Transient inhibition of 53BP1 increases the frequency of targeted integration in human hematopoietic stem and progenitor cells

Genome editing by homology directed repair (HDR) is leveraged to precisely modify the genome of therapeutically relevant hematopoietic stem and progenitor cells (HSPCs). Here, we present a new approach to increasing the frequency of HDR in human HSPCs by the delivery of an inhibitor of 53BP1 (named "i53") as a recombinant peptide. We show that the use of i53 peptide effectively increases the frequency of HDR-mediated genome editing at a variety of therapeutically relevant loci in HSPCs as well as other primary human cell types. We show that incorporating the use of i53 recombinant protein allows high frequencies of HDR while lowering the amounts of AAV6 needed by 8-fold. HDR edited HSPCs were capable of long-term and bi-lineage hematopoietic reconstitution in NSG mice, suggesting that i53 recombinant protein might be safely integrated into the standard CRISPR/AAV6-mediated genome editing protocol to gain greater numbers of edited cells for transplantation of clinically meaningful cell populations.

A novel FOXP3 knockout-humanized mouse model for pre-clinical safety and efficacy evaluation of Treg-like cell products

Forkhead box P3 (FOXP3) is an essential transcription factor for regulatory T cell (Treg) function. Defects in Tregs mediate many immune diseases including the monogenic autoimmune disease immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome (IPEX), which is caused by FOXP3 mutations. Treg cell products are a promising modality to induce allograft tolerance or reduce the use of immunosuppressive drugs to prevent rejection, as well as in the treatment of acquired autoimmune diseases. We have recently opened a phase I clinical trial for IPEX patients using autologous engineered Treg-like cells, CD4LVFOXP3. To facilitate the pre-clinical studies, a novel humanized-mouse (hu-mouse) model was developed whereby immune-deficient mice were transplanted with human hematopoietic stem progenitor cells (HSPCs) in which the FOXP3 gene was knocked out (FOXP3KO) using CRISPR-Cas9. Mice transplanted with FOXP3KO HSPCs had impaired survival, developed lymphoproliferation 10-12 weeks post-transplant and T cell infiltration of the gut, resembling human IPEX. Strikingly, injection of CD4LVFOXP3 into the FOXP3KO hu-mice restored in vivo regulatory functions, including control of lymphoproliferation and inhibition of T cell infiltration in the colon. This hu-mouse disease model can be reproducibly established and constitutes an ideal model to assess pre-clinical efficacy of human Treg cell investigational products.

CRISPR-based gene editing enables FOXP3 gene repair in IPEX patient cells

The prototypical genetic autoimmune disease is immune dysregulation polyendocrinopathy enteropathy X-linked (IPEX) syndrome, a severe pediatric disease with limited treatment options. IPEX syndrome is caused by mutations in the forkhead box protein 3 (FOXP3) gene, which plays a critical role in immune regulation. As a monogenic disease, IPEX is an ideal candidate for a therapeutic approach in which autologous hematopoietic stem and progenitor (HSPC) cells or T cells are gene edited ex vivo and reinfused. Here, we describe a CRISPR-based gene correction permitting regulated expression of FOXP3 protein. We demonstrate that gene editing preserves HSPC differentiation potential, and that edited regulatory and effector T cells maintain their in vitro phenotype and function. Additionally, we show that this strategy is suitable for IPEX patient cells with diverse mutations. These results demonstrate the feasibility of gene correction, which will be instrumental for the development of therapeutic approaches for other genetic autoimmune diseases.

