Characteristics of the Normal Electroencephalogram. Ii. The Effect of Varying Blood Sugar Levels on the Occipital Cortical Potentials in Adults During Quiet Breathing 1

Abstract

Although the rOle of blood sugar level in the slowing of cortical rhythms during hyperventilation is now very generally recognized, its effect on the electroencephalogram during quiet breathing has not been fully studied in the normal human subject.Gibbs, Williams, and Gibbs (1), using the spectrum analyzer, concluded from a series of 4 adult normals that between extreme limits, alterations of blood sugar level have no effect on the frequency of the brain waves at normal depths of ventilation. Lennox, Gibbs, and Gibbs (2) found an upper limit of 50 mgm. for the blood sugar level to affect the electroencephalogram during normal breathing.Davis (3) made a more extensive study on 30 normals to whom injections of insulin were given in order to lower the blood sugar below fasting levels. She found that, within 20 minutes of the injection, there was a reduction in the alpha rhythm with the appearance of 8 cycle waves. Within 30 minutes of the injection, delta waves dominated the picture. Her study was made while the subjects were breathing normally. Hoagland (4, 5) and his coworkers made a study of the alpha rhythm in schizophrenics at blood sugars so low as to induce loss of consciousness.The present study is an attempt to establish the influence of blood sugar level upon the electroencephalogram at stages of unimpaired consciousness in the normal subject. METHODThe subjects for these experiments were all young adults, mostly college students (29 males, 16 females), This study was aided by a grant from the Harrington Fund.between the ages of 17 and 38. A brief medical history was taken and, in most cases, a brief physical examination was made before the experiment. Only those whose history indicated the absence of medical, neurological, and psychiatric disease, and whose physical examinations were within normal limits were included in the series. As a result of these brief preliminary examinations, the data on 15 individuals out of the 60 who volunteered were discarded from the series.The routine procedure was as follows: The subject reported to the laboratory in the morning, fasting. He was asked to lie down for a period of at least 30 minutes during which time the history was taken, a brief physical examination made, and the scalp electrodes attached.A sample of blood was drawn for the microdetermination of capillary blood sugar, and the subject was attached, by a mouth mask fitted with flutter valves, to a large spirometer with an open circuit for a period of approximately 8 minutes. He breathed outside air from the spirometer at the normal rate and depth of ventilation for a period of 2 minutes, and was then told to breathe as deeply as he could, inhaling and exhaling to the rhythm of a metronome clicking 30 times a minute. The depth of ventilation could be followed on the spirometer scale, and if the subject was not reaching the required depth for his body weight, he was urged to breathe deeper. (A study of the effects of the hyperventilation period will appear in a later paper in this series.)After the 3-minute...

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