ELECTRICAL PATTERNS OF AUGMENTING AND RECRUITING WAVES IN DEPTHS OF SENSORIMOTOR CORTEX OF CAT

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Abstract
Augmenting and recruiting responses have been analyzed by recording at measured depths within the sensorimotor cortex with fine wire and glass microelectrodes during low-frequency stimulation of the thalamus of the cat. For augmenting waves, the profile of potential change in depth and in time revealed a short-latency sink which developed in layers HI, IV and V of the cortex and migrated to the surface 20-30 msec. after the stimulus. The deep negativity was coincident in time with the surface-positive component of the wave and with tightly clustered bursts of action potentials in those same layers. For recruiting waves, similar profiles revealed only gradients of potential change through the cortex. After a long latent period, negativity appeared first in the most superficial layers, deeper layers swinging from positive to negative during the ensuing 20 msec. The recruiting waves were accompanied by dispersed and irregular unitary action potentials in layers III-V of the cortex. Although the basic patterns of the two waveforms were found to be entirely different, variants which appeared to be the results of admixtures were encountered. The similarity between the augmenting waves and the primary responses which have been reported by others seems so striking as to suggest that both the primary response and the augmenting wave are the result of impulses in a common class of thalamocortical fibers. The differences between recruiting and augmenting waves suggest that the recruiting waves are generated by an entirely different mechanism which may not be entirely intracortical in its organization.

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