Student Theses and Dissertations

Date of Award

1965

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Abstract

With the hope of elucidating neurophysiological mechanisms involved in cutaneous modality discrimination, a comparison was made between activity recorded from single fibers in the dorsal columns and lateral funiculus of the cat spinal cord. Information obtained from human subjects with spinal lesions had indicated that the main impairment following dorsal column transection was one of tactile discrimination and position sense, whereas the major impairments following lateral column lesions involved thermal sensations and paino It was considered of interest to determine whether individual fibers in these regions were responsive to more than one kind of cutaneous stimulation (touch and cooling for example) or whether individual fibers were specific, responding to only one kind of stimulation. If single fibers were found to be polymodal, the possibility had to be considered that stimuli related to a particular modality might set up a characteristic temporal pattern of discharge which would differ in a reproducible fashion from patterns elicited by stimuli related to other modalities. In this way information regarding the kind of cutaneous stimulation which had occurred might be preserved in a polymodal pathway. It was found that all fibers in the dorsal columns which could be influenced from the skin were driven to highest frequencies by mechanical stimulation. Rapidly moving stimulators were the most effective. Mechanical or thermal stimuli vigorous enough to damage the skin caused inactivation of cutaneous dorsal column units. Rapidly adapting units were the most frequently encountered in the dorsal columns, and these showed no response to thermal stimuli. More slowly adapting dorsal column units responded weakly to rapid cooling, the activity during this response being more regular than that typically seen during mechanically evoked activity of equivalent frequency. The possibility therefore exists that slowly adapting dorsal column units convey information concerning both mechanical events and cooling, but the fact that the highest frequencies which occur in response to rapid cooling are never more than 10% of the maximal frequency occurring in response to appropriate mechanical stimulation suggests that the cooling response may be of minor importance.

Comments

A thesis submitted to the Faculty of The Rockefeller Institute in partial fulfillment of the requirements for the degree of Doctor of Philosophy

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