Acoustically evoked potentials in the visual cortex and superior coliculus of the freely moving rat and their variability.

Hooded rats of the Long-Evans strain with chronically implanted electrodes in the visual cortex (VC, area 17), superior colliculus (CS), olfactory bulb (BO) and the prefrontal cortex (FC) were stimulated by series of 20 clicks (0.4 per s) during spontaneous behaviour. Different behavioural patterns were identified and classified by observation, recorded movement patterns, respiration rate and EEG patterns. Averaged acoustically evoked potentials in the visual system showed reproducible changes of all their components in correlation to behavioural patterns. Components N10 and N32 in the CS, resp. N14 and N32 in the VC changed differently during behavioural activation. The early negative component did not decrease while the later ones became significantly smaller during progressive activation, except during attentive behaviour in which they were facilitated. From the results can be concluded that a great number of neurons in the visual system of the rat should be involved in heteromodal information processing which is modified in correlation to the changing behavioural pattern.