ELECTROENCEPHALOGRAPHIC PATTERNS FROM THE BASE OF THE BRAIN

Electroencephalographic recordings from the base of the brain give valuable supplementary information to data obtained from conventional scalp recordings. Various locations of the deep lead are possible—subsphenoid, spheno-ethmoidal or subfrontal.

Several varieties of basal patterns are described and illustrated. The effect of visual stimulation, overbreathing, drugs, spontaneous and induced electrical discharges in epileptics, and of gross intracranial pathology is described.

In general the basal rhythm response to various stimuli is similar to that of the cortical (superficial) rhythm. Visual stimulation flattens the basal rhythm and blocks the alpha activity. Hyperventilation induces a build-up in size of potentials and a slowing of rhythm, which may be greater or less than that of the cortex. Autonomic drugs (epinephrine and mecholyl) appear to affect base more than cortex. Sodium amytal in amounts sufficient to produce intoxication but not sleep, results in high voltage fast waves in base as well as cortex.

Electrical paroxysms typical of epilepsy usually are more pronounced at the cortex than at the base.

The basal lead is a valuable adjunct in localization of gross intracranial pathology.