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Effect of long interval interhemispheric inhibition on intracortical inhibitory and facilitatory circuits
Author(s) -
Udupa Kaviraja,
Ni Zhen,
Gunraj Carolyn,
Chen Robert
Publication year - 2010
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2010.189548
Subject(s) - neuroscience , inhibitory postsynaptic potential , transcranial magnetic stimulation , interstimulus interval , facilitation , psychology , motor cortex , stimulation , silent period , lateralization of brain function , primary motor cortex , evoked potential
Stimulation of the primary motor cortex (M1) of one hemisphere of the brain inhibits the opposite M1, a process known as interhemispheric inhibition (IHI). An early phase of IHI peaks at about ∼10 ms after stimulation of the opposite hemisphere and is termed short latency interhemispheric inhibition (SIHI). A later phase peaks at about 40 ms and has been termed long latency interhemispheric inhibition (LIHI). The objective of the present study is to test how LIHI interacts with cortical inhibitory and facilitatory circuits, including short interval intracortical inhibition (SICI), intracortical facilitation (ICF) and long interval intracortical inhibition (LICI). We studied 10 healthy volunteers. LIHI from right to left hemisphere was elicited by stimulating the right M1 at an interstimulus interval (ISI) of 40 ms before stimulation of the left M1. Conditioning and test stimuli to elicit SICI, ICF and LICI were given to left M1. The effects of different sizes of test motor‐evoked potential (MEP amplitudes; 0.2, 1 and 2 mV) were examined for SICI, ICF, LICI and LIHI. Using paired‐pulse and triple‐pulse protocols, how LIHI interacts with SICI, ICF and LICI were investigated. We found SICI increased, while LICI and LIHI decreased with increasing test MEP amplitude. The presence of LIHI did not change the degree of SICI and intracortical facilitation (ICF), and their effects of these circuits were additive. On the other hand, LICI and LIHI were reduced in the presence of each other. We conclude that different sets of cortical neurons mediate LIHI, SICI, ICF and LICI. GABA B ‐mediated LICI and LIHI have inhibitory interactions with each other while LIHI has an additive effect with GABA A ‐mediated SICI.