Dynamics of evoked potentials in the dog auditory cortex during the formation of goal-directed behavior after ablation of the medial geniculate bodies

Conclusions

• 1. After bilateral extirpation of the medial geniculate bodies, additional channels of communication with many relays along their course are brought into play by way of compensation to conduct information to the auditory cortex. EP continue to be recorded in the auditory cortex but their latent period is increased to 12–15 msec, the duration of the principal negative wave is increased (to 40 msec), and splitting chiefly of its ascending front is observed.

• 2. Integrative processes organized in the medial geniculate bodies exert a definite influence on the character of activity of the functional system at the auditory cortical level. Ascending excitation, relayed by the medial geniculate bodies, activates certain synapses on apical dendrites of pyramidal cells and determines the formation of EP of a definite configuration: They participate in the formation of the early negative waves, the first positive component, and the ascending front of the principal negative wave of the EP.

• 3. After removal of the medial geniculate body the auditory cortex participates in the formation of processes of afferent synthesis (in the active period of reflex formation the amplitude of EP increases, the principal negative component lengthens to 45–55 msec, and splitting of its fronts takes place), and also in the preparation for decision making (the conditioned reflex is preceded by a “double EP,” which is probably connected with potentiation of reverberation excitation in the compensatory channels of communication.