Biomedical subjects

Lawrence C Sincich

Publications and source records attributed to Lawrence C Sincich.

9 recordsLinked to original sources

PubMed2006

Neurons in V1 patch columns project to V2 thin stripes.

In the primate, connections between primary visual cortex (V1) and the second visual area (V2) are segregated according to the characteristic pattern of cytochrome oxidase (CO) activity in each of these cortical areas. Patches supply thin stripes, whereas interpatches supply pale stripes and thick stripes. Previously, the projection from patches to thin stripes was reported to arise exclusively from layer 2/3. In this present report, we made injections of a retrograde tracer, cholera toxin-B (CTB-Au), into macaque V2 thin stripes to re-examine the laminar origin of their input from V1. While the great majority of cells indeed resided in layer 2/3, small populations were also present in layers 4A, 4B, and 5/6. The location of CTB-filled cells in each layer was analyzed to determine the relationship with CO patches. Cells in layers 2/3, 4A, and 4B were aggregated into patches, forming columns that project to thin stripes. Surprisingly, cells in layer 5/6 were scattered, seemingly at random. These findings confirm that the main V1 projection to V2 stripes emanates from patches in layer 2/3. However, multiple V1 layers innervate V2 thin stripes, and the projection from layer 5/6 does not respect the patch/interpatch dichotomy.

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PubMed2005

Input to V2 thin stripes arises from V1 cytochrome oxidase patches.

Parallel streams from the primary visual cortex (V1) to the second visual area (V2) are thought to mediate different aspects of visual perception in primates. One hypothesis is that the projection from cytochrome oxidase patches to thin stripes is responsible for color, whereas a separate pathway from interpatches to pale stripes mediates form. Recently, the notion of segregated pathways has been challenged by a report showing that patches and interpatches project equally to thin stripes. We made injections of a retrograde tracer, cholera toxin-B (CTB-Au), into macaque V2 thin stripes and counted the number of labeled cells in patches versus interpatches in layer 2/3. Analysis of eight thin-stripe injections showed that a mean of 81% of labeled cells were located in patches (defined as 33% of the surface area of V1). This result confirms that the projection to thin stripes arises predominately from patches. To assess the segregation of patch and interpatch projections, we injected CTB-Au in a pale stripe and horseradish peroxidase in an adjacent thin stripe. In both successful cases, interdigitated fields of labeled cells were present in V1. Less than 1% of cells were double-labeled, indicating that the populations of cells supplying thin stripes and pale stripes are quite independent. This finding means that different signals are likely conveyed by patches and interpatches to V2.

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PubMed2005

The circuitry of V1 and V2: integration of color, form, and motion.

Primary and secondary visual cortex (V1 and V2) form the foundation of the cortical visual system. V1 transforms information received from the lateral geniculate nucleus (LGN) and distributes it to separate domains in V2 for transmission to higher visual areas. During the past 20 years, schemes for the functional organization of V1 and V2 have been based on a tripartite framework developed by Livingstone & Hubel (1988) . Since then, new anatomical data have accumulated concerning V1's input, its internal circuitry, and its output to V2. These new data, along with physiological and imaging studies, now make it likely that the visual attributes of color, form, and motion are not neatly segregated by V1 into different stripe compartments in V2. Instead, there are just two main streams, originating from cytochrome oxidase patches and interpatches, that project to V2. Each stream is composed of a mixture of magno, parvo, and konio geniculate signals. Further studies are required to elucidate how the patches and interpatches differ in the output they convey to extrastriate cortex.

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PubMed2004

Bypassing V1: a direct geniculate input to area MT.

Thalamic nuclei are thought to funnel sensory information to the brain's primary cortical areas, which in turn transmit signals afresh to higher cortical areas. Here we describe a direct projection in the macaque monkey from the lateral geniculate nucleus (LGN) to the motion-selective middle temporal area (MTor V5), a cortical area not previously considered 'primary'. The constituent neurons are mostly koniocellular, send virtually no collateral axons to primary visual cortex (V1) and equal about 10% of the V1 population innervating MT. This pathway could explain the persistence of motion sensitivity in subjects following injury to V1, suggesting more generally that residual perception after damage in a primary area may arise from sparse thalamic input to 'secondary' cortical areas.

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PubMed2003

Independent projection streams from macaque striate cortex to the second visual area and middle temporal area.

The interareal wiring of the neocortex is usually depicted as a network of single point-to-point connections, often side-stepping the possibility that some neurons may project to multiple cortical areas. The prevalence of such neurons is unknown; if they are abundant, cortical circuits are more likely to be connectionally diffuse. We used a dual-tracer approach to determine whether single neurons in the macaque primary visual cortex (V1) project to two extrastriate areas, the second visual area (V2) and the middle temporal area (MT). We found two large intermingled groups of single-labeled neurons in layer 4B of V1 projecting independently to either V2 or MT. A third, sparser group of double-labeled neurons projected to both areas; we termed these manifold neurons. We also found that MT-projecting cells were distributed indiscriminately with respect to cytochrome oxidase compartment in layer 4B, revealing a subpopulation that provides a potential source of patch input from V1 to MT. The results demonstrate that primary sensory cortices can use multiple projection strategies to distribute signals to higher areas, and suggest that feedforward projections may route signals with more specificity than feedback pathways.

