residual scores were calculated. Residuals had a heritable component equal to or slightly less than that of the main dependent measure for each task (see Table 1), and the overall pattern of correlations among the remaining dependent measures was unchanged, with only the correlation of the residual score of head dipping and rearing approaching significance (r = 0.53, P < 0.06; data not shown). Thus, a genetically similar, heritable component exists between these two behaviors that cannot be completely explained by locomotor activity.
