Cerebral Action Potentials. ∗

Abstract

The following observations, some confirmatory, based on experiments on 8 cats and 2 monkeys, were made during an exploration of the cerebral cortex and underlying structures for spontaneous and evoked activity. Anatomical relations given are only approximate; the work is being continued with the aid of a Horsley-Clark stereotaxic instrument. Action potentials picked up by an Adrian-Bronk electrode, amplified, and fed into a loud speaker and high-voltage cathode ray oscillograph, were the index of activity. Numerous controls have convinced us that extraneous pick-up did not confuse true action potentials in the phenomena described. For example, during penetrating movement of the needle of less than 1 mm. there appeared successively: nothing, strong auditory responses, nothing, strong optic responses, nothing. Clearly, responses may be highly localized, and a non-specific spread is excluded.

Auditory responses were obtained from the temporal cortical surface, projection tracts, auditory thalamus, and lower structures in the monkey, from all but cortex in the cat. With the electrodes on a large tract, responses were obtained to stimuli near the human threshold. Different sounds (e. g., watch tick and voice) and pitches are recorded most strongly at different needle positions, indicating a spatial separation of impulses set up by different pitches. Similarly, a fairly sharp di-, tri- or polyphasic wave appears on the oscillograph for each watch tick. The form differs from R. to L. ear for one needle position, and for one ear at different needle positions.

Considerable discharge was usually present in the pathways even without deliberate sound stimulation. In the monkey, a stimulus at 660 d.v. gave a standing wave of the same frequency on leading from auditory tracts, a completely asynchronous discharge, stronger at the start, from the cortical surface. In the cat and monkey, melodies could usually be recognized on leading from auditory tracts, although words were garbled.