Maladaptive striatal plasticity and abnormal reward-learning in cervical dystonia

Abstract

In monogenetic generalized forms of dystonia, in vitro neurophysiological recordings have demonstrated direct evidence for abnormal plasticity at the level of the cortico-striatal synapse. It is unclear whether similar abnormalities contribute to the pathophysiology of cervical dystonia, the most common type of focal dystonia. We investigated whether abnormal cortico-striatal synaptic plasticity contributes to abnormal reward-learning behavior in patients with focal dystonia. Forty patients and forty controls performed a reward-gain and loss-avoidance reversal learning task. Participant’s behavior was fitted to a computational model of the basal ganglia incorporating detailed cortico-striatal synaptic learning rules. Model comparisons were performed to assess the ability of four hypothesised receptor specific abnormalities of cortico-striatal long term potentiation (LTP) and Long Term Depression (LTD): increased or decreased D1:LTP/LTD and increased or decreased D2: LTP/LTD to explain abnormal behavior in patients. Patients were selectively impaired in the post-reversal phase of the reward task. Individual learning rates in the reward reversal task correlated with the severity of the patient’s motor symptoms. A model of the striatum with decreased D2:LTP/ LTD best explained the patient’s behavior, suggesting excessive D2 cortico-striatal synaptic depotentiation could underpin biased reward learning in patients with cervical dystonia. Reversal learning impairment in cervical dystonia may be a behavioural correlate of D2 specific abnormalities in cortico-striatal synaptic plasticity. Reinforcement learning tasks with computational modeling could allow the identification of molecular targets for novel treatments based on their ability to restore normal reward-learning behavior in these patients.