The functional logic of cortico-pulvinar connections

The pulvinar is an 'associative' thalamic nucleus, meaning that most of its input and output relationships are formed with the cerebral cortex. The function of this circuitry is little understood and its anatomy, though much investigated, is notably recondite. This is because pulvinar connection patterns disrespect the architectural subunits (anterior, medial, lateral and inferior pulvinar nuclei) that have been the traditional reference system. This article presents a simplified, global model of the organization of cortico-pulvinar connections so as to pursue their structure-function relationships. Connections between the cortex and pulvinar are topographically organized, and as a result the pulvinar contains a 'map' of the cortical sheet. However, the topography is very blurred. Hence the pulvinar connection zones of nearby cortical areas overlap, allowing indirect transcortical communication via the pulvinar. A general observation is that indirect cortico-pulvino-cortical circuits tend to mimic direct cortico-cortical pathways: this is termed 'the replication principle'. It is equally apt for certain pairs (or groups) of nearby cortical areas that happen not to connect with each other. The 'replication' of this non-connection is achieved by discontinuities and dislocations of the cortical topography within the pulvinar, such that the associated pair of connection zones do not overlap. Certain of these deformations can be used to divide the global cortical topography into specific sub-domains, which form the natural units of a connectional subdivision of the pulvinar. A substantial part of the pulvinar also expresses visual topography, reflecting visual maps in occipital cortex. There are just two well-ordered visual maps in the pulvinar, that both receive projections from area V1, and several other occipital areas; the resulting duplication of cortical topography means that each visual map also acts as a separate connection domain. In summary, the model identifies four topographically ordered connection domains, and reconciles the coexistence of visual and cortical maps in two of them. The replication principle operates at and below the level of domain structure. It is argued that cortico-pulvinar circuitry replicates the pattern of cortical circuitry but not its function, playing a more regulatory role instead. Thalamic neurons differ from cortical neurons in their inherent rhythmicity, and the pattern of cortico-thalamic connections must govern the formation of specific resonant circuits. The broad implication is that the pulvinar acts to coordinate cortical information processing by facilitating and sustaining the formation of synchronized trans-areal assemblies; a more pointed suggestion is that, owing to the considerable blurring of cortical topography in the pulvinar, rival cortical assemblies may be in competition to recruit thalamic elements in order to outlast each other in activity.

The Organization of Connections between Areas V5 and V2 in Macaque Monkey Visual Cortex

Area V2 of the cerebral cortex of higher primates has a complex cytochrome oxidase architecture whose most characteristic element is a set of stripes running orthogonal to its long axis. These stripes can be related to the segregation between the various pathways in which V2 participates. In the macaque monkey the more metabolically active stripes are alternately thick and thin and only one set, the thick stripes, is found to possess clusters of labelled cells following injections of horseradish peroxidase - wheatgerm agglutinin into area V5. Some of these clusters, but not all, coincide with substructures inside the thick stripes. V2 of the owl monkey has a similar organization except that the diversification into thick and thin stripes is less prominent, both in terms of their appearance and in that more than every alternate stripe is connected to area MT, the likely homologue of V5. The return projection from V5 to V2 is more widespread than the origin of the forward projection. It extends not only between the clusters of V5-efferent cells within the thick stripes but also across the intervening thin stripes and less active interstripes. Because the latter subserve functions different from those of the thick stripes it would seem that their receipt of a back projection from an area to which they do not project, V5, may be relevant to the process of intergration of signals relating to different attributes of vision.

Modular Connections between Areas V2 and V4 of Macaque Monkey Visual Cortex

We have studied the connections between two visual areas of macaque monkey cortex, V2 and V4, by injecting wheat-germ agglutinin horseradish peroxidase (HRP-WGA) into V4 and examining the distribution of labelled cells and terminals in V2, in relation to its characteristically striped cytochrome oxidase architecture. The cells projecting from V2 to V4 are arranged in bands and the number of bands per cycle of cytochrome oxidase stripes varies (one cycle consists of a thin stripe, a thick stripe and two interstripes). In the Type 1 connectivity pattern, there is just one band per cycle, centred over the thin stripes but normally spreading into the neighbouring interstripes. In the Type 2 connectivity pattern there are two bands per cycle, generally rather narrower and centred over the interstripes. Thick stripes are mostly free of labelled cells. The return projection from V4 to V2, whilst being concentrated in the vicinity of the labelled cells, is more diffusely distributed and invades the territory of all the stripes.

