Date of Award
Dissertation - Restricted
Doctor of Philosophy (PhD)
Electrical and Computer Engineering
A study of the effects of diffuse electrical currents on the primary visual pathways was undertaken to provide additional information about the mechanisms underlying the production of unresponsiveness by electroanesthesia (EA) currents. For these studies, the EA currents were applied by means of external electrodes from the nasion to the inion of squirrel monkeys (Saimiri sciureus). Summaries of the pertinent studies dealing with the effects of EA currents on cerebral potentials are included. A review of the neuroanatomy and electrophysiology of the visual system is presented. Instrumentation, recording techniques, materials, and data processing methods are discussed for the acquisition of neuropotentials during the presence of EA currents. For the EA studies in the visual pathways, data of the effects of rectangular currents on the "on" and "off" population responses are presented. The effects of both direct and rectangular EA currents upon the electroretinogram, as well as the effects of rectangular, direct, and sinusoidal EA currents on unit potential firing patterns from the cells in the lateral geniculate nucleus (LGN), are reported. Measurements of the current density in the retina during EA are given. The discussion of the results is centered about the degree of susceptibility of the receptors, bipolar cells, and ganglion cells to the diffuse EA currents and the nature of the action of these currents. A mathematical model for the spontaneous activity of a single ganglion cell and the receptor, bipolar, and amacrine cells which make up its receptive field has been developed. The model suggests that changes in excitability and synaptic transmission secondary to local polarizations of the retinal elements are sufficient to account for the alterations observed in the spontaneous activity of the LGN cells. In addition, a study of the physiological effects of the low-level electrotherapeutic sleep (ETS) current is reported. The experimental results include the effects of the ETS currents on evoked potentials in the somatosensory and visual systems, on electroencephalograms and electroyograms, and electromyograms, and on heart rate and respiration.