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Biomedical subjects

W M Jenkins

Publications and source records attributed to W M Jenkins.

At least 55 records · Page 3Linked to original sources
PubMed1988

Somatotopically inappropriate projections from thalamocortical neurons to the SI cortex of the cat demonstrated by the use of intracortical microstimulation.

Single thalamocortical neurons with receptive fields on the toes were antidromically activated by the passage of 300-microseconds, 0.5- to 10-microA pulses through glass micropipette electrodes placed within somatotopically identified regions of the digit representation of the cat first somatosensory (SI) cortex. The somatotopy of the cortex was determined using recordings from single cortical neurons (see "Methods"), and the positions of the all tracks were marked on an enlarged photograph of the postcruciate cortex. In two of the three protocols, a very precise map of the boundary between two adjacent toes was produced prior to attempting intracortical microstimulation. Slopes of the threshold-distance curves at the sites of the lowest recorded thresholds were on the order of 0.8 microA/10 micron. This value, together with information on the anatomy of the cortical arborizations of thalamocortical neurons (Landry and Deschenes, 1981), suggested that currents of 2 and 5 microA would not activate the cortical processes of thalamocortical neurons at distances greater than 50 and 90 microns, respectively. With currents below 5 microA, thalamocortical neurons could be antidromically activated at a number of sites at depths between 340 and 930 microns (layer IV and upper layer III) and between 1,050 and 1,460 microns (layer VI). A total of 13 thalamocortical neurons could be antidromically activated using current pulses of between 0.8 and 5.0 microA, from within tracks at tangential distances of 250-830 microns from the nearest track through the somatotopically appropriate region. Within somatotopically inappropriate regions, cortical neurons frequently had receptive fields on a toe adjacent to that bearing the receptive field of the thalamic neuron(s) under study. The possible relationship of somatotopically inappropriate projections to the reorganization of cortical somatotopy following digit amputation, paw amputation, and nerve section is discussed.

Action Potentials↗
PubMed1987

Variability in hand surface representations in areas 3b and 1 in adult owl and squirrel monkeys.

Detailed microelectrode maps of the hand representation were derived in cortical areas 3b and 1 from a series of normal adult owl and squirrel monkeys. While overlap relationships were maintained, and all maps were internally topographic, many map features varied significantly when examined in detail. Variable features of the hand representations among different monkeys included a) the overall shapes and sizes of hand surface representations; b) the actual and proportional areas of representations of different skin surfaces and the cortical magnifications of representations of specific skin surfaces, which commonly varied severalfold in area 3b and manyfold in area 1; c) the topographic relationships among skin surface representations, with skin surfaces that were represented adjacently in some monkeys represented in locations many hundreds of microns apart in others; d) the internal orderliness of representations; e) the completeness of representations of the dorsal hand surfaces; and f) the skin surfaces represented along the borders of the hand representation. Owl monkey maps were, in general, internally more strictly topographic than squirrel monkey maps. In both species, area 3b was more strictly topographic and less variable than was area 1. The degree of individual variability revealed in these experiments is difficult to reconcile with the hypothesis that details of cortical maps are ontogenetically specified during a period in early life. Instead, we propose that differences in the details of cortical map structure are the consequence of individual differences in lifelong use of the hands. This conclusion is consistent with earlier studies of the consequences of peripheral nerve transection and digital amputation, which revealed that cortical maps are dynamically maintained and are alterable as a function of use or nerve injury in these monkeys (Merzenich et al., '83a,b, '84a; Merzenich, '86; Jenkins et al., '84; Jenkins and Merzenich, '87).

Afferent Pathways↗
PubMed1987

Anesthetic state does not affect the map of the hand representation within area 3b somatosensory cortex in owl monkey.

Receptive fields defined for small clusters of neurons within the middle cortical layers of area 3b differed little in size or in the skin locations represented among: alert, nitrous oxide-anesthetized, deep sodium pentobarbital-anesthetized, and ketamine-anesthetized owl monkeys. Repeated recordings from nearly identical cortical loci yielded nearly identical multi-unit receptive fields under different conditions of anesthesia.

Afferent Pathways↗
PubMed1987

Age-dependent capacity for somatosensory cortex reorganization in chronic spinal cats.

Primary somatosensory cortex was mapped in chronic spinal cats that were spinalized (T12) at two weeks and 6 weeks of age. The magnitude of cortical reorganization is age-dependent. In cats spinalized at two weeks, extensive reorganization of the deafferented hindlimb region resulted in a second complete map of intact tactile input from the trunk and forelimb, while in cats transected at 6 weeks of age, trunk afferent input only partially activated the deafferented hindlimb region.

Aging↗
PubMed1986

Cochlear implantation in children: the problem of head growth.

Successful implantation in children requires that provision be made for later head growth. The timing and magnitude of this growth was determined by measurements made from high-resolution computerized tomographic images of developing temporal bones. The temporal bone scans of 103 children of varying ages were studied. The development of the petrous and squamous portion of the temporal bone was at its greatest in the first 2 years of life. The order of magnitude of growth varied with the different axes measured.

Adolescent↗
PubMed1984

Role of cat primary auditory cortex for sound-localization behavior.

Small lesions designed to completely destroy the cortical zone of representation of a restricted band of frequency were introduced within the primary auditory cortex (AI) in adult cats. Physiological mapping was used to guide placement of lesions. Sound-localization performance was evaluated prior to and after induction of these lesions in a seven-choice free-sound-field apparatus. All tested cats had profound contralateral hemifield deficits for the localization of brief tones at frequencies roughly corresponding to those whose representations were destroyed by the lesion. Sound-localization performance was normal at all other test frequencies. In a single adult cat, a massive lesion destroyed nearly all auditory cortex unilaterally, with only the representation of a narrow band of frequency within AI spared by the lesion. This cat had normal abilities for azimuthal sound localization across that frequency band but a profound contralateral deficit for the azimuthal localization of brief sounds at all other frequencies. Recorded sound-localization deficits were permanent. Localization of long-duration tones was not affected by a unilateral AI lesion. These studies indicate that, at least in cats, AI is necessary for normal binaural sound-localization behavior; among auditory cortical fields, AI is sufficient for normal binaural sound-localization behavior; sound-location representation is organized by frequency channel in the auditory forebrain; and AI in each hemisphere contributes to only contralateral free-sound-field location representation.

Animals↗
PubMed1984

Histopathological and ultrastructural findings in a case of Papillon-Lefèvre syndrome.

Gingiva from a 3-year-old Iranian boy suffering from Papillon-Lefèvre syndrome was examined by light and electron microscopy. Deep pockets associated with predominantly Gram-negative plaque were present. The gingival lesion was dominated by plasma cells, many of which were degenerate. Russell bodies were a prominent feature. No defect of epithelium was detected.

Child, Preschool↗