Imitation is a basic, early human ability that persists throughout life. This study of the behavioral modes of imitation aimed at extending previous investigations of healthy subjects and some callosotomy patients conducted by our group.

Twenty-five subjects (age 25–52 years; 13 males; all right-handed but 2 women and 1 man) and 11 callosotomy patients (11 men; mean age 42 years; all right-handed; 3 complete callosotomies) participated in this study. The task involved the imitation of left or right upper limb intransitive meaningful and meaningless gestures made by a model facing the observer, shown in a video. The frequency of imitation according to a mirror perspective (spatial correspondence between model and observer sides) or an anatomical perspective (nominal correspondence of sides) was recorded.

In the control group spontaneous imitation, which involved no instructions, was mainly through a mirror perspective (63%; p<0.05). When instructed to use the same or the opposite limb as the model (driven imitation), where the meaning of "same" and "opposite" was left to the observer's interpretation, nearly all subjects (92%; p<0.001) used an anatomical strategy. In contrast, most callosotomy patients used the mirror strategy both in spontaneous (62%; p < 0.001) and in driven imitation (64%; p<0.001). In line with our previous findings, the present data confirm that the choice of imitation strategies is influenced by the callosotomy in ways that are still largely unknown.