Intracortical circuits modulate transcallosal inhibition in humans

• DOI: 10.1113/jphysiol.2007.134510
• Publication Date: 2007-06-08T00:30:19Z
• Authors: L. Avanzino; J. T. H. Teo; J. C. Rothwell
• Keywords: Silent period; Interstimulus interval; Stimulus (psychology); Facilitation; Corticospinal tract

Previous results using paired-pulse transcranial magnetic stimulation (TMS) have suggested that the excitability of transcallosal (TC) connections between hand areas two motor cortices is modulated by intracortical inhibitory circuits in same way as corticospinal tract (CTS) projections to spinal motoneurons. Here we describe further similarities TC and CTS control (1) an I-wave facilitation protocol (2) preconditioning with rTMS. In experiment 1, pathways was measured interhemispheric inhibition (IHI) ipsilateral silent period (iSP), whilst recording EMG response evoked first dorsal interosseous muscle contralateral conditioning stimulus (cMEP). The intensity adjusted threshold for evoking IHI iSP, then pairs stimuli were applied randomly at interstimulus intervals (ISIs) from 1.3 4.3 ms. iSP facilitated ISI=1.5 ms 3.0 ms, respectively, MEP hand. We suggest receive I-wave-like similar seen projections. 2, short interval (SICIiSP), cMEP (SICIcMEP) examined before after 600 pulses 5 Hz rTMS 90% resting threshold. Both SICIiSP SICIcMEP reduced, iSP; unchanged. This shows population interneurons neurons respond those neurons. Taken together, data experiments layer III V pyramidal give rise pathways, are controlled neuronal circuitry properties.