Conditioned turning in rats: dopaminergic involvement in the initiation of movement rather than the movement itself.

Adult rats received unilateral 6-hydroxydopamine lesions of the mesotelencephalic dopamine pathway following training to turn selectively in one direction for sugar-water reinforcement. The lesion abolished the rats' ability to turn selectively away from the lesioned side, whereas reinforced turning towards the lesioned side remained intact. The pattern of results suggested that the deficit was not attributable to primary motor, sensory or motivational impairments, but to an inability following lesion to initiate movement towards the opposite side.