the neurons tested during feeding, 25.8% responded when the food was seen by the monkey, 6.2% when he tasted it, and 22.4% during a cue given by the experimenter that a food or non-food object was about to be presented. However, only few of these neurons had responses to the same stimuli presented in different situations.It is concluded that many neurons in the head of the caudate nucleus and the most anterior part of the putamen respond in relation to events which are used as cues to prepare for the performance of tasks, including feeding, in which movements must be initiated. Other neurons respond in relation to the stimuli used and the movements made in these tasks. However, the majority of these neurons do not have unconditional sensory or motor responses. It is therefore suggested that the anterior neostriatum contains neuronal mechanisms which are important in the process by which environmental cues are used in the preparation of behavioral responses, and in the initiation of particular behavioral responses made in particular situations to particular environmental stimuli. Deficits in the initiation of movements following damage to striatal pathways may arise in part because of interference with these functions of the anterior neostriatum.     

Single neuron responses in amygdala of alert monkey during complex sensory stimulation with affective significance

Among other deficits, amygdalectomy impairs the ability of the animal to recognize the affective significance of a stimulus. In the present study, neuronal activity in the amygdala (AM) was recorded from alert monkeys while they performed tasks leading to the presentation of rewarding or aversive stimuli. Of 585 AM neurons tested, 312 (53.3%) responded to at least one stimulus in one or more of 5 major groups: 40 vision related, 26 audition related, 41 ingestion related, 117 multimodal, and 14 selective. Ingestion-related neurons were subdivided according to their responses to other stimuli: oral sensory, oral sensory plus vision, and oral sensory plus audition. Depending upon their responsiveness to the affective significance of the stimuli, neurons in the vision- and audition-related categories were divided into 2 subclasses: vis-I (26/40), vis-II (14/40), aud-I (8/26), and aud-II (18/26). All 4 subtypes usually responded to unfamiliar stimuli but seldom responded to neutral familiar stimuli. Types vis-I and aud-I responded to both positive and negative familiar stimuli. Types vis-II and aud-II responded to certain familiar negative stimuli but not to familiar positive stimuli. In vis-I neurons, responses were stronger for palatable foods than for less palatable foods. No neurons within vision-related, audition-related, and multimodal categories responded solely to positive or to negative stimuli. Of the 27 oral sensory neurons 9 were tested with saline or salted food, and 8 responded to normally aversive oral sensory stimuli in the same manner as they did to normal food or liquid (water or juice). In contrast to oral sensory neurons, all responses of 4 oral sensory-plus-vision and all of 4 selective neurons tested, as well as bar pressing behavior, were modulated by altering the affective significance of the food. These results suggest that the AM is one of the candidates for stimulus-affective association based on associative learning and memory.     

Functional role of the limbic system and basal ganglia in motivated behaviors

It has been suggested that the cortico- and limbic-striatal systems are important in various motor functions such as motivated behaviors. In this paper we review our previous studies to investigate neuronal mechanisms of feeding behaviors. We recorded neuronal activity from the amygdala, caudate nucleus, globus pallidus, and substantia nigra during feeding behavior in monkeys, and compared neuronal responses recorded from these brain areas. First, of 710 amygdalar neurons tested, 129 (18.2%) responded to single sensory stimulation (48 to vision, 32 to audition, 49 to ingestion), 142 (20%) to multimodal stimulation, and 20 to only one item with affective significance. Eight food related amygdalar neurons were tested in reversal by salting food or introducing saline, and all responses were modulated by reversal. These results suggest that the amygdala might be important in ongoing recognition of the affective significance of complex stimuli (food-nonfood discrimination).

Second, activity was recorded from 351 neurons in the head of the caudate nucleus of monkeys during an operant feeding task. The 16% of these neurons responded in the discrimination phase. Some of these neurons responded specifically to food. The magnitude of these food-specific neurons depend on the rewarding nature of the food (reward value), and was inversely related to the latency of the onset of bar press. Of the caudate neurons, 10% responded in the bar press phase. Activity of most neurons which responded in the bar press phase was not correlated to individual bar presses. Cooling of the dorsolateral prefrontal cortex abolished sustained responses during bar pressing, but did not abolish the feeding behavior. However, bar press speed tended to be delayed by prefrontal cooling.

