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M Sur

Publications and source records attributed to M Sur.

At least 109 records · Page 6Linked to original sources
PubMed1985

Termination patterns of individual X- and Y-cell axons in the visual cortex of the cat: projections to area 18, to the 17/18 border region, and to both areas 17 and 18.

Horseradish peroxidase was injected intracellularly into single, physiologically identified X- and Y-cell geniculocortical axons that projected to area 18, to the 17/18 border region, or to both areas 17 and 18 via branching axons. The axon terminal fields in cortex were labeled anterogradely, and the cell bodies of the axons in the A-laminae, lamina C, and the medial interlaminar nucleus (MIN) of the dorsal lateral geniculate nucleus (LGN) were labeled retrogradely. The laminar projections in area 18 of eight Y-cells and one geniculate, non-Y-cell were analyzed. Most of the cells arborized densely within layer IVa and the lower 200 to 400 microns of layer III. Most provided little or no input to layer IVb or layer VI. Thus, the laminar projections of Y-cells to layer IV of area 18 were similar to those of their area 17 counterparts, although the input to layer III was greater and rose much higher in area 18 than in area 17. The terminal arbors in area 18 were two to three times larger in lateral extent than those in area 17. They spread over 2.0 to 2.8 mm2 of layer IV and occupied proportionately much greater regions of area 18 than the Y-cell arbors in area 17. This may partially account for the large receptive fields of cortical cells in area 18, and it indicates that a small region of area 18 may receive converging inputs from a relatively wide retinotopic region of the LGN. The terminal arbors were also highly asymmetric, generally being two to four times longer anteroposteriorly than mediolaterally. These asymmetric arbors may form the structural basis for the anisotropic organization of the retinotopic map in area 18. We recovered three cells (two Y, one X) whose axons arborized in the border zone between areas 17 and 18. One Y-cell axon had a receptive field located in the ipsilateral visual hemifield and it arborized in a small region restricted almost exclusively to the border zone. The other two cells had receptive fields on or adjacent to the vertical meridian, and they terminated on either side of the 17/18 border region as well as within it. Thus, geniculate afferents representing the ipsilateral hemifield or the vertical meridian appear to have different patterns of termination on and adjacent to the 17/18 border zone. Also, some X-cell input may invade area 18 in the region immediately adjacent to the border zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1984

The somatotopic organization of the ventroposterior thalamus of the squirrel monkey, Saimiri sciureus.

Multiunit microelectrode mapping techniques were used to investigate the organization of the somatosensory thalamus in squirrel monkeys. Receptive fields and response characteristics were determined for closely spaced recording sites along arrays of electrode penetrations that passed through the ventral thalamus dorsoventrally, rostrocaudally, or lateromedially. The results were related to thalamic architecture and led to the following conclusions: (1) A large, single, systematic representation of the body surface occupied most or all of the ventroposterior nucleus, VP. The nucleus was further defined by a distinct cytoarchitectonic appearance, produced by densely packed, deeply stained neurons. (2) Recording sequences in VP were characterized by (a) abrupt shifts in receptive field locations over short recording distances indicating that the electrode had crossed discontinuities or folds in the representation, (b) long sequences of overlapping receptive fields indicating regions of continuous representation and the maintenance of adjacency in the map, and (c) similar receptive field locations for sites along the trajectory of a penetration indicating regions of isorepresentation. Major somatotopic discontinuities were associated with crossing narrow cell-poor laminae that partially divided VP into subnuclei related to the hand, foot, trunk, and tail in lateral VP and the face in medial VP. Somatotopic discontinuities occurred for electrode penetrations in all three planes, but discontinuities were greater and more frequent for lateromedial electrode penetrations. Lines of isorepresentation and gradual change were most extensive in the rostrocaudal and dorsoventral planes. We hypothesize that the disruptions, regions of isorepresentation, and regions of gradual change result from the thickening, splitting, and folding of a two-dimensional representation of the skin surface to occupy a three-dimensional volume. (3) The magnifications of various skin surfaces in VP were variable so that some skin surfaces, especially the tips of the digits, occupied relatively large portions of the nucleus, while other skin surfaces such as the trunk activated little tissue. It appeared that regions of isorepresentation varied in extent according to magnification factor and position in the map. (4) Within VP, neurons could be classified as slowly adapting or rapidly adapting to maintained skin indentation. Each type of neuron formed small groups or clusters in the nucleus so that several successive recording sites typically encountered one type before a sequence of the other type was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1984

The position sensitivity of retinal X- and Y-cells in cats.

We have devised a measure of a retinal ganglion cell's sensitivity to changes in the spatial position of a grating stimulus. At maximum, this relative position sensitivity is a scaled product of the stimulus spatial frequency and the cell's fundamental component of response to that spatial frequency. We obtained the relative position sensitivity as a function of spatial frequency for 13 X-cells and 14 Y-cells. X-cell functions peak at significantly higher spatial frequencies than do those of Y-cells. At their peaks, X-cells display significantly higher values of relative position sensitivity than do Y-cells. However, Y-cells have higher position sensitivity at lower spatial frequencies, but exhibit less of a range of variation from maximum to minimum than do X-cells. These results are consistent with a hypothesis that Y-cells provide the crucial substrate for form vision at lower spatial frequencies, while X-cells are important for details carried by the higher spatial frequencies.

Animals↗
PubMed1984

Modular distribution of neurons with slowly adapting and rapidly adapting responses in area 3b of somatosensory cortex in monkeys.

Recordings from the representations of the glabrous digits in area 3b of the somatosensory cortex of owl and macaque monkeys revealed two types of neurons. Rapidly adapting (RA) neurons responded only at the onset and offset of a 1-s skin indentation. Slowly adapting (SA) neurons also responded to stimulus onset and offset but, in addition, they responded throughout the 1-s skin indentation. RA neurons were found in all cortical layers while SA neurons were found only in the middle cortical layers. In electrode penetrations perpendicular to the layers, some penetrations encountered only RA neurons (RA penetrations), while other penetrations first encountered RA neurons, then SA neurons, and finally RA neurons again (SA penetrations). When closely spaced electrode penetrations were made throughout the representation of a single digit, it was apparent that RA and SA penetrations were not randomly distributed. The distribution suggested the existence of separate clusters or bands of SA and RA neurons in the middle layers of cortex. The predominant orientation of the SA and RA regions was rostrocaudally along the lengths of the digit representations. The SA and RA bands varied in width, had no systematic position in the representation of individual digits, and often crossed from the representation of one digit to another. Because of overlapping receptive fields for neurons in adjoining bands, the SA and RA bands appeared to represent the digits separately. This would allow all skin surfaces for each digit to be subserved by both types of neurons.

Animals↗
PubMed1983

Representations of the body surface in areas 3b and 1 of postcentral parietal cortex of Cebus monkeys.

The somatotopic organization of postcentral parietal cortex was determined with microelectrode mapping methods in a New World monkey, Cebus albifrons. As in previous studies in macaque, squirrel and owl monkeys, two separate representations of the body surface were found in regions corresponding to the architectonic fields 3b and 1. The two representations were roughly mirror-images of each other, with receptive field locations matched for recording sites along the common border. As in other monkeys, the glabrous digit tips of the hand and foot pointed rostrally in the Area 3b representation and caudally in the Area 1 representation. Both representations proceeded in parallel from the tail on the medial wall of the cerebral hemisphere to the teeth and tongue in lateral cortex along the Sylvian fissure. Compared with the other monkeys, the tail of the cebus monkey, which is prehensile, was represented in a very large region of cortex in Areas 3b and 1. Like its close relative, the squirrel monkey, the representation of the trunk and parts of the limbs were reversed in orientation in both Area 3b and Area 1 in cebus monkeys as compared to owl and macaque monkeys. The reversals of organization for some but not all parts of the representations in cebus and squirrel monkeys suggest that one line of New World monkeys acquired a unique but functionally adequate pattern of somatotopic organization for the two adjoining fields.

Animals↗
PubMed1983

Topographic reorganization of somatosensory cortical areas 3b and 1 in adult monkeys following restricted deafferentation.

Two to nine months after the median nerve was transected and ligated in adult owl and squirrel monkeys, the cortical sectors representing it within skin surface representations in Areas 3b and 1 were completely occupied by 'new' and expanded representations of surrounding skin fields. Some occupying representations were 'new' in the sense that (1) there was no evidence that these skin surfaces were represented in this region prior to median nerve transection; and (2) these skin surfaces retained their normal representation elsewhere within these two cortical representations of hand surfaces. Large 'new' representations of the dorsal surfaces of digits 1 and 2 (innervated by the radial nerve) and large 'new' representations of the hypothenar eminence (innervated by the ulnar nerve) were consistently recorded. Some surrounding skin surface representations expanded into the former median nerve zone, so that bordering skin surfaces (the ulnar insular palmar pad, the third digital palmar pad, glabrous ulnar digit 3, radial hand dorsum) were represented over far larger than normal cortical areas. These expanded representations of always-innervated skin sometimes appeared to move in entirety into the former median nerve representational zone (e.g. in the zone of representation of glabrous digit 4) were also consistently recorded. Reorganizational changes following median nerve sections were much more variable in Area 1 than in Area 3b. The topographic order of the reorganized cortical zone was comparable to normal. In at least most cortical sectors, there was a consistent, maintained relationship between receptive field size and magnification, i.e. as representations enlarged, receptive fields were correspondingly reduced in size. These studies indicate that topographic representations of the skin surface in adult monkeys are maintained dynamically. They clearly reveal that this projection system retains a self-organizing capacity in adult monkeys. They suggest that processes perhaps identical to a part of the original developmental organizing processes (by which details of field topographics are established) are operational throughout life in this projection system in primates. Some of the implications of these studies for the neural origins of tactile perception are discussed.

Afferent Pathways↗
PubMed1983

Progression of change following median nerve section in the cortical representation of the hand in areas 3b and 1 in adult owl and squirrel monkeys.

In an earlier study (Neuroscience 8, 33-55, 1983), we found that the cortex representing the skin of the median nerve within parietal somatosensory fields 3b and 1 was completely occupied by 'new' inputs from the ulnar and radial nerves, 2-9 months after the median nerve was cut and tied in adult squirrel and owl monkeys. In this report, we describe the results of studies directed toward determining the time course and likely mechanisms underlying this remarkable plasticity. Highly detailed maps of the hand surface representation were derived in monkeys before, immediately after, and at subsequent short and intermediate time stages after median nerve section. In one monkey, maps were derived before nerve section, immediately after nerve section, and 11, 22 and 144 days later. Thus, direct comparisons in cortical map structure could be made over time in this individual monkey. In other experiments, single maps were derived at given post-section intervals. These studies revealed that: (1) large cortical sectors were 'silenced' by median nerve transection. (2) Significant inputs restricted to the dorsum of the radial hand and the dorsum of digits 1, 2 and 3 were immediately 'unmasked' by median nerve transection. (3) These immediately 'unmasked' regions were topographically crude, and represented only fragments of this dorsal skin. They were transformed, over time, into very large, highly topographic and complete representations of dorsal skin surfaces. (4) Representations of bordering glabrous skin surfaces progressively expanded to occupy larger and larger portions of the former median nerve cortical representational zone. (5) These 'expanded' representations of ulnar nerve-innervated skin surfaces sometimes moved, in entirety, into the former median nerve representational zone. (6) Almost all of the former median nerve zone was driven by new inputs in a map derived 22 days after nerve section. At shorter times (3, 6 and 11 days), 'reoccupation' was still incomplete. (7) Very significant changes in map dimensions within and outside of the former median skin cortical field were seen after the 'reoccupation' of the deprived cortex by 'new' inputs was initially completed. (8) Progressive changes were recorded within the original ulnar and radial nerve cortical representational zones, as skin surfaces originally overtly represented wholly within these regions expanded into the former median nerve zone. (9) Throughout the studied period, the cortical representational loci of many skin sites appeared to change continually and often markedly. (10) The locations of map discontinuities also shifted significantly over time. (11) Concomitant with changes in representational magnification over time, inverse changes in receptive field sizes were recorded.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1982

Monocular deprivation affects X- and Y-cell retinogeniculate terminations in cats.

The X- and Y-cell pathways in cats form two functionally distinct, parallel systems from the retina through the lateral geniculate nucleus (LGN) to the visual cortex1-4. We recently used the technique of intraaxonal injection of horseradish peroxidase (HRP) to demonstrate major differences between X- and Y-cells in their retinogeniculate termination patterns5 (compare Figs 1 alpha and 2 alpha). Normally, axons of X-cells innervate geniculate lamina A or A1 (depending on the eye of origin) in narrow zones oriented perpendicular to the lamination. Some X-cells also terminate sparsely (that is, with few boutons) in the medial interlaminar nucleus (MIN), a subdivision of the LGN. Y-cell axons terminate either in laminae C and A (from the contralateral retina) or in lamina A1 (from the ipsilateral retina) in broad zones5,6, and most also terminate densely (with many boutons) in the MIN. We now report that cats raised with monocular lid suture develop abnormal retinogeniculate termination patterns. Many X-cell axons arising from the deprived eye have unusually broad terminal fields in lamina A or A1, and some also densely innervate the MIN. Many Y-cell axons from the deprived eye have dramatically shrunken or absent terminal fields in the A laminae and MIN. These changes constitute the most peripheral effects of monocular deprivation discovered so far, are consistent with previous reports of functional abnormalities among deprived geniculate neurones4,7,8 ad suggest possible mechanisms by which the visual environment influences neuronal development.

Animals↗
PubMed1982

Retinogeniculate terminations in cats: morphological differences between X and Y cell axons.

We injected horseradish peroxidase into single, physiologically identified, optic tract axons of X and Y cells in cats and studied their termination patterns in the lateral geniculate nucleus. All X cell axons innervate lamina A or A1 in narrow zones, and some sparsely innervate the medical interlaminar nucleus. All Y cell axons have broad terminal zones in laminae A and C (from the contralateral retina) or lamina A1 (if ipsilateral), and most innervate the medial interlaminar nucleus densely.

Animals↗
PubMed1982

Representations of the body surface in cortical areas 3b and 1 of squirrel monkeys: comparisons with other primates.

Microelectrode multiunit mapping techniques were used to determine the somatotopic organization of postcentral parietal cortex in the squirrel monkey Saimiri sciurus. Recordings were largeLy confined to architectonic areas 3b and 1. Results were compared to those from similar studies of owl (Merzenich et al., '78) and macaque (Nelson et al., '80) monkeys. As in these previous investigations, separate representations of the body surface were found in areas 3b and 1 of squirrel monkeys. These representations were organized in parallel, so that both proceeded from the tail on the medial wall of the cerebral hemisphere, to the lips and oral cavity on the lateral margin of these areas along the sylvian fissure. The representations were also roughly mirror images of each other so that whatever skin surface was represented rostrally in area 3b was represented caudally in area 1, and similar skin surfaces were represented along the common border. However, the representations were not identical. For example, the split representations of the leg differed so that the distal leg was represented in cortex lateral to that devoted to the foot in area 1 and medial to the foot in area 3b. Remarkably, the representations of some body parts were reversed in orientation in both area 3b and area 1 in squirrel monkeys as compared to owl and macaque monkeys. The face, arm, trunk, and leg representations were all reversed in squirrel monkeys, while the orientations of the hand and foot representations were the same. For example, the dorsal trunk is trunk is represented at the 3b/1 border in owl and macaque in area the ventral trunk is represented at th 3b/1 border in squirrel monkeys. These reversals of somatotopic organization in part but not all of the representations in areas 3b and 1 suggest that both fields are divided into sectors where the basic somatotopic orientation is independently determined, that the orientation of some of these sectors is subject to reversal in evolution, and that matching sectors in areas 3b and 1 are not independent in somatotopic organization.

Animals↗
PubMed1982

Linear and nonlinear W-cells in C-laminae of the cat's lateral geniculate nucleus.

1. We used standard, single-cell recording techniques to study the response properties of 34 W-cells in the C-laminae of the cat's lateral geniculate nucleus. By W-cell, we mean a poorly responsive geniculate neuron that receives slowly conducting retinal afferents; these are quite distinct from geniculate X- and Y-cells. Our measurements included response latency to optic chiasm stimulation, plots of the receptive-field center, time course of response, and responses to counterphased, sine-wave gratings. This last measurement also involved the determination of contrast sensitivity, which is defined as the inverse of the contrast needed to evoke a threshold response at a particular spatial and temporal frequency of the grating. Many of these responses were compared to those of geniculate X- and Y-cells recorded in the A-laminae. 2. Each of the W-cells responded with a latency of at least 2.0 ms to optic chiasm stimulation, and most (76%) exhibited a latency of at least 2.5 ms. However, only 26 of these W-cells responded to visual stimuli, and these responses were weak or "sluggish," as has been reported previously. Receptive fields of these W-cells tended to be large, compared to those of X- and Y-cells, and included 11 on-center, 13 off-center, and 2 on-off center fields. 3. W-cells exhibited either linear (12 cells) or nonlinear (14 cells) spatial and temporal summation, as determined from their responses to counterphased, sine-wave gratings. Linearity of spatial summation was determined by measuring contrast sensitivity as a function of the grating's spatial phase. The linear W-cells' responses were sinusoidally phase dependent, and the nonlinear W-cells' responses were independent of spatial phase. Linearity of temporal summation was determined by the presence or absence of harmonic distortion in the response relative to the grating's counterphase rate. Linear W-cells responded chiefly at the grating's fundamental temporal frequency, whereas much of the nonlinear W-cells' responses occurred at the second harmonic of the grating's temporal frequency. Thus, nonlinear W-cells exhibited many of the characteristics previously described for Y-cells. 4. Spatial and temporal contrast-sensitivity functions were determined for seven linear and eight nonlinear W-cells. Overall sensitivity values of the linear and nonlinear W-cells were comparable, but these groups differed in terms of the nature of the response component (linear or nonlinear) that was more sensitive. 5. The linear W-cells in our sample included both tonic (comparable to the "sluggish-transient" type of retinal ganglion cells) types, while all nonlinear W-cells were phasic. Otherwise, no difference between linear and nonlinear W-cells was seen for latency to optic chiasm stimulation, receptive-field size, overall contrast sensitivity, responsiveness to visual stimuli, overall spatial resolution, or temporal resolution. 6...

Animals↗
PubMed1981

The organization of somatosensory area II in tree shrews.

Microelectrode multiunit recording methods were used to determine the somatotopic organization of the second somatosensory area, S-II, in tree shrews. Neurons were activated by light tactile stimuli, and receptive fields were located on the contralateral body surface only. The orientation of S-II was such that the top of the head adjoined S-I and the distal limbs pointed away from S-I so that the representation could be characterized as "erect". In general, the distortions of the body surface in S-II were similar to those found in S-I of the tree shrew (Sur et al., '80), with the exception that proportionately less cortex was devoted to the glabrous nose. The representation in S-II was more continuous than that in S-I. Finally, cortex bordering S-II caudally was found to be responsive to generally more intense somatosensory stimuli such as taps to the body surface.

Animals↗
PubMed1981

Physiological and anatomical evidence for a discontinuous representation of the trunk in S-I of tree shrews.

Microelectrode mapping methods revealed that the representation of the body surface in the first somatosensory area of cortex, S-I, of the tree shrew is unique in that only the ventral trunk was found in the usual location of the trunk representation in cortex of the dorsolateral surface of the cerebral hemisphere. Instead, the dorsal trunk was found as an extension of the representation of the posterior leg in cortex on the medial wall. The separation of the representation of the trunk occurs along a line that is counter to the orientation of the dorsal root dermatomes, so that S-I of the tree shrew clearly cannot be characterized as a serial representation of dermatomes. Anatomical studies of connections support the conclusion that the representation of the trunk is split in S-I. Both the representation of the dorsal trunk on the medial wall of the cerebral hemisphere and S-I of the dorsolateral surface were found to project to S-II when horseradish peroxidase was injected into S-II.

Animals↗
PubMed1980

Representation of the body surface in somatosensory area I of tree shrews, Tupaia glis.

Microelectrode mapping methods were used to determine the organization of the first somatosensory area, S-I, of tree shrews. Tree shrews were chosen for study because of their generalized body form, phylogenetic relationship to primates, and smooth, easily mapped cortex. A systematic representation of the contralateral body surface was found in an architectonically distinct zone identified as somatic koniocortex. Overall features of somatotopic organization were similar to S-I of other mammals, S-I of prosimian primates, and the Area 3b "S-I proper" representation of monkeys. Like Area 3b in monkeys and the somatic koniocortex in galagos, S-I in tree shrews is bordered caudally by cortex also responsive to somatosensory stimuli. Several aspects of S-I organization in tree shrews appear to be primitive and generalized. These include the representation of the trunk with the ventrum at the caudal margin of S-I, the restriction of the glabrous digits of the hand and foot to the rostral half of the representation and pointed rostralward, the representation of an anterior strip of the forelimb lateral to the hand, and a posterior strip of hindlimb medial to the foot representation. As in a number of other mammals, a large portion of S-I in tree shrews is devoted to the head. However, the proportion of S-I activated from the glabrous nose is greater in tree shrews than iun any previously studied mammal. We conclude that S-I of tree shrews has both specialized and generalized features, and that the generalized features importantly relate to an understanding of the evolution of the primate somatosensory system.

Animals↗
PubMed1980

Receptive fields of neurons in areas 3b and 1 of somatosensory cortex in monkeys.

Receptive fields of neurons within the separate representations of the glabrous hand in areas 3b and 1 of somatosensory cortex were studied in cynomolgus monkeys. Many neurons in area 1 have center-surround receptive fields with separate 'on' and 'off' zones, while neurons in area 3b exhibit largely uniform or homogeneous receptive fields.

Animals↗
PubMed1980

Representations of the body surface in postcentral parietal cortex of Macaca fascicularis.

The somatotopic organization of the postcentral parietal cortex of the Old World monkey, Macaca fascicularis, was determined with multi-unit microelectrode recordings. The results lead to the following conclusions: 1) There are at least two complete and systematic representations of the contralateral body surface in the cortex of the postcentral gyrus. One representation is contained within Area 3b, the other within Area 1. 2) While there are important differences in the organization of the two representations, they are basically mirror-images of each other. 3) Each representation maintains body-surface adjacency by cortical adjacency in some mediolateral regions. In other regions, two types of discontinuities can be described: first, in which adjacent body surfaces are represented in separate cortical loci; second, in which adjacent cortical regions represent disparate body-surface regions. The internal organization of each representation is better described as a composite of somatotopic regions (Merzenich et al., '78) than as a serial array of dermatomal bands, or as a "homunculus." 4) While architectonic Area 2 responds to stimulation of deep body tissue, at least parts of Area 2 also respond to cutaneous stimulation. The organiation of the cutaneous representation of the hand in Area 2 is basically a mirror-image of the hand representation in Area 1. 5) Area 3a is activated by deep body tissue stimulation, suggesting the possibility of a fourth body representation within the traditional "S-I" region of somatosensory cortex in macaques. In accord with a previous study in a New World monkey (Merzenich et al., '78), we suggest that the cutaneous representation in Area 3b be considered as SI proper, and that the cutaneous representation in Area 1 be termed the posterior cutaneous field. Furthermore, based on the orientation of the representations of the body surface, as well as other factors, we suggest that the representation in Area 3b is homologous to "SmI" (or "SI") in non-primates.

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