Discrete telencephalic lesions accelerate the habituation rate of behavioral arousal responses in Siamese fighting fish (Betta splendens).

Stereotaxic electrolytic lesions were made in the dorsomedial telencephalic area, laterally to the dorsal commissure, in male Siamese Fighting Fish (Betta splendens). The startle and orienting responses to regularly delivered taps on the side of the aquarium were recorded for lesioned, sham-operated and unoperated groups. Lesioned fish showed increased reactivity to environmental modifications, including tonic immobility and changes in body color. Although no changes in the arousal responses were detected, the lesioned fish showed an increased frequency of startle responses and habituated to the orienting responses faster than sham-operated and unoperated animals. The long-term inter-session retention of habituation was also decreased. The effects observed are the opposite of those obtained after complete or unilateral telencephalic ablation in teleosts and suggest the existence of antagonic telencephalic systems playing a modulatory role in arousal control.