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W Welker

Publications and source records attributed to W Welker.

12 recordsLinked to original sources
PubMed1988

Somatosensory projections of cerebellar granule cell layer of giant bushbaby, Galago crassicaudatus.

Recent neurophysiological studies of the granule cell (GC) layer in opossums and rats revealed extensive somatosensory projections to the cerebellar hemispheres and caudal vermis. These projections are organized as asomatotopic mosaics that are species-specific. To determine whether similar projections exist in a primate with a relatively small and simple cerebellum, we explored the GC layer of exposed folial crowns of anterior and posterior lobe cerebellar cortex of anesthetized giant galagos using juxtathreshold natural stimulation of mechanoreceptors and in-depth microelectrode micromapping techniques. We found (1) that stimulation of somatosensory mechanoreceptors by gentle touch, deep pressure, muscle stretch and joint movement revealed projections to the GC layer throughout the mediolateral extent of crus II, paramedian lobule, pyramis and rostral uvula (crus I was unresponsive); (2) that mosaic patterns of peripheral sources and submodality of projections were different for each lobule, and (3) that there were intraspecies and individual differences in subfoliation and in details of projections. Except for differences in mosaic pattern and relative size of different projections, these findings are similar to those in opossums and rats. These data suggest that somatosensory inputs to the cerebellum are not only functionally significant, but that they exist widely among mammals.

Animals↗
PubMed1985

Tactile cutaneous representation in cerebellar granule cell layer of the opossum, Didelphis virginiana.

Recent studies of the albino rat revealed extensive cutaneous somatosensory projections to the granule cell (GC) layer of the cerebellar hemispheres and the caudal vermis. These projections are organized asomatotopically in patchy mosaics. To determine whether similar projections exist in a marsupial, we explored the GC layer of the cerebellar cortex of anesthetized Virginia opossums using in-depth microelectrode micromapping and juxtathreshold cutaneous natural stimulation techniques. We found: Somatosensory projections to the GC layer exist throughout the mediolateral extent of the folia of the posterior lobe. The anterior lobe was not explored. The submodality of most receptive fields was 'gentle-touch' cutaneous, but some were located in muscle, joint, or other deep-lying structures. Peripheral projections to the GC layer are organized asomatotopically. Adjacent body parts project disjunctively to nonadjacent GC regions, and the overall pattern of peripheral projections forms a patchy columnar mosaic. Many body parts send projections to multiple loci. Ipsilateral projections predominate. Mechanoreceptors from face, snout, mouth and teeth activate the bulk of GC loci on crus I and crus II. The paramedian lobule receives projections from the entire ipsilateral body; the pyramis is activated from hindlimb and forelimb; the uvula from the upper arm and vibrissae. Different folia have different combinations and arrangements of disjunctive patchy peripheral projections. Individual differences in pattern of foliation and body representation occur. Except for differences in mosaic pattern and relative size of different projections, these findings are similar to those in rats and cats. These data suggest that somatosensory (especially cutaneous) inputs to the cerebellum are not only functionally significant, but that they exist widely among mammals.

Animals↗
PubMed1984

Fractured cutaneous projections to the granule cell layer of the posterior cerebellar hemisphere of the domestic cat.

Snider 's pioneering studies of tactile responses in the cerebellar cortex of cats and monkeys suggested that posterior regions of the cerebellar hemispheres receive somatotopically organized projections. However, recent studies in rats, using high-density, in depth microelectrode mapping methods, have shown that tactile projections to the granule cell layer of the cerebellar hemispheres are somatotopically disrupted. We reexamined the organization of cutaneous projections to cerebellar hemispheric cortex in cats by using micromapping methods. Natural stimulation of cutaneous surfaces evokes short-latency (mossy-fiber-induced) multiple unit responses in the cerebellar granule cell layer of crus II and paramedian lobule in both ketamine- and barbiturate-anesthetized cats. Facial structures are represented in several of the most caudomedial folia of crus II as well as in three of the rostral folia of the paramedian lobule. In several of these paramedian folia, facial projections are interspersed with projections from the forelimb. Forelimb structures alone are represented in two intermediate folia of the paramedian lobule. No cutaneous projections were found from the trunk or hindlimb. All projections were from ipsilateral receptive fields. In four folia of crus II and six folia of the paramedian lobule, cutaneous projections form a mosaic of patchlike projections. Within single patches, projections are somatotopically organized, but projections to adjacent patches come from noncontiguous body regions. Within a single folium , a particular facial region may be represented in two or three spatially separated patches. Facial patches are small, usually less than 1 mm2. Forelimb patches are usually larger, often extending the full length and breadth of a folial crown. Patches with like receptive fields are not organized in zonal sagittal strips. Rather than being somatotopically organized, cutaneous mossy fiber projections to granule cells in cats, as in rats, reveal a more complex mosaic pattern of organization.

Afferent Pathways↗
PubMed1984

Reevaluation of motor cortex and of sensorimotor overlap in cerebral cortex of albino rats.

The organization of motor cortex and the sensorimotor overlap zone was examined by in-depth electrical stimulation using micromapping procedures in rats. The cutaneous somatic sensory, as well as the efferent motor projections to the hindlimb and forelimb sensorimotor overlap zone were studied in the same animals. Low-threshold movements were elicited from portions of 3 architectonic areas: the lateral agranular, dysgranular and granular areas. Cutaneous light touch projections occur only within the granular area. Cutaneous projections to, and motor projections from individual punctures in the granular overlap zone did not always involve homologous body parts. The total motor cortex exhibits a general musculotopic pattern of organization.

Animals↗
PubMed1984

Patterns of afferent projections to transitional zones in the somatic sensorimotor cerebral cortex of albino rats.

The organization of somatosensory projections to the dysgranular areas of somatic sensory cortex was mapped in albino rats. Receptive fields that activate layer IV granule cells in these dysgranular zones were: cutaneous and deep (including muscle), roughly somatotopic, larger, and required stronger stimulation (tap) than the cutaneous light touch RFs of the adjacent granule cell zones.

Afferent Pathways↗
PubMed1981

Principles of organization of a cerebro-cerebellar circuit. Micromapping the projections from cerebral (SI) to cerebellar (granule cell layer) tactile areas of rats.

We defined spatial patterns of organization of projections from somatosensory cerebral cortex (SI) to the somatosensory cerebellar cortex of anesthetized albino rats using microelectrode (stimulation and recording) micromapping methods and low-threshold cutaneous (tactile) stimulation. Two sampling strategies were used: (1) a single cerebral SI locus in layers V-VI was stimulated electrically, while a responding region of the cerebellar granule cell (GC) layer was systematically mapped with a recording electrode; (2) the SI stimulating electrode was used as the mapping electrode while the cerebellar GC electrode remain fixed. We found highly specific patterns of connections between somatotopically organized SI cortex and the somatotopically fractured tactile cerebellar cortex. Using threshold stimulating currents in SI, the projections from small populations of neural elements were found to be highly restricted, terminating within the confines of only those tactile cerebellar hemispheric locations having the same receptive fields (RFs). These SI-GC projections conform to the patchy mosaic pattern of organization previously shown for peripheral tactile projections. SI projections to GC patches were either contralateral or ipsilateral, depending on the laterality of the peripheral projections to that patch. Each SI focus projected to only a portion of a patch; projections from several adjacent SI loci overlapped serially within a patch. As with the peripherally evoked GC layer responses, SI-evoked GC responses were organized in a columnar fashion and were maximal at middle levels of the GC layer; SI-GC latencies were 5-8 ms. These data reveal that this tactile-related cerebro-cerebellar circuit exhibits precisely organized patterns of projection.

Animals↗
PubMed1978

Tactile projections to granule cells in caudal vermis of the rat's cerebellum.

We discovered a small tactile area in a single a folium of the uvula of the cauday vermis of the rat's cerebellum. Gentle mechanical stimulation of relatively small cutaneous receptive fields (RFs) activated multiple units in the granule cell (GC) layer in a portion of a single folium in rats anesthetized with sodium pentobarbital. The total size of this area on each side of the midline is about 1.5 mm2, yet micromapping within this tiny region using tungsten ball microelectrodes and a high puncture sampling density (about 75 punctures/mm2) revealed a highly differentiated pattern of cutaneous projections to the GC layer. All peripheral projections are ipsilateral; the two homologous areas from each side adjoining at the midline of folium 9a. The larger projection areas from cutaneous RFs are mostly from mystacial vibrissae and upper lip, but small projection sites from the remainder of the head, neck and forelimb also are present. The pattern of projections were patch-like, forming a fractured somatotopic pattern or mosaic, with some somatotopic and some nonsomatotopic features. Each RF activated units in a vertical column in the GC layer. This area has not been described in any mammal, and its functional role can now be studied.

Afferent Pathways↗
PubMed1976

Mapping the brain. Historical trends in functional localization.

This essay presents a brief review and evaluation of some guiding concepts during the past century of inquiry into localization of brain functions. Mapping methods are described and discussed as one useful set of approaches to defining functional localization. Each neurobiological discipline: neuroanatomy, neurophysiology, neurochemistry neuropsychology, neuroethology, clinical neurology, biophysics and bioengineering, all use map-making strategies in their search for valid spatial and temporal definitions of the phenomena in their field of interest. Particular emphasis is given to neurophysiological mapping procedures. How these procedures have evolved to become important tools for testing hypotheses about the neuroelectric, behavioral and psychological functions of specific neuroanatomical structures is discussed. The continued importance is emphasized of neurophysiological mapping as a basic set of descriptive sampling strategies for testing hypotheses about specific neural mechanisms and their adaptive operations.

Animals↗
PubMed1975

Diversity of coding profiles of mechanoreceptors in glabrous skin of kittens.

We examined stimulul-response (S-R) profiles of 35 single mechanoreceptive afferent units having small receptive fields in glabrous forepaw skin of 24 anesthetized domestic kittens. Single unit activity was recorded with tungsten microelectrodes from cervical dorsal root ganglia. The study was designed to be as quantitatively descriptive as possible. We indented each unit's receptive field with a broad battery of simple, carefully controlled stimuli whose major parameters, including amplitude, velocity, acceleration, duration, and interstimulus interval were systematically varied. Stimuli were delivered by a small probe driven by a feedback-controlled axial displacement generator. Single unit discharge data were analyzed by a variety of direct and derived measures including dot patterns, peristimulus histograms, instantaneous and mean instantaneous firing rates, tuning curves, thresholds for amplitude and velocity, adaptation rates, dynamic and static sensitivities, and others. We found that with respect to any of the S-R transactions examined, the properties of our sample of units were continuously and broadly distributed. Any one unit might exhibit either a slow or rapid rate of adaptation, or might superficially appear to preferentially code a single stimulus parameter such as amplitude or velocity. But when the entire range of responsiveness of units to the entire stimulus battery was surveyed by a variety of analytic techniques, we were unable to find any justifiable basis for designation of discrete categories of S-R profiles. Intermediate response types were always found, and in general, all units were both broadly tuned and capable of responding to integrals of several stimulus parameters, our data argue against the usefulness of evaluating a unit's S-R coding capabilities by means of a limited ste of stimulation of response analysis procedures.

Adaptation, Physiological↗