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Biomedical subjects

M Sur

Publications and source records attributed to M Sur.

119 records · Page 7Linked to original sources
PubMed1980

Representation of the body surface in somatic koniocortex in the prosimian Galago.

Microelectrode mapping methods were used to determine the organization of somatosensory cortex in galagos, a prosimian primate. A systematic representation of the controlateral body surface was found within somatic koniocortex with an organization comparable to that of Area 3b of parietal cortex of monkeys (S-I proper) and primary somatosensory cortex (S-I) of other mammals. Limited studies of the response properties of single neurons within the representation revealed further similarities with the 3b field of monkeys. We conclude that somatic koniocortex of galagos and Area 3b of monkeys are homologous, and suggest the term S-I proper for the representation in both prosimians and monkeys. Differences in the details of S-I proper in galagos and monkeys suggest a more primitive organization in galagos.

Animals↗
PubMed1979

Connections of areas 3b and 1 of the parietal somatosensory strip with the ventroposterior nucleus in the owl monkey (Aotus trivirgatus).

Anatomical tracers were injected into electrophysiologically defined sites in somatosensory cortical Area 3b (SI proper) and Area I (posterior cutaneous field) of owl monkeys after these cortical subdivisions had been extensively explored in microelectrode mapping experiments. These mapping experiments revealed that both Areas 3b and 1 contain complete and separate representations of the body surface (Merzenich et al., '78). Restricted injections of the retrograde tracer, horseradish peroxidase (HRP), into either Area 3b or Area 1 labeled neurons within a band of cells in the ventroposterior nucleus (VP). The location of the labeled band in VP varied with the location of the injection site in both representations, and the labeled region of VP was overlapping for injections in corresponding body parts in the two representations. Neurons projecting to the hand and foot cortical representations were in architectonically identified subnuclei. Because injections into either Area 3b or Area 1 labeled over half of the neurons in the appropriate regions of VP, it appears that some neurons in VP project to both cortical representations. Finally, injections of HRP combined with the anterograde tracer, 3H-proline, indicate that VP neurons are reciprocally interconnected with both Areas 3b and 1.

Animals↗
PubMed1979

Multiple representations of the body within the primary somatosensory cortex of primates.

Microelectrode mapping experiments indicate that the classical primary somatosensory cortex of monkeys consists of as many as four separate body representations rather than just one. Two complete body surface representations occupy cortical fields 3b and 1. In addition, area 2 contains an orderly representation of predominantly "deep" body tissues. Area 3a may constitute a fourth representation.

Animals↗
PubMed1979

The organization of the second somatosensory area (SmII) of the grey squirrel.

Microelectrode mapping methods were used to determine the organization of the second somatosensory representation, SmII, in grey squirrels. A systematic representation of the contralateral body surface was found in lateral parietal cortex adjoining the first somatosensory representation, SmI (Sur et al., '78a). The representation of the body in SmII was found to be much less distorted than in SmI. Under our recording conditions, almost all recording sites were activated from strictly contralateral body locations. The most important finding was that the basic orientation of the body representation in SmII is "erect" rather than "inverted." This orientation allows SmII and SmI to be adjoined along a common border representing the top of the head and face. This type of border has been called congruent (Allman and Kaas, '75; Kaas, '77), and it may have significance in the development of sensory representations.

Animals↗
PubMed1978

The representation of the body surface in somatosensory area I of the grey squirrel.

Microelectrode mapping methods were used to determine the organization of primary somatosensory cortex, SmI, in grey squirrels. A systematic representation of the contralateral body surface was found within somatic konicortex. This primary representation differs from maps of SmI in other mammals in at least two significant ways. The first way in which SmI of squirrels differs from the organization reported for other mammals is that SmI of squirrels contains a double representation of the hand and parts of the forearm. The glabrous skin of the digits is represented twice in a mirror image fashion joined at the finger tips. The hairy skin of the digits, wrist, and parts of the forearm are also represented twice, once on each side of the joined representations of the glabrous skin. A second unique feature of SmI of squirrels is that there is a small region of cortex completely surrounded by SmI that was unresponsive to light cutaneous stimuli under our recording conditions. This unresponsive zone is easily identified in brain sections by architectonic features that deviate from sensory koniocortex and approach motor cortex. A third significant finding was that the back is rostral to the belly in the representation of the trunk in SmI of squirrels. This is the reverse of the orientation reported elsewhere for SmI of mammals, but corresponds to the orientation of the trunk representation in Area 3b of owl monkeys (Kaas et al., '78; Merzenich et al., '78). This similarity supports an earlier contention that the representation of the body in Area 3b of primates is the homolog of SmI in other mammals (Merzenich et al., '78).

Abdomen↗
PubMedDate not supplied

Development of X- and Y-cell retinogeniculate terminations in kittens.

