PMID- 10712469
OWN - NLM
STAT- MEDLINE
DCOM- 20000411
LR  - 20171213
IS  - 0022-3077 (Print)
IS  - 0022-3077 (Linking)
VI  - 83
IP  - 3
DP  - 2000 Mar
TI  - Facilitatory I wave interaction in proximal arm and lower limb muscle 
      representations of the human motor cortex.
PG  - 1426-34
AB  - Transcranial magnetic stimulation (TMS) of the human motor cortex elicits direct 
      and indirect (I) waves in the corticospinal tract. Facilitatory I wave 
      interaction has been demonstrated with a suprathreshold first stimulus (S1) 
      followed by a subthreshold to threshold second stimulus (S2). Intracortical 
      inhibition (ICI) and intracortical facilitation (ICF) can be studied by another 
      paired TMS paradigm with a subthreshold conditioning stimulus (CS) followed by a 
      suprathreshold test stimulus. Facilitatory I wave interaction in motor 
      representations other than the hand area and its relationship to ICI and ICF has 
      not been studied. We studied I wave interaction, ICI and ICF in an intrinsic hand 
      muscle (abductor pollicis brevis, APB), in a proximal arm muscle (biceps brachii, 
      BB) and in a lower limb muscle (tibialis anterior, TA) in 11 normal subjects. I 
      wave facilitation was studied by paired TMS at 24 interstimulus intervals (ISIs) 
      from 0.5 to 5.1 ms. For APB and TA, facilitation occurred in three distinct peaks 
      at ISIs of 0.9-1.7, 2. 5-3.5, and 4.1-5.1 ms. For BB, facilitation was 
      significant for the first two peaks. The latencies of the peaks were similar 
      among different muscles, but the magnitude of facilitation was much greater for 
      APB and TA compared with BB. For all three muscles, changing the S2 to 
      transcranial electrical stimulation (TES) resulted in much less facilitation of 
      the first peak. For APB, there was significant I wave facilitation with S2 at 72% 
      motor threshold (MT). The same stimulus used as the CS did not elicit ICF at ISI 
      of 15 ms, suggesting that the threshold for eliciting I wave facilitation is 
      lower than that for ICF. For BB and TA, there was no I wave facilitation with S2 
      at 90% of APB MT, and the same stimulus used as CS led to ICI. Thus in BB and TA 
      the threshold for eliciting ICI is lower than that for I wave facilitation. We 
      conclude that the circuits that mediate I wave interactions are present in the 
      proximal arm and lower limb representations of the motor cortex. I wave 
      facilitation occurs predominately in the cortex and may be primarily related to 
      the monosynaptic corticomotoneuronal (CM) system. The reduced I wave facilitation 
      for BB compared with APB and TA may be related to less extensive CM projection 
      and involvement of other polysynaptic descending pathways. I wave facilitation, 
      ICI, and ICF appears to be mediated by different neuronal circuits.
FAU - Chen, R
AU  - Chen R
AD  - Division of Neurology and The Toronto Western Hospital Research Institute, 
      University Health Network, University of Toronto, Toronto, Ontario M5T 2S8, 
      Canada.
FAU - Garg, R
AU  - Garg R
LA  - eng
PT  - Clinical Trial
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - United States
TA  - J Neurophysiol
JT  - Journal of neurophysiology
JID - 0375404
SB  - IM
MH  - Adult
MH  - Arm/innervation/*physiology
MH  - Electromagnetic Fields
MH  - Electromyography
MH  - Electrophysiology
MH  - Evoked Potentials, Motor/physiology
MH  - Female
MH  - Hand/innervation/physiology
MH  - Humans
MH  - Leg/innervation/*physiology
MH  - Male
MH  - Middle Aged
MH  - Motor Cortex/cytology/*physiology
MH  - Neural Pathways/cytology/physiology
EDAT- 2000/03/11 09:00
MHDA- 2000/04/15 09:00
CRDT- 2000/03/11 09:00
PHST- 2000/03/11 09:00 [pubmed]
PHST- 2000/04/15 09:00 [medline]
PHST- 2000/03/11 09:00 [entrez]
AID - 10.1152/jn.2000.83.3.1426 [doi]
PST - ppublish
SO  - J Neurophysiol. 2000 Mar;83(3):1426-34. doi: 10.1152/jn.2000.83.3.1426.