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M P Stryker

Publications and source records attributed to M P Stryker.

At least 19 recordsLinked to original sources
PubMed1992

Origin of orientation tuning in the visual cortex.

The results of recent experiments have thrown new light on the neuronal connections underlying orientation-selective responses in the primary visual cortex of adult animals. The pattern of afferent input from the lateral geniculate nucleus to the cortex appears to be specific for orientation, while intracortical inhibitory connections appear to be non-specific in this respect. Experimental and theoretical studies have suggested that the development of cortical cell orientation tuning is an activity-dependent process.

Animals↗
PubMed1991

Relation of cortical cell orientation selectivity to alignment of receptive fields of the geniculocortical afferents that arborize within a single orientation column in ferret visual cortex.

Neurons in the primary visual cortex of higher mammals are arranged in columns, and the neurons in each column respond best to light-dark borders of particular orientations. The basis of cortical cell orientation selectivity is not known. One possible mechanism would be for cortical cells to receive input from several lateral geniculate nucleus (LGN) neurons with receptive fields that are aligned in the visual field (Hubel and Wiesel, 1962). We have investigated the relationship between the arrangement of the receptive fields of geniculocortical afferents and the orientation preferences of cortical cells in the orientation columns to which the afferents provide visual input. Radial microelectrode penetrations were made into primary visual cortex of anesthetized adult sable ferrets. Cortical cells were recorded throughout the depth of the cortex, and their orientation preferences were determined. Cortical cell responses were then eliminated by superfusion of the cortex with either kainic acid (Zahs and Stryker, 1988) or muscimol. After the drug treatment, responses from many single units with distinct receptive fields were recorded. These responses were presumed to be those of geniculocortical afferents, because they had the response properties characteristic of LGN neurons, and because they could be recorded only in cortical layers that receive geniculate input. In 16 of 18 cases, the afferent receptive fields recorded in a single penetration covered an elongated region of visual space. In these penetrations, the best-fit line through the centers of the afferent receptive fields generally paralleled the preferred orientation of cortical cells recorded at the same site in cortex. These results are consistent with the Hubel and Wiesel (1962) model for the construction of oriented visual cortical receptive fields from geniculate inputs with aligned receptive fields.

Afferent Pathways↗
PubMed1990

Retinofugal fibres change conduction velocity and diameter between the optic nerve and tract in ferrets.

In earlier studies of central nervous fibre tracts, it was tacitly assumed that individual axons are relatively uniform along their length. In the retinofugal pathway in particular, axon diameter, myelin thickness and correlated conduction properties have been treated as constant throughout the optic nerve, chiasm and tract. We report here that the conduction velocities of fibres contributing to the early components of the compound action potential are significantly greater in the optic tract than in the optic nerve of ferrets, and also that the diameters of the largest retinofugal fibres increase from nerve to tract. This observation raises significant questions about the developmental mechanisms in the central nervous system that relate the axons, their diameters, and the glia with which they are myelinated. In addition, it indicates that studies that have relied on the constancy of conduction velocity along the retinofugal course may require reappraisal.

Action Potentials↗
PubMed1989

Ocular dominance column development: analysis and simulation.

The visual cortex of many adult mammals has patches of cells that receive inputs driven by the right eye alternating with patches that receive inputs driven by the left eye. These ocular dominance patches (or "columns") form during early life as a consequence of competition between the activity patterns of the two eyes. A mathematical model of several biological mechanisms that can account for this development is presented. Analysis of this model reveals the conditions under which ocular dominance segregation will occur and determines the resulting patch width. Simulations of the model also exhibit other phenomena associated with early visual development, such as topographic refinement of cortical receptive fields, the confinement of input cell connections to patches, monocular deprivation plasticity including a critical period, and the effect of artificially induced strabismus. The model can be used to predict the results of proposed experiments and to discriminate among various mechanisms of plasticity.

Afferent Pathways↗
PubMed1989

Visual responses in adult cat visual cortex depend on N-methyl-D-aspartate receptors.

