The influence of gender, hand dominance, and upper extremity length on motor evoked potentials.
Motor evoked potentials (MEPs) induced through transcranial magnetic stimulation (TMS) are susceptible to several sources of variability including gender, hand dominance, and upper extremity length. Conflicting evidence on the relationship between MEPs and subject characteristics has been reported.


OBJECTIVE
The purposes of this study were to determine if MEPs are different between genders and between right- and left-hand dominant subjects, and to determine if MEPs are correlated with upper extremity length.


METHODS
Using a case-control design, we recorded MEPs from 45 healthy subjects (age 21.6 ± 2.0 years; 24 females, 21 males) with a MagStim200 stimulating coil positioned over the primary motor cortex. Evoked responses were recorded by surface EMG electrodes from the abductor pollicis brevis, abductor digiti minimi and first dorsal interosseous muscles contralateral to the site of TMS. Evoked responses were analyzed to determine motor thresholds, latencies and amplitudes. Central motor conduction time (CMCT) was estimated from MEP, M response, and F wave latencies.


RESULTS
Gender and hand dominance did not significantly influence thresholds, MEP amplitudes, or CMCT (P > .05). MEP latencies were moderately correlated with upper extremity length (R = .62 right median, R = .50 left median, R = .45 right ulnar, R = .51 left ulnar MEP latency, P < .01). An ANCOVA using upper extremity length as the covariate demonstrated no significant differences between genders (Wilk's λ = .89, F = 2.45, P = .10). After adjusting MEP latencies to upper limb length, no significant differences were observed between dominant and non-dominant limbs (F = .002, P = .97 median, and F = .03, P = .56 ulnar) nor between genders (F = 2.7, P = .11 median; F = .05, P = .82 ulnar).


CONCLUSIONS
Variability in MEP latencies between genders was due to differences in upper extremity length. Adjusting MEP latencies to upper limb length is recommended for more accurate comparison and meaningful interpretation between subjects. Hand dominance and gender do not significantly influence motor thresholds, MEP amplitude, or CMCT.
Department of Rehabilitation Sciences, College of Health Sciences, University of Kentucky, Wethington 204C, Lexington, KY 40536-0200, USA. Scott.Livingston@uky.edu
Scott C
SC
Livingston
Howard P
HP
Goodkin
Christopher D
CD
Ingersoll
D001132:Arm / Q000033:anatomy & histology* / Q000502:physiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000502:physiology*; D006801:Humans; D008297:Male; D008954:Models, Biological; D009068:Movement / Q000502:physiology*; D012737:Sex Factors; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult