Microwave‐induced hyperthermia and the visually evoked electrocortical response of the guinea pig

Abstract

Five experimentally naive female guinea pigs, all young adults, were observed during a succession of 11 experiments for visually evoked electrocortical responses (VERs). In each experiment, VERs were recorded within minutes after an animal had received a hyperthermalizing dose of microwave radiation in a 2450-MHz field. Latency of the N• component of the VER, an inverse index of conduction velocity of primary visual fibers, was recorded via an electroencephalograph on a signal-averaging computer. Cortical and rectal temperatures were observed and recorded during measurement of VERs. The mean latency from onset of photic stimulation to the N• peak diminished from 42.8 to 37.7 ms at respective cortical temperatures of 37.0 and 40.5 øC, which represents a mean increase of conduction velocity of 3.4 percent per incremented Celsius degree. While cortical and rectal temperatures were highly correlated, the former were invariably lower by nearly 2 øC, although they diverged slightly at higher elevations. Above a cortical temperature of 41.5 øC, evidence of reversible and irreversible thermal toxicity was observed.

Endogenous hyperthermia in normal human subjects: I. Experimental study of evoked potentials and reaction time

“…::l T was reliable and reflects a mean change per Celsius degree of 2.8 %. This reduction compares closely with the reduction of 3.4% per Celsius degree observed in the Nl component of the FEP of guinea pigs that underwent acute elevations of temperature in a 2450-MHz microwave field (see Bruce-Wolfe & Justesen, 1979, with Bruce-Wolfe, Hetschel, Justesen, & Reeves, 1981. In spite of the phylogenetic gap between Cavia porcellus and Homo sapiens, this close agreement inspires a measure of confidence that the temperature-CNS function involving primary processing of photic stimuli is highly general for the two species.…”

“…In other recent studies, investigators have used EP measures to assess the effects of microwave-induced hyperthermia on the electrophysiological activity of modality-specific neuronal populations. Bruce-Wolfe and Justesen (1979) elevated cortical temperatures of guinea pigs from 37.5° to 41.0°C, then observed an inverse relation between .1 Ts of temperature and latencies to the N 1 component of the flash-elicited EP, which declined from a mean of 41 msec to 35.5 msec, a change of 3.7 % per Celsius degree. These findings were later confirmed in rats (see Bruce-Wolfe, Justesen, & Riffle, 1984;Bruce-Wolfe, Justesen, Riffle, & Gilbert, 1983).…”