The Organization of Connections between Areas V5 and V1 in Macaque Monkey Visual Cortex

Area V5 or MT of primate extrastriate visual cortex is specialized for involvement in the analysis of motion and receives input from two layers, 4B and 6, of the striate cortex or V1. Injections of horseradish peroxidase - wheatgerm agglutinin into V5 reveal a patchy distribution of labelled cells and axonal terminals in layer 4B, suggesting the presence of a segregated and functionally specialized subsystem within the layer. The patches are similar in size and frequency to the cytochrome oxidase blobs of layers 2 and 3, but bear little systematic relationship to them. V5-efferent cells in layer 6, however, tend to avoid the cores of the blobs. The back projection from V5 is continuously distributed in layers 6 and 1, though it is absent inside representations of the central 10 degrees in the latter; it is also diffusely distributed between the patches in layer 4B and over a territory wider than that occupied by labelled cells. It is thus inferred that the back projection probably influences (a) V5-efferent cells other than those projecting to the injected site in V5, and (b) cells projecting to locations other than V5. There are no major changes in the cortical frequency of V5-efferent cells with eccentricity in the visual field representation. The V5-efferent cells of layer 6 are tenfold less frequent than those of layer 4B and as a population may therefore be involved with only a limited sector of directions of movement. Furthermore, their topographic distribution does not always coincide exactly with that of the layer 4B population, as if a site in V5 receives information about slightly non-corresponding regions of the visual field from the two layers.

Corticopulvinar connections of areas V5, V4, and V3 in the macaque monkey: a dual model of retinal and cortical topographies

The connection zones of cortical areas V3, V4, and V5 (MT) with the thalamic pulvinar nucleus in the macaque monkey were identified. A combination of single- and dual-tracer techniques was used to study their topography and to establish whether these zones occupy separate or overlapping pulvinar territories. In each case, the retinotopic distribution of tracer in the pulvinar was charted by reference to its parallel distribution within the maps of cortical areas V1 and V2. Each of the areas V3, V4, and V5 were found to connect with both the 1° and the 2° maps located within the inferior and lateral pulvinar nuclei and to respect the previously identified topographies of these maps. However, V5 connects to a narrow zone lining the rostrolateral margin of the lateral and inferior pulvinar and V4 to a broader zone within the body of these two nuclei, which is adjacent to but separate from the V5 zone; the V3 zone overlaps both. Focal injections into cortex produce columns of pulvinar label whose trajectory defines a line of isorepresentation. The lines of isorepresentation in the 1° and 2° maps are approximately linear and parallel and adopt a rostrolateral to caudomedial axis; in the 1° map, this axis is roughly perpendicular to the facet of the inferior pulvinar that lies adjacent to the lateral geniculate nucleus. The connections of V5 and V4 can be modelled as successive zones along the axis of isorepresentation, with registered visual topographies. The scheme is extended by existing reports that inferotemporal cortex connects to the caudomedial pole of this axis-reflecting an occipitotemporal cortical gradient, in that V1 and other prestriate areas, e.g., V3, connect to the opposite pole. Thus a simple model of the mapped volume in the pulvinar arises, in which a unidimensional cortical topography is represented orthogonally to retinal topography. Adjoining this volume medially, within the inferior and medial pulvinar, is a second, heavier zone of V5 connectivity, which is poorly topographic. Both the medial and the rostrolateral zones of V5 connectivity may overlap with previously identified regions of tectal input to the pulvinar.

A visuo-somatomotor pathway through superior parietal cortex in the macaque monkey: cortical connections of areas V6 and V6A

This report addresses the connectivity of the cortex occupying middle to dorsal levels of the anterior bank of the parieto-occipital sulcus in the macaque monkey. We have previously referred to this territory, whose perimeter is roughly circumscribed by the distribution of interhemispheric callosal fibres, as area V6, or the 'V6 complex'. Following injections of wheatgerm agglutinin conjugated to horseradish peroxidase (WGA-HRP) into this region, we examined the laminar organization of labelled cells and axonal terminals to attain indications of relative hierarchical status among the network of connected areas. A notable transition in the laminar patterns of the local, intrinsic connections prompted a sub-designation of the V6 complex itself into two separate areas, V6 and V6A, with area V6A lying dorsal, or dorsomedial to V6 proper. V6 receives ascending input from V2 and V3, ranks equal to V3A and V5, and provides an ascending input to V6A at the level above. V6A is not connected to area V2 and in general is less heavily linked to the earliest visual areas; in other respects, the two parts of the V6 complex share similar spheres of connectivity. These include regions of peripheral representation in prestriate areas V3, V3A and V5, parietal visual areas V5A/MST and 7a, other regions of visuo-somatosensory association cortex within the intraparietal sulcus and on the medial surface of the hemisphere, and the premotor cortex. Subcortical connections include the medial and lateral pulvinar, caudate nucleus, claustrum, middle and deep layers of the superior colliculus and pontine nuclei. From this pattern of connections, it is clear that the V6 complex is heavily engaged in sensory-motor integration. The specific somatotopic locations within sensorimotor cortex that receive this input suggest a role in controlling the trunk and limbs, and outward reaching arm movements. There is a secondary contribution to the brain's complex oculomotor circuitry. That the medial region of the cortex is devoted to tightly interconnected representations of the sensory periphery, both visual and somatotopic-which are routinely stimulated in concert-would appear to be an aspect of the global organization of the cortex which must facilitate multimodal integration.

