Intracranial potentials correlated with an event-related potential, P300, in the cat

Intracranial recordings of long-latency, event-related potentials were obtained from paralyzed, artificially respirated cats. A modified oddball paradigm was employed in which cats were presented with a randomized series of two tones, a 'frequent' 4 kHz stimulus and a 'rare' 1 kHz stimulus. A tail shock was administered 700 ms after onset of the rare tone. Under these circumstances the stimulus elicited a positive component at the vertex similar to the human P300. Intracranial potentials associated with the rare tone usually manifested components of greater amplitude than did potentials associated with the frequent tone. A positive component occurring in latency between 200 and 350 ms only accompanied the presentation of the rare stimulus. The P300 component, which was positive at the dura, appeared as a negative component within a few millimeters of the surface over a wide area of the marginal and suprasylvian gyri. Changing the probability of the rare stimulus resulted in a reduction in the amplitudes of both the intracranial negative component and the P300 recorded at the skull. Components of large amplitude associated with the rare stimulus were obtained from the region of the hippocampus. These components reversed polarity, sometimes more than once, as the electrode was advanced. Substantial latency differences were often observed between the P300 recorded at the skull and P300-like intracranial components associated with the rare stimulus. These results suggest that the cortices of the marginal and suprasylvian gyri and the hippocampal region contribute to the generation of the cat P300.