The autonomic nervous system (ANS) regulates involuntary bodily functions. Autonomic dysfunction is well documented in Parkinson's disease (PD), affecting patients quality of life. Evidence in essential tremor (ET), another prevalent movement disorder, remains scarce and limited — due to the use of nonstandardized metrics and sometimes uncontrolled conditions — with contradicting results across studies. This study aims to characterize autonomic responses in ET by employing standardized heart rate variability (HRV) metrics alongside electrodermal activity (EDA) analysis under controlled experimental conditions of mental stress, addressing another gap in the literature that has solely focused on physical stressors.
ECG and EDA signals were recorded from 5 PD patients, 5 ET patients, and 5 age-matched healthy controls during rest and during a cognitive stress task, the Serial Subtraction Task (SST). ECG was acquired with a Holter device, HRV computed, and the LF/HF power ratio was used as a measure of ANS reaction. EDA was measured with wearable device and the literature-validated Ampsum (sum of the phasic spikes of the EDA) was used as a measure of sympathetic activation.
Preliminary results indicate reduced sympathetic activation, as measured by the average increment of EDA-derived Ampsum, in both PD (0.0053 ± 0.0062 a.u.) and ET (0.0119 ± 0.0152 a.u.) patients compared to controls (0.0491 ± 0.0535 a.u.) during mental stress, aligning with prior findings on physical stressors. In contrast, HRV results, as measured by the increment in LF/HF ratio were inconclusive (PD: 0.8294 ± 1.6315 n.u. ET: 1.9885 ± 4.7176 n.u. controls: 2.1814 ± 1.9968 n.u.), potentially due to small sample size, and confounding factors such as altered respiration during SST.
These findings suggest that ET may involve a form of dysautonomia affecting sympathetic function. Further research with larger cohorts and standardized methodologies is necessary to clarify the nature and extent of autonomic involvement in ET.