Effects of alcohol consumption on lateralized aggression in Anolis carolinensis

Previous work has suggested that the lizard Anolis carolinensis, like many other reptiles, has a functionally split brain. Specifically, the left eye of this species projects primarily to the right hemisphere (and vice versa), there is no corpus callosum, and the physical placement of the eyes restricts their field(s) of vision to one region of hemispace. The current experiment used this preparation to examine the effect of alcohol administration and withdrawal on lateralized brain functioning during territorial aggression. Thirteen adult males were divided into control (CON) or alcohol (ETOH) groups. Baseline territorial aggression was assessed, following which ETOH subjects were then given twice daily solutions of 19% alcohol. After 19 days of ETOH consumption, territorial aggression was again assessed. Eye use during aggressive encounters was measured either following short periods (24 h) of alcohol withdrawal, or 90 m following alcohol consumption. Control subjects were found to have a predominance of left eye/right hemisphere-mediated aggressive responses, as has previously been reported. Alcohol withdrawn subjects were found to have a suppression of left eye/right hemisphere-mediated aggression. This reached statistical significance on several measures of aggression, including the number of dewlaps and headbob (P < 0.001) and the total number of aggressive responses (P = 0.001). Consumption of ETOH reversed this pattern and reinstated the normal pattern of left eye/right hemisphere dominance during aggression. Conversely, right eye/left hemisphere mediation of aggression was found to be increased, or not affected, during alcohol withdrawal, and to show no differences from CON following ETOH administration. Extrapolating from other recent findings in this species, these results suggest that the stress caused by ETOH withdrawal on the CNS may differentially effect the right hemisphere of the brain while having little effect on the left.