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RANDALL J. NELSON, Ph.D.
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Research InterestsClassically defined somatic sensory cortex (SI) is divided into several areas, each of which, receives short latency afferent input from cutaneous mechanoreceptors and proprioceptive elements. We have sought to determine the role of cutaneous and proprioceptive information play in the initiation and execution of active movements when this information serves as the trigger for a motor task, and whether this information is continuously available to SI cortex. Preliminary results indicate that some SI neurons, sensitive to joint manipulation, are inhibited by palmar vibratory stimulation only in the context of active movement. Presentation of the stimulus in a situation in which the animal does not intend to move doesn't result in inhibition. Other SI neurons are excited by the presentation of the vibratory stimuli but are inhibited 60-80 msec before movement. Neurons in the motor cortex exhibit peak discharge at this time and it is also the time when psychophysical thresholds for tactile perception in humans is elevated. Recent recordings in the neostriatum, an area known to be involved in the initiation and execution of movement, indicate that neurons often modulate their activity well before the motor cortex or SI. Neurons in the neostriatum commonly fire differently depending upon the current behavioral context in which an animal is engaged. These results indicate that the cells in SI cortex may be under the influence of centrally as well as peripherally generated inhibitory mechanisms. We conclude that these are centrally generated because one type exists only in the context of movement and the second occurs at about the same time as motor cortex activity and thus, maybe due to efference copy mechanisms. The neostriatal regions activated early before movement are among the candidates for the sources of these centrally-generated influences. An understanding of normal mechanisms of the control of somatic sensation is one of the first steps toward the ability to determine what dysfunctions occur during stroke and how retraining may help to ameliorate deficits. Recent Publications
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