Functional demarcation of a border between areas V6 and V6A in the superior parietal gyrus of the macaque monkey

We have compared physiological data recorded from three alert macaque monkeys with separate observations of local connectivity, to locate and characterize the functional border between two related but distinct visual areas on the caudal face of the superior parietal gyrus. We refer to these areas as V6 and V6A. The occupy almost the entire extent of the anterior bank of the parieto-occipital sulcus, V6A being the more dorsal. These two areas are strongly interconnected. Anatomically, we have defined the border as the point at which labelled axon terminals first adopt a recognizably 'descending' pattern in their laminar characteristics, after injections of wheatgerm agglutinin-horseradish peroxidase into the dorsal half of the gyrus (in presumptive V6A). A similar principle was used to recognize the same border by the pattern of input from area V5, except that in this case the relevant transition in laminar characteristics is that between an 'intermediate' pattern (in V6) and an 'ascending' pattern (in V6A). V6A was found to be distinct from V6 in a number of its physiological properties. Unlike V6, it contains visually unresponsive cells as well as units with craniotopic receptive fields ('real-position' cells), units tuned to very slow stimulus speeds, units with complex visual selectivities and units with activity related to attention. V6A was also found to have a larger mean receptive field size and scatter than V6. By contrast, response properties related to the basic orientation and direction of moving bar stimuli were indistinguishable between V6 and V6A, as was the influence of gaze direction on cell activity in the two areas. Two-dimensional maps of the recording sites allowed reconstruction of the V6/V6A border. For comparison, the anatomical results were rendered on two-dimensional maps of identical format to those used to summarize the physiological data. After normalizing for relative size, the physiological and connectional estimates of the border between V6 and V6A were found to coincide, at least within the range of individual variation between hemispheres. An architectonic map in the same format was also made from a hemisphere stained for myelin and Nissl substance. Area PO, defined by its general density of myelination was not distinct in this material, but several architectural features were traceable and one of these was also found to approximate the V6/V6A border. The particular criteria that distinguish V6 from V6A differ from a recent description of areas PO and POd in the Cebus monkey; we believe it most likely that PO and POd together may correspond to V6.

Segregation and convergence of specialised pathways in macaque monkey visual cortex

At the level of cortical area V2, the various visual inputs to the cortex have reorganised to form 3 distinct channels. Anatomically these are embodied in the thick and thin dark stripes, and paler interstripes characteristic of cytochrome oxidase architecture. Do the outputs of these compartments remain segregated at higher levels of processing, or are they in turn combined and repackaged? To examine this question we have injected distinct orthograde tracers into the functionally distinct areas V4 and V5 of one hemisphere in 3 macaque monkeys (Macaca fascicularis). V4 is known to receive input from both thin stripes and interstripes of V2, but some parts of V4 receive only interstripe afferents, others receive a relatively greater contribution from the thin stripes. Thus V4 itself is thought to possess subcompartments of at least two distinct types, acting to extend the blob-thin stripe and interblob-interstripe pathways through V1 and V2. The experiments reported here reveal no further divergence between these channels: both types of V4 subcompartment make rather similar patterns of connection with further visual areas and subcortical structures. In contrast to V4, area V5 receives input from the thick stripes of V2. V4 and V5 are weakly interconnected, at best, and there is limited direct convergence in their two sets of ascending connections. For instance, both areas send output to area LIP; but V4 targets the dorsal half of the area, and V5 the ventral half, with some minor overlap. Projections to the superior temporal sulcus are also mainly separate, although we found instances of direct convergence in areas FST and possibly V4t. Segregation is also the rule for subcortical connections to the pulvinar from these two areas. In summary, the segregated outputs of V2 can remain largely distinct through at least two subsequent stages of cortical processing.

