Some principles of somatosensory cortical organization in rats and humans
Author(s)Moore, Christopher I., 1968-
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This thesis research elucidated principles of somatosensory cortical al organization at the level of the receptive field, cortical map, and cortical area in the rat and human. throughout these studies, a central focus was on the connection between each level of organization and the capacity for cortical reorganization. The rat and human somatoscnsory systems each bring unique opportunities to the study of somatosensory function. Rat SI provides a well-researched system in which detailed, invasive studies can be conducted. Human SI, while less readily available to detailed analysis, is ultimately the relevant preparation for studying the relation between cortical map organization and human perception. In Chapter 1, I examined the convergence of subthreshold (non-action potential evoking) sensory input in individual neuro!\S using whole-cell in vivo recording techniques. Individual neurons in rat SI integrated subthreshold information from an extensive peripheral field, spanning on average 2 vibrissae in each direction from the vibrissa that evoked the largest input (the primary vibrissa). Inputs across the subthreshold receptive field were not homogeneous, as the latency to onset, rise time and prevalence of inhibition varied as a function of the strength of excitatory input and the time poststimulus when they are assessed. These spatial and temporal variables constrain the suprathreshold output of the receptive field, and define the substrate for context-dependent integration of input. In Chapter 2, I described studies of the rat SI vibrissa representation conducted using intrinsic-signal optical imaging. Studies at this level of abstraction PoCG. During tactile stimulation, a precentral gyrus region, corresponding to area 6, and a PoCG region, corresponding to areas 3b,1 and 2, were activated. The borders of these two regions defined an inactive gap in the central sukus region, corresponding to area 3a. Conversely, during proprioceptive/motor stimulation, all three representations were activated. This pattern of activation suggests a strong analogy between the organization of primate and human somatosensory processing streams within the PoCG. Experiment 4 of Chapter 3 presents evidence for the reorganization of human somatosensory cortex following massive deafferentation using perceptual report and fMRI. In agreement with the hypothesis that cortical reorganization is the substrate for phantom perceptions (Ramachandran, 1993; Teuber et al., 1949), two spinal-cord injured (SCI) subjects reported a somatotopic pattern of referred sensations. Further, a subject with phantom perceptions demonstrated greater signal change in the palm representation than an SCI subject without phantom sensations, and normal control subjects (NCS). This finding is in good agreement with increased amplitude in the uncut vibrissa representation following vibrissa trimming/pairing, and suggests that the mechanisms of human cortical reorganization are potentially similar to those observed in rat SI. Taken alone, these studies represent advances in our understanding of the principles of somatosensory cortical organization in rats and humans. In total, these studies provide evidence on three levels of organization, from rat subthreshold receptive fields to human cortical maps, for the importance of dynamic processes in cortical function.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 1998.Includes bibliographical references (p. 125-146).
DepartmentMassachusetts Institute of Technology. Department of Brain and Cognitive Sciences
Massachusetts Institute of Technology
Brain and Cognitive Sciences