TY - JOUR
T1 - Interhemispheric inhibition in distal and proximal arm representations in the primary motor cortex
AU - Harris-Love, Michelle L.
AU - Perez, Monica A
AU - Chen, Robert
AU - Cohen, Leonardo G.
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2007/3
Y1 - 2007/3
N2 - Interhemispheric inhibitory interactions (IHI) operate between homologous distal hand representations in primary motor cortex (M1). It is not known whether proximal arm representations exhibit comparable effects on their homologous counterparts. We studied IHI in different arm representations, targeting triceps brachii (TB, n = 13), first dorsal interosseous (FDI, n = 13), and biceps brachii (BB, n = 7) muscles in healthy volunteers. Transcranial magnetic stimulation test stimuli (TS) were delivered to M1 contralateral to the target muscle preceded 10 ms by a conditioning stimulus (CS) to the opposite M1 at 110-150% resting motor threshold (RMT). IHI was calculated as the ratio between motor-evoked potential (MEP) amplitudes in conditioned relative to unconditioned trials. Mean RMTs were 38.9, 46.9, and 46.0% of stimulator output in FDI, TB, and BB muscles, respectively. IHI was 0.45 ± 0.41 (FDI), 0.78 ± 0.38 (TB), and 0.52 ± 0.32 (BB, P < 0.01) when test MEP amplitudes were matched and 0.28 ± 0.17 (FDI) and 0.85 ± 0.31 (TB, P < 0.05) when TS intensities expressed as percentage RMT were matched. Significant IHI (P < 0.05) was identified with minimal CS intensities (expressed as percentage stimulator output) in the 30 s for FDI, 60 s for TB, and 40 s for BB. Additionally, a CS of roughly 120% RMT suppressed the test MEP but not a test H-reflex in BB, suggesting IHI observed in BB is likely mediated by a supraspinal mechanism. We conclude that IHI differs between different arm muscle representations, comparable between BB and FDI but lesser for TB. This finding suggests the amount of IHI between different arm representations does not strictly follow a proximal-to-distal gradient, but may be related to the role of each muscle in functional movement synergies.
AB - Interhemispheric inhibitory interactions (IHI) operate between homologous distal hand representations in primary motor cortex (M1). It is not known whether proximal arm representations exhibit comparable effects on their homologous counterparts. We studied IHI in different arm representations, targeting triceps brachii (TB, n = 13), first dorsal interosseous (FDI, n = 13), and biceps brachii (BB, n = 7) muscles in healthy volunteers. Transcranial magnetic stimulation test stimuli (TS) were delivered to M1 contralateral to the target muscle preceded 10 ms by a conditioning stimulus (CS) to the opposite M1 at 110-150% resting motor threshold (RMT). IHI was calculated as the ratio between motor-evoked potential (MEP) amplitudes in conditioned relative to unconditioned trials. Mean RMTs were 38.9, 46.9, and 46.0% of stimulator output in FDI, TB, and BB muscles, respectively. IHI was 0.45 ± 0.41 (FDI), 0.78 ± 0.38 (TB), and 0.52 ± 0.32 (BB, P < 0.01) when test MEP amplitudes were matched and 0.28 ± 0.17 (FDI) and 0.85 ± 0.31 (TB, P < 0.05) when TS intensities expressed as percentage RMT were matched. Significant IHI (P < 0.05) was identified with minimal CS intensities (expressed as percentage stimulator output) in the 30 s for FDI, 60 s for TB, and 40 s for BB. Additionally, a CS of roughly 120% RMT suppressed the test MEP but not a test H-reflex in BB, suggesting IHI observed in BB is likely mediated by a supraspinal mechanism. We conclude that IHI differs between different arm muscle representations, comparable between BB and FDI but lesser for TB. This finding suggests the amount of IHI between different arm representations does not strictly follow a proximal-to-distal gradient, but may be related to the role of each muscle in functional movement synergies.
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U2 - 10.1152/jn.01331.2006
DO - 10.1152/jn.01331.2006
M3 - Article
C2 - 17215494
AN - SCOPUS:33947152883
VL - 97
SP - 2511
EP - 2515
JO - Journal of Neurophysiology
JF - Journal of Neurophysiology
SN - 0022-3077
IS - 3
ER -