Abstract
Patients with Parkinson’s disease (PD) show cognitive impairments, including difficulty in shifting attention between perceptual dimensions of complex stimuli. Inactivation of the subthalamic nucleus (STN) has been shown to be effective in ameliorating the motor abnormalities associated with striatal dopamine (DA) depletion, but it is possible that STN inactivation might result in additional, perhaps attentional, deficits. This study examined the effects of: DA depletion from the dorsomedial striatum (DMS); lesions of the STN area; and the effects of the two lesions together, on the ability to shift attentional set in the rat.In a single session, rats performed the intradimensional/extradimensional (ID/ED) test of attentional set-shifting. This comprises a series of seven, two-choice discriminations, including acquisitions of novel discriminations in which the relevant stimulus is either in the currently attended dimension (ID) or the currently unattended dimension (ED shift) and reversals (REVs) following each acquisition stage.Bilateral lesions were made by injection of 6-hydroxydopamine (6-OHDA) into the DMS, resulting in a selective impairment in reversal learning. Large bilateral ibotenic acid lesions centered on the STN resulted in an increase in trials to criterion in the initial stages, but learning rate improved within the session. There was no evidence of a ‘cost’ of set-shifting – the ED stage was completed in fewer trials than the ID stage – and neither was there a cost of reversal learning. Strikingly, combined lesions of both regions did not resemble the effects of either lesion alone and resulted in no apparent deficits.
Highlights
The subthalamic nucleus (STN) has been found to be an effective target for functional neurosurgical treatments designed to ameliorate the motor symptoms of Parkinson’s disease (PD) (Henderson and Dunnett, 1998; Bronstein et al, 2011)
We examined the roles of the STN and dorsomedial striatum (DMS) DA in a wellestablished test of cognitive flexibility – the intradimen sional/extradimensional (ID/ED) attentional set-shifting task – that has been adapted for rats (Birrell and Brown, 2000; Tait et al, 2014)
There is no explicit boundary for the DMS region, reduced tyrosine hydroxylase was evident bilaterally in the dorsomedial portion of the striatum of all DMS-lesioned rats, not extensively in all animals
Summary
The subthalamic nucleus (STN) has been found to be an effective target for functional neurosurgical treatments designed to ameliorate the motor symptoms of Parkinson’s disease (PD) (Henderson and Dunnett, 1998; Bronstein et al, 2011). Baunez and Robbins (1997, 1999) addressed the issue of cognitive impairments following lesions of the STN, using the five-choice serial reaction time task (5CSRTT; see Carli et al, 1983), which includes measures of attention. They demonstrated multiple deficits, many of which required an explanation beyond a simple failure of motor inhibition, from which they concluded that the STN played an important role in attentional processing.
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