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Table 1 Summary of the methodology and results from the studies reviewed

From: Peripheral electrical stimulation to reduce pathological tremor: a review

Article Population Strategy Stim. location Stim. pulse width [us] Stim. frequency [Hz] Stimulation protocol Tremor assessment Main results Physiological mechanism
Bó et al. [20] 10 ET (moderate-severe) FES: co-contraction SF: heterogeneous wrist and finger muscles 150 40 10-50 s/trial, stim ON vs stim OFF, 5–7 trials Kinematics, tremor power at wrist Most significant acute tremor attenuation: 37.18%-94.68% Increasing joint stiffness
Britton et al. [38] 10 ET; 9 PD, 8 HV Single shock > MT SF: median nerve 500 Single shock Single shock sEMG Significant EMG reduction from 90 to 210 ms post stimulus Afferences reset central tremor oscillators
Dideriksen et al. [42] 4 ET; 5 PD (mild-severe) afferent < MT: out-of-phase EMG based SF (2 ET, 3 PD), IM (2 ET, 2 PD): wrist flexors-extensors 400 100 150 s/trial, stim ON vs stim OFF, 20% and 40% DC, 10 trials Kinematics, tremor power at wrist Average highest acute reduction: 54 ± 20% (IM) and 50 ± 41% (SF) Ia afferent fibers, reciprocal inhibition
Dosen et al. [16] 2 ET; 4 PD (mild-severe) FES and afferent < MT: out-of-phase EMG based SF: wrist/finger flexors-extensors 300 100 120 s/trial, stim ON vs stim OFF, 5 trials per modality Kinematics, tremor power at wrist Average acute reduction: 60 ± 14% (> MT) and 42 ± 5% (< MT) (p < 0.05) Generation of opposite forces to tremor oscillations; Ia afferent fibers, reciprocal inhibition
Gallego et al. [39] 4 ET; 2 PD (mild-severe) FES: co-contraction SF: wrist flexors-extensors 250 or 300 30 or 40 30 s/trial; stim ON vs stim OFF, 6–12 trials Kinematics, tremor power at wrist Average acute reduction: 52.33 ± 25.48% (p < 0.05) Increasing joint stiffness
Gillard et al. [29] 3 PD, 3 HV FES: out-of-phase accelerometer based SF: wrist/finger flexors-extensors * * 30 s/trial, stim ON vs stim OFF, 10 trials Kinematics at finger/wrist Average acute reduction: 84.50 ± 2.20% Out-of-phase forces
Grimaldi et al. [17] 1 PD, 1 ET, 1 cerebellar syndrome FES: co-contraction SF: wrist/elbow flexors-extensors 100 30  ~ 30 s/task, stim ON vs stim OFF, 15 trials (5 tasks) Kinematics at finger/wrist/elbow; CNF-TES scale Most significant acute tremor attenuation in one ET patient: ~ 50% Increasing joint stiffness
Hao et al. [32] 8 PD (moderate) afferent < MT: continuous (EMG triggered) SF: radial nerve (dorsal skin of hand) 200 250 15 s/trial, stim OFF(5 s)- ON(5 s)-OFF(5 s), 9–13 trials Kinematics and sEMG at finger/wrist/elbow flexors-extensors Average acute reduction: 61.56 (kinematics across degrees of freedom); 47.97% EMG across degrees of freedom) Cutaneous afferents and propriospinal interneurons
Heo et al. [21] 18 ET (moderate) afferent < MT: continuous SF: wrist/elbow flexors-extensors 300 100 15 s/trial, Pre-Stim ON-Post 5 min, 9 trials Kinematics at finger/forearm/arm Average acute reduction: 90% (finger), 58% (hand), -50% (forearm); Post 5 min: 88% (finger), 61% (hand), 27% (forearm) Afferences might modulate supraspinal tremor oscillators