The cat retinogeniculocortical pathways are organized chiefly into two parallel independent neuronal streams, one involving X-cells of the retina and lateral geniculate nucleus, and the other, Y-cells. Development of the Y-cell pathway is more seriously affected by visual deprivation than is the X-cell pathway and we reasoned that some insight into the underlying mechanisms of these effects could be gained from studies of normal development. We therefore injected horseradish peroxidase into physiologically identified X- and Y-cell retinogeniculate axons to examine the postnatal development of their terminations in kittens. As we report here, at 3-4 weeks of age, most optic tract axons can be identified physiologically as members of the X- or Y-cell class. X-cell terminal fields in lamina A or A1 are wider at 3-4 weeks than they are in adults, while Y-cell terminal fields are narrower than in adults. During the second and third postnatal months, X-cell terminal arbors progressively contract while Y-cell arbors expand so that, by 12 weeks of age, the adult pattern is seen. These data, and the results of our earlier study of the effects of monocular lid suture on these terminal arbors, suggest that enlargement of Y-cell terminations in geniculate lamina A or A1 during development may be accompanied by competitive pruning of X-cell terminations within these same laminae.

Animals↗
PubMedDate not supplied

Short-term synaptic plasticity in the visual cortex during development.

The maturation of short-term synaptic plasticity was studied in slices of the visual cortex obtained from rats during the first 47 days of postnatal life. Responses of cortical neurons to repetitive stimulation of the white matter at frequencies >5 Hz were examined by recording intracellularly at the resting membrane potential level. Paired-pulse facilitation, an increase in the excitatory intracellular response following an initial response, was present in approximately 40% of the neurons studied from postnatal day 5 (P5) to P10. Most of the remaining neurons studied at these ages did not reveal paired-pulse interactions. There was a progressive, age-related increase in the proportion of cells displaying paired-pulse depression, a decrease in the second excitatory response relative to the first, and a concomitant decrease in the proportion of cells displaying paired-pulse facilitation. Thus, at P31-P47 approximately half of the neurons revealed depression of synaptic transmission following an initial stimulus, while most of the other neurons displayed a lack of temporal interactions. At these later ages, inhibitory potentials also displayed paired-pulse interactions. Maturation of paired-pulse depression of the excitatory response is temporally correlated with the development of intracortical inhibitory mechanisms and may reflect subtractive or shunting inhibition in the postsynaptic neuron as well as presynaptic inhibitory mechanisms. Consistent with a role of GAGAergic inhibition, application of GABA receptor antagonists produced reversible blockade of paired-pulse depression. In conclusion, cortical neurons display substantial maturation in short-term synaptic plasticity during the first postnatal month. Temporal facilitation may be important in enhancing excitatory neurotransmission at a time when synapses are very immature. In the mature cortex, suppressive temporal interactions could provide an important substrate for neuronal processing of visual information.

Animals↗
PubMedDate not supplied

A local circuit approach to understanding integration of long-range inputs in primary visual cortex.

Integration of inputs by cortical neurons provides the basis for the complex information processing performed in the cerebral cortex. Here, we have examined how primary visual cortical neurons integrate classical and nonclassical receptive field inputs. The effect of nonclassical receptive field stimuli and, correspondingly, of long-range intracortical inputs is known to be context-dependent: the same long-range stimulus can either facilitate or suppress responses, depending on the level of local activation. By constructing a large-scale model of primary visual cortex, we demonstrate that this effect can be understood in terms of the local cortical circuitry. Each receptive field position contributes both excitatory and inhibitory inputs; however, the inhibitory inputs have greater influence when overall receptive field drive is greater. This mechanism also explains contrast-dependent modulations within the classical receptive field, which similarly switch between excitatory and inhibitory. In order to simplify analysis and to explain the fundamental mechanisms of the model, self-contained modules that capture nonlinear local circuit interactions are constructed. This work supports the notion that receptive field integration is the result of local processing within small groups of neurons rather than in single neurons.

Contrast Sensitivity↗
PubMedDate not supplied

[Combination of new electrophysiological and imaging techniques in the study of primary visual cortex function].

INTRODUCTION: This work summarizes current research focused on explaining orientation selectivity of primary visual cortex (V1), and describes the electrophysiological and imaging techniques than are being used. DEVELOPMENT: The study of orientation selectivity in V1 is key to understanding the cortical mechanisms implicated in the processing of sensory information, but this enterprise has proved more challenging than previously thought and there is no consensus about the best model to explain V1 neurons activity. Ongoing research is focused on determining the importance of the different inputs that a cortical cell receives (thalamic and lateral cortical inputs), and their link to cortical architecture. To achieve that, current research is combining optical imaging techniques with intracellular recordings of V1 neurons. Recent findings have found differences in the synaptic integration performed by neurons located in the iso orientation domains vs orientation centers of the functional V1 map. CONCLUSIONS: Data describing synaptic activity combined with the cortical functional structure are yielding new clues about V1 computation, suggesting that there is more than one mechanism capable of generating orientation selectivity.

Electrophysiology↗