A mini-review of the pathophysiology of task-specific tremor: insights from electrophysiological and neuroimaging findings

Task-specific tremor (TST) is a specific type of tremor that occurs when performing or attempting to perform a specific task, such as writing or playing a musical instrument. The clinical entity of TST remains heterogeneous. Some TSTs can only be induced by conducting a specific task, while others can be elicited when adopting a particular position simulating a task. The pathophysiology of TST is controversial. Whether TST is an isolated tremor syndrome, a spectrum of dystonic tremor syndrome (DTS), or essential tremor (ET) is not yet clear. Evidence from electrophysiological studies suggests that TST patients have normal reciprocal inhibition responses but abnormal motor cortical excitability, especially relating to the maladaptive long-interval intracortical inhibitory circuitry. The blink recovery study and eyeblink classical conditioning studies demonstrated possible hyperexcitability of the brainstem circuits and cerebellar dysfunction in patients with TST. Functional MRI studies have further shown that patients with TST have reduced functional connectivity in the cerebellum, similar to patients with DTS and ET. Due to variable methodologies and the sparsity of functional MRI studies in TST, it remains uncertain if patients with TST share the connectivity abnormalities between the cortical or subcortical areas that have been demonstrated in patients with DTS. Comprehensive electrophysiological and functional neuroimaging studies may help to elucidate the pathophysiology of TST.