The proposed research is designed to extend current information about the mechanisms responsible for encoding the frequency and amplitude of vibrotactile stimuli. Although vibrotaction has been the subject of numerous psychophysical and neurophysiological investigations, and specific hypotheses were advanced twenty years ago by LaMotte and Mountcastle as to the cortical population codes for vibrotactile stimulus frequency and amplitude, no study to date has directly imaged either the global primary somatosensory cortical response to vibrotactile stimulation, or the effect of that response on its response to subsequent input drive. Nor has the global pattern of somatosensory cortical response been related effectively to the behavior of its individual neurons. In the proposed research these objectives will be met by using four types of recordings made in cats and stimulus conditions known to produce vibrotactile adaptation in humans. In each experiment the impact of preceding activity on the global pattern of response of SI forepaw cortex to a controlled vibrotactile stimulus will first be characterized at high temporal and spatial resolution using near-infrared (IR; reflectance at 730 850 nm) optical imaging of intrinsic signals. Microelectrode penetrations will then be carried out within salient regions of the overall IR activity pattern. The microelectrode penetrations will provide samples of both (i) stimulus-evoked and spontaneous spike discharge activity recorded extracellularly from single neurons, and (ii) local field potentials (LFPs) reflecting the summated activity of small neuronal aggregates. To detect and control for possible contributions by stimulus-related changes in the responsivity of skin mechanoreceptive afferents (MRAs), concurrent recordings of the stimulus-evoked MRA volley will be carried out. Analysis of the recorded neuroelectrical data will employ a variety of novel procedures designed to facilitate measurement of the well-known entrainment of neural activity associated with rhythmic skin stimuli. The applicants' preliminary studies have demonstrated that the novel procedures to be used yield useful single trial measures of the coding of vibrotactile stimulus parameters by both single SI neurons and the MRA population. Following characterization of the time-dependencies of the cortical IR and SU responses, and of the MRA population to conditions of vibrotactile stimulation known to be associated with perceptual adaptation in humans, they will investigate the effects on those time dependencies of intravenous or topical administration of drugs known to modify glutaminergic neurotransmission via selective actions on NMDA receptors (ketamine, phencyclidine, and AP-5). All experimental findings will be assessed in terms of their consistency with the applicants' working model of stimulus-evoked, NMDA receptor-dependent, corticocortical interactions within somatosensory cortex - a model which incorporates connectional details and incorporate neurotransmitter mechanisms common to all regions of neocortex. The research is anticipated to lead directly to improved understanding of the mechanisms of vibrotactile stimulus coding in SI, and in the longer term to help elucidate the cortical mechanisms involved in conditions as diverse as schizophrenia and various forms of substance abuse.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS034979-03
Application #
2655529
Study Section
Sensory Disorders and Language Study Section (CMS)
Program Officer
Kitt, Cheryl A
Project Start
1996-02-10
Project End
2001-01-31
Budget Start
1998-02-01
Budget End
2001-01-31
Support Year
3
Fiscal Year
1998
Total Cost
Indirect Cost
Name
University of North Carolina Chapel Hill
Department
Physiology
Type
Schools of Medicine
DUNS #
078861598
City
Chapel Hill
State
NC
Country
United States
Zip Code
27599
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Kohn, Adam; Whitsel, Barry L (2002) Sensory cortical dynamics. Behav Brain Res 135:119-26
Whitsel, B L; Kelly, E F; Xu, M et al. (2001) Frequency-dependent response of SI RA-class neurons to vibrotactile stimulation of the receptive field. Somatosens Mot Res 18:263-85
Whitsel, B L; Kelly, E F; Delemos, K A et al. (2000) Stability of rapidly adapting afferent entrainment vs responsivity. Somatosens Mot Res 17:13-31
Tommerdahl, M; Delemos, K A; Whitsel, B L et al. (1999) Response of anterior parietal cortex to cutaneous flutter versus vibration. J Neurophysiol 82:16-33
Whitsel, B L; Favorov, O; Delemos, K A et al. (1999) SI neuron response variability is stimulus tuned and NMDA receptor dependent. J Neurophysiol 81:2988-3006
Tommerdahl, M; Whitsel, B L; Favorov, O V et al. (1999) Responses of contralateral SI and SII in cat to same-site cutaneous flutter versus vibration. J Neurophysiol 82:1982-92
Vierck Jr, C J; Cannon, R L; Fry, G et al. (1997) Characteristics of temporal summation of second pain sensations elicited by brief contact of glabrous skin by a preheated thermode. J Neurophysiol 78:992-1002