PMID- 12802553
OWN - NLM
STAT- MEDLINE
DCOM- 20030923
LR  - 20181113
IS  - 0014-4819 (Print)
IS  - 0014-4819 (Linking)
VI  - 151
IP  - 3
DP  - 2003 Aug
TI  - Two phases of short-interval intracortical inhibition.
PG  - 330-7
AB  - Short-interval intracortical inhibition (SICI) is a widely used method to study 
      cortical inhibition, and abnormalities have been found in several neurological 
      and psychiatric disorders. Previous studies suggested that SICI involves two 
      phases and the first phase may be explained by axonal refractoriness. Our 
      objectives are to further investigate the mechanisms of the two phases of SICI. 
      SICI was studied in 11 normal volunteers by a paired transcranial magnetic 
      stimulation (TMS) paradigm applied to the left motor cortex with a subthreshold 
      conditioning stimulus (80% resting motor threshold for rest condition and 95% 
      active motor threshold for active condition) followed by a suprathreshold test 
      stimulus at interstimulus intervals (ISIs) of 1-4.5 ms in steps of 0.5 ms. 
      Motor-evoked potentials (MEPs) were recorded from the right first dorsal 
      interosseous muscle. Three different test stimulus intensities adjusted to 
      produce 0.2, 1 and 4 mV MEPs at rest were studied with the target muscle relaxed 
      and during 20% maximum contraction. Maximum inhibition was observed at ISIs of 1 
      ms and 2.5 ms for the rest condition and the difference among ISIs was reduced 
      with voluntary contraction. SICI increased with larger test MEP amplitude and 
      decreased with voluntary contraction. At test MEP of 0.2 mV, some subjects showed 
      facilitation and this is likely related to short-interval intracortical 
      facilitation. For rest SICI, the correlation between adjacent ISIs was much 
      higher from 3 to 4.5 ms than from 1 to 2.5 ms or between 1 and 2.5 ms. There was 
      no correlation between SICI at different test MEP amplitudes. We conclude that 
      maximum SICI at ISIs of 1 and 2.5 ms are mediated by different mechanisms. SICI 
      at 1 ms cannot be fully explained by axonal refractoriness and synaptic 
      inhibition may be involved. SICI is a complex phenomenon and inhibition at 
      different ISIs may be mediated by different inhibitory circuits.
FAU - Roshan, Lailoma
AU  - Roshan L
AD  - Division of Neurology and Krembil Neuroscience Centre, Toronto Western Research 
      Institute, University Health Network, University of Toronto, 5W-445, 399 Bathurst 
      Street, Toronto, Ontario, M5T 2S8, Canada.
FAU - Paradiso, Guillermo O
AU  - Paradiso GO
FAU - Chen, Robert
AU  - Chen R
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
DEP - 20030612
PL  - Germany
TA  - Exp Brain Res
JT  - Experimental brain research
JID - 0043312
SB  - IM
MH  - Adult
MH  - Analysis of Variance
MH  - Cerebral Cortex/*physiology
MH  - Electromyography/methods
MH  - Evoked Potentials, Motor/*physiology
MH  - Female
MH  - Humans
MH  - Male
MH  - Middle Aged
MH  - Muscle Contraction/physiology
MH  - Neural Inhibition/*physiology
MH  - Synaptic Transmission/physiology
EDAT- 2003/06/13 05:00
MHDA- 2003/09/25 05:00
CRDT- 2003/06/13 05:00
PHST- 2003/03/11 00:00 [received]
PHST- 2003/04/16 00:00 [accepted]
PHST- 2003/06/13 05:00 [pubmed]
PHST- 2003/09/25 05:00 [medline]
PHST- 2003/06/13 05:00 [entrez]
AID - 10.1007/s00221-003-1502-9 [doi]
PST - ppublish
SO  - Exp Brain Res. 2003 Aug;151(3):330-7. doi: 10.1007/s00221-003-1502-9. Epub 2003 
      Jun 12.