Heo et al. [22] 18 ET (mild-severe) afferent < MT: continuous SF: wrist/elbow flexors-extensors 300 100 Spiral drawing task, Pre-Stim ON-Post 5 min, 9 trials Kinematics at finger/forearm/arm Acute average reduction: 12%. Significant differences (p < 0.05) for Pre-Stim and ON-Post 5 min Afferences might modulate supraspinal tremor oscillators
Heo et al. [34] 14 PD (mild-severe) afferent < MT: continuous SF: wrist flexors-extensors 300 100 15 s/trial, Pre-Stim ON-Post 5 min, 9 trials Kinematics at finger/forearm/arm Reduction in 50–71% of patients. Average acute: 68% (finger), 62% (hand), 53% (forearm); Post 5 min: 56% (finger), 59% (hand), 60% (forearm) Afferences might modulate supraspinal tremor oscillators
Heo et al. [35] 14 PD (same Heo et al. [34]), 9 SWEEDs afferent < MT: continuous SF: wrist flexors-extensors 300 100 15 s/trial, Pre-Stim ON-Post 5 min, 9 trials Kinematics at finger/forearm/arm No reduction data. Only significant differences (p < 0.05) for Pre-Stim ON in PD. No reduction for SWEEDs Afferences might modulate supraspinal tremor oscillators
Isaacson et al. [26] 263 ET (mild-severe) afferent < MT: out-of-phase kinematics (open-loop) SF: radial and median nerves at wrist Clinical-trial: 3 months, 2 × 40 min stim session/day TETRAS, select BF-ADL tasks, kinematics at wrist, CGI-I, PGI-I, QUEST 62% (TETRAS) and 68% (BF-ADL) of severe/moderate patients improving to mild/slight Afferences modulate ventral intermediate nucleus
Javidan et al. [40] 3 ET, 4 PD, 6 cerebellar tremor FES: out-of-phase kinematics based SF: wrist, elbow flexors-extensors 100 30 20 min/trial, Stim ON vs Stim OFF, unknown number of trials Kinematics at wrist Average acute reduction at wrist: 73 ± 14% (ET), 62 ± 5% (PD), 62 ± 38% (cerebellar tremor) Generation of opposite forces to tremor oscillations
Jitkritsadakul et al. [30] 34 PD (moderate)  > MT: continuous SF: fingers APB, FDI, SDI 150 50 10 s/trial, Pre-Stim ON, 2 trials Kinematics and sEMG at finger/forearm/arm; UPDRS Average acute reduction (tremor power): 49.57 ± 38.89% (p < 0.05) Afferences interfere with the cerebello-thalamo-cortical circuit
Jitkritsadakul et al. [33] 30 PD (moderate)  > MT: continuous SF: fingers APB, FDI, SDI 150 50 10 s stim, Pre-Stim ON; 30 min session; Sham vs Stim Kinematics at hand (glove); UPDRS; VAS Average acute reduction (RMS, x-axes): 60.22 ± 38.85% (p < 0.05); significantly different from sham group Afferences interfere with the cerebello-thalamo-cortical circuit
Kim et al. [25] 9 ET (moderate-severe) afferent < MT: out-of-phase kinematics based and open-loop SF: radial nerve at wrist 200 50, 100, 200 20 s/trial, stim. OFF (10 s)-ON (10 s); open-loop, closed-loop; 12.5%, 25% and 37% DC; 18 trials Kinematics at wrist; TETRAS; qualitative assessment Average acute reduction: 42.17 ± 3.09% (p < 0.05). No differences open vs closed loop Not proposed
Lin et al. [23] 23 ET (moderate-severe)  < MT: out-of-phase kinematics (open-loop) SF: radial and median nerves at wrist 300 150 Pre, 40 min stim, Post; Sham vs Stim group TETRAS (spiral) Average post reduction (TETRAS): 60 ± 8.4% (p < 0.05), significantly different from sham group Afferences modulate ventral intermediate nucleus
Mones et al. [28] 5 PD Single shock above MT SF: ipsilateral and contralateral ulnar nerve at wrist 500 Single shock Single shock iEMG No change in tremor amplitude. Change in tremor frequency after shock Afferences reset central tremor oscillators