We have investigated the role of the N-methyl-D-aspartate (NMDA) receptor, a subtype of glutamate receptor, in the responses of cells in adult cat visual cortex. After intracortical infusion of the NMDA receptor antagonist DL-2-amino-5-phosphonovalerate (DL-APV) for one day, iontophoretic responses to NMDA, to kainate, and to quisqualate revealed a receptor blockade specific to NMDA receptors and extending several millimeters from the cannula. In this region, neuronal responses to visual stimulation were profoundly suppressed, in a manner strongly correlated with the degree of NMDA receptor blockade. Neither NMDA receptor blockade nor activity suppression was caused by the inactive stereoisomer L-APV. Hence, we conclude that NMDA receptors make a major contribution to normal excitatory transmission in adult visual cortex.

2-Amino-5-phosphonovalerate↗
PubMed1988

Organization of primary visual cortex (area 17) in the ferret.

Anatomical and electrophysiological mapping techniques were used to determine topographic organization and arrangement of ocular dominance columns in the primary visual cortex of ferrets. From its border with area 18 on the posterior lateral gyrus, area 17 extends around the caudal pole of the hemisphere and over the splenial gyrus to the caudal bank of the splenial sulcus. The visuotopic map is oriented with the isoazimuth lines approximately parallel to the long axis of the posterior lateral gyrus and the isoelevation lines approximately perpendicular to the isoazimuths. Central azimuths are represented on the posterior lateral gyrus and peripheral azimuths are represented on the splenial gyrus; the inferior visual field maps medially and the superior visual field maps laterally. As in other species, the representation of the central visual field is expanded. The ferret has a considerable degree of binocular vision. Receptive fields driven through the ipsilateral eye extended more than 20 degrees into the contralateral visual field. Within the region of area 17 corresponding to the binocular portion of the visual field, tritiated proline injected into one eye transneuronally labelled an ipsilateral projection as a series of patchy bands roughly complementary to gaps in the labelled contralateral projection. Physiological ocular dominance columns were evident as well in that neurons and groups of neurons recorded in this region showed clustered ocular dominance preferences. Most single neurons studied were binocularly driven.

Animals↗
PubMed1988

Modification of retinal ganglion cell axon morphology by prenatal infusion of tetrodotoxin.

The cellular mechanisms by which the axons of individual neurons achieve their precise terminal branching patterns are poorly understood. In the visual system of adult cats, retinal ganglion cell axons from each eye form narrow cylindrical terminal arborizations restricted to alternate non-overlapping layers within the lateral geniculate nucleus (LGN). During prenatal development, axon arborizations from the two eyes are initially simple in shape and are intermixed with each other; they then gradually segregate to form complex adult-like arborizations in separate eye-specific layers by birth. Here we report that ganglion cell axons exposed to tetrodotoxin (TTX) to block neuronal activity during fetal life fail to form the normal pattern of terminal arborization. Individual TTX-treated axon arborizations are not stunted in their growth, but instead produce abnormally widespread terminal arborizations which extend across the equivalent of approximately two eye-specific layers. These observations suggest that during fetal development of the central nervous system, the formation of morphologically appropriate and correctly located axon terminal arborizations within targets is brought about by an activity-dependent process.

Animals↗
PubMed1988

Prenatal tetrodotoxin infusion blocks segregation of retinogeniculate afferents.

In the adult mammalian visual system, ganglion cell axons from the two eyes are segregated from each other into separate layers within their principal target, the lateral geniculate nucleus. The involvement of spontaneously generated action potential activity in the process of segregation was investigated during the fetal period in which segregation normally occurs in the cat, between embryonic day 45 (E45) and birth (E65). Tetrodotoxin, which blocks the voltage-sensitive sodium channel, was used to prevent action potentials. Fetuses received continuous intracranial infusions of tetrodotoxin from osmotic minipumps implanted in utero on E42. After a 2-week infusion, intraocular injections of anterograde tracers revealed that tetrodotoxin prevented segregation. The contralateral projection filled the lateral geniculate nucleus uniformly, and the ipsilateral projection expanded to occupy most of what would normally be contralaterally innervated layer A. Thus, in the fetus, long before the onset of vision, spontaneous action potential activity is likely to be present in the visual system and to contribute to the segregation of the retinogeniculate pathway.

Afferent Pathways↗
PubMed1988

Neural plasticity without postsynaptic action potentials: less-active inputs become dominant when kitten visual cortical cells are pharmacologically inhibited.

