Hyperkinetic disorders and loss of synaptic downscaling

In this Perspective the authors provide a comparison of recent neurophysiological findings on the pathophysiology of three major movement disorders: Huntington's disease, l -DOPA-induced dyskinesia and dystonia. Both clinical and preclinical studies show that these hyperkinetic disorders share mechanisms underlying synaptic scaling and synaptic plasticity alterations in the basal ganglia–thalamo-cortical network. Recent clinical and preclinical studies have shown that hyperkinetic disorders such as Huntington's disease, dystonia and l -DOPA-induced dyskinesia in Parkinson's disease are all characterized by loss of the ability to reverse synaptic plasticity and an associated increase in the excitability of excitatory neuronal inputs to a range of cortical and subcortical brain areas. Moreover, these changes have been detected in humans with hyperkinetic disorders either via direct recordings from implanted deep brain electrodes or noninvasively using transcranial magnetic stimulation. Here we discuss the mechanisms underlying the loss of bidirectional plasticity and the possibility that future interventions could be devised to reverse these changes in patients with hyperkinetic movement disorders.