Comparison of evoked potential changes during classical and instrumental conditioning in cats.

The waveform changes of cortical evoked potentials to click conditioned stimuli were analyzed by a complex computer program developed for sorting nonhomogeneous series of evoked potentials. The changes of evoked responses manifested themselves mainly in the middlelatency waves, while the first components showed only a slight fluctuation during the whole conditioning. A late negative component of 40-50 ms latency was clearly related to the attentive state of the animal. The evoked potentials with increased negative component appeared in different sequences in 'the two conditioning paradigms and in the different phases of the learning process.