Are central cholinergic paths involved in habituation of exploration and distraction?

Experiment 1 tested the generality of Carlton's hypothesis that central muscarinic cholinergic pathways are involved in habituation of exploration. The effects of 3 muscarinic antagonists were tested in a holeboard, under 2 test conditions, i.e. with objects absent or present. Both the frequency and the duration of head-dipping were used as measures of exploration. Scopolamine prevented habituation only of the frequency of head-dipping, and only when objects were present. Atropine and benzhexol did not impair the habituation of either frequency of duration of head-dipping in either test condition. The impairment of habituation seemed therefore to be specific to scopolamine, and to the more complex test condition, and thus there was little to justify the suggestion that central cholinergic paths were generally involved. Experiment 2 investigated the effects of muscarinic antagonists on habituation of distraction. None of the drugs affected the distraction to tones, nor the subsequent habituation to these stimuli. Central cholinergic paths do not therefore seem to be involved in habituation of this behavioral response.