Head-dipping by rats with lesions of superior colliculus during extended testing in hole-board.

It has previously been shown that rats with large lesions of the superior colliculus fail to head-dip during a 5 min hole-board test. To investigate whether this was a permanent deficit in exploratory behaviour arising from inability to produce the appropriate responses, collicular rats were tested in a hole-board for 60 min or more. The period before their first head-dip (mean 27 min 40 sec) was much longer than for unoperated animals (mean 22 sec), but subsequently the collicular rats showed a pattern of head-dipping that was similar (although not identical) to that of the control rats. It appears that rats with lesions of the superior colliculus are not permanently prevented from exploring the hole-board by inability to produce the required response, but rather that they may have difficulty in discovering certain features of novel environments.