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PubMed2002

Pale cytochrome oxidase stripes in V2 receive the richest projection from macaque striate cortex.

Once the visual pathway reaches striate cortex, it fans out to a number of extrastriate areas. The projections to the second visual area (V2) are known to terminate in a patchy manner. V2 contains a system of repeating pale-thin-pale- thick stripes of cytochrome oxidase (CO) activity. We examined whether the patchy terminal fields arising from primary visual cortex (V1) projections are systematically related to the CO stripes in V2. Large injections of an anterograde tracer, [(3)H]proline, were made into V1 of both hemispheres in 5 macaques. The resulting V2 label appeared in layers 2-6, with the densest concentration in layer 4. In 21/29 injections, comparison of adjacent flatmount sections processed either for autoradiography or CO activity showed that the heaviest [(3)H]proline labeling was located in pale CO stripes. In 7/29 injections, there was no clear enrichment of labeling in the CO pale stripes. In 1 injection, the proline label correlated with dark CO stripes. On a fine scale, CO levels vary within V2 stripes, giving them an irregular, mottled appearance. In all stripe types, the density of proline label would often wax and wane in opposing contrast to these local fluctuations in CO density. Our data showed that V1 input is generally anti-correlated with the intensity of CO staining in V2, with strongest input to pale stripes. It is known that the pulvinar projects preferentially to dark stripes. Therefore, V2 receives interleaved projections from V1 and the pulvinar. Because these projections favor different stripe types, they may target separate populations of neurons.

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PubMed2002

Divided by cytochrome oxidase: a map of the projections from V1 to V2 in macaques.

Current models partition the primate visual system into dorsal (magno) and ventral (parvo, konio) streams. Perhaps the strongest evidence for this idea has come from the pattern of projections between the primary visual area (V1) and the second visual area (V2). Prior studies describe three distinct pathways: magno to thick stripes, parvo to pale stripes, and konio to thin stripes. We now demonstrate that V1 output arises from just two sources: patch columns and interpatch columns. Patch columns project to thin stripes and interpatch columns project to pale and thick stripes. Projection of interpatches to common V2 stripe types (pale and thick) merges parvo and magno inputs, making it likely that these functional channels are distributed strongly to both dorsal and ventral streams.

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PubMedDate not supplied

An albino-like decussation error in the optic chiasm revealed by anomalous ocular dominance columns.

We report a unique anomaly in the ocular dominance column pattern of a single, normally pigmented macaque monkey. The column pattern contained large monocular areas inserted between the normal columns and the dorsal V1 border. These monocular regions received transneuronal input from the contralateral eye, indicating that a small population of temporal ganglion cells erroneously decussated at the optic chiasm. Projection of the column pattern back onto the visual field showed that the monocular wedges represented a approximately 5-deg sector of ipsilateral field. This corresponded to the extent of naso-temporal overlap of ganglion cells in the normal retina, suggesting an error in axon guidance affecting cells close to the vertical midline of the retina. The consequences of the crossing error in this animal were threefold: it produced an anomalous monocular zone near the V1 border, the vertical meridian was not represented at the V1 border, and points near the vertical meridian were represented twice in the brain, once in each hemisphere.

Albinism↗

PubMedDate not supplied

Complete flatmounting of the macaque cerebral cortex.

The elaborate folding of the brain surface has posed a practical impediment to investigators engaged in mapping the areas of the cerebral cortex. This obstacle has been overcome partially by the development of methods to erase the sulci and gyri by physically flattening the cortex prior to sectioning. In this study, we have prepared a step-by-step atlas of the flatmounting process for the entire cerebral cortex in the macaque monkey. The cortex was dissected from the white matter, unfolded, and flattened in a single piece of tissue by making three relieving cuts. The flatmount was sectioned at 60-75 microm and processed for cytochrome oxidase (CO) or myelin. From animal to animal there was nearly a twofold variation in the surface area of individual cortical regions, and of the whole cortex. In each specimen, a close correlation was found between V1 surface area (mean = 1343 mm2), V2 surface area (mean = 1012 mm2), hippocampal area (mean = 181 mm2), and total cerebral cortex area (mean = 10,430 mm2). The complete pattern of CO stripes in area V2 was labeled clearly in several cases; the number of cycles of thick-pale-thin-pale stripes ranged from 26 to 34. Characteristic patterns of strong CO activity were encountered in areas V3, MT, auditory and somatosensory cortex. In some animals we made injections of a retrograde tracer, gold-conjugated cholera toxin B subunit, into area V2 to identify all sources of cortical input. In addition to previously described inputs, we identified three new regions in the occipitotemporal region that project to V2. Flatmounting the cerebral cortex is a simple, efficient method that can be used routinely for mapping areas and connections in the macaque brain, the most widely used primate model of the human brain.

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