Table 1. Summary of Neurophysiological Studies in ET, by Year of Publication.
| Study | Methods Evaluated | TMS Measures Assessed | Findings |
|---|---|---|---|
| Britton et al.10 | Single pulse TMS M1 (suprathreshold) | Tremor phase, resetting index | Pulse to M1 resets ET tremor and PD tremor phase; latency to first peak significantly longer in PD tremor than ET tremor |
| Pascual-Leone9 | Single pulse TMS M1 (suprathreshold) | Tremor phase | Pulse to M1 resets tremor motor unit activity; resetting correlated with stimulus intensity and duration of post-stimulus silent period |
| Romeo et al.14 | Single pulse TMS M1 | Resting motor threshold, CSP, SICI | No difference in ET subjects compared to HC |
| Pinto et al.34 | Single pulse TMS cerebellum and paired pulse TMS: Cerebellar-M1 | MEP, CBI, tremor phase | Did reduce MEP at ISI 5–7 ms, but degree of inhibition not different in ET vs. HC (n = 9 vs. 10)No tremor reset with cerebellar TMS but there was w/ M1 TMS |
| Shukla et al.15 | Single pulse TMS M1, maximum stimulatory intensity | CSP | No statistically significant difference between ET subjects and HC; no correlation with disease duration |
| Molnar et al.13 | Single pulse TMS M1 with and without active DBS | MEPs, SICI, ICF, LICI | DBS facilitates MEPs especially at higher intensities; DBS has no effect on SICI or ICF, nor LICI ET subjects had reduced ICF at rest compared to HC but otherwise SICI, LICI and active ICF were no different from HC |
| Lo et al.11 | Motor imagery before and during single pulse TMS measures to M1 | RMT and MEPs | Motor imagery increase MEPs in HC but not ET; RMT were reduced during motor imagery in HC and ET |
| Mazzocchio et al.12 | Single pulse TMS to M1 in both adducted and abducted shoulder positions | MEPs | In subjects with ET, MEPs were facilitated in the abducted position, similar to HC, opposite of those with parkinsonian tremor |
| Avanzino et al.17 | Cerebellar rTMS using figure of 8 coil, handle up, right lateral cerebellum, 1 Hz at 90% RMT for 10 minutes | Touch duration and intertapping interval | At baseline, ET subjects have longer touch duration (TD) and shorter intertapping interval (ITI); 1 Hz TMS appear to restore TD and ITI to normal values |
| Chuang et al.16 | Premotor and motor cTBS | MEP, SICI, Tremor frequency and amplitude | cTBS reduces MEP in both HC and ET, but less durable in ET subjects; Reduces SICI No change in tremor frequency but significantly reduced tremor amplitude |
| Lu et al.33 | Single and paired pulse TMS (LICI paradigm) to M1, SMA and cerebellum | Tremor reset | M1 and SMA single pulse resets postural tremor in ET subjects Cerebellar single and paired pulse TMS did not reset postural tremor in ET |
| Brittain et al.50 | Cerebellar transcranial alternating current (tACS): active electrode (35 cm2): 3 cm lateral to inion | Frequency tolerance (stability of tremor over range of tremor frequencies) | ET has narrow frequency tolerance while PD tremor has broad frequency tolerance Cerebellar tACS is able to entrain ET tremor more than PD tremor |
| Hanajima et al.40 | Paired pulse cerebellar-M1 pulse using double cone 110-mm coil | CBI | CBI reduced in ET compared to HC |
Abbreviations: CBI, Cerebello-brain Inhibition; cTBS, Continuous Theta Burst Stimulation; CSP, Cortical Silent Period; DBS, Deep Brain Stimulation; ICF, Intracortical Facilitation; ISI, Interstimulus Interval; LICI, Long Intracortical Inhibition; M1, Primary Motor Cortex; MEP, Motor Evoked Potential; RMT, Resting Motor Threshold; rTMS, Repetitive TMS; SICI, Short Intracortical Inhibition; SMA, Supplementary Motor Area; tACS, Transcranial Alternating Current Stimulation; TMS, Transcranial Magnetic Stimulation.