PMID- 12611955
OWN - NLM
STAT- MEDLINE
DCOM- 20030509
LR  - 20220316
IS  - 0022-3077 (Print)
IS  - 0022-3077 (Linking)
VI  - 89
IP  - 3
DP  - 2003 Mar
TI  - Organization of ipsilateral excitatory and inhibitory pathways in the human motor 
      cortex.
PG  - 1256-64
AB  - Motor cortex stimulation has both excitatory and inhibitory effects on 
      ipsilateral muscles. Excitatory effects can be assessed by ipsilateral 
      motor-evoked potentials (iMEPs). Inhibitory effects include an interruption of 
      ipsilateral voluntary muscle activity known as the silent period (iSP) and a 
      reduction in corticospinal excitability evoked by conditioning stimulation of the 
      contralateral motor cortex (interhemispheric inhibition, IHI). Both iSP and IHI 
      may be mediated by transcallosal pathways. Their relationship to the 
      contralateral corticospinal projection and whether iSP and IHI represent the same 
      phenomenon remain unclear. The neuronal population activated by transcranial 
      magnetic stimulation (TMS) is highly dependent on the direction of the induced 
      current in the brain. We examined the relationship among iMEP, iSP, IHI, and the 
      contralateral corticospinal system by examining the effects of different stimulus 
      intensities and current directions. Surface electromyography (EMG) was recorded 
      from both first dorsal interosseous (FDI) muscles. The iSP in the right FDI 
      muscle was obtained by right motor cortex stimulation during voluntary muscle 
      contraction. IHI was examined by conditioning stimulation of the right motor 
      cortex followed by test stimulation of the left motor cortex at interstimulus 
      intervals (ISIs) of 2-80 ms. The induced current directions tested in the right 
      motor cortex were anterior medial (AM), posterior medial (PM), posterior lateral, 
      and anterior lateral (AL). Contralateral MEPs (cMEPs) had the lowest threshold 
      with the AM direction and the shortest latency with the PM direction. iMEPs were 
      present in 8 of 10 subjects. Both iMEP and IHI did not show significant 
      directional preference. iSP was observed in all subjects with the highest 
      threshold for the AL direction and the longest duration for the AM direction. 
      cMEP, iSP, and IHI all increased with stimulus intensity up to approximately 75% 
      stimulator output. Target muscle activation decreased IHI at 8-ms ISI but had 
      little effect on IHI at 40-ms ISI. iSP and IHI at 8-ms ISI did not correlate at 
      any stimulus intensities and current directions tested, and factor analysis 
      showed that they are explained by different factors. However, active IHI at 40-ms 
      ISI was explained by the same factor as iSP. The different directional preference 
      for cMEP compared with iMEP and IHI suggests that these ipsilateral effects are 
      mediated by populations of cortical neurons that are different from those 
      activating the corticospinal neurons. iSP and IHI do not represent the same 
      phenomenon and should be considered complementary measures of ipsilateral 
      inhibition.
FAU - Chen, Robert
AU  - Chen R
AD  - Division of Neurology, Krembil Neuroscience Center and Toronto Western Research 
      Institute, University Health Network, University of Toronto, Toronto, Ontario M5T 
      2S8, Canada. robert.chen@uhn.on.ca
FAU - Yung, Derek
AU  - Yung D
FAU - Li, Jie-Yuan
AU  - Li JY
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20021030
PL  - United States
TA  - J Neurophysiol
JT  - Journal of neurophysiology
JID - 0375404
SB  - IM
MH  - Adult
MH  - Aged
MH  - Electric Stimulation
MH  - Electromyography
MH  - Evoked Potentials, Motor/*physiology
MH  - Female
MH  - Functional Laterality/physiology
MH  - Humans
MH  - Magnetics
MH  - Male
MH  - Middle Aged
MH  - Motor Cortex/*cytology/*physiology
MH  - Muscle, Skeletal/innervation/physiology
MH  - Neural Inhibition/*physiology
MH  - Neural Pathways
MH  - Pyramidal Tracts/cytology/physiology
MH  - Rest/physiology
EDAT- 2003/03/04 04:00
MHDA- 2003/05/13 05:00
CRDT- 2003/03/04 04:00
PHST- 2003/03/04 04:00 [pubmed]
PHST- 2003/05/13 05:00 [medline]
PHST- 2003/03/04 04:00 [entrez]
AID - 00950.2002 [pii]
AID - 10.1152/jn.00950.2002 [doi]
PST - ppublish
SO  - J Neurophysiol. 2003 Mar;89(3):1256-64. doi: 10.1152/jn.00950.2002. Epub 2002 Oct 
      30.