Objective: To examine whether Essential Tremor (ET) is associated with subtle changes in emotion processing, in parallel with those observed in the cognitive domain, using an experimental task involving emotion perception and reactivity.

Background: Essential Tremor is a highly prevalent movement disorder characterized by intention tremor and mild cognitive-executive changes. These features are commonly attributed to abnormal cerebellar changes, resulting in disruption of cerebellar-thalamic-cortical networks. Less attention has been paid to alterations in basic emotion processing in ET, despite known cerebellar-limbic interconnectivity. In the current study, we tested the hypothesis that a psychophysiologic index of emotional reactivity, the emotion modulated startle reflex, would be muted in individuals with ET relative to controls.

Methods: Participants included 19 ET patients and 18 age and education-matched controls, who viewed standard sets of pleasant, unpleasant and neutral pictures (IAPS) for 6 sec. each. During picture viewing, white noise bursts (95db, 50ms) were binaurally presented to elicit startle eyeblinks measured over the orbicularis oculi. Subjective picture ratings of valence and arousal were obtained. The ET and control groups were not demented or depressed based on cognitive and mood screening.

Results: At baseline, the groups did not differ in startle eyeblink latency or amplitude. A repeated measures ANOVA revealed a significant Group X Affect interaction (F2,70=3.90,p<0.03,ηp2=0.10). Consistent with past literature, controls had larger startle eyeblink amplitudes while viewing unpleasant than neutral or positive pictures (p< .001). In ET, startle eyeblinks were not modulated by emotion. This modulation failure was not due to medication effects, nor was it due to abnormal picture ratings.

Conclusions: Our hypothesis was supported. Neuroanatomically, it is unclear whether diminished startle modulation in ET is secondary to aberrant cerebellar input into limbic and/or frontal regions involved in emotional processing or to more direct disruption between the cerebellum and brainstem startle circuitry. If the former is correct, these findings may be the first to reveal dysregulation of emotional networks in ET.

This abstract was also presented at the 44th annual meeting of the International Neuropsychological Society, Boston, MA (February 3-6, 2016).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/emotional-modulation-of-the-startle-reflex-in-essential-tremor-evidence-of-altered-cerebellar-input-into-limbic-circuitry/