Date of Award
Fall 1972
Document Type
Dissertation - Restricted
Degree Name
Doctor of Philosophy (PhD)
Department
Biomedical Engineering
First Advisor
Sances, Anthony
Second Advisor
Heinen, James A.
Abstract
A study of the effects of diffuse electrical currents on cortical unit potential activity was undertaken to provide additional information about the mechanisms which underlie the production of unresponsiveness by these currents. For the study, the currents were passed through electrodes placed at the inion and nasion of squirrel monkeys (Saimiri sciureus) and stumptail macaque monkeys (Macaca arctoides). The currents used for squirrel monkeys consisted of direct current (DC) biased pulses of 70 Hz and 3 ms duration. Direct current applied at a level of 2.5 mA was followed by the application of rectangular current which was increased over several minutes to a level of 5.0 mA. Similar currents of greater magnitude were used for the macaque monkeys. A review of the neuroanatomy of the neocortex is presented. Instrumentation, recording techniques, materials, and signal processing methods were developed for the acquisition of unit potentials during the application of noise to signal levels of approximately 100 to 1. Poststimulus and time interval histogram techniques were also developed for purposes of analysis. The analysis of the data from the studies involving spontaneous unit potential activity indicates that a number of reversible changes take place during the application of diffuse electrical currents. The firing rates during the application of direct currents are routinely increased. The spontaneous firing rates recorded in the sensorimotor cortex at depths approximating layer two and below are consistently reduced at current levels of unresponsiveness. Unit activity has routinely been observed which appears to fire in synchronism or in multiple intervals of the applied rectangular pulses...