We tested whether pharmacological impairment of OF-habituation after the administration (i.p.) of scopolamine (SCP; muscarinic antagonist) or MK-801 (MK; NMDA antagonist) was able to disrupt or alter grooming syntaxes. Amnesic drugs were daily administered during four consecutive days 20-min prior to a 15-min OF. On the fifth day, rats were given vehicle and tested as previously mentioned. We found that neither SCP nor MK altered the behavioral kinetics of locomotion. However, SCP and MK strongly inhibited the emission of rearing behavior. In despite of such inhibition, the emission of rearing leveled off in all groups on the last testing day. Further, MK but specially SCP, strongly disrupts grooming syntax. Overall, MK and SCP decreased the time spent on grooming behavior, causing only a mild reduction on its frequency of emission of this behavior. Further, both drugs increased the emission of the short, head-directed sequences of grooming, called here as cephalic grooming, but dramatically abolished the emission of the most complex forms of this behavior. In despite of such strong modulation on grooming syntax, neither MK not SCP altered grooming emission on the last testing day. The evidence provided here suggest that, in despite of the inhibition of exploratory and self-compensating behaviors along the OF exposures, back-ground mechanisms of information processing allows habituation to occur.Universidad de Costa Rica/[837-B8-123]/UCR/Costa RicaUniversidad de Costa Rica/[723-B9-197]/UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Sociales::Instituto de Investigaciones Psicológicas (IIP)UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Centro de Investigación en Neurociencias (CIN
