The human dorsal premotor cortex facilitates the excitability of ipsilateral primary motor cortex via a short latency cortico-cortical route

TY - JOUR

T1 - The human dorsal premotor cortex facilitates the excitability of ipsilateral primary motor cortex via a short latency cortico-cortical route

AU - Groppa, Sergiu

AU - Schlaak, Boris H

AU - Münchau, Alexander

AU - Werner-Petroll, Nicole

AU - Dünnweber, Janin

AU - Bäumer, Tobias

AU - van Nuenen, Bart F L

AU - Siebner, Hartwig R

N1 - Copyright © 2010 Wiley-Liss, Inc.

PY - 2012/2

Y1 - 2012/2

N2 - In non-human primates, invasive tracing and electrostimulation studies have identified strong ipsilateral cortico-cortical connections between dorsal premotor- (PMd) and the primary motor cortex (M1(HAND) ). Here, we applied dual-site transcranial magnetic stimulation (dsTMS) to left PMd and M1(HAND) through specifically designed minicoils to selectively probe ipsilateral PMd-to-M1(HAND) connectivity in humans. A suprathreshold test stimulus (TS) was applied to M1(HAND) producing a motor evoked potential (MEP) of about 0.5 mV in the relaxed right first dorsal interosseus muscle (FDI). A subthreshold conditioning stimulus (CS) was given to PMd 2.0-5.2 ms after the TS at intensities of 50-, 70-, or 90% of TS. The CS to PMd facilitated the MEP evoked by TS over M1(HAND) at interstimulus intervals (ISI) of 2.4 or 2.8 ms. There was a second facilitatory peak at ISI of 4.4 ms. PMd-to-M1(HAND) facilitation did not change as a function of CS intensity. Even at higher intensities, the CS alone failed to elicit a MEP or a cortical silent period in the pre-activated FDI, excluding a direct spread of excitation from PMd to M1(HAND). No MEP facilitation was present while CS was applied rostrally over lateral prefrontal cortex. Together our results indicate that our dsTMS paradigm probes a short-latency facilitatory PMd-to-M1(HAND) pathway. The temporal pattern of MEP facilitation suggests a PMd-to-M1(HAND) route that targets intracortical M1(HAND) circuits involved in the generation of indirect corticospinal volleys. This paradigm opens up new possibilities to study context-dependent intrahemispheric PMd-to-M1(HAND) interactions in the intact human brain.

AB - In non-human primates, invasive tracing and electrostimulation studies have identified strong ipsilateral cortico-cortical connections between dorsal premotor- (PMd) and the primary motor cortex (M1(HAND) ). Here, we applied dual-site transcranial magnetic stimulation (dsTMS) to left PMd and M1(HAND) through specifically designed minicoils to selectively probe ipsilateral PMd-to-M1(HAND) connectivity in humans. A suprathreshold test stimulus (TS) was applied to M1(HAND) producing a motor evoked potential (MEP) of about 0.5 mV in the relaxed right first dorsal interosseus muscle (FDI). A subthreshold conditioning stimulus (CS) was given to PMd 2.0-5.2 ms after the TS at intensities of 50-, 70-, or 90% of TS. The CS to PMd facilitated the MEP evoked by TS over M1(HAND) at interstimulus intervals (ISI) of 2.4 or 2.8 ms. There was a second facilitatory peak at ISI of 4.4 ms. PMd-to-M1(HAND) facilitation did not change as a function of CS intensity. Even at higher intensities, the CS alone failed to elicit a MEP or a cortical silent period in the pre-activated FDI, excluding a direct spread of excitation from PMd to M1(HAND). No MEP facilitation was present while CS was applied rostrally over lateral prefrontal cortex. Together our results indicate that our dsTMS paradigm probes a short-latency facilitatory PMd-to-M1(HAND) pathway. The temporal pattern of MEP facilitation suggests a PMd-to-M1(HAND) route that targets intracortical M1(HAND) circuits involved in the generation of indirect corticospinal volleys. This paradigm opens up new possibilities to study context-dependent intrahemispheric PMd-to-M1(HAND) interactions in the intact human brain.

KW - Evoked Potentials, Motor

KW - Hand

KW - Humans

KW - Male

KW - Motor Cortex

KW - Muscle, Skeletal

KW - Neural Pathways

KW - Prefrontal Cortex

KW - Reaction Time

KW - Transcranial Magnetic Stimulation

U2 - 10.1002/hbm.21221

DO - 10.1002/hbm.21221

M3 - Journal article

C2 - 21391274

SN - 1065-9471

VL - 33

SP - 419

EP - 430

JO - Human Brain Mapping

JF - Human Brain Mapping

IS - 2

ER -