Retinotopic maps in human prestriate visual cortex: the demarcation of areas V2 and V3

We have used PET (positron emission tomography) to chart the mapping of the retina in human occipital visual cortex and hence to locate the secondary and tertiary visual areas, V2 and V3. A group of four non-selected male volunteers was presented with dynamic stimuli that were aligned with either the vertical or the right horizontal meridians (VM or HM) from 0 degree to 29 degrees eccentricity; the vertical stimuli were restricted to either the inferior or the superior hemifields. PET scans were performed using intravenous infusion of H215O and a Siemens-CTI 953B PET scanner with 3D data acquisition. Subjects received 18 scans, divided equally among the right HM, the superior VM, and the inferior VM. Data were analyzed with SPM software. The group average result confirmed our experimental hypothesis that human occipital visual cortex has retinotopic maps similar to those of the macaque monkey. Thus human areas V2 and V3 can be defined on the basis that the border between them is formed by the HM and that the outer border of V3 is demarcated by a second representation of the VM that runs approximately parallel to the primary representation of the VM at the V1/V2 border. Furthermore, as in many mammals, the extrastriate representation of the HM is "split", such that the superior contralateral quadrant is mapped in lower V2 and V3, occupying the ventral surface of human cortex, and the inferior contralateral quadrant is mapped in upper V2 and V3, which extend over the lateral and medial surfaces of each hemisphere. After stereotaxic normalization, the position of V3 defined by retinal topography was found to correspond to that surmised from our previous PET studies employing moving stimuli.

Visual processing. The odd couple

Two distinct pathways in the visual cortex shadow each other from start to finish. Why?

The brain activity related to residual motion vision in a patient with bilateral lesions of V5

We have used the technique of PET to chart the cortical areas activated by visual motion in the brain of a patient with a severe impairment in the ability to recognize the motion of objects (akinetopsia), following bilateral lesions which have so far been presumed to include area V5. High resolution MRI of her brain showed that the zone occupied by area V5 had indeed been destroyed bilaterally. Positron emission tomography activation images, co-registered to the MRIs, showed three principal regions of the cortex activated by motion. These were located (i) bilaterally in the precuneus of superior parietal cortex (area 7 of Brodmann); (ii) bilaterally in the cuneus (a region considered to represent upper V3); (iii) in the left lingual and fusiform gyri (possibly lower V3 and adjacent areas). In contrast to normal subjects, there was no significant activation of area V1 or V2. The stimuli used for scanning were chosen by prior testing of the patient's visual capacities. The control stimulus was a static random distribution of light squares on a dark background. In the moving stimulus these squares moved coherently, the direction of motion changing periodically between the cardinal directions (left, right, up and down). It was ascertained that the patient could correctly identify these directions. We also found (i) that her occasional errors were always in the direction opposite to the motion presented, so that her identification of axis of motion (i.e. vertical or horizontal) was 100% correct; (ii) that when a few static squares were added to the moving the display her identification of direction fell to chance but her identification of the axis of motion remained 100%; (iii) that when a few squares moving opposite and orthogonal to the predominant direction of motion were incorporated, her performance on both direction and axis fell to chance; (iv) that she was unable to identify motion in oblique directions between the horizontal or vertical axes, always guessing one of the cardinal directions. In accounting for her residual vision in terms of cortex, which remains active, we hypothesize; (i) that the bilateral loss of V5 has affected direction sensitive mechanisms at other sites in the cortex which are interconnected with V5 and (ii) that in consequence her performance on our tests reflects the properties of dynamic orientation selective mechanisms that were also differentially activated by the stimuli used during scanning.

