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Biomedical subjects

C R Michael

Publications and source records attributed to C R Michael.

At least 19 recordsLinked to original sources
PubMed1988

Retinal afferent arborization patterns, dendritic field orientations, and the segregation of function in the lateral geniculate nucleus of the monkey.

Optic tract fibers and cell bodies in the lateral geniculate nucleus of the monkey were studied intracellularly with micropipette electrodes containing the marker enzyme horseradish peroxidase. Single optic-tract fibers always projected to only one of the six geniculate layers. The majority of the axons innervating the four parvocellular laminae were red/green opponent color units; their terminations formed cylindrical columns that were perpendicular to the layers. In similar fashion, the geniculate cells in the parvocellular layers were mostly red/green units with narrow, bipolar dendritic fields oriented normal to the laminar borders. The majority of the retinal axons ending in parvocellular layers 6 and 5 were on-center units; nearly all geniculate cells in these two laminae were also on-center neurons. In layers 4 and 3 most terminating optic-tract fibers, as well as the geniculate cells themselves, were off-center units. All axons projecting to the magnocellular layers were broad-band units with spherical terminal arborizations. The magnocellular geniculate neurons, which were also broad band, had extensive spherical dendritic fields that often crossed laminar borders. Thus, the terminal patterns of each class of retinogeniculate axon closely resembled the dendritic orientations of the functionally related geniculate target cells.

Afferent Pathways↗
PubMed1985

Laminar segregation of color cells in the monkey's striate cortex.

In the monkey's striate cortex concentric cells with double opponent color properties were restricted to layers 4A and 4C beta; this cell type was also found in the lower half of 4C alpha but there it was always of the broad band class. Concentric cells of any type were absent from 4B. Simple cells were found in abundance in 4B and upper 4C alpha and were always broad band while those few found in 4A and 4C beta were usually double opponent color but sometimes were broad band. Color-sensitive complex and hypercomplex cells were found in the supragranular and infragranular layers (2, 3, 5 and 6). Double opponent concentric cells were occasionally seen in the supragranular layers but never in the infragranular laminae.

Animals↗
PubMed1984

Terminal patterns of single, physiologically characterized optic tract fibers in the cat's lateral geniculate nucleus.

We have examined the patterns of termination of single, physiologically identified optic tract fibers in the dorsal lateral geniculate nucleus (LGNd) of the cat. The axons were impaled with a recording micropipette and characterized by their responses to light and by their conduction latencies to electrical stimulation of the optic nerve. Horseradish peroxidase was then iontophoretically injected from the pipette into the single fibers. Subsequent histological processing and serial reconstruction revealed the fibers' destinations, patterns of arborization, and the spatial distributions of their terminal boutons. Axons classified as type X invariably projected to layer A or A1 of the LGNd and some sent a collateral into the medial interlaminar nucleus (MIN). Axons of the Y type terminated in layer A or A1 and the MIN. Those from the contralateral eye nearly always had an additional termination in the magnocellular C layer, whereas those from the ipsilateral eye occasionally terminated in layer C1. In the A layers axons distributed their terminal boutons in columns that spanned the widths of the layers. The columns differed in size, shape, and density depending on whether they were from X, Y-on, or Y-off axons. The columns from both X-on and X-off axons were narrow cylinders averaging about 150 micron in width. The columns usually contained fewer than a thousand boutons and about 60% of the boutons were concentrated in the upper halves of the layers. The Y columns were wider, averaging about 375 micron in width, and contained around 1500 boutons. About 70% of the Y boutons were concentrated in the lower halves of the layers. Y-on columns were often broader at the tops and the bottoms of the layers than near the centers, giving them an hourglass shape. The Y-off columns were broader at the bottoms of the layers than at the tops, giving them the shape of a cone or a truncated cone. These distinctive bouton distributions suggest the presence of a sublaminar organization in the A layers based on differences in the density and lateral spread of the terminations of X, Y-on, and Y-off afferents.

Animals↗
PubMed1980

Projection patterns of single physiologically characterized optic tract fibres in cat.

Because the axons of retinal ganglion cells are the sole channels carrying information from the eye, the organization of their central projections is important in visual processing. However, their detailed destinations and patterns of synaptic distribution at the level of single, functionally identified cells are not known. Most anatomical studies involve populations of cells or fibres and do not examine their physiological properties; physiological studies involving intracellular recording and injection of marker substances into cell bodies of single cells do not reveal distant axon terminals because the markers stain the fibres for only a few millimetres from the perikarya. To examine the central projections of retinal ganglion cells we have impaled single optic tract fibres near their sites of termination and injected them iontophoretically with the marker enzyme horseradish peroxidase (HRP). We now report that this method has revealed the thalamic and midbrain ramifications of single physiologically characterized axons. The individual optic-tract fibres branch repeatedly, sending collaterals to the superior colliculus (SC), the medial interlaminar nucleus (MIN), and to one or more laminae within the dorsal lateral geniculate nucleus (LGNd). In different nuclei the single axons form arborizations of characteristically different shapes and distribute their synaptic terminals in columns (LGNd), sheets (MIN) or widely spread patches (SC).

Animals↗
PubMed1978

Color vision mechanisms in monkey striate cortex: dual-opponent cells with concentric receptive fields.

1. I have recorded with tungsten microelectrodes from single cells in the monkey's visual cortex and have specifically studied those neurons which were sensitive to the color of the stimulus. In the primate striate cortex there are four classes of color-coded cells. The cells described in this paper have concentric receptive fields with one red-green opponent-color system in the field center and the opposite organization in the surround. These dual-opponent cells were nost sensitive to the simultaneous presentation of two different colors, one covering the field center and the other illuminating the surround. They are probable involved in the perception of simultaneous color-contrast phenomena. 2. Spectral sensitivity curves revealed that both the field centers and the surrounds received opposite types of inputs from red-sensitive and green-sensitive cones. None of the cells tested had inputs from rods. 3. Area-sensitivity curves showed that peripheral suppression was present for both phases of the center opponent-color system. The boundary between the center and the surround was the same for both sets of opponent systems. Some cells had "silent" surrounds, which did not respond to annular stimuli. 4. Multiple-unit recordings from a concentric cell and one of its presumed afferents yielded information regarding its possible synaptic inputs. In some cases the cells appeared to receive contacts from red/green opponent-color geniculated fibers with circular receptive fields that lacked an antagonistic surround (similar to Wiesel and Hubel's (37) type II class). In other instances the afferents had on-center, off surround receptive fields or the reverse, but received inputs from only one cone type, either red or green (similar to Wiesel and Hubel's type III class). 5. Concentric cells were always driven by only one eye. 6. The laminar distribution of these cells was limited almost entirely to layer IV and its subdivisions. 7. The cumulative evidence presented in this paper indicates that the concentric cells probably received direct geniculate inputs and, therefore, they are the first cortical stage in the integration of color-contrast information.

Animals↗
PubMed1973

Color vision.

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Animals↗