Effects of task demands on the responses of color-selective neurons in the inferior temporal cortex

Categorization and fine discrimination are two different functions in visual perception, and we can switch between these two functions depending on the situation or task demands. To explore how visual cortical neurons behave in such situations, we recorded the activities of color-selective neurons in the inferior temporal (IT) cortex of two monkeys trained to perform a color categorization task, a color discrimination task and a simple fixation task. Many IT neurons changed their activity depending upon the task, although color selectivity was well conserved. A majority of neurons showed stronger responses during the categorization task. Moreover, for the population of IT neurons as a whole, signals contributing to performing the categorization task were enhanced. These results imply that judgment of color category by color-selective IT neurons is facilitated during the categorization task and suppressed during the discrimination task as a consequence of task-dependent modulation of their activities.     

Relationship between color discrimination and neural responses in the inferior temporal cortex of the monkey

Earlier studies suggest that the inferior temporal (IT) cortex of the monkey plays a key role in color discrimination. Here, we examined the quantitative relationship between color judgment in monkeys and the responses of color-selective neurons in the anterior part of the IT cortex (area TE) by comparing neuronal activity and behavior recorded simultaneously while the monkeys performed a color-judgment task. We first compared the abilities of single neurons and monkeys to discriminate color. To calculate a neuron's ability to discriminate color, we computed a neurometric function using receiver-operating-characteristics analysis. We then compared the neural and behavioral thresholds for color discrimination and found that, in general, the neural threshold was higher than the behavioral threshold, although occasionally the reverse was true. Variation in the neural threshold across the color space corresponded well with that of the behavioral threshold. We then calculated the choice probability (CP), which is a measure of the correlation between the trial-to-trial fluctuations in neuronal responses and the monkeys' color judgment. On average, CPs were slightly but significantly greater than 0.5, indicating the activities of these TE neurons correlate positively with the monkeys' color judgment. This suggests that individual color-selective TE neurons only weakly contribute to color discrimination and that a large population of color-selective TE neurons contribute to the performance of color discrimination.     

Functional connectivity of the frontal eye fields in humans and macaque monkeys investigated with resting-state fMRI

Although the frontal eye field (FEF) has been identified in macaque monkeys and humans, practical constraints related to invasiveness and task demands have limited a direct cross-species comparison of its functional connectivity. In this study, we used resting-state functional MRI data collected from both awake humans and anesthetized macaque monkeys to examine and compare the functional connectivity of the FEF. A seed region analysis revealed consistent ipsilateral functional connections of the FEF with fronto-parietal cortical areas across both species. These included the intraparietal sulcus, dorsolateral prefrontal cortex, anterior cingulate cortex, and supplementary eye fields. The analysis also revealed greater lateralization of connectivity with the FEF in both hemispheres in humans than in monkeys. Cortical surface-based transformation of connectivity maps between species further corroborated the remarkably similar organization of the FEF functional connectivity. The results support an evolutionarily preserved fronto-parietal system and provide a bridge for linking data from monkey and human studies.     

Cortical afferents to the smooth-pursuit region of the macaque monkey’s frontal eye field