Third, activity of 358 neurons was recorded from the monkey globus pallidus, and 204 neurons responded during the feeding task. In the globus pallidus, few neurons responded to food in the discrimination phase. On the other hand, activity of most responsive neurons changed during bar press and/or ingestion phases. Activity of about half of these responsive neurons was directly related to specific feeding motor acts such as arm extension, flexion, bar pressing, grasping, chewing, etc. Some of these neurons showed motor-related responses with gradual and preparatory responses. These motor-related neurons were located mainly in the caudodorsal part of the globus pallidus. On the other hand, about one third, especially in the rostroventral part of the globus pallidus, showed dissociating responses in that they responded during bar pressing for food or during ingestion in an operant task, but not during bar pressing for nonfood or during forcible ingestion. The response magnitude of the neurons during arm extension and bar pressing depended on the nature of the food.

Fourth, activity of 261 neurons was recorded from the substantia nigra pars reticulata. Most of responding neurons (more than two-thirds of the recorded neurons) responded during the bar press and/or ingestion phases. Activity of the one-third of neurons was related to specific motor execution such as arm extension, flexion and bar pressing, but not to motor preparation. These neurons were located mainly in the rostral part of the nucleus. More than one-third of the recorded neurons responded during feed and/or drinking acts and intra- and perioral sensory stimuli, and were located mainly in the caudomedial part of the nucleus.

Based upon these responses and known anatomical evidence, various information including that from the amygdala and prefrontal cortex is integrated in the basal ganglia, and converted to coordinated motivated behaviors such as feeding behavior.

     

Medial orbitofrontal cortex codes relative rather than absolute value of financial rewards in humans

Functional imaging studies in recent years have confirmed the involvement of orbitofrontal cortex (OFC) in human reward processing and have suggested that OFC responses are context-dependent. A seminal electrophysiological experiment in primates taught animals to associate abstract visual stimuli with differently valuable food rewards. Subsequently, pairs of these learned abstract stimuli were presented and firing of OFC neurons to the medium-value stimulus was measured. OFC firing was shown to depend on the relative value context. In this study, we developed a human analogue of this paradigm and scanned subjects using functional magnetic resonance imaging. The analysis compared neuronal responses to two superficially identical events, which differed only in terms of the preceding context. Medial OFC response to the same perceptual stimulus was greater when the stimulus predicted the more valuable of two rewards than when it predicted the less valuable. Additional responses were observed in other components of reward circuitry, the amygdala and ventral striatum. The central finding is consistent with the primate results and suggests that OFC neurons code relative rather than absolute reward value. Amygdala and striatal involvement in coding reward value is also consistent with recent functional imaging data. By using a simpler and less confounded paradigm than many functional imaging studies, we are able to demonstrate that relative financial reward value per se is coded in distinct subregions of an extended reward and decision-making network.     

Single unit activity during a Go/NoGo task in the "prefrontal cortex" of pigeons.

Single unit activity was recorded during a delayed auditory/visual Go/NoGo task from the neostriatum caudolaterale (NCL) of pigeons, a multimodal associative avian forebrain structure comparable to the prefrontal cortex (PFC). The animals were trained to mandibulate (to open their beak) during the Go period after which they received a drop of water as reward. Neuronal activity changes were observed during the delay period (DELAY) between auditory and visual stimulation, to the onset of the visual stimulus or to the delivery of the reward. In some neurons, responses were related to the behavioral significance of the stimulus such that the neuronal activity was statistically different between Go and NoGo trials. Moreover, some units anticipated the upcoming reward or changed their firing frequency in a correlated manner prior to beak movements. These neuronal activity patterns suggest that the NCL provides a neural network that participates in the integration and processing of external stimuli in order to generate goal directed behavior.     

Single unit activity during a Go/NoGo task in the “prefrontal cortex” of pigeons

Single unit activity was recorded during a delayed auditory/visual Go/NoGo task from the neostriatum caudolaterale (NCL) of pigeons, a multimodal associative avian forebrain structure comparable to the prefrontal cortex (PFC). The animals were trained to mandibulate (to open their beak) during the Go period after which they received a drop of water as reward. Neuronal activity changes were observed during the delay period (DELAY) between auditory and visual stimulation, to the onset of the visual stimulus or to the delivery of the reward. In some neurons, responses were related to the behavioral significance of the stimulus such that the neuronal activity was statistically different between Go and NoGo trials. Moreover, some units anticipated the upcoming reward or changed their firing frequency in a correlated manner prior to beak movements. These neuronal activity patterns suggest that the NCL provides a neural network that participates in the integration and processing of external stimuli in order to generate goal directed behavior.     