The cerebral activity related to the visual perception of forward motion in depth

We have used the technique of PET to chart the areas of human cerebral cortex specifically responsive to an optical flow stimulus simulating forward motion in depth over a flat horizontal surface. The optical flow display contained about 2000 dots accelerating in radial directions away from the focus of expansion, which subjects fixated at the centre of the display monitor. Dots remained of constant size, but their density decreased from the horizon, lying across the middle of the screen, to the foreground at the lower screen margin; the top half of the display was void. For the control stimulus the dot motions were randomized, removing any sensation of motion in depth and diminishing the impression of a flat terrain. Comparison of the regional cerebral blood flow (rCBF) elicited by the optical flow and control stimuli was thus intended to reveal any area selectively responsive to the radial velocity field that is characteristic of optical flow in its simplest natural form. Six subjects were scanned, and analysed as a group. Four subjects were analysed as individuals, their PET data being co-registered with MRIs of the cerebrum to localize rCBF changes to individual gyri and sulci. There were three main areas of activation associated with optical flow: the dorsal cuneus (area V3) and the latero-posterior precuneus (or superior parietal lobe) in the right hemisphere, and the occipito-temporal ventral surface, in the region of the fusiform gyrus, in both hemispheres. There was no significant activation of V1/V2, nor of V5. These results show that higher stages of motion take place in both the 'dorsal' and 'ventral' visual pathways, as these are commonly conceived, and that both may be fed by area V3. The information potentially derivable from optical flow concerns the direction of heading, and the layout of the visual environment, a form of three-dimensional structure-from-motion. The perceptual division of labour between the various activated areas cannot be directly inferred, though it is a reasonable supposition that the parietal activation reflects the utility of optic flow for guiding self-motion.

Area V5 of the human brain: evidence from a combined study using positron emission tomography and magnetic resonance imaging

In pursuing our work on the organization of human visual cortex, we wanted to specify more accurately the position of the visual motion area (area V5) in relation to the sulcal and gyral pattern of the cerebral cortex. We also wanted to determine the intersubject variation of area V5 in terms of position and extent of blood flow change in it, in response to the same task. We therefore used positron emission tomography (PET) to determine the foci of relative cerebral blood flow increases produced when subjects viewed a moving checkerboard pattern, compared to viewing the same pattern when it was stationary. We coregistered the PET images from each subject with images of the same brain obtained by magnetic resonance imaging, thus relating the position of V5 in all 24 hemispheres examined to the individual gyral configuration of the same brains. This approach also enabled us to examine the extent to which results obtained by pooling the PET data from a small group of individuals (e.g., six), chosen at random, would be representative of a much larger sample in determining the mean location of V5 after transformation into Talairach coordinates. After stereotaxic transformation of each individual brain, we found that the position of area V5 can vary by as much as 27 mm in the left hemisphere and 18 mm in the right for the pixel with the highest significance for blood flow change. There is also an intersubject variability in blood flow change within it in response to the same visual task. V5 nevertheless bears a consistent relationship, within each brain, to the sulcal pattern of the occipital lobe. It is situated ventrolaterally, just posterior to the meeting point of the ascending limb of the inferior temporal sulcus and the lateral occipital sulcus. In position it corresponds almost precisely with Flechsig's Feld 16, one of the areas that he found to be myelinated at birth.

Visuotopic organization of the lateral suprasylvian area and of an adjacent area of the ectosylvian gyrus of cat cortex: a physiological and connectional study