In primates, the frontal eye field (FEF) contains separate representations of saccadic and smooth-pursuit eye movements. The smooth-pursuit region (FEFsem) in macaque monkeys lies principally in the fundus and deep posterior wall of the arcuate sulcus, between the FEF saccade region (FEFsac) in the anterior wall and somatomotor areas on the posterior wall and convexity. In this study, cortical afferents to FEFsem were mapped by injecting retrograde tracers (WGA-HRP and fast blue) into electrophysiologically identified FEFsem sites in two monkeys. In the frontal lobe, labeled neurons were found mostly on the ipsilateral side in the (1) supplementary eye field region and lateral area F7; (2) area F2 along the superior limb of the arcuate sulcus; and (3) in the buried cortex of the arcuate sulcus extending along the superior and inferior limbs and including FEFsac and adjacent areas 8, 45, and PMv. Labeled cells were also found in the caudal periprincipal cortex (area 46) in one monkey. Labeled cells were found bilaterally in the frontal lobe in the deep posterior walls of the arcuate sulcus and postarcuate spurs and in cingulate motor areas 24 and 24c. In postcentral cortical areas all labeling was ipsilateral and there were two major foci of labeled cells: (1) the depths of the intraparietal sulcus including areas VIP, LIP, and PEa, and (2) the anterior wall and fundus of the superior temporal sulcus including areas PP and MST. Smaller numbers of labeled cells were found in superior temporal sulcal areas FST, MT, and STP, posterior cingulate area 23b, area 3a within the central sulcus, areas SII, RI, Tpt in the lateral sulcus, and parietal areas 7a, 7b, PEc, MIP, DP, and V3A. Many of these posterior afferent cortical areas code visual-motion (MT, MST, and FST) or visual-motion and vestibular (PP, VIP) signals, consistent with the responses of neurons in FEFsem and with the overall physiology and anatomy of the smooth-pursuit eye movement system.     

Neuronal correlates of face identification in the monkey anterior temporal cortical areas

To investigate the neuronal basis underlying face identification, the activity of face neurons in the anterior superior temporal sulcus (STS) and the anterior inferior temporal gyrus (ITG) of macaque monkeys was analyzed during their performance of a face-identification task. The face space was composed by the activities of face neurons during the face-identification task, based on a multidimensional scaling (MDS) method; the face space composed by the anterior STS neurons represented facial views, whereas that composed by the anterior ITG neurons represented facial identity. The temporal correlation between the behavioral reaction time of the animal and the latency of face-related neuronal responses was also analyzed. The response latency of some of the face neurons in the anterior ITG exhibited a significant correlation with the behavioral reaction time, whereas this correlation was not significant in the anterior STS. The correlation of the latency of face-related neuronal responses in the anterior ITG with the behavioral reaction time was not found to be attributed to the correlation between the response latency and the magnitude of the neuronal responses. The present results suggest that the anterior ITG is closely related to judgments of facial identity, and that the anterior STS is closely related to analyses of incoming perceptual information; face identification in monkeys might involve interactions between the two areas.     

Enhancement of inferior temporal neurons during visual discrimination

1. Previous results have shown that spatially directed attention enhances the stimulus-elicited responses of neurons in some areas of the brain. In the inferior temporal (IT) cortex, however, directing attention toward a stimulus mildly inhibits the responses of the neurons. Inferior temporal cortex is involved in pattern discrimination, but not spatial localization. If enhancement signifies that a neuron is participating in the function for which that part of cortex is responsible, then pattern discrimination, not spatial attention, should enhance responses of IT neurons. The influence of pattern discrimination behavior on the responses of IT neurons was therefore compared with previously reported suppressive influences of both spatial attention and the fixation point. 2. Single IT neurons were recorded from two monkeys while they performed each of five tasks. One task required the monkey to make a pattern discrimination between a bar and a square of light. In the other four tasks the same bar of light appeared, but the focus of spatial attention could differ, and the fixation point could be present or absent. Either attention to (without discrimination of) the bar stimulus or the presence of the fixation point attenuated responses slightly. These two suppressive influences produced a greater attenuation when both were present. 3. The visual conditions and motor requirements when the bar stimulus appeared in the discrimination task were identical to those of the trials in the stimulus attention task. However, one-half of the responsive neurons showed significantly stronger responses to the bar stimulus when it appeared in the discrimination task than when it appeared in the stimulus attention task. For most of these neurons, discrimination just overcame the combined effect of the two suppressive influences. For six other neurons, the response strength was significantly greater during the discrimination task than during any other task. 4. The monkeys achieved an overall correct performance rate of 90% in both the discrimination and stimulus attention tasks. To achieve this performance in the discrimination task they adopted a strategy in which they performed one trial type, bar stimulus attention trials, perfectly (100%) and the other trial type, pattern trials, relatively poorly (84% correct).(ABSTRACT TRUNCATED AT 400 WORDS)     

