Evolution of evoked potentials during conditioning in immobilized cats.

To establish the relevancy of motor feedback in the evolution of evoked potentials during conditioning, recordings were made from the Caudate Nucleus (CN), the Lateral Geniculate Body (LGB), the Mesencephalic Reticular Formation (MRF), the Occipital Cortex (OC) and the Cerebellar Cortex (Cer. C) in immobilized and non-immobilized cats before and during classical conditioning. As a result of the conditioning we observed an enhancement of the average evoked potentials (AEP) recorded in CN and in LGB in those animals able to perform the conditioned response. In contrast, the AEP recorded in CN diminished in the immobilized animals, and no changes were observed in the recordings made from the other structures, except for the appearance of polyphasic components of small amplitude and high frequency (200 Hz) in the average evoked potentials' 2nd peak, recorded from LGB. From these results we conclude that the motor feedback produced by the execution of the response is important to establish the AEP changes observed in the CN.

Modification of motor activity, passive avoidance conditioning and evoked potentials by microinjections of strychnine in both caudate nuclei in cats.

Passive avoidance conditioning (PAC) seems to depend on inhibitory actions within the caudate nucleus (CN). Thus topical application of strychnine could block these influences. In cats, with permanently implanted cannulae in the head of the CN, bilateral microinjections of 100 micrograms of strychnine produced a stereotyped behavior of grooming and running with the extremities flexed to dark places. When placed into a two compartment chamber for a PAC acquisition they would not move from the dark compartment to the illuminated one. After decreasing the illumination some cats crossed and the acquisition test was performed. Twenty four hours later they showed the learned response. A second retention test was not modified by another strychnine application. These results contrast with those obtained by picrotoxin microinjections which disrupt the retention of a PAC. However, strychnine affects the evoked potentials (EP) recorded in CN by n. centralis medialis (NCM) stimulation by decreasing a positive peak, which probably represents post-synaptic inhibition and increasing the late positive component. In the lateral geniculate body strychnine affected a late positive wave and in the occipital cortex it increased the initial negative peaks and decreased the late positive ones of the potentials evoked by flash stimulation. These findings suggest a more suitable role of the CN in the regulation of visual information, which is probably related with the attention processes.