An excessive activation of postsynaptic dopamine receptors as induced by the administration of L‐dopa,d‐amphetamine or apomorphine produce an abnormal behaviour characterized by a loss of inhibitory control over behaviour and an impairment of associative mechanisms. This is in contrast to the modulation of components of normal behaviour by the administration of lower doses of these drugs. It is further concluded that the administration of drugs which inhibit brain dopamine neurotransmission results in an inability to initiate voluntary movements without effects on associative mechani