PMID- 9625881
OWN - NLM
STAT- MEDLINE
DCOM- 19980901
LR  - 20240322
IS  - 0022-3751 (Print)
IS  - 1469-7793 (Electronic)
IS  - 0022-3751 (Linking)
VI  - 510 ( Pt 1)
IP  - Pt 1
DP  - 1998 Jul 1
TI  - Inhibitory influence of the ipsilateral motor cortex on responses to stimulation 
      of the human cortex and pyramidal tract.
PG  - 249-59
AB  - 1. The ability of the primary motor cortex (M1) to modulate motor responses in 
      ipsilateral hand muscles seems to be important for normal motor control and 
      potentially also for recovery after brain lesions. It is not clear which pathways 
      mediate this ipsilateral modulation. Transcallosal connections have been 
      proposed, but are known to be sparse between cortical hand motor representations 
      in primates. The present study was performed to determine whether descending 
      ipsilateral modulation of motor responses might also be mediated below the 
      cortical level in humans. 2. A paired-pulse protocol was used, in which 
      motor-evoked potentials (MEPs) were produced by cortical transcranial magnetic 
      stimulation (cTMS) or by electrical stimulation of the pyramidal tract at the 
      level of the pyramidal decussation (pdTES), in both preactivated and relaxed hand 
      muscles. Paired stimuli were applied at various interstimulus intervals (ISIs) 
      between 2 and 100 ms. The conditioning stimulus (CS) was always magnetic, and 
      delivered to the M1 ipsilateral to the target hand, prior to the test stimulus 
      (TS). The magnetic TS was delivered to the M1 contralateral to the target hand; 
      the electrical TS was applied through electrodes placed over the mastoid process 
      bilaterally. Further experiments included cortical electrical stimulation and 
      H-reflexes. The MEP amplitudes were averaged separately for each ISI and the 
      control condition (no CS), and expressed as a percentage of the unconditioned 
      response. 3. Conditioning stimulation of the ipsilateral M1 resulted in 
      significant inhibition of magnetically evoked MEPs, and also of MEPs produced by 
      pdTES. Inhibition occurred at ISIs between 6 and 50 ms, and was observed in 
      preactivated and relaxed muscles. Higher CS intensities caused greater inhibition 
      of both cTMS- and pdTES-evoked MEPs. 4. While the conditioning effects on 
      magnetically evoked muscle responses could be explained by a transcallosal 
      mechanism, the effects on pdTES-evoked MEPs cannot, because they are elicited 
      subcortically and are therefore not susceptible to inhibitory mechanisms 
      transmitted at the cortico-cortical level. 5. In conclusion, the present results 
      provide novel evidence that the inhibitory influence of the human M1 on 
      ipsilateral hand muscles is to a significant extent mediated below the cortical 
      level, and not only through cortico-cortical transcallosal connections. They 
      point to a concept of inhibitory interaction between the two primary motor 
      cortices that is relayed at multiple levels along the neuroaxis, thus perhaps 
      providing a structurally redundant system which may become important in case of 
      lesions.
FAU - Gerloff, C
AU  - Gerloff C
AD  - Human Cortical Physiology Unit, Medical Neurology Branch, National Institute of 
      Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 
      20892-1428, USA.
FAU - Cohen, L G
AU  - Cohen LG
FAU - Floeter, M K
AU  - Floeter MK
FAU - Chen, R
AU  - Chen R
FAU - Corwell, B
AU  - Corwell B
FAU - Hallett, M
AU  - Hallett M
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - England
TA  - J Physiol
JT  - The Journal of physiology
JID - 0266262
SB  - IM
MH  - Adult
MH  - Conditioning, Psychological/physiology
MH  - Electric Stimulation
MH  - Evoked Potentials, Motor/physiology
MH  - Female
MH  - H-Reflex/physiology
MH  - Hand
MH  - Humans
MH  - Magnetics
MH  - Male
MH  - Middle Aged
MH  - Motor Cortex/*physiology
MH  - Muscle, Skeletal/physiology
MH  - Neural Inhibition/*physiology
MH  - Physical Stimulation/methods
MH  - Pyramidal Tracts/*physiology
MH  - Wrist
PMC - PMC2231019
EDAT- 1998/06/17 00:00
MHDA- 1998/06/17 00:01
PMCR- 1999/07/01
CRDT- 1998/06/17 00:00
PHST- 1998/06/17 00:00 [pubmed]
PHST- 1998/06/17 00:01 [medline]
PHST- 1998/06/17 00:00 [entrez]
PHST- 1999/07/01 00:00 [pmc-release]
AID - 10.1111/j.1469-7793.1998.249bz.x [doi]
PST - ppublish
SO  - J Physiol. 1998 Jul 1;510 ( Pt 1)(Pt 1):249-59. doi: 
      10.1111/j.1469-7793.1998.249bz.x.