Deficits in response space following unilateral striatal dopamine depletion in the rat

Hungry rats were trained to report the occurrence and location of brief, unpredictable visual stimuli presented to the left of their heads in 1 of 2 response locations. After training, they received unilateral infusions of 6-hydroxydopamine, depleting dopamine throughout the head of the caudate putamen, either on the left or the right side, that is, either ipsilateral or contralateral to the side on which they were required to respond. Following an ipsilateral lesion there were no impairments in localization of the visual discriminanda and there was no lengthening of reaction time. The contralaterally lesioned rats, however, showed considerably lengthened reaction times to both stimuli and a profound bias to the nearer of the 2 response locations. Evidence from probe trials in which the visual stimuli were presented separately or simultaneously showed that the impairment was not due to a failure to localize the stimuli in contralateral space but, rather, resulted from a deficit in directing responses in contralateral space. It is suggested that this may be due to a distortion in the representation of response space.