We have explored the visuotopic organization of the territory surrounding the middle suprasylvian sulcus (MSS) of cat cerebral cortex by electrophysiological mapping, and by tracing the topography of its cortical and subcortical connections using wheatgerm-agglutinin horseradish peroxidase (WGA-HRP). Observations from the two approaches were concordant, and confirmed the presence of two separate visual areas in the MSS that approximate, but do not exactly correspond, to the location and internal organization of the posterior medial and posterior lateral lateral suprasylvian (PMLS, PLLS) areas of Palmer et al. (1978). We define as part of the lateral suprasylvian (LS) area the territory on the medial bank and caudal end of the lateral bank of the MSS that receives a topographically organized projection from the region of area 17 representing the lower visual quadrant. This territory is connected with other structures that are themselves striate-recipient (cortical areas 18 and 19, and the lateral division of the lateral posterior (LPl) nucleus), and with a variety of nuclei that receive direct retinal input, such as the C-laminae of the LGd, the medial interlaminar nucleus (MIN), and the superficial layers of the superior colliculus (SC). Its connections with the LPl, LGd, MIN, and SC correspond topographically with the input from area 17. Revised maps of area LS were produced from the physiological and connectional data: its rostral border is formed by a representation of lower visual elevations with the horizontal meridian represented caudally, and its lateral border is formed by the vertical meridian; area LS shares a representation of the center of gaze with the visual area of the lateral bank at its caudal end. The adjacent lateral bank area has larger receptive fields than area LS, and very different connectivity. It receives no input from area 17 and little input from striate-recipient structures, including area LS, but instead is connected to more remote extrastriate visual areas, such as the anterior ectosylvian visual (AEV) area in insular cortex, and to zones of the thalamus in receipt of tectal input (LPm and the lateromedial-suprageniculate nuclear complex). According to both mapping approaches, the lateral bank area contains representations of both the upper and lower visual quadrants but a rather limited degree of visuotopic order. We refer to it as the posterior ectosylvian visual (PEV) area, because it appears to be functionally and connectionally dissociated from area LS, but is possibly a functional antecedent of area AEV.

Organization of reciprocal connections between area 17 and the lateral suprasylvian area of cat visual cortex

The lateral suprasylvian (LS) area (or Clare-Bishop area) is a region of visual cortex in the cat which has been defined as an isolated projection zone of area 17 (V1 or striate cortex) within the suprasylvian sulcus. We have studied the overall topography and detailed pattern of connection between these two visual areas following injections of WGA-HRP into one or the other. The projection from area 17 to LS is formed largely (approximately 90%) from supragranular layer neurons that are distributed, in the coronal plane, in multiple regularly spaced patches. These patches are especially prominent in regions of area 17 representing central vision along and around the horizontal meridian. In reconstructions of serial coronal sections, and in flatmounts of the same region, the patches are seen to align so that in the plane tangential to the cortical surface they appear as a system of parallel bands whose main axis of elongation is rostro-ventral to caudo-dorsal, or near parallel to the area 17/18 border. The mean periodicity of the bands is about 1.0 mm. The projection from area 17 terminates mainly in layers 4, 3, and 2 of area LS, and also appears patchy in the coronal plane. Reconstruction of the cortical surface view again reveals a system of rostrocaudal bands, but with a mean periodicity of 2 mm. The back projection is less periodically organized, arising predominantly (approximately 80%) from a continuous sheet of infragranular neurons in area LS and terminating mainly in layer 1 of area 17, across the underlying patch and interpatch zones of the supragranular projection cells. However, neurons in layers 2 and upper 3 of area LS, which form the minority origin of the back projection, are mostly located in columnar registration with the patches of area 17 terminals. The bands of supragranular layer neurons projecting to area LS are aligned obliquely to the iso-orientation domains of area 17, indicating a further component to its organization. It is suggested that this may correspond to a segregation of the X and Y channels in area 17, with outputs to area LS selectively arising from the Y pathway, in accordance with previous reports.

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The functional logic of cortical connections

Patterns of anatomical connections in the visual cortex form the structural basis for segregating features of the visual image into separate cortical areas and for communication between these areas at all levels to produce a coherent percept. Such multi-stage integration may be a common strategy throughout the cortex for producing complex behaviour.

Segregation of pathways leading from area V2 to areas V4 and V5 of macaque monkey visual cortex

V5 and V4 are areas of macaque monkey prestriate visual cortex that are specialized for involvement in different aspects of visual perception, namely motion for V5 (refs 1-4) and colour vision, with other possible functions, for V4 (refs 2, 5-9). Thus, it is unlikely that they should be fed the same information for further processing, yet both receive a strong input from patches of the upper layers of V2 (refs 10, 11), the area immediately adjoining the primary visual cortex, V1. V2, however, seems to comprise functionally distinct subregions, which can be revealed by staining the tissue for the mitochondrial enzyme cytochrome oxidase. Here we report that V4 and V5 are connected with separate cytochrome oxidase-defined subregions of V2, suggesting that cortical pathways dealing with motion and colour perception are segregated in their passage through V2, and reinforcing evidence for functional specialization in the visual cortex.