Connections of the medial posterior parietal cortex (area 7m) in the monkey

The afferent and efferent cortical and subcortical connections of the medial posterior parietal cortex (area 7m) were studied in cebus (Cebus apella) and macaque (Macaca fascicularis) monkeys using the retrograde and anterograde capabilities of the horseradish peroxidase (HRP) technique. The principal intraparietal corticocortical connections of area 7m in both cebus and macaque cases were with the ipsilateral medial bank of the intraparietal sulcus (MIP) and adjacent superior parietal lobule (area 5), inferior parietal lobule (area 7a), lateral bank of the IPS (area 7ip), caudal parietal operculum (PGop), dorsal bank of the caudal superior temporal sulcus (visual area MST), and medial prestriate cortex (including visual area PO and caudal medial lobule). Its principal frontal corticocortical connections were with the prefrontal cortex in the shoulder above the principal sulcus and the cortex in the shoulder above the superior ramus of the arcuate sulcus (SAS), the area purported to contain the smooth eye movement-related frontal eye field (FEFsem) in the cebus monkey by other investigators. There were moderate connections with the cortex in the rostral bank of the arcuate sulcus (purported to contain the saccade-related frontal eye field; FEFsac), supplementary eye field (SEF), and rostral dorsal premotor area (PMDr). Area 7m also had major connections with the cingulate cortex (area 23), particularly the ventral bank of the cingulate sulcus. The principal subcortical connections of area 7m were with the dorsal portion of the ventrolateral thalamic (VLc) nucleus, lateral posterior thalamic nucleus, lateral pulvinar, caudal mediodorsal thalamic nucleus and medial pulvinar, central lateral, central superior lateral, and central inferior intralaminar thalamic nuclei, dorsolateral caudate nucleus and putamen, middle region of the claustrum, nucleus of the diagonal band, zona incerta, pregeniculate nucleus, anterior and posterior pretectal nuclei, intermediate layer of the superior colliculus, nucleus of Darkschewitsch and dorsomedial parvicellular red nucleus (macaque cases only), dorsal, dorsolateral and lateral basilar pontine nuclei, nucleus reticularis tegmenti pontis, locus ceruleus, and superior central nucleus. The findings are discussed in terms of the possibility that area 7m contains a "medial parietal eye field" and belongs to a neural network of oculomotor-related structures that plays a role in the control of eye movement.     

Distributed cortical networks for focused auditory attention and distraction

We used behavioral measures and functional magnetic resonance imaging (fMRI) to study the effects of parametrically varied task-irrelevant pitch changes in attended sounds on loudness-discrimination performance and brain activity in cortical surface maps. Ten subjects discriminated tone loudness in sequences that also included infrequent task-irrelevant pitch changes. Consistent with results of previous studies, the task-irrelevant pitch changes impaired performance in the loudness discrimination task. Auditory stimulation, attention-enhanced processing of sounds and motor responding during the loudness discrimination task activated supratemporal (auditory cortex) and inferior parietal areas bilaterally and left-hemisphere (contralateral to the hand used for responding) motor areas. Large pitch changes were associated with right hemisphere supratemporal activations as well as widespread bilateral activations in the frontal lobe and along the intraparietal sulcus. Loudness discrimination and distracting pitch changes activated common areas in the right supratemporal gyrus, left medial frontal cortex, left precentral gyrus, and left inferior parietal cortex.     

Vestibular projections in the human cortex

There is considerable evidence from studies on cats and monkeys that several cortical areas such as area 2v at the tip of the intraparietal sulcus, area 3av in the sulcus centralis, the parietoinsular vestibular cortex adjacent to the posterior insula (PIVC) and area 7 in the inferior parietal lobule are involved in the processing of vestibular information. Microelectrode recordings from these areas have shown that: (1) most of these cortical neurons are connected trisynaptically to the labyrinthine endorgans and (2) they receive converging vestibular, visual and somatosensory inputs. These data suggest that a multimodal cortical system is involved in postural and gaze control. In humans, recent positron emission tomography (PET) scans and functional magnetic resonance imaging (fMRI) studies have largely confirmed these data. However, because of the limited temporal resolution of these two methods, the minimum time of arrival of labyrinthine inputs from the vestibular hair cells to these cortical areas has not yet been determined. In this study, we used the evoked potential method to attempt to answer this question. Due to its excellent temporal resolution, this method is ideal for the investigation of the tri- or polysynaptic nature of the vestibulocortical pathways. Eleven volunteer patients, who underwent a vestibular neurectomy due to intractable Meniere's disease (MD) or acoustic neurinoma resection, were included in this experiment. Patients were anesthetized and the vestibular nerve was electrically stimulated. The evoked potentials were recorded by 30 subcutaneous active electrodes located on the scalp. The brain electrical source imaging (BESA) program (version 2.0, 1995) was used to calculate dipole sources. The latency period for the activation of five distinct cortical zones, including the prefrontal and/or the frontal lobe, the ipsilateral temporoparietal cortex, the anterior portion of the supplementary motor area (SMA) and the contralateral parietal cortex, was 6 ms. The short latency period recorded for each of these areas indicates that several trisynaptic pathways, passing through the vestibular nuclei and the thalamic neurons, link the primary vestibular afferents to the cortex. We suggest that all these areas, including the prefrontal area, process egomotion information and may be involved in planning motor synergies to counteract loss of equilibrium.     

Neural networks active during tactile form perception: common and differential activity during macrospatial and microspatial tasks.

Prior studies have shown that tactile perception recruits activity not only in somatosensory but also in visual cortical areas. The present study used functional magnetic resonance imaging to investigate the distribution of neural activity during tactile perception of 2D form. In a macrospatial form task, raised letters (uppercase T and V) were presented upside-down. In a microspatial form task, a bar, either with or without a gap, was presented. Stimuli were applied to the immobilized right index fingerpad. Six neurologically normal volunteers were studied in a block design paradigm, with alternating blocks of rest and covert discrimination between the two alternatives for a task. Each task was studied in a separate run. Contrasting macrospatial form discrimination against rest revealed activity in an extensive, bilateral network of cortical and subcortical regions, including areas of somatosensory cortex and the intraparietal sulcus (IPS), occipito-temporal cortex, dorsal and ventral premotor cortex, medial superior frontal cortex, lateral inferior frontal cortex, thalamus and cerebellar hemispheres. Contrasting (microspatial) gap detection against rest showed activity in a similar network, with the notable exception of the occipito-temporal cortical regions. A direct contrast between the two tasks yielded greater activity for the macrospatial than microspatial task in these occipito-temporal regions bilaterally, and also in foci near the right IPS and in the right cerebellar hemisphere. The occipito-temporal cortical activations were in the lateral occipital complex, a part of the ventral visual pathway active during visual form perception. Thus, macrospatial form perception preferentially recruits this region of extrastriate visual cortex, compared to microspatial form perception.     

Differential involvement of the human temporal lobe structures in short- and long-term memory processes assessed by intracranial ERPs

Intracranial event-related potentials (ERPs) elicited during a recognition memory task were recorded in 25 epileptic patients by using depth electrodes sampling four different regions within the temporal lobe (amygdala, hippocampus, anterior and posterior temporal cortices). The task was a continuous recognition memory task in which repeated items were presented after 6 or 19 intervening items following their first presentation. This study was performed to investigate the respective role of the different temporal lobe structures in short-term memory (STM) and long-term memory (LTM) processing. Subregions of the temporal lobe were differently involved in these two memory systems. The posterior temporal cortex is specifically involved in STM processing, whereas the amygdala, hippocampus, and anterior temporal cortex contribute to both STM and LTM. Moreover, it appeared that the latter structures play their own role in LTM. The anterior temporal cortex and amygdala may contribute to recency discrimination, and the hippocampus seems rather to be involved in maintaining memory traces. These findings suggest that the temporal lobe structures may function in a complementary way by subserving different aspects of information processing.     

Faces and objects in macaque cerebral cortex

How are different object categories organized by the visual system? Current evidence indicates that monkeys and humans process object categories in fundamentally different ways. Functional magnetic resonance imaging (fMRI) studies suggest that humans have a ventral temporal face area, but such evidence is lacking in macaques. Instead, face-responsive neurons in macaques seem to be scattered throughout temporal cortex, with some relative concentration in the superior temporal sulcus (STS). Here, using fMRI in alert fixating macaque monkeys and humans, we found that macaques do have discrete face-selective patches, similar in relative size and number to face patches in humans. The face patches were embedded within a large swath of object-selective cortex extending from V4 to rostral TE. This large region responded better to pictures of intact objects compared to scrambled objects, with different object categories eliciting different patterns of activity, as in the human. Overall, our results suggest that humans and macaques share a similar brain architecture for visual object processing.     

Ventrolateral prefrontal cortex activity associated with individual differences in arbitrary delayed paired-association learning performance: A functional magnetic resonance imaging study

To describe the neural substrates of successful episodic long-term memory encoding, we collected functional magnetic-resonance imaging data as participants completed an arbitrary delayed auditory paired-association learning task. During the task, subjects learned predefined but hidden stimulus pairs by trial and error based on visual feedback. Delay period activity represents the retrieval of the relationship between the cue item and its candidate for associates, that is, working memory. Our hypothesis was that the neural substrates of working memory would be related to long-term memory encoding in a performance-dependent manner. Thus, inter-individual variance in performance following a fixed learning set would be associated with differing neural activations during the delay period. The number of learning trials was adjusted such that performance following completion of the learning set varied across subjects. Each trial consisted of the successive presentation of two stimuli (first stimulus and second stimulus [S2]) with a fixed delay interval, allowing extraction of sustained activity during the delay period. Sustained activities during the delay period were found in the bilateral dorsolateral prefrontal cortex, intraparietal sulcus, and left ventrolateral prefrontal cortex, as well as the premotor and pre-supplementary motor areas. The activities did not change in strength across learning, suggesting that these effects represent working memory components. The sustained activity in the ventrolateral prefrontal region was correlated with task performance. Task performance was also positively correlated with the decrement in S2/feedback-related activity during learning in the superior temporal sulcus, a region previously shown to be involved in association learning. These findings are consistent with lesion and neuroimaging studies showing that the ventrolateral prefrontal cortex plays an important role in long-term memory encoding, and raise the possibility that working memory processes interact with long-term memory formation as represented by the covariation of activity in the superior temporal sulcus and the ventrolateral prefrontal cortex.     

Afferent cortical connections of the motor cortical larynx area in the rhesus monkey

The present study describes the cortical input into the motor cortical larynx area. The retrograde tracer horseradish peroxidase-conjugated wheat germ agglutinin was injected into the electrophysiologically identified motor cortical larynx area in three rhesus monkeys (Macaca mulatta). Retrogradely labeled cells were found in the surrounding premotor cortex (areas 6V and 6D), primary motor cortex (area 4), primary somatosensory cortex (areas 3, 1 and 2), anterior and posterior secondary somatosensory cortex and the probable homologue of Broca's area (areas 44 and 45); furthermore, labeling was found in the supplementary motor area, anterior and posterior cingulate cortex (areas 24 and 23), prefrontal and orbital frontal cortex (areas 8A, 46V, 47/12L, 47/12O, 13), agranular, dysgranular and granular insula as well as in the cortex within the upper bank of the middle third of the superior temporal sulcus (area TPO). The majority of these regions are reciprocally connected with the motor cortical larynx area [Brain Res 949 (2000) 23]. The laryngeal motor cortical input is discussed in relation to the connections of other motor cortical areas and its role in vocal control.     

Topographic maps of visual spatial attention in human parietal cortex

Functional magnetic resonance imaging (fMRI) was used to measure activity in human parietal cortex during performance of a visual detection task in which the focus of attention systematically traversed the visual field. Critically, the stimuli were identical on all trials (except for slight contrast changes in a fully randomized selection of the target locations) whereas only the cued location varied. Traveling waves of activity were observed in posterior parietal cortex consistent with shifts in covert attention in the absence of eye movements. The temporal phase of the fMRI signal in each voxel indicated the corresponding visual field location. Visualization of the distribution of temporal phases on a flattened representation of parietal cortex revealed at least two distinct topographically organized cortical areas within the intraparietal sulcus (IPS), each representing the contralateral visual field. Two cortical areas were proposed based on this topographic organization, which we refer to as IPS1 and IPS2 to indicate their locations within the IPS. This nomenclature is neutral with respect to possible homologies with well-established cortical areas in the monkey brain. The two proposed cortical areas exhibited relatively little response to passive visual stimulation in comparison with early visual areas. These results provide evidence for multiple topographic maps in human parietal cortex.     

Acetylcholinesterase histochemistry in the macaque thalamus reveals territories selectively connected to frontal, parietal and temporal association cortices

The patterns of histochemical staining for acetylcholinesterase (AChE) activity in the macaque thalamus were analyzed and compared with the distribution of cells and terminals labeled from injections of axonal tracers in the dorsolateral and orbital prefrontal cortex, in area 7a of the posterior parietal cortex and in the polysensory cortex of the superior temporal sulcus. AChE histochemistry is very useful in delineating the thalamic nuclei connected with the association cortex and in uncovering thalamic subdivisions that are barely evident on cytoarchitectonic grounds. Moreover, AChE activity reveals previously unrecognized heterogeneities within several thalamic nuclei, like the ventral anterior (VA), where a new ventromedial subdivision (VAvm) is described, the medial pulvinar (PuIM) or the mediodorsal nucleus (MD). In this nucleus three distinct chemical domains are present: the medial, ventral and lateral sectors characterized by low, moderate and high AChE activities, respectively. The staining pattern of the lateral sector is markedly heterogeneous with patches of intense AChE activity surrounded by a moderately stained matrix. The MD medial sector is connected with the orbitofrontal cortex, whereas the AChE-rich patches in the lateral sector are selectively connected with the dorsolateral prefrontal, parietal and temporal association cortices. In the PulM, a dorsomedial AChE-rich patch is selectively connected with the orbitofrontal cortex, whereas the surrounding territory, which shows moderate AChE activity, is preferentially connected with the parietal and temporal cortices. Chemically specific domains in the anterior, ventral anterior, midline, and intralaminar thalamic nuclei are also connected with the examined association cortices. These findings indicate that the topographic patterns of the thalamo-cortical connections of primate association areas conform to the chemical architecture of the thalamus. This implies that because each cortical area is connected to a particular set of thalamic regions, the influence of the thalamus on cortical function is exclusive for each area, highly diverse among the various association areas, and subject to a wide range of modulation at the thalamic level.     

Afferent connections of the prelunate visual association cortex (areas V4 and DP)

Summary The afferent and efferent connections of the prelunate visual association area V4 of macaque monkeys were investigated by means of the horseradish peroxidase (HRP) method. The specific thalamic afferents from the dorsolateral segment of the medial pulvinar and the lateral segment of the inferior pulvinar were topographically organized. A band of cells was labelled in the intralaminar nuclei (nucl. centr. med. and lat., reaching into LD and the most dorsal part of VL), and a few cells in the interlaminar layers of the lateral geniculate body. Other diencephalic afferents included the claustrum, the nucleus basalis Meynert and the pars compacta of the substantia nigra. Ipsilateral cortical areas which projected into V4 included area 18 (V2), the inferior parietal cortex, the anterior and posterior parts of the superior temporal sulcus, the frontal eye fields and the temporo-basal association cortex on the lateral half of the parahippocampal gyrus and around the occipito-temporal sulcus. In the contralateral cortex, discontinuous regions in areas V4 and V5 on the prelunate gyrus and some cells at the 17/18-border were labelled. All regions in which labelled cells were found and, in addition a restricted region in the dorsal cap of the head and the tail of the caudate nucleus showed fibre and terminal labelling. In addition mesencephalic afferents and efferents were identified but not investigated in detail. An attempt to estimate the quantitative contribution of the various afferent systems to the prelunate cortex was made by counting the labelled cells in the different areas. The afferent and efferent organization of the prelunate visual association area indicates that it is incorporated in a network of cortical and subcortical regions involved in various aspects of visual behavior.     

Spatial working memory in human extrastriate cortex

The performance of spatial working memory tasks is known to evoke activity in a set of higher-order association areas, including the prefrontal cortex, posterior parietal cortex and the frontal and supplementary eye fields. Recent physiological studies in monkey have shown that memory-related activity also is found in extrastriate cortex [J. Neurophysiol. 84 (2000) 677]. We conducted functional magnetic resonance imaging studies to determine whether human extrastriate cortex contributes to the on-line maintenance of spatial information in an eye movement task. We found that performance of memory-guided saccades, as compared to visually guided saccades, elicited significant activation in two areas of extrastriate cortex: the posterior superior temporal sulcus (PST) and lateral occipitotemporal cortex (LOT). Both areas also were activated during the basic sensorimotor task of visually guided saccades as compared to fixation. We further determined that area LOT is close to but distinct from motion-sensitive area MT+. These findings demonstrate that areas PST and LOT, along with higher-level association cortex, help to encode and maintain spatial representations.     

Rhinal cortex lesions produce mild deficits in visual discrimination learning for an auditory secondary reinforcer in rhesus monkeys.

Aspiration, but not neurotoxic, lesions of the amygdala impair performance on a visual discrimination learning task in which an auditory secondary reinforcer signals which of 2 stimuli will be reinforced with food. Because aspiration lesions of the amygdala interrupt projections of the rhinal cortex traveling close to the amygdala, it was hypothesized that damage to the rhinal cortex would severely impair learning in this task. Rhesus monkeys (Macaca mulatta) were trained to solve visual discrimination problems based on an auditory secondary reinforcer, were given lesions of the rhinal cortex or the perirhinal cortex alone, and were then retested. The monkeys displayed a reliable, albeit mild, deficit in postoperative performance. It is concluded that the aspiration lesions of the amygdala that produced a severe impairment did so because they interrupted connections of temporal cortical fields beyond the rhinal cortex that are also involved in learning in this task.     

Two distinct projection areas from tongue nerves in the frontal operculum of macaque monkeys as revealed with evoked potential mapping

Projection areas in the cerebral cortex from tongue nerves were investigated in anesthetized macaque monkeys (Macaca fuscata). Three tongue nerves (lingual nerve, chorda tympani, and a lingual branch of the glossopharyngeal nerve) were electrically stimulated and thereby evoked mass field potentials were recorded with microelectrodes roving through the exposed and buried frontal operculum. Two distinct tongue nerve projection areas were thus located; one in the lower part of the precentral gyrus ventral to the inferior precentral sulcus, and the other in the medial part of the buried frontal operculum. The former corresponds to the "cortical masticatory area", previously defined in macaque monkeys as involved in somatic sensation as well as mastication. However, the prominent projection from the chorda tympani and glossopharyngeal nerve branch, containing taste fibers, to this area suggests its involvement in taste sensation. The latter corresponds to the "pure gustatory area" defined in squirrel monkeys in both location and cytoarchitecture. However, projection to this area from the lingual nerve, which contains only somatic nerve fibers, suggests its involvement in somatic sensation, as well.