Long Trace Eyeblink Conditioning Is Largely Preserved in Essential Tremor.

ABSTRACT

The cerebellum and the prefrontal cortex are assumed to play a role in the pathophysiology of essential tremor (ET). Trace eyeblink conditioning with a long interstimulus interval relies on an intact function of the hippocampus, prefrontal cortex (PFC), and, although marginally, of the cerebellum. The aim of the present study was to evaluate whether long trace eyeblink conditioning is impaired in patients with ET. In 18 patients with ET and 18 controls, a long trace conditioning paradigm was applied. Following 100 paired conditioned response-unconditioned response trials, 30 conditioned response alone trials were given as extinction trials. The degree of tremor and the presence of accompanying cerebellar signs were determined based on clinical scales. The acquisition of conditioned eyeblink responses was not impaired in the group of all patients compared to controls (mean total incidences of conditioned responses in patients 23.3 ± 14.5%, in controls 24.1 ± 13.9%; P = 0.88). In the subgroup of six patients with cerebellar signs, incidences of conditioned responses were numerically but not significantly lower (16.4 ± 9.9%) compared to patients without cerebellar signs (26.8 ± 15.5%; P = 0.16). Trace eyeblink conditioning with a long interstimulus interval was not impaired in subjects with ET. Patients with clinical cerebellar signs presented slightly reduced conditioning. Areas of the PFC contributing to trace eyeblink conditioning appear less affected in ET. Future studies also using a shorter trace interval should include a larger group of subjects in all stages of ET.