Two types of habituation in chicks: differential dependence on cholinergic activity

The role of cholinergic activity in habituation in chickens was tested using spontaneous alternation (SA) and reduction in response suppression to an auditory startle stimulus. While central reduction of cholinergic activity via atropine sulfate administration reduced SA and by inference, habituation, habituation to the tone was unimpaired, suppression decreasing with signal repetition even after a higher dose of atropine than that found effective in disrupting SA-indexed habituation. These findings confirmed an earlier suggested dissociation between habituation to externally produced stimuli e.g. startel stimuli, independent of cholinergic activity, and habituation to self=produced stimulation, e.g. exploration, spontaneous alternation, dependent on cholinergic functioning.