Models of synaptic plasticity in the nervous system have conventionally assumed a mechanism in which spike activity of a postsynaptic cell enhances the efficacy of recently active presynaptic inputs. Making use of the prompt and dramatic response of the visual cortex to occlusion of vision in one eye during the critical period, we tested the role of postsynaptic activity in ocular dominance plasticity. To do so, we selectively blocked cortical cell discharges with a continuous intracortical infusion of the inhibitory neurotransmitter agonist muscimol during a period of monocular deprivation. This drug inhibits cortical cell discharges with no apparent effect on the activity of their presynaptic geniculocortical inputs. Recording from single cortical cells after they had recovered from the muscimol-induced blockade, we found a consistent shift in the responsiveness of the visual cortex in favor of the less-active, closed eye, while the normal shift in favor of the more-active, open eye was evident in regions not affected by the treatment. Such an inhibition-coupled expression of plasticity in favor of the less-active, closed eye cannot be explained by a nonspecific disruption of cortical function. We interpret these results to indicate (i) that the postsynaptic cell is crucially involved in plasticity of the visual cortex, (ii) that the direction of cortical plasticity depends on postsynaptic membrane conductance or polarization, and (iii) that plasticity can occur in the absence of postsynaptic spike activity.

Action Potentials↗
PubMed1988

Segregation of ON and OFF afferents to ferret visual cortex.

1. ON-center and OFF-center cells are found in separate sublaminae of the ferret's lateral geniculate nucleus (LGN). The purpose of these experiments was to determine whether this segregation is maintained in the projection from the LGN to primary visual cortex (area 17). 2. The distribution of the geniculocortical afferents within area 17 was studied by recording in layer IV after cortical neurons were silenced with kainic acid. 3. In 28 radial penetrations made into layer IV of five kainate-treated ferrets, the center types of 289 single units with response characteristics identical to those of geniculate cells were noted. A Monte Carlo analysis of these data demonstrated that the geniculocortical afferents cluster according to center type. 4. There was no tendency for ON and OFF afferents to occupy separate sublayers within layer IV. 5. The organization of the afferents in the plane of layer IV was studied by making closely spaced electrode penetrations across the dorsal exposed surface of the cortex in three kainate-treated ferrets. A Monte Carlo analysis of these results demonstrated that afferents segregate on the basis of center type, as well as on the basis of ocular dominance, into patches in the plane of layer IV. 6. The surface-mapping results and the results of experiments in which electrode penetrations were made tangential to layer IV indicated that center-type patches can extend over several hundred micrometers. A Monte Carlo analysis of the sizes of the ocular dominance patches and center-type patches provided further support for this conclusion.

Animals↗
PubMed1978

Ocular dominance in layer IV of the cat's visual cortex and the effects of monocular deprivation.

1. The relation between the physiological pattern of ocular dominance and the anatomical distribution of geniculocortical afferents serving each eye was studied in layer IV of the primary visual cortex of normal and monocularly deprived cats. 2. One eye was injected with radioactive label. After allowing sufficient time for transeuronal transport, micro-electrode recordings were made, and the geniculocoritcal afferents serving the injected eye were located autoradiographically. 3. In layer IV of normal cats, cell were clustered according to eye preference, and fewer cells were binocularly driven than in other layers. Points of transition between groups of cells dominated by one eye and those dominated by the other were marked with electrolytic lesions. A good correspondence was found between the location of cells dominated by the injected eye and the patches of radioactively labelled geniculocortical afferents. 4. Following prolonged early monocular deprivation, the patches of geniculocortical afferents in layer IV serving the deprived eye were smaller, and those serving the non-deprived eye larger, than normal. Again there was a coincidence between the patches of radioactively labelled afferents and the location of cells dominated by the injected eye. 5. The deprived eye was found to dominate a substantial fraction (22%) of cortical cells in the fourth layer. In other cortical layers, only 7% of the cells were dominated by the deprived eye. 6. These findings suggest that the thalamocortical projection is physically rearranged as a consequence of monocular deprivation, as has been demonstrated for layer IVc of the monkey's visual cortex (Hubel, Wiesel & Le Vay, 1977).

Animals↗