Biology subjects

Neige, C.

Publications and source records attributed to Neige, C..

3 recordsLinked to original sources

bioRxiv2022

The recruitment of indirect-waves within primary motor cortex during motor imagery: A directional Transcranial Magnetic Stimulation study

Motor imagery (MI) refers to the mental simulation of an action without any overt movement. While numerous transcranial magnetic stimulation (TMS) studies provided evidence for a modulation of corticospinal excitability and intracortical inhibition during MI, the neural signature within the primary motor cortex is not clearly established. In the current study, we used directional TMS to probe the modulation of the excitability of early and late indirect-waves (I-waves) generating pathways during MI. Corticospinal responses evoked by TMS with posterior-anterior (PA) and anterior-posterior (AP) current flow within primary motor cortex evoke preferentially early and late I-waves, respectively. Seventeen participants were instructed to stay at rest or to imagine isometric maximal contractions of the right flexor carpi radialis. We demonstrated that the increase of corticospinal excitability during MI is greater with PA than AP orientation. By using paired-pulse stimulations, we confirmed that short-interval intracortical inhibition (SICI) increased during MI in comparison to rest with PA orientation whereas we found that it decreased with AP orientation. Overall, these results indicate that the specific early I-waves generating pathway activated by PA orientation is probably more sensitive to the corticospinal excitability and intracortical inhibition modulations induced by MI.

neuroscience↗

bioRxiv2022

Probing the influence of SMA and vmPFC on the motor system with dual-site transcranial magnetic stimulation

Dual-site transcranial magnetic stimulation (TMS) has been widely employed to investigate the influence of cortical structures on the primary motor cortex (M1). Here, we leveraged this technique to probe the causal influence of two key areas of the medial frontal cortex, namely the supplementary motor area (SMA) and the medial orbitofrontal cortex (mOFC), on M1. We show that SMA stimulation facilitates M1 activity across short (6 and 8 ms) and long (12 ms) inter-stimulation intervals, putatively recruiting cortico-cortical and cortico-subcortico-cortical circuits, respectively. Crucially, magnetic resonance imaging revealed that this facilitatory effect depended on a key morphometric feature of SMA: individuals with larger SMA volumes exhibited more facilitation from SMA to M1. Notably, we also provide evidence that the facilitatory effect of SMA stimulation at short intervals did not arise from spinal interactions of volleys descending simultaneously from SMA and M1. On the other hand, mOFC stimulation moderately suppressed M1 activity at both short and long intervals, irrespective of mOFC volume. These results suggest that dual-site TMS is an interesting tool to study the differential influence of SMA and mOFC on M1 activity, paving the way for the multi-modal assessment of these fronto-motor circuits in health and disease. Key pointsO_LIDual-site TMS has been widely employed to investigate effective connectivity between cortical structures and the primary motor cortex (M1). C_LIO_LIHere, we probed the causal influence of the supplementary motor area (SMA) and the medial orbitofrontal cortex (mOFC) on M1 activity. C_LIO_LISMA stimulation facilitates M1 activity at both short and long inter-stimulation intervals; this facilitatory effect is related to SMA volume. C_LIO_LImOFC stimulation moderately suppresses M1 activity, independent of mOFC volume. C_LIO_LIThe findings pave the way for multi-modal assessment of fronto-motor circuits in health and disease. C_LI

neuroscience↗

bioRxiv2019

Unravelling the modulation of intracortical inhibition during motor imagery: An adaptive threshold-hunting study

Motor imagery (MI) is the mental simulation of an action without any apparent muscular contraction. By means of transcranial magnetic stimulation, few studies revealed a decrease of short-interval intracortical inhibition (SICI) within the primary motor cortex. However, this decrease is ambiguous, as one would expect greater inhibition during MI to prevent overt motor output. The current study investigated the extent of SICI modulation during MI through a methodological and a conceptual reconsideration of i) the importance of parameters to assess SICI (Exp.1) and ii) the inhibitory process within the primary motor cortex as an inherent feature of MI (Exp.2). Participants performed two tasks: 1) rest and 2) imagery of isometric abduction of the right index finger. Using transcranial magnetic stimulation, motor evoked potentials were elicited in the right first dorsal interosseous muscle. An adaptive threshold-hunting paradigm was used, where the stimulus intensity required to maintain a fixed motor evoked potential amplitude was quantified. To test SICI, we conditioned the test stimulus with a conditioning stimulus (CS) of different intensities. Results revealed an Intensity by Task interaction showing that SICI decreased during MI as compared to rest only for the higher CS intensity (Exp.1). At the lowest CS intensities, a Task main effect revealed that SICI increased during MI (Exp.2). SICI modulation during MI depends critically on the CS intensity. By optimising CS intensity, we have shown that SICI circuits may increase during MI, revealing a potential mechanism to prevent the production of a movement while the motor system is activated. HighlightsO_LIExcitatory and inhibitory neural processes interact during motor imagery, as the motor regions are activated but no movement is produced. C_LIO_LIThe current study investigated the extent of short interval intracortical inhibition modulation (SICI) during motor imagery. C_LIO_LIWhen using optimal settings, SICI increased during motor imagery, likely to prevent the production of an overt movement. C_LI

neuroscience↗