An fMRI version of the Farnsworth-Munsell 100-Hue test reveals multiple color-selective areas in human ventral occipitotemporal cortex.

Studies of patients with cerebral achromatopsia have suggested that ventral occipitotemporal cortex is important for color perception. We created a functional magnetic resonance imaging (fMRI) version of a clinical test commonly used to assess achromatopsia, the Farnsworth-Munsell 100-Hue test. The test required normal subjects to use color information in the visual stimulus to perform a color sequencing task. A modification of the test requiring ordering by luminance was used as a control task. Subjects were also imaged as they passively viewed colored stimuli. A limited number of areas responded more to chromatic than achromatic stimulation, including primary visual cortex. Most color-selective activity was concentrated in ventral occipitotemporal cortex. Several areas in ventral cortex were identified. The most posterior, located in posterior fusiform gyrus, corresponded to the area activated by passive viewing of colored stimuli. More anterior and medial color-selective areas were located in the collateral sulcus and fusiform gyrus. These more anterior areas were not identified in previous imaging studies which used passive viewing of colored stimuli, and were most active in our study when visual color information was behaviorally relevant, suggesting that attention influences activity in color-selective areas. The fMRI version of the Farnsworth-Munsell test may be useful in the study of achromatopsia.     

Population dynamics of face-responsive neurons in the inferior temporal cortex

Neurons in the inferior temporal (IT) cortex of monkeys respond selectively to complex visual stimuli, such as faces. Single neurons in the IT cortex encode different kinds of information about visual stimuli in their temporal firing patterns. To understand the temporal aspects of the information encoded at a population level in the IT cortex, we applied principal component analysis (PCA) to the responses of a population of neurons. The responses of each neuron were recorded while visual stimuli that consisted of geometric shapes and faces of humans and monkeys were presented. We found that global categorization, i.e. human faces versus monkey faces versus shapes, occurred in the earlier part of the population response, and that fine categorization occurred within each member of the global category in the later part of the population response. A cluster analysis, a mixture of Gaussians analysis, confirmed that the clusters in the earlier part of the responses represented the global category. Moreover, the clusters in the earlier part separated into sub-clusters corresponding to either human identity or monkey expression in the later part of the responses, and the global categorization was maintained even after the appearance of the sub-clusters. The results suggest that a hierarchical relationship of the test stimuli is represented temporally by the population response of IT neurons.     

A study of pyramidal cell structure in the cingulate cortex of the macaque monkey with comparative notes on inferotemporal and primary visual cortex

Recent studies have revealed a marked degree of variation in the pyramidal cell phenotype in visual, somatosensory, motor and prefrontal cortical areas in the brain of different primates, which are believed to subserve specialized cortical function. In the present study we carried out comparisons of dendritic structure of layer III pyramidal cells in the anterior and posterior cingulate cortex and compared their structure with those sampled from inferotemporal cortex (IT) and the primary visual area (V1) in macaque monkeys. Cells were injected with Lucifer Yellow in flat-mounted cortical slices, and processed for a light-stable DAB reaction product. Size, branching pattern, and spine density of basal dendritic arbors was determined, and somal areas measured. We found that pyramidal cells in anterior cingulate cortex were more branched and more spinous than those in posterior cingulate cortex, and cells in both anterior and posterior cingulate were considerably larger, more branched, and more spinous than those in area V1. These data show that pyramidal cell structure differs between posterior dysgranular and anterior granular cingulate cortex, and that pyramidal neurons in cingulate cortex have different structure to those in many other cortical areas. These results provide further evidence for a parallel between structural and functional specialization in cortex.     

Cortical connections of area V4 in the macaque

To determine the locus, full extent, and topographic organization of cortical connections of area V4 (visual area 4), we injected anterograde and retrograde tracers under electrophysiological guidance into 21 sites in 9 macaques. Injection sites included representations ranging from central to far peripheral eccentricities in the upper and lower fields. Our results indicated that all parts of V4 are connected with occipital areas V2 (visual area 2), V3 (visual area 3), and V3A (visual complex V3, part A), superior temporal areas V4t (V4 transition zone), MT (medial temporal area), and FST (fundus of the superior temporal sulcus [STS] area), inferior temporal areas TEO (cytoarchitectonic area TEO in posterior inferior temporal cortex) and TE (cytoarchitectonic area TE in anterior temporal cortex), and the frontal eye field (FEF). By contrast, mainly peripheral field representations of V4 are connected with occipitoparietal areas DP (dorsal prelunate area), VIP (ventral intraparietal area), LIP (lateral intraparietal area), PIP (posterior intraparietal area), parieto-occipital area, and MST (medial STS area), and parahippocampal area TF (cytoarchitectonic area TF on the parahippocampal gyrus). Based on the distribution of labeled cells and terminals, projections from V4 to V2 and V3 are feedback, those to V3A, V4t, MT, DP, VIP, PIP, and FEF are the intermediate type, and those to FST, MST, LIP, TEO, TE, and TF are feedforward. Peripheral field projections from V4 to parietal areas could provide a direct route for rapid activation of circuits serving spatial vision and spatial attention. By contrast, the predominance of central field projections from V4 to inferior temporal areas is consistent with the need for detailed form analysis for object vision.     

Connectivity-based subdivisions of the human right "temporoparietal junction area": evidence for different areas participating in different cortical networks

Controversy surrounds the role of the temporoparietal junction (TPJ) area of the human brain. Although TPJ has been implicated both in reorienting of attention and social cognition, it is still unclear whether these functions have the same neural basis. Indeed, whether TPJ is a precisely identifiable cortical region or a cluster of subregions with separate functions is still a matter of debate. Here, we examined the structural and functional connectivity of TPJ, testing whether TPJ is a unitary area with a heterogeneous functional connectivity profile or a conglomerate of regions with distinctive connectivity. Diffusion-weighted imaging tractrography-based parcellation identified 3 separate regions in TPJ. Resting-state functional connectivity was then used to establish which cortical networks each of these subregions participates in. A dorsal cluster in the middle part of the inferior parietal lobule showed resting-state functional connectivity with, among other areas, lateral anterior prefrontal cortex. Ventrally, an anterior TPJ cluster interacted with ventral prefrontal cortex and anterior insula, while a posterior TPJ cluster interacted with posterior cingulate, temporal pole, and anterior medial prefrontal cortex. These results indicate that TPJ can be subdivided into subregions on the basis of its structural and functional connectivity.     

The effect of visual experience on the development of functional architecture in hMT+

We investigated whether the visual hMT+ cortex plays a role in supramodal representation of sensory flow, not mediated by visual mental imagery. We used functional magnetic resonance imaging to measure neural activity in sighted and congenitally blind individuals during passive perception of optic and tactile flows. Visual motion-responsive cortex, including hMT+, was identified in the lateral occipital and inferior temporal cortices of the sighted subjects by response to optic flow. Tactile flow perception in sighted subjects activated the more anterior part of these cortical regions but deactivated the more posterior part. By contrast, perception of tactile flow in blind subjects activated the full extent, including the more posterior part. These results demonstrate that activation of hMT+ and surrounding cortex by tactile flow is not mediated by visual mental imagery and that the functional organization of hMT+ can develop to subserve tactile flow perception in the absence of any visual experience. Moreover, visual experience leads to a segregation of the motion-responsive occipitotemporal cortex into an anterior subregion involved in the representation of both optic and tactile flows and a posterior subregion that processes optic flow only.     

Unilateral deficits in visual perception and learning after unilateral inferotemporal cortex lesions in macaques

This study adapted the method of partial lesions, combined with controlled fixation, to study the perceptual role of macaque inferotemporal (IT) cortex. Unilateral lesions were made in IT cortex of three monkeys, without section of the corpus callosum, and visual function was tested ipsilateral and contralateral to the lesion. The observed changes were compared to the effects of bilateral lesions of IT cortex in one monkey, the approach used in most previous studies. Unilateral lesions produced far less profound, although more selective, loss on the tested visual abilities than did bilateral lesions. All three monkeys with unilateral lesions showed decreased chromatic sensitivity, but sparing of achromatic sensitivity, and severely disrupted learning and performance of visual matching to sample, and in all cases, the visual loss was contralateral to the site of the lesion. Unexpectedly, the magnitude of the contralateral loss was not increased by later section of the corpus callosum and anterior commissure in one of the monkeys, a lesion that removes interhemispheric input to contralateral from ipsilateral temporal cortex neurons. These results support physiological findings that show that the response of IT cortex neurons is dominated by the contralateral visual field, despite the bilateral activation many IT neurons receive. Comparison to earlier studies of lesions of area V4, which provides input to IT cortex, shows that V4 and IT lesions produce qualitatively different effects.     

Cholinergic immunoreactive fibers in monkey anterior temporal cortex.

Cholinergic processes in anterior temporal cortex of rhesus monkeys were identified using immunocytochemical techniques for ChAT. Labeled fibers were present throughout the temporal pole and anterior aspects of the superior temporal, middle temporal, and inferior temporal gyri. ChAT-immunoreactive fibers were most dense in layer I to superficial layer III throughout anterior temporal cortex. In temporal pole, agranular and dysgranular regions had a greater density of labeled fibers in superficial layers as compared to granular regions. In addition to the superficial concentration of cholinergic fibers in lateral temporal regions, numerous labeled fibers were also present in deep cortical layers in the inferior temporal gyrus of lateral temporal cortex, with lesser concentrations of immunoreactive fibers present in these layers in superior and middle temporal gyri. These patterns of cholinergic innervation may reflect the degree of cholinergic modulation of functions in anterior temporal cortex.     

Visual areas in the lateral temporal cortex of the ferret (Mustela putorius)

Using systematic electrophysiological mapping, architectonics and the global pattern of interhemispheric connectivity, we have identified three visual areas in the lateral most part of the posterior suprasylvian gyrus. The most posterior and largest area we call area 20a and anterior to this we defined a smaller area, area 20b. These areas lie lateral to the visual areas 18, 19 and 21 and posterior to a third, but incompletely defined, visual area, area PS. Areas 20a and 20b, emphasize the representation of the upper hemifield. Their interhemispheric connections conform to the so called 'midline rule' in that they are abundant in regions representing central portions of the visual field, scarce or absent elsewhere. These areas are probably homologous to the homonymous areas of the cat and might be indicative of a Bauplan from which the temporal areas of primates may have evolved.     

Serial and parallel processing in the human auditory cortex: a magnetoencephalographic study

Although anatomical, histochemical and electrophysiological findings in both animals and humans have suggested a parallel and serial mode of auditory processing, precise activation timings of each cortical area are not well known, especially in humans. We investigated the timing of arrival of signals to multiple cortical areas using magnetoencephalography in humans. Following click stimuli applied to the left ear, activations were found in six cortical areas in the right hemisphere: the posteromedial part of Heschl's gyrus (HG) corresponding to the primary auditory cortex (PAC), the anterolateral part of the HG region on or posterior to the transverse sulcus, the posterior parietal cortex (PPC), posterior and anterior parts of the superior temporal gyrus (STG), and the planum temporale (PT). The mean onset latencies of each cortical activity were 17.1, 21.2, 25.3, 26.2, 30.9 and 47.6 ms respectively. These results suggested a serial model of auditory processing along the medio-lateral axis of the supratemporal plane and, in addition, implied the existence of several parallel streams running postero-superiorly (from the PAC to the belt region and then to the posterior STG, PPC or PT) and anteriorly (PAC-belt-anterior STG).     

Perceptual deficits after lesions of inferotemporal cortex in macaques

This study used a novel approach to examine a much studied question, the nature of visual deficits caused by lesions of the inferotemporal cortex (IT). Unlike many previous studies of IT lesions, we de-emphasized early, non-specific disruptions of testing caused by the lesions, and instead concentrated on permanent changes in thresholds. This approach produced unexpected results that suggest a re-evaluation of the traditional view of the role of the IT cortex in shape perception and such related visual abilities as perceptual invariances, visual grouping, the visibility of illusory contours and the performance of oddity discriminations. In addition, the measurement of stable, post-lesion hue discrimination thresholds gave us a different perspective on the severity of color vision deficits which result from lesions of the IT cortex. We found that shape distortion thresholds were not permanently elevated by IT lesions and, indeed, showed no greater transitory disruption than did other visual abilities. This result is inconsistent with the common view that IT is critical to shape discriminations. Two other visual abilities that would be expected to be disrupted by IT lesions - the visual grouping of misoriented line segments and shape invariances (failure of irrelevant stimulus changes to disrupt shape distortion thresholds) - were not affected by IT lesions. However, shape discriminations based on illusory contours and some oddity discriminations were severely and permanently affected. Our results also showed that IT lesions caused permanent, moderate to large impairments of color vision, but not color blindness. Bilateral damage to area TEO caused no disruption of performance on any of the abovediscriminations. Our results suggest that the IT cortex in macaques may be critical to the visibility of illusory contours and the performance of some oddity discriminations, that it plays some role in color perception, but that it is not essential for shape, grouping discriminations or perceptual shape invariances.     

Functional organization of color domains in V1 and V2 of macaque monkey revealed by optical imaging

Areas V1 and V2 of Macaque monkey visual cortex are characterized by unique cytochrome-oxidase (CO)-staining patterns. Initial electrophysiological studies associated CO blobs in V1 with processing of surface properties such as color and brightness and the interblobs with contour information processing. However, many subsequent studies showed controversial results, some supporting this proposal and others failing to find significant functional differences between blobs and interblobs. In this study, we have used optical imaging to map color-selective responses in V1 and V2. In V1, we find striking "blob-like" patterns of color response. Fine alignment of optical maps and CO-stained tissue revealed that color domains in V1 strongly associate with CO blobs. We also find color domains in V1 align along centers of ocular dominance columns. Furthermore, color blobs in V1 have low orientation selectivity and do not overlap with centers of orientation domains. In V2, color domains coincide with thin stripes; orientation-selective domains coincide with thick and pale stripes. We conclude that color and orientation-selective responses are preferentially located in distinct CO compartments in V1 and V2. We propose that the term "blob" encompasses both the concept of "CO blob" and "color domain" in V1.     

Where is 'dorsal V4' in human visual cortex? Retinotopic, topographic and functional evidence

In flattened human visual cortex, we defined the topographic homologue of macaque dorsal V4 (the 'V4d topologue'), based on neighborhood relations among visual areas (i.e. anterior to V3A, posterior to MT+, and superior to ventral V4). Retinotopic functional magnetic resonance imaging (fMRI) data suggest that two visual areas ('LOC' and 'LOP') are included within this V4d topologue. Except for an overall bias for either central or peripheral stimuli (respectively), the retinotopy within LOC and LOP was crude or nonexistent. Thus the retinotopy in the human V4d topologue differed from previous reports in macaque V4d. Unlike some previous reports in macaque V4d, the human V4d topologue was not significantly color-selective. However, the V4d topologue did respond selectively to kinetic motion boundaries, consistent with previous human fMRI reports. Because striking differences were found between the retinotopy and functional properties of the human topologues of 'V4v' and 'V4d', it is unlikely that these two cortical regions are subdivisions of a singular human area 'V4'.     

Visual Memory, Visual Imagery, and Visual Recognition of Large Field Patterns by the Human Brain: Functional Anatomy by Positron Emission Tomography

We measured the regional cerebral blood flow (rCBF) in 11 healthyvolunteers with PET (positron emission tomography). The mainpurpose was to map the areas of the human brain that changedrCBF during (1) the storage, (2) retrieval from long-term memory,and (3) recognition of complex visual geometrical patterns.A control measurement was done with subjects at rest. Perceptionand learning of the patterns increased rCBF in V1 and in 17cortical fields located in the cuneus, the lingual, fusiform,inferior temporal, occipital, and angular gyri, the precuneus,and the posterior part of superior parietal lobules. In addition,rCBF increased in the anterior hippocampus, anterior cingulategyrus, and in several fields in the prefrontal cortex. Recognitionof the patterns increased rCBF in 18 identically located fieldsoverlapping those activated in learning. In addition, recognitionprovoked differentially localized increases in the pulvinar,posterior hippocampus, and prefrontal cortex. Learning and recognitionof the patterns thus activated identical visual regions, butdifferent extravisual regions. A surprising finding was thatthe hippocampus was also active in recognition. Recall of thepatterns from long-term memory was associated with rCBF increasesin yet difierent fields in the prefrontal cortex, and the anteriorcingulate cortex. In addition, the posterior inferior temporallobe, the precuneus, the angular gyrus, and the posterior superiorparietal lobule were activated, but not any spot within theoccipital cortex. Activation of V1 or immediate visual associationareas is not a prerequisite for visual imagery for the patterns.The only four fields activated in storage recall and recognitionwere those in the posterior inferior temporal lobe, the precuneus,the angular gyrus, and the posterior superior parietal lobule.These might be the storage sites for such visual patterns. Ifthis is true, storage, retrieval, and recognition of complexvisual patterns are mediated by higher-level visual areas. Thus,visual learning and recognition of the same patterns make useof identical visual areas, whereas retrieval of this materialfrom the storage sites activates only a subset of the visualareas. The extravisual networks mediating storage, retrieval,and recognition differ, indicating that the ways by which thebrain accesses the storage sites are different.     

Distribution of activity across the monkey cerebral cortical surface, thalamus and midbrain during rapid, visually guided saccades

To examine the distribution of visual and oculomotor activity across the macaque brain, we performed functional magnetic resonance imaging (fMRI) on awake, behaving monkeys trained to perform visually guided saccades. Two subjects alternated between periods of making saccades and central fixations while blood oxygen level dependent (BOLD) images were collected [3 T, (1.5 mm)3 spatial resolution]. BOLD activations from each of four cerebral hemispheres were projected onto the subjects' cortical surfaces and aligned to a surface-based atlas for comparison across hemispheres and subjects. This surface-based analysis revealed patterns of visuo-oculomotor activity across much of the cerebral cortex, including activations in the posterior parietal cortex, superior temporal cortex and frontal lobe. For each cortical domain, we show the anatomical position and extent of visuo-oculomotor activity, including evidence that the dorsolateral frontal activation, which includes the frontal eye field (on the anterior bank of the arcuate sulcus), extends anteriorly into posterior principal sulcus (area 46) and posteriorly into part of dorsal premotor cortex (area 6). Our results also suggest that subcortical BOLD activity in the pulvinar thalamus may be lateralized during voluntary eye movements. These findings provide new neuroanatomical information as to the complex neural substrates that underlie even simple goal-directed behaviors.     

Color discrimination involves ventral and dorsal stream visual areas

We used positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) in human subjects to investigate whether the ventral and dorsal visual stream cooperate when active judgements about color have to be made. Color was used as the attribute, because it is processed primarily in the ventral stream. The centrally positioned stimuli were equiluminant shades of brown. The successive color discrimination task was contrasted to a dimming detection task, in which retinal input was identical but with double the number of motor responses. The stimulus presentation rate was parametrically varied and a constant performance level was obtained for all conditions. The visual activation sites were identified by retinotopic mapping and cortical flattening. In addition, one psychophysical and two fMRI experiments were performed to control for differences in visuospatial attention and motor output. Successive color discrimination involved early visual areas, including V1 and VP and the ventral color-responsive region, as well as anterior and middle dorsal intraparietal sulcus, dorsal premotor cortex and pre-SMA. Cortical regions involved in dimming detection and motor output included area V3A, hMT/V5+, lateral occipital sulcus, posterior dorsal intraparietal sulcus, primary motor cortex and SMA. These experiments demonstrated that even with color as the attribute, successive discrimination, in which a decision process has to link visual signals to motor responses, involves both ventral and dorsal visual stream areas.     

Category-specific conceptual processing of color and form in left fronto-temporal cortex

To investigate the cortical basis of color and form concepts, we examined event-related functional magnetic resonance imaging (fMRI) responses to matched words related to abstract color and form information. Silent word reading elicited activity in left temporal and frontal cortex, where category-specific activity differences were also observed. Whereas color words preferentially activated anterior parahippocampal gyrus, form words evoked category-specific activity in fusiform and middle temporal gyrus as well as premotor and dorsolateral prefrontal areas in inferior and middle frontal gyri. These results demonstrate that word meanings and concepts are not processed by a unique cortical area, but by different sets of areas, each of which may contribute differentially to conceptual semantic processing. We hypothesize that the anterior parahippocampal activation to color words indexes computation of the visual feature conjunctions and disjunctions necessary for classifying visual stimuli under a color concept. The predominant premotor and prefrontal activation to form words suggests action-related information processing and may reflect the involvement of neuronal elements responding in an either-or fashion to mirror neurons related to adumbrating shapes.     

Coexistence of widespread clones and large radial clones in early embryonic ferret cortex.

Cell lineage analysis in rodents has shown that the cerebral cortex is formed from both widespread and large radial clustered clones representing partly distinct lineages and producing differing cell types. Since previous cell lineage analysis of the ferret cortex using retroviral libraries showed that most neurons labeled at E33-E35 formed widespread clones, we determined whether clones labeled earlier in neurogenesis showed a greater tendency to form coherent radial clones. Clones labeled at E27-E29 occasionally consisted of widespread multineuron clones (13% of PCR-defined clones), but commonly consisted of small clusters of two to four neurons (65%). Moreover, 6/21 hemispheres contained a single, much larger (6-150 cells) radial cluster. Although large clusters were observed in 28% of experiments, they contained many neurons, accounting for 38% of retrovirally labeled cells. The large clusters showed at most few widely scattered sibling cells, either by histological analysis or by PCR analysis, suggesting that radial and widespread clones coexist but are lineally separate at early stages of corticogenesis. Coexistence of large radial and widespread neuronal clones appears to be an evolutionarily conserved mechanism for cortical neurogenesis.     

Three systems of insular functional connectivity identified with cluster analysis

Despite much research on the function of the insular cortex, few studies have investigated functional subdivisions of the insula in humans. The present study used resting-state functional connectivity magnetic resonance imaging (MRI) to parcellate the human insular lobe based on clustering of functional connectivity patterns. Connectivity maps were computed for each voxel in the insula based on resting-state functional MRI (fMRI) data and segregated using cluster analysis. We identified 3 insular subregions with distinct patterns of connectivity: a posterior region, functionally connected with primary and secondary somatomotor cortices; a dorsal anterior to middle region, connected with dorsal anterior cingulate cortex, along with other regions of a previously described control network; and a ventral anterior region, primarily connected with pregenual anterior cingulate cortex. Applying these regions to a separate task data set, we found that dorsal and ventral anterior insula responded selectively to disgusting images, while posterior insula did not. These results demonstrate that clustering of connectivity patterns can be used to subdivide cerebral cortex into anatomically and functionally meaningful subregions; the insular regions identified here should be useful in future investigations on the function of the insula.