Munhoz et al. [18] 5 ET, 2 peripheral neuropathy TENS > MT: continuous SF: brachial plexus on neck, C7 spinous process 250 5, 10, 50, 100 Pre, 15 min stim, Post Kinematics at wrist, WHIGET scale No significant reduction Wrong afferent fibers targeted or stimulation parameters
Muceli et al. [36] 1 PD afferent < MT: out-of-phase EMG based SF: wrist/finger flexors-extensors 200 100 60 s/trial, stim ON(30 s) vs stim OFF(30 s), 2 trials Kinematics, tremor power at wrist Acute reduction in one patient: 58% Ia afferent fibers, reciprocal inhibition
Pahwa et al. [24] 77 ET (moderate-severe) afferent < MT: out-of-phase kinematics (open-loop) SF: radial and median nerves at wrist 300 150 Pre, 40 min stim, Post; Sham vs Stim group TETRAS, select BF-ADL tasks, CGI-I scale Average post reduction (task 4 TETRAS): 46% (stim group) different from 24% (sham group) Afferences modulate ventral intermediate nucleus
Pascual-Valdunciel et al. [27] 11 ET (moderate) afferent < MT: EMG based (SATS), continuous SF: median and radial nerves at arm; IM: FCR and ECR 400 (SF), 200 (IM) 100 Pre; 60 s/trial, stim ON(30 s) vs stim OFF(30 s), > 6 trials, continuous/SATS; Post; Post24h Kinematics at wrist/elbow/shoulder; FTM scale; contralateral arm Average acute reduction at wrist: 32%; Post reduction after SATS-IM (6/6) patients Ia afferent fibers, reciprocal inhibition, propriospinal system
Popovic et al. [41] 3 ET, 4 PD, 5 HV FES: out-of-phase EMG based SF: wrist, elbow flexors-extensors 250 40 approx. 60 s/trial, stim ON vs stim OFF** Kinematics at wrist Average acute reduction: 67 ± 13% Generation of opposite forces to tremor oscillations
Spiegel et al. [37] 8 PD  > MT SF: median (IP and CL) and ulnar (IP) nerves at wrist 200 2, 3, 5 approx. 316 s/trial, single shock, post 5 min, 4 trials without shock-4 trials with shock sEMG Tremor amplitude not reported. Change in tremor frequency after stimulation Afferences interfere with central tremor oscillators
Widjaja et al. [19] 1 ET FES: out-of-phase model based (EMG + kinematics) SF: wrist flexors-extensors 200 25 40 s/trial, Stim ON vs Stim OFF, 1 trial Kinematics at wrist Individual acute tremor attenuation: 57% Generation of opposite forces to tremor oscillations
Xu et al. [31] 2 PD (moderate) afferent < MT: continuous (EMG triggered) SF: radial nerve (dorsal skin of hand) 200 250 15 s/trial, stim OFF(5 s)-ON(5 s)- OFF(5 s), 9–13 trials Kinematics and sEMG at finger/wrist/elbow flexors-extensors Significant acute reduction compared to OFF (p < 0.05). No values provided Cutaneous afferents and propriospinal interneurons
  1. ET essential tremor, PD Parkinson's disease, HV healthy volunteer, sEMG surface EMG, SF surface stimulation, IM intramuscular stimulation, BF-ADL Bain and Findley ADL, CGI-I, PGI-I Clinical and Patient Global Impression scores, QUEST Quality of Life in Essential Tremor, APB abductor pollicis brevis, FDI first dorsal interossei, SDI second dorsal interossei, SATS selective and adaptive timely stimulation, IP ipsilateral, CL contralateral, DC duty cycle, VAS visual analog scale, iEMG intramuscular EMG.
  2. *Not described in paper; **: ((3 s stim + 1 s pause)*3 + 9 s pause)*3 reps
  3. † not described in paper but clinical study based on prior (Pahwa et al. [24]) study and most likely replicated those parameters