Abstract
Dual-site transcranial magnetic stimulation to the primary motor cortex (M1) and dorsolateral prefrontal cortex (DLPFC) can be used to probe functional connectivity between these regions. The purpose of this study was to characterize the effect of DLPFC stimulation on ipsilateral M1 excitability while participants were at rest and contracting the left- and right-hand first dorsal interosseous muscle. Twelve participants were tested in two separate sessions at varying inter-stimulus intervals (ISI: 4, 5, 6, 7, 8, 9, 10, 11, 12, 15, and 20 ms) at two different conditioning stimulus intensities (80% and 120% of resting motor threshold). No significant effect on ipsilateral M1 excitability was found when applying a conditioning stimulus over DLPFC at any specific inter-stimulus interval or intensity in either the left or right hemisphere. Our findings suggest neither causal inhibitory nor faciliatory influences of DLPFC on ipsilateral M1 activity while participants were at rest or when performing an isometric contraction in the target hand muscle.
Highlights
Motor and cognitive function depends on neural activity in a number of spatially distributed but interconnected brain regions
We investigate the effect of different interstimulus intervals (ISIs) and conditioning stimulus (CS) intensities applied over dorsolateral prefrontal cortex (DLPFC) on corticospinal excitability of ipsilateral M1 while participants were at rest for left (Experiments 1) and right (Experiments 3) hemispheres using Dual-site transcranial magnetic stimulation (ds Transcranial Magnetic Stimulation (TMS)) technique
We used a conditioning-test ds TMS approach to examine the temporal and functional interactions of frontal cortico-cortical circuits, focusing on inputs to M1 from ipsilateral DLPFC while participants were at rest or contracting the target muscle
Summary
Motor and cognitive function depends on neural activity in a number of spatially distributed but interconnected brain regions. The dorsolateral prefrontal cortex (DLPFC), which includes Brodmann’s areas (BA) 46 and 9 [1,2], closely works with primary motor cortex (M1) to form fundamental circuitry involved in motor tasks of varying complexity [3]. Through its diverse anatomical projections to motor areas [4,5,6,7,8], DLPFC is a key node that mediates many higher-level aspects of motor control such as executive function [9], response selection [10], response initiation [11] and response inhibition [12]. Brain networks associated with both cognitive and motor function are often impaired in Age-related declines in motor and cognitive performance often correspond with pathological changes in interregional connectivity within the motor system [14,15,16,17,18].
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