EVENT-RELATED THETA-RHYTHMS IN CAT HIPPOCAMPUS AND PREFRONTAL CORTEX DURING AN OMITTED STIMULUS PARADIGM

In a recent study on human subjects which performed a time prediction task in an omitted stimulus paradigm we found an increase in the ampli tudes of evoked potentials (EPs) for the stimulus preceding the omitte d stimuli, probably due to expectancy and focused attention. The ampli tude increases were dominant over frontal and parietal association are as and were mainly reflected in enhancements of the theta (3-6 Hz) com ponents. In the present study we analyse the responses of the auditory cortex (GEA, gyrus ectosylvianus anterior), different parts of hippoc ampus (CA1, CA3), reticular formation (RF), and motor cortex (MC) of t he cat brain using a similar paradigm. Similar theta component increas es of the EPs were obtained in various parts of the hippocampus, which were dominant in pyramidal cell layers (CA3, CA4), and in motor corte x. The results are interpreted as signs of a diffuse theta response sy stem in the brain including mainly the hippocampus and frontal and par ietal association areas. The diffuse theta system is probably involved in general attention and expectancy processes.