The Parallelism in Changes of Sensory Function and Electroencephalogram in Anoxia and the Effect of Hypercapnia Under these Conditions*

Abstract

The purpose of the expt. was to determine whether any correlation existed between the subjective sensory changes observed in anoxia and the activity of the brain. The critical fusion frequency (CFF) of vision was used as the measure of sensory changes and the recording of the electroencephalogram (EEG) from the occipital lobes served as the indicator of changes in the central nervous structures involved in vision. Five medical students, ages 20-25 yrs., were used as exptl. subjects. The CFF was detd. by means of a neon tube in direct vision, observations being made monocularly with an artificial pupil; the visual field was 2[degree]. Gas mixtures were inhaled from Douglas bags. A parallelism was found between the subjective sensory changes in anoxia as measured by the CFF and the objective neuronic changes occurring in the occipital lobes as recorded by the EEG. The exptl. results suggest that the loss in sensory function observed in anoxia is not due to such ill-defined functions of the C. N. S. as may be the basis of attention but that it results from an impairment to the functioning of the retino-geniculate-striate system. This seems evident since visual functions are impaired only when changes in the EEG occur at the same time. Degrees of anoxia which did not alter the CFF significantly had no effect on the EEG. Addition of 3% CO2 to low % O2 mixtures had the effect of largely offsetting both the subjective symptoms of anoxia and the changes in CFF and EEG.