Gerard Derosiere

Prefrontal cortex activity during motor tasks with additional mental load requiring attentional demand: a near-infrared spectroscopy study.

Functional near-infrared spectroscopy (fNIRS) is suitable for investigating cerebral oxygenation changes during motor and/or mental tasks. In the present study, we investigated how an additional mental load during a motor task at two submaximal loadings affects the fNIRS-measured brain activation over the right prefrontal cortex (PFC). Fifteen healthy males performed isometric grasping contractions at 15% and 30% of the maximal voluntary contraction (MVC) with or without an additional mental (i.e., arithmetic) task. Mental performance, force variability, fNIRS and subjective perception responses were measured in each condition. The performance of the mental task decreased significantly while the force variability increased significantly at 30% MVC as compared to 15% MVC, suggesting that performance of dual-task required more attentional resources. PFC activity increased significantly as the effort increased from 15% to 30% MVC (p<.001). Although a larger change in the deoxyhemoglobin was observed in dual-task conditions (p=.051), PFC activity did not change significantly as compared to the motor tasks alone. In summary, participants were unable to invest more attention and effort in performing the more difficult levels in order to maintain adequate mental performance.

Global and Specific Motor Inhibitory Mechanisms during Action Preparation

Understanding the neural mechanisms that enable people to choose and perform appropriate actions when pursuing a goal is an intricate challenge for contemporary neuroscience. This human behavior is thought to rely in part on excitatory influences increasing the neural activity associated with each

Primary motor cortex contributes to the implementation of implicit value-based rules during motor decisions.

Abstract In the present study, we investigated the functional contribution of the human primary motor cortex (M1) to motor decisions. Continuous theta burst stimulation (cTBS) was used to alter M1 activity while participants performed a decision‐making task in which the reward associated with the subjects’ responses (right hand finger movements) depended on explicit and implicit value‐based rules. Subjects performed the task over two consecutive days and cTBS occurred in the middle of Day 2, once the subjects were just about to implement implicit rules, in addition to the explicit instructions, to choose their responses, as evident in the control group (cTBS over the right somatosensory cortex). Interestingly, cTBS over the left M1 prevented subjects from implementing the implicit value‐based rule while its implementation was enhanced in the group receiving cTBS over the right M1. Hence, cTBS had opposite effects depending on whether it was applied on the contralateral or ipsilateral M1. The use of the explicit value‐based rule was unaffected by cTBS in the three groups of subject. Overall, the present study provides evidence for a functional contribution of M1 to the implementation of freshly acquired implicit rules, possibly through its involvement in a cortico‐subcortical network controlling value‐based motor decisions. HighlightsWe used cTBS to study the role of M1 in value‐based motor decisions.Subjects learned to use explicit and implicit rules in a decision‐making task.When applied over left M1, cTBS altered the ability to implement the implicit rule.When applied over right M1, cTBS enhanced the implementation of the implicit rule.cTBS over M1 had no impact on the ability to use the explicit rule.

Relationship Between Submaximal Handgrip Muscle Force and NIRS-Measured Motor Cortical Activation

The purpose of the present study was to investigate the relationship between submaximal muscle force and oxygenation in the motor cortex of the human brain using near infrared spectroscopy (NIRS). Nine healthy subjects performed isometric handgrip contractions ranging from 10 to 50% of maximum voluntary contraction (MVC) in a 30-s exertion with a 60 s of recovery for three repetitions. Motor cortex activity was quantified with NIRS-derived parameters. We showed significant positive linear and non-linear relationships between muscle force output and total- and oxy-hemoglobin (R >0.98, P < 0.01). Overall, our findings showed that submaximal muscle force and brain activity revealed with NIRS strongly correlate in the motor cortex area, both at group and at subject level from 30% MVC. We concluded that motor-related cerebral cortex in human brain function by NIRS encoded force amplitude during motor task linearly from 30% MVC.

Towards assessing corticospinal excitability bilaterally: Validation of a double-coil TMS method

BACKGROUND For several decades, Transcranial magnetic stimulation (TMS) has been used to monitor corticospinal excitability (CSE) changes in various contexts. Habitually, single-coil TMS is applied over one primary motor cortex (M1), eliciting motor-evoked potentials (MEPs) in a contralateral limb muscle, usually a hand effector. However, in many situations, it would be useful to obtain MEPs in both hands simultaneously, to track CSE bilaterally. Such an approach requires stimulating both M1 concurrently while avoiding interference between the two descending stimuli. NEW METHOD We examined MEPs obtained at rest using a double-coil TMS approach where the two M1 are stimulated with a 1ms inter-pulse interval (double-coil1ms). MEPs were acquired using double-coil1ms (MEPdouble) or single-coil (MEPsingle) TMS, at five different intensities of stimulation (100, 115, 130, 145 or 160% of the resting motor threshold, rMT). Given the 1ms inter-pulse interval in double-coil1ms trials, MEPdouble were either evoked by a 1st (MEPdouble-1) or a 2nd (MEPdouble-2) TMS pulse. RESULTS All MEPTYPE (MEPTYPE=MEPsingle, MEPdouble-1 and MEPdouble-2) were equivalent, regardless of the hand within which they were elicited, the intensity of stimulation or the pulse order. COMPARISON WITH EXISTING METHOD This method allows one to observe state-related CSE changes for the two hands simultaneously on a trial-by-trial basis. CONCLUSION These results infer the absence of any neural interactions between the two cortico-spinal volleys with double-coil1ms TMS. Hence, this technique can be reliably used to assess CSE bilaterally, opening new research perspectives for scientists interested in physiological markers of activity in the motor output system.

Using a Double-Coil TMS Protocol to Assess Preparatory Inhibition Bilaterally

Transcranial magnetic stimulation (TMS) applied over the primary motor cortex (M1), elicits motor-evoked potentials (MEPs) in contralateral limb muscles which are valuable indicators of corticospinal excitability (CSE) at the time of stimulation. So far, most studies have used single-coil TMS over one M1, yielding MEPs in muscles of a single limb—usually the hand. However, tracking CSE in the two hands simultaneously would be useful in many contexts. We recently showed that, in the resting state, double-coil stimulation of the two M1 with a 1 ms inter-pulse interval (double-coil1 ms TMS) elicits MEPs in both hands that are comparable to MEPs obtained using single-coil TMS. To further evaluate this new technique, we considered the MEPs elicited by double-coil1 ms TMS in an instructed-delay choice reaction time task where a prepared response has to be withheld until an imperative signal is displayed. Single-coil TMS studies have repetitively shown that in this type of task, the motor system is transiently inhibited during the delay period, as evident from the broad suppression of MEP amplitudes. Here, we aimed at investