The Brain/MINDS Marmoset Connectivity Resource: An open-access platform for cellular-level tracing and tractography in the primate brain.

The primate brain has unique anatomical characteristics, which translate into advanced cognitive, sensory, and motor abilities. Thus, it is important that we gain insight on its structure to provide a solid basis for models that will clarify function. Here, we report on the implementation and features of the Brain/MINDS Marmoset Connectivity Resource (BMCR), a new open-access platform that provides access to high-resolution anterograde neuronal tracer data in the marmoset brain, integrated to retrograde tracer and tractography data. Unlike other existing image explorers, the BMCR allows visualization of data from different individuals and modalities in a common reference space. This feature, allied to an unprecedented high resolution, enables analyses of features such as reciprocity, directionality, and spatial segregation of connections. The present release of the BMCR focuses on the prefrontal cortex (PFC), a uniquely developed region of the primate brain that is linked to advanced cognition, including the results of 52 anterograde and 164 retrograde tracer injections in the cortex of the marmoset. Moreover, the inclusion of tractography data from diffusion MRI allows systematic analyses of this noninvasive modality against gold-standard cellular connectivity data, enabling detection of false positives and negatives, which provide a basis for future development of tractography. This paper introduces the BMCR image preprocessing pipeline and resources, which include new tools for exploring and reviewing the data.

Remodeling of lateral geniculate nucleus projections to extrastriate area MT following long-term lesions of striate cortex.

Here, we report on a previously unknown form of thalamocortical plasticity observed following lesions of the primary visual area (V1) in marmoset monkeys. In primates, lateral geniculate nucleus (LGN) neurons form parallel pathways to the cortex, which are characterized by the expression of different calcium-binding proteins. LGN projections to the middle temporal (MT) area only originate in the koniocellular layers, where many neurons express calbindin. In contrast, projections to V1 also originate in the magnocellular and parvocellular layers, where neurons express parvalbumin but not calbindin. Our results demonstrate that this specificity is disrupted following long-term (1 to 3 y) unilateral V1 lesions, indicating active rearrangement of the geniculocortical circuit. In lesioned animals, retrograde tracing revealed MT-projecting neurons scattered throughout the lesion projection zone (LPZ, the sector of the LGN that underwent retrograde degeneration following a V1 lesion). Many of the MT-projecting neurons had large cell bodies and were located outside the koniocellular layers. Furthermore, we found that a large percentage of magno- and parvocellular neurons expressed calbindin in addition to the expected parvalbumin expression and that this coexpression was present in many of the MT-projecting neurons within the LPZ. These results demonstrate that V1 lesions trigger neurochemical and structural remodeling of the geniculo-extrastriate pathway, leading to the emergence of nonkoniocellular input to MT. This has potential implications for our understanding of the neurobiological bases of the residual visual abilities that survive V1 lesions, including motion perception and blindsight, and reveals targets for rehabilitation strategies to ameliorate the consequences of cortical blindness.

Managing competing goals - a key role for the frontopolar cortex.

Humans are set apart from other animals by many elements of advanced cognition and behaviour, including language, judgement and reasoning. What is special about the human brain that gives rise to these abilities? Could the foremost part of the prefrontal cortex (the frontopolar cortex), which has become considerably enlarged in humans during evolution compared with other animals, be important in this regard, especially as, in primates, it contains a unique cytoarchitectural field, area 10? The first studies of the function of the frontopolar cortex in monkeys have now provided critical new insights about its precise role in monitoring the significance of current and alternative goals. In human evolution, the frontopolar cortex may have acquired a further role in enabling the monitoring of the significance of multiple goals in parallel, as well as switching between them. Here, we argue that many other forms of uniquely human behaviour may benefit from this cognitive ability mediated by the frontopolar cortex.

A blueprint of mammalian cortical connectomes.

The cerebral cortex of mammals exhibits intricate interareal wiring. Moreover, mammalian cortices differ vastly in size, cytological composition, and phylogenetic distance. Given such complexity and pronounced species differences, it is a considerable challenge to decipher organizational principles of mammalian connectomes. Here, we demonstrate species-specific and species-general unifying principles linking the physical, cytological, and connectional dimensions of architecture in the mouse, cat, marmoset, and macaque monkey. The existence of connections is related to the cytology of cortical areas, in addition to the role of physical distance, but this relation is attenuated in mice and marmoset monkeys. The cytoarchitectonic cortical gradients, and not the rostrocaudal axis of the cortex, are closely linked to the laminar origin of connections, a principle that allows the extrapolation of this connectional feature to humans. Lastly, a network core, with a central role under different modes of network communication, characterizes all cortical connectomes. We observe a displacement of the network core in mammals, with a shift of the core of cats and macaque monkeys toward the less neuronally dense areas of the cerebral cortex. This displacement has functional ramifications but also entails a potential increased degree of vulnerability to pathology. In sum, our results sketch out a blueprint of mammalian connectomes consisting of species-specific and species-general links between the connectional, physical, and cytological dimensions of the cerebral cortex, possibly reflecting variations and persistence of evolutionarily conserved mechanisms and cellular phenomena. Our framework elucidates organizational principles that encompass but also extend beyond the wiring economy principle imposed by the physical embedding of the cerebral cortex.

Structural Attributes and Principles of the Neocortical Connectome in the Marmoset Monkey.

The marmoset monkey has become an important primate model in Neuroscience. Here, we characterize salient statistical properties of interareal connections of the marmoset cerebral cortex, using data from retrograde tracer injections. We found that the connectivity weights are highly heterogeneous, spanning 5 orders of magnitude, and are log-normally distributed. The cortico-cortical network is dense, heterogeneous and has high specificity. The reciprocal connections are the most prominent and the probability of connection between 2 areas decays with their functional dissimilarity. The laminar dependence of connections defines a hierarchical network correlated with microstructural properties of each area. The marmoset connectome reveals parallel streams associated with different sensory systems. Finally, the connectome is spatially embedded with a characteristic length that obeys a power law as a function of brain volume across rodent and primate species. These findings provide a connectomic basis for investigations of multiple interacting areas in a complex large-scale cortical system underlying cognitive processes.

Afferent Connections of Cytoarchitectural Area 6M and Surrounding Cortex in the Marmoset: Putative Homologues of the Supplementary and Pre-supplementary Motor Areas.

Cortical projections to the caudomedial frontal cortex were studied using retrograde tracers in marmosets. We tested the hypothesis that cytoarchitectural area 6M includes homologues of the supplementary and pre-supplementary motor areas (SMA and pre-SMA) of other primates. We found that, irrespective of the injection sites' location within 6M, over half of the labeled neurons were located in motor and premotor areas. Other connections originated in prefrontal area 8b, ventral anterior and posterior cingulate areas, somatosensory areas (3a and 1-2), and areas on the rostral aspect of the dorsal posterior parietal cortex. Although the origin of afferents was similar, injections in rostral 6M received higher percentages of prefrontal afferents, and fewer somatosensory afferents, compared to caudal injections, compatible with differentiation into SMA and pre-SMA. Injections rostral to 6M (area 8b) revealed a very different set of connections, with increased emphasis on prefrontal and posterior cingulate afferents, and fewer parietal afferents. The connections of 6M were also quantitatively different from those of the primary motor cortex, dorsal premotor areas, and cingulate motor area 24d. These results show that the cortical motor control circuit is conserved in simian primates, indicating that marmosets can be valuable models for studying movement planning and control.

Claustral Input to the Macaque Medial Posterior Parietal Cortex (Superior Parietal Lobule and Adjacent Areas).

The projections from the claustrum to cortical areas within and adjacent to the superior parietal lobule were studied in 10 macaque monkeys, using retrograde tracers, computerized reconstructions, and quantitative methods. In contrast with the classical view that posterior parietal areas receive afferents primarily from the dorsal and posterior regions of the claustrum, we found that these areas receive more extensive projections, including substantial afferents from the anterior and ventral regions of the claustrum. Moreover, our findings uncover a previously unsuspected variability in the precise regions of the claustrum that originate the projections, according to the target areas. For example, areas dominated by somatosensory inputs for control of body movements tend to receive most afferents from the dorsal-posterior claustrum, whereas those which also receive significant visual inputs tend to receive more afferents from the ventral claustrum. In addition, different areas within these broadly defined groups differ in terms of quantitative emphasis in the origin of projections. Overall, these results argue against a simple model whereby adjacency in the cortex determines adjacency in the sectors of claustral origin of projections and indicate that subnetworks defined by commonality of function may be an important factor in defining claustrocortical topography.

Histology-Based Average Template of the Marmoset Cortex With Probabilistic Localization of Cytoarchitectural Areas.

The rapid adoption of marmosets in neuroscience has created a demand for three dimensional (3D) atlases of the brain of this species to facilitate data integration in a common reference space. We report on a new open access template of the marmoset cortex (the Nencki-Monash, or NM template), representing a morphological average of 20 brains of young adult individuals, obtained by 3D reconstructions generated from Nissl-stained serial sections. The method used to generate the template takes into account morphological features of the individual brains, as well as the borders of clearly defined cytoarchitectural areas. This has resulted in a resource which allows direct estimates of the most likely coordinates of each cortical area, as well as quantification of the margins of error involved in assigning voxels to areas, and preserves quantitative information about the laminar structure of the cortex. We provide spatial transformations between the NM and other available marmoset brain templates, thus enabling integration with magnetic resonance imaging (MRI) and tracer-based connectivity data. The NM template combines some of the main advantages of histology-based atlases (e.g. information about the cytoarchitectural structure) with features more commonly associated with MRI-based templates (isotropic nature of the dataset, and probabilistic analyses). The underlying workflow may be found useful in the future development of 3D brain atlases that incorporate information about the variability of areas in species for which it may be impractical to ensure homogeneity of the sample in terms of age, sex and genetic background.

A collaborative resource platform for non-human primate neuroimaging.

Neuroimaging non-human primates (NHPs) is a growing, yet highly specialized field of neuroscience. Resources that were primarily developed for human neuroimaging often need to be significantly adapted for use with NHPs or other animals, which has led to an abundance of custom, in-house solutions. In recent years, the global NHP neuroimaging community has made significant efforts to transform the field towards more open and collaborative practices. Here we present the PRIMatE Resource Exchange (PRIME-RE), a new collaborative online platform for NHP neuroimaging. PRIME-RE is a dynamic community-driven hub for the exchange of practical knowledge, specialized analytical tools, and open data repositories, specifically related to NHP neuroimaging. PRIME-RE caters to both researchers and developers who are either new to the field, looking to stay abreast of the latest developments, or seeking to collaboratively advance the field .

Visual responses in the dorsolateral frontal cortex of marmoset monkeys.

The marmoset monkey (Callithrix jacchus) has gained attention in neurophysiology research as a new primate model for visual processing and behavior. In particular, marmosets have a lissencephalic cortex, making multielectrode, optogenetic, and calcium-imaging techniques more accessible than other primate models. However, the degree of homology of brain circuits for visual behavior with those identified in macaques and humans is still being ascertained. For example, whereas the location of the frontal eye fields (FEF) within the dorsolateral frontal cortex has been proposed, it remains unclear whether neurons in the corresponding areas show visual responses-an important characteristic of FEF neurons in other species. Here, we provide the first description of receptive field properties and neural response latencies in the marmoset dorsolateral frontal cortex, based on recordings using Utah arrays in anesthetized animals. We find brisk visual responses in specific regions of the dorsolateral prefrontal cortex, particularly in areas 8aV, 8C, and 6DR. As in macaque FEF, the receptive fields were typically large (10°-30° in diameter) and the median responses latency was brisk (60 ms). These results constrain the possible interpretations about the location of the marmoset FEF and suggest that the marmoset model's significant advantages for the use of physiological techniques may be leveraged in the study of visuomotor cognition.NEW & NOTEWORTHY Behavior and cognition in humans and other primates rely on networks of brain areas guided by the frontal cortex. The marmoset offers exciting new opportunities to study links between brain physiology and behavior, but the functions of frontal cortex areas are still being identified in this species. Here, we provide the first evidence of visual receptive fields in the marmoset dorsolateral frontal cortex, an important step toward future studies of visual cognitive behavior.

Altered Sensitivity to Motion of Area MT Neurons Following Long-Term V1 Lesions.

Primates with primary visual cortex (V1) damage often retain residual motion sensitivity, which is hypothesized to be mediated by middle temporal area (MT). MT neurons continue to respond to stimuli shortly after V1 lesions; however, experimental and clinical studies of lesion-induced plasticity have shown that lesion effects can take several months to stabilize. It is unknown what physiological changes occur in MT and whether neural responses persist long after V1 damage. We recorded neuronal responses in MT to moving dot patterns in adult marmoset monkeys 6-12 months after unilateral V1 lesions. In contrast to results obtained shortly after V1 lesions, we found that fewer MT neurons were direction selective, including neurons expected to still receive projections from remaining parts of V1. The firing rates of most cells increased with increases in motion strength, regardless of stimulus direction. Furthermore, firing rates were higher and more variable than in control MT cells. To test whether these observations could be mechanistically explained by underlying changes in neural circuitry, we created a network model of MT. We found that a local imbalance of inhibition and excitation explained the observed firing rate changes. These results provide the first insights into functional implications of long-term plasticity in MT following V1 lesions.

Topographic Organization of the 'Third-Tier' Dorsomedial Visual Cortex in the Macaque.

The boundaries of the visual areas located anterior to V2 in the dorsomedial region of the macaque cortex remain contentious. This region is usually conceptualized as including two functional subdivisions: the dorsal component of area V3 (V3d) laterally and another area named the parietooccipital area (PO) or V6 medially. However, the nature of the putative border between V3d and PO/V6 has remained undefined. We recorded the receptive fields of multiunit clusters in male macaques and reconstructed the locations of recording sites using histological sections and computer-generated maps. Immediately adjacent to dorsomedial V2, we observed a representation of the lower contralateral quadrant that represented the vertical meridian at its rostral border. This region formed a simple eccentricity gradient from ∼<5° in the annectant gyrus to >60° in the parietooccipital medial sulcus. There was no topographic reversal where one would expect to find the border between V3d and PO/V6. Rather, near the midline, this lower quadrant map continued directly into a representation of the peripheral upper visual field without an intervening lower quadrant representation. Therefore, cortex previously assigned to the medial part of V3d and to PO/V6 forms a single map that includes parts of both quadrants. Together with previous observations that V3d and PO/V6 are densely myelinated relative to adjacent cortex and share similar input from V1, these results suggest that they are parts of a single area (for which we suggest the designation V6), which is distinct from the one forming the ventral component of the third-tier complex.SIGNIFICANCE STATEMENT The primate visual cortex has a large number of areas. Knowing the extent of each visual area and how they can be distinguished from each other is essential for the interpretation of experiments aimed at understanding visual processing. Currently, there are conflicting models of the organization of the dorsomedial visual cortex rostral to area V2 (one of the earliest stages of cortical processing of vision). By conducting large-scale electrophysiological recordings, we found that what were originally thought to be distinct areas in this region (dorsal V3 and the parietooccipital area PO/V6), together form a single map of the visual field. This will help to guide future functional studies and the interpretation of the outcomes of lesions involving the dorsal visual cortex.

Correlated Variability in the Neurons With the Strongest Tuning Improves Direction Coding.

Sensory perception depends on neuronal populations creating an accurate representation of the external world. The amount of information that a population can represent depends on the tuning of individual neurons and the trial-by-trial variability shared among neurons. Although on average, pairwise spike-count correlations between neurons are positive, the distribution is wide, and the relationship between correlations and encoding is not straightforward. Here, we examine how single-neuron and population-level factors impact the efficacy of the neural code. We recorded responses to moving visual stimuli from motion-sensitive neurons in the middle temporal area of anesthetized marmosets (Callithrix jacchus) and trained decoders to assess how correlated and uncorrelated populations encoded stimulus motion direction. We found that the most responsive, direction-selective, and least variable neurons are the most relied-upon neurons in an uncorrelated population. In correlated populations, the same neurons do the most to shape the shared variability across the population in a way that facilitates decoding, and decoding is improved by the presence of temporally stable correlations. This suggests that the least variable neurons with the strongest stimulus representations enhance the population code by providing a strong signal and shaping correlations in variability orthogonally to the locus defined by the mean response.

Neuronal Distribution Across the Cerebral Cortex of the Marmoset Monkey (Callithrix jacchus).

Using stereological analysis of NeuN-stained sections, we investigated neuronal density and number of neurons per column throughout the marmoset cortex. Estimates of mean neuronal density encompassed a greater than 3-fold range, from >150 000 neurons/mm3 in the primary visual cortex to ~50 000 neurons/mm3 in the piriform complex. There was a trend for density to decrease from posterior to anterior cortex, but also local gradients, which resulted in a complex pattern; for example, in frontal, auditory, and somatosensory cortex neuronal density tended to increase towards anterior areas. Anterior cingulate, motor, premotor, insular, and ventral temporal areas were characterized by relatively low neuronal densities. Analysis across the depth of the cortex revealed greater laminar variation of neuronal density in occipital, parietal, and inferior temporal areas, in comparison with other regions. Moreover, differences between areas were more pronounced in the supragranular layers than in infragranular layers. Calculations of the number of neurons per unit column revealed a pattern that was distinct from that of neuronal density, including local peaks in the posterior parietal, superior temporal, precuneate, frontopolar, and temporopolar regions. These results suggest that neuronal distribution in adult cortex result from a complex interaction of developmental/ evolutionary determinants and functional requirements.

High-Expanding Regions in Primate Cortical Brain Evolution Support Supramodal Cognitive Flexibility.

Primate cortical evolution has been characterized by massive and disproportionate expansion of a set of specific regions in the neocortex. The associated increase in neocortical neurons comes with a high metabolic cost, thus the functions served by these regions must have conferred significant evolutionary advantage. In the present series of analyses, we show that evolutionary high-expanding cortex - as estimated from patterns of surface growth from several primate species - shares functional connections with different brain networks in a context-dependent manner. Specifically, we demonstrate that high-expanding cortex is characterized by high internetwork functional connectivity; is recruited flexibly over many different cognitive tasks; and changes its functional coupling pattern between rest and a multimodal task-state. The capacity of high-expanding cortex to connect flexibly with various specialized brain networks depending on particular cognitive requirements suggests that its selective growth and sustainment in evolution may have been linked to an involvement in supramodal cognition. In accordance with an evolutionary-developmental view, we find that this observed ability of high-expanding regions - to flexibly modulate functional connections as a function of cognitive state - emerges gradually through childhood, with a prolonged developmental trajectory plateauing in young adulthood.

Cortical Afferents of Area 10 in Cebus Monkeys: Implications for the Evolution of the Frontal Pole.

Area 10, located in the frontal pole, is a unique specialization of the primate cortex. We studied the cortical connections of area 10 in the New World Cebus monkey, using injections of retrograde tracers in different parts of this area. We found that injections throughout area 10 labeled neurons in a consistent set of areas in the dorsolateral, ventrolateral, orbital, and medial parts of the frontal cortex, superior temporal association cortex, and posterior cingulate/retrosplenial region. However, sites on the midline surface of area 10 received more substantial projections from the temporal lobe, including clear auditory connections, whereas those in more lateral parts received >90% of their afferents from other frontal areas. This difference in anatomical connectivity reflects functional connectivity findings in the human brain. The pattern of connections in Cebus is very similar to that observed in the Old World macaque monkey, despite >40 million years of evolutionary separation, but lacks some of the connections reported in the more closely related but smaller marmoset monkey. These findings suggest that the clearer segregation observed in the human frontal pole reflects regional differences already present in early simian primates, and that overall brain mass influences the pattern of cortico-cortical connectivity.

Improved color constancy in honey bees enabled by parallel visual projections from dorsal ocelli.

How can a pollinator, like the honey bee, perceive the same colors on visited flowers, despite continuous and rapid changes in ambient illumination and background color? A hundred years ago, von Kries proposed an elegant solution to this problem, color constancy, which is currently incorporated in many imaging and technological applications. However, empirical evidence on how this method can operate on animal brains remains tenuous. Our mathematical modeling proposes that the observed spectral tuning of simple ocellar photoreceptors in the honey bee allows for the necessary input for an optimal color constancy solution to most natural light environments. The model is fully supported by our detailed description of a neural pathway allowing for the integration of signals originating from the ocellar photoreceptors to the information processing regions in the bee brain. These findings reveal a neural implementation to the classic color constancy problem that can be easily translated into artificial color imaging systems.

Robust Visual Responses and Normal Retinotopy in Primate Lateral Geniculate Nucleus following Long-term Lesions of Striate Cortex.

Lesions of striate cortex (V1) trigger massive retrograde degeneration of neurons in the LGN. In primates, these lesions also lead to scotomas, within which conscious vision is abolished. Mediation of residual visual capacity within these regions (blindsight) has been traditionally attributed to an indirect visual pathway to the extrastriate cortex, which involves the superior colliculus and pulvinar complex. However, recent studies have suggested that preservation of the LGN is critical for behavioral evidence of blindsight, raising the question of what type of visual information is channeled by remaining neurons in this structure. A possible contribution of LGN neurons to blindsight is predicated on two conditions: that the neurons that survive degeneration remain visually responsive, and that their receptive fields continue to represent the region of the visual field inside the scotoma. We tested these conditions in male and female marmoset monkeys (Callithrix jacchus) with partial V1 lesions at three developmental stages (early postnatal life, young adulthood, old age), followed by long recovery periods. In all cases, recordings from the degenerated LGN revealed neurons with well-formed receptive fields throughout the scotoma. The responses were consistent and robust, and followed the expected eye dominance and retinotopy observed in the normal LGN. The responses had short latencies and preceded those of neurons recorded in the extrastriate middle temporal area. These findings suggest that the pathway that links LGN neurons to the extrastriate cortex is physiologically viable and can support residual vision in animals with V1 lesions incurred at various ages.SIGNIFICANCE STATEMENT Patients with a lesion of the primary visual cortex (V1) can retain certain visually mediated behaviors, particularly if the lesion occurs early in life. This phenomenon ("blindsight") not only sheds light on the nature of consciousness, but also has implications for studies of brain circuitry, development, and plasticity. However, the pathways that mediate blindsight have been the subject of debate. Recent studies suggest that projections from the LGN might be critical, but this finding is puzzling given that the lesions causes severe cell death in the LGN. Here we demonstrate in monkeys that the surviving LGN neurons retain a remarkable level of visual function and could therefore be the source of the visual information that supports blindsight.

Distributed representation of vocalization pitch in marmoset primary auditory cortex.

The pitch of vocalizations is a key communication feature aiding recognition of individuals and separating sound sources in complex acoustic environments. The neural representation of the pitch of periodic sounds is well defined. However, many natural sounds, like complex vocalizations, contain rich, aperiodic or not strictly periodic frequency content and/or include high-frequency components, but still evoke a strong sense of pitch. Indeed, such sounds are the rule, not the exception but the cortical mechanisms for encoding pitch of such sounds are unknown. We investigated how neurons in the high-frequency representation of primary auditory cortex (A1) of marmosets encoded changes in pitch of four natural vocalizations, two centred around a dominant frequency similar to the neuron's best sensitivity and two around a much lower dominant frequency. Pitch was varied over a fine range that can be used by marmosets to differentiate individuals. The responses of most high-frequency A1 neurons were sensitive to pitch changes in all four vocalizations, with a smaller proportion of the neurons showing pitch-insensitive responses. Classically defined excitatory drive, from the neuron's monaural frequency response area, predicted responses to changes in vocalization pitch in <30% of neurons suggesting most pitch tuning observed is not simple frequency-level response. Moreover, 39% of A1 neurons showed call-invariant tuning of pitch. These results suggest that distributed activity across A1 can represent the pitch of natural sounds over a fine, functionally relevant range, and exhibits pitch tuning for vocalizations within and outside the classical neural tuning area.

Relation of koniocellular layers of dorsal lateral geniculate to inferior pulvinar nuclei in common marmosets.

Traditionally, the dorsal lateral geniculate nucleus (LGN) and the inferior pulvinar (IPul) nucleus are considered as anatomically and functionally distinct thalamic nuclei. However, in several primate species it has also been established that the koniocellular (K) layers of LGN and parts of the IPul have a shared pattern of immunoreactivity for the calcium-binding protein calbindin. These calbindin-rich cells constitute a thalamic matrix system which is implicated in thalamocortical synchronisation. Further, the K layers and IPul are both involved in visual processing and have similar connections with retina and superior colliculus. Here, we confirmed the continuity between calbindin-rich cells in LGN K layers and the central lateral division of IPul (IPulCL) in marmoset monkeys. By employing a high-throughput neuronal tracing method, we found that both the K layers and IPulCL form comparable patterns of connections with striate and extrastriate cortices; these connections are largely different to those of the parvocellular and magnocellular laminae of LGN. Retrograde tracer-labelled cells and anterograde tracer-labelled axon terminals merged seamlessly from IPulCL into LGN K layers. These results support continuity between LGN K layers and IPulCL, providing an anatomical basis for functional congruity of this region of the dorsal thalamic matrix and calling into question the traditional segregation between LGN and the inferior pulvinar nucleus.