Topographic distribution of modality-specific amygdalar neurons in alert monkey

Neuronal activity in the amygdala (AM) was recorded from alert monkeys during performance of tasks that led to presentation of rewarding or aversive stimuli. The tasks had 3 phases: (1) discrimination (visual, auditory), (2) operant response (bar pressing), and (3) ingestion (reward) or avoidance (aversion). Neuronal activity was analyzed and compared during each of these phases. Of 585 AM neurons tested, 312 (53.3%) responded to at least one stimulus in one or more of 5 major groups: vision related, audition related, ingestion related, multimodal, and selective. Forty neurons (6.8%) in the anterior dorsolateral capsule of the basolateral nuclei responded exclusively to visual stimuli (vision related). Twenty-six neurons (4.4%) further posterior in the basolateral group responded only to auditory stimuli (audition related). During ingestion an additional 41 neurons (7.0%) increased their activity (ingestion related). These were in the corticomedial group and at the boundaries between the nuclei of the basolateral group. Of these, 27 responded only in the ingestion phase, 11 during ingestion and at the sight of food, and 3 during ingestion and to certain sounds. Throughout the AM other neurons (n = 117, 20.0%) responded to visual, auditory, and somesthetic stimuli and, when tested, to involuntary ingestion of liquid (multimodal). Of these, 40 responded transiently (phasic; 36 excited, 4 inhibited). The remaining 77 maintained their altered activity into the subsequent phases of the task (tonic; 69 excited, 8 inhibited). In each of these 4 categories, most cells were activated primarily by novel or unfamiliar stimuli, and their responses habituated during repeated stimulation. A small number of cells in the basolateral and the basomedial nuclei (n = 14, 2.4%) were highly selective in that they responded specifically to one biologically significant object or sound more than to any other stimuli (selective). Some of these neurons responded to both sight and ingestion of a specific food. In summary, most AM neurons responded vigorously to novel stimuli, and some of the neurons had multimodal responsiveness. These results suggest the AM is related to processing of new environmental stimuli and to those cross-modal association.     

Neurons in the amygdala of the monkey with responses selective for faces

To investigate the functions of the amygdala in visual information processing and in emotional and social responses, recordings were made from single neurons in the amygdala of the monkey. A population of neurons (40 of more than 1000 recorded in 4 monkeys) was investigated which responded primarily to faces. These neurons typically (1) responded to some human or monkey faces, which were presented to the monkey through a large aperture shutter so that response latencies could be measured, or were simply shown to the monkey, (2) responded to 2-dimensional representations of these faces, as well as to real 3-dimensional faces, (3) had no responses or only small (less than half maximum) responses to gratings, simple geometrical, other complex 3-D stimuli, or to arousing and aversive stimuli, (4) had response latencies of 110-200 ms, (5) were located in the basal accessory nucleus of the amygdala, (6) responded differently to different faces, as shown by measures of d', and could thus over a population of such neurons code information useful for making different responses to different individuals, (7) could in some cases (9/11 tested) respond to parts of faces, and (8) in a few cases (4/19 tested) responded more to a face which produced an emotional response. A comparison made in three monkeys of the responses of these neurons with the responses of 77 neurons with face-selective responses recorded in the cortex of the superior temporal sulcus (STS) showed that the amygdaloid neurons had longer response latencies (110-200 compared to 90-140 ms), and were in some respects more selective in their responses to different faces. It is suggested that the deficits in social and emotional behavior produced by amygdala lesions could be due in part to damage to a neuronal system specialized in utilizing information from faces so that appropriate social and emotional responses can be made to different individuals.     

Responses of striatal neurons in the behaving monkey. 2. Visual processing in the caudal neostriatum

The activity of single neurons was recorded in the tail of the caudate nucleus and adjoining part of the ventral putamen, which receive projections from the inferior temporal visual cortex, in order to investigate the functions of these regions. Of 195 neurons analyzed in two macaque monkeys, 109 (56%) responded to visual stimuli, with latencies of 90-150 ms for the majority of the neurons. The neurons responded to a limited range of complex visual stimuli, and in some cases responded to simpler stimuli such as bars and edges. Typically (in 75% of cases) the neurons habituated rapidly, within 1-8 exposures, to each visual stimulus, but remained responsive to other visual stimuli with a different pattern. This habituation was orientation specific, in that the neurons responded to the same pattern shown in an orthogonal orientation. The habituation was also relatively short-term, in that at least partial dishabituation to one stimulus could be produced by a single intervening presentation of a different visual stimulus. These neurons were relatively unresponsive in a visual discrimination task, having habituated to the stimuli which had been presented in the task on many previous trials. It is suggested on the basis of these results and other studies that these neurons are involved in pattern-specific habituation to repeated visual stimuli, and in attention an orientation to a changed visual stimulus pattern. Changes in attention and orientation to stimuli as a result of damage to the striatum and its afferent and efferent pathways may arise in part because of damage to neurons with responses of this type.     

Influence of substantia innominata neuronal activity on neocortex neuronal reactions during conditioned reflex

Impulse activity of substantia innominata (SI) and motor cortex neurons was studied in cats during conditioned placing with food reinforcement. It was shown that SI neurons have been activated first directly by sound stimuli and later by food reward. Stimulation of SI did not change the background activity of neocortex neurons but promoted the modulation of impulse response to conditioned stimuli. The modulating effect of the SI has a mainly excitatory character, that manifested itself either in a change and increase of the impulse responses of cortical neurons which responded initially to sound stimuli, or in the appearance of impulse responses in those neurons which showed no initial reaction to conditioned sound stimuli.     

Single neuron activity in dorsolateral prefrontal cortex of monkey during operant behavior sustained by food reward

The activity of 190 neurons was recorded from the dorsolateral prefrontal cortex of monkeys during an operant task that consisted of 3 phases: visual discrimination of food and non-food, bar pressing to gain access to the food and ingestion. In area 8, a fairly large proportion of the 49 recorded neurons responded in both the visual discrimination (37%) and motor initiation (35%) phases. Some functional heterogeneity seems evident within area 8 since visual discrimination responses were rostral, visuokinesis was central and motor initiation was in the caudal bank of the arcuate sulcus. Neurons in area 9 responded primarily (37%) during the bar pressing phase and less during the visual discrimination phase. Neurons in area 10 responded variously during most phases of the task--food discrimination, bar pressing, and ingestion. Neurons in the periprincipal sulcal area usually responded in the visual discrimination phase, but some which did not respond to food presented in front of the subject responded to meaningful visual or auditory cues that were related to food reward. The data suggest that neurons in the dorsolateral prefrontal cortex have multiple functions related to all phases of complex, learned feeding behavior. Functional roles of the prefrontal cortex and the lateral hypothalamus in development of feeding behavior are discussed.     

Color properties of the receptive fields of visual cortex neurons in the squirrel

The colour-sensitive properties of the visual cortex neurons were studied in the squirrel. All the neurons responded to achromatic, green and blue visual stimuli; responses to red stimuli were slight or absent. According to responses to patterned visual stimuli the neurons were classified as non-selective, directionally-selective and orientation-selective (simple and complex). No colour-opponent properties were revealed in any of these neuronal groups: neuronal responses were qualitatively the same to achromatic, green and blue stimuli, and the receptive fields organization was independent of the stimulus colour. These data are discussed with respect to the fact of presence of colour-opponent cells in the retina and lateral geniculate nucleus of squirrel.     

Responses of the neurons of the parietal associative cortex of the cat brain to indifferent and conditioned acoustic stimuli

Neuronal responses of the associative cortex (field 5) to indifferent and to conditioned sound stimuli were studied. The number of neurons responding to the conditioned sound during classical reflex increased two times. A percentage of inhibitory responses of neurons to conditioned acoustic stimulus during placing reflex grew. Neurons were found which responded to the conditioned sound only in the absence of the conditioned movement during instrumental food reflex. Despite the fact that the associative cortex participates in the analysis of sensory signals and in evaluation of their biological significance, its main functional property is its involvement in the initiation of behavioral reaction to the conditioned stimulus.     

Tolerances of responses to visual patterns in neurons of the posterior inferotemporal cortex in the macaque against changing stimulus size and orientation, and deleting patterns

Neuronal activities were recorded in areas TEO and TE of the inferotemporal cortex in four hemispheres of two monkeys during the performance of a visual pattern discrimination task. Tolerances of responses to patterns against changing stimulus size and orientation, and deleting patterns halves were investigated and compared between TEO and TE neurons. Of 311 neurons tested, 80 (26%) responded to one or more patterns out of four standard patterns. Of these 80 neurons, 50 (63%) were recorded in area TEO and 30 (38%) in area TE. Neurons responsive to patterns were recorded in both areas TEO and TE, however degrees of tolerance of responses were different between TEO and TE neurons. Tolerances of TEO neurons were moderate and degrees of tolerance varied from neuron to neuron. Responses to particular patterns were dependent on stimulus size, stimulus orientation, and/or completeness of patterns. By contrast, tolerances of TE neurons were generally strong. Responses to particular patterns were not affected by changing stimulus size, changing stimulus orientation nor deleting patterns halves. These results suggest that area TEO rather than area TE is involved in detecting and processing particular visual shapes.