Effects of Electromagnetic Fields on the Visually Evoked Response in the Visual Cortex
Authors:   ,   Andrews University, Holm Arni 
Published: June 2023

Problem. This study sought to determine if electromagnetic fields affect the visually evoked response of the visual cortex. From the fact that nerve impulses are propagated by the motions of electrically charged ions, the question arose whether the presence of an external electromagnetic field might affect either the propagation of nerve impulses traveling through the optical nerve pathway or the functioning of the visual cortex itself. Method. Evoked responses were produced in the visual cortex of cats by visual stimulation (light flashes). Surface electrodes, located at the visual cortex (and connected to a preamplifier and an oscilloscope) detectedthe evoked responses which (after being modulated by a frequency modulator) were recorded on magnetic tapes. From each of 5 cats, 42 samples (consisting of 80 light flashes each) were recorded. These samples were made up of 4 series. In the first series were samples collected at field frequencies of 1, 60, 120, 180, 240, and 300 cycles/second at a constant field strength of 5 gauss and a sample collected before each of these with the field off (control samples). In the second series were samples collected at field frequencies of 200, 400, 600, 800, and 1,000 kilocycles/second also at a constant field strength of 5 gauss and corresponding 5 control samples. The samples in the third series were collected at field strength values of 1 to 5 gauss (by increments of 1) at a constant frequency of 60 cycles/second and 5 corresponding control samples. The fourth series consisted of samples collected at field strength values of 1 to 5 gauss at a constant frequency of 400 kilocycles/second and 5 control samples. The recorded evoked responses in each sample were averaged by a computer (a signal averager) and graphed by an x-y plotter which resulted in a single graph representing the mean of a given sample. Numerical information obtained from these graphs became the basis for the statistical analyses performed on the data collected in the study. The independent variable in the study was the field which was manipulated through its frequency and strength.The dependent variables were latency and amplitude of the visual cortex responses. Conclusions. Statistical analyses confirmed a research hypothesis stating that the latencies of visual cortex responses recorded in the absence of the field are different from those of responses recorded in the presence of the field. This difference, found at 60 c/s and 2 gauss and at 400 Kc/s and 4 gauss, was significant at the .05 level. Another research hypothesis, stating that a similar difference exists with respect to amplitude, was also confirmed. That difference, observed at 120 c/s and at 200 Kc/s, both at 5 gauss, and at 60 c/s and 2 gauss, was significant at the .01 level in each case. A correlation between the latency of responses recorded in the presence of the field and the frequency of the acting field was observed in the 200-1,000 Kc frequency series. The correlation is negative and is -.992 where highest (significant at the .01 level). It was concluded from the findings of the study that it appears that man-made electromagnetic fields cause a slight change in the latency and a substantial change in the amplitude of visually evoked responses in the visual cortex of cats. It was also concluded that a correlation exists between the latency of responses in the visual cortex recorded in the presence of an electromagnetic field and the frequency of the acting field in the frequency range of 200-1,000 Kc/s. Three other research hypotheses, made with respect to certain possible correlations, were not upheld by the findings of the study.