Effects of perinatal testosterone on handedness of gerbils: support for part of the Geschwind-Galaburda hypothesis.

When assuming their species-typical tripodal stance, male Mongolian gerbils (Meriones unguiculatus) use their right forepaw for support more frequently than do females. This experiment determined whether, as N. Geschwind and A. M. Galaburda (1987) have proposed, the direction of such sexually dimorphic lateral asymmetry of forelimb use is affected by perinatal exposure to testosterone (TP). It was found that male gerbils injected with TP when 4 days old were significantly less likely to rest on their right forepaw when in a tripodal stance than were their oil-injected siblings. Female gerbils injected with TP when 6 days old were more likely than oil-injected controls to use their right forepaws for support. The findings demonstrate effects of perinatal exposure to TP on handedness in gerbils and suggest that the relationship between TP exposure and asymmetrical forelimb use is not always as direct as Geschwind and Galaburda's model suggests.