Brain mediation of Anolis social dominance displays. I. Differential basal ganglia activation

Ritualistic displays of aggressive intent are important social signals, often obviating physically dangerous engagement. To date, however, brain regions mediating such behaviors are not established. Here we used male Anolis carolinensis together with an in vivo 14C-2-deoxyglucose method to determine patterns of brain activation during elicitation of this animal's dominance displays vs. other behaviors. By patching one eye regional brain activation in the hemisphere receiving display-evocative visual stimuli ('seeing' side) was compared to activity in the contralateral brain that did not see specific stimuli ('patched' side); this was quantitated as the ratio of seeing/patched activity for brain regions of interest. Lone males displaying dominantly to mirrors activated dorsolateral basal ganglia (BG) in the seeing, compared to the patched hemisphere; this was not seen in various non-displaying controls. Degree of dorsolateral BG activation also correlated with a measure of dominant display activity, but not with locomotion. In socially stable pairs, displaying dominants showed similar activation of dorsolateral BG, but deactivated ventromedial BG; non-dominant cagemates displaying submissively had the opposite pattern. When cohabiting peacefully without displaying, paired dominants' and subordinates' brain activity patterns were similar to each other. Thus, different BG subsystems seem involved in dominant vs. submissive display behaviors. Given similarities in both social displays and BG organization, homologous brain systems might have similar functions in members of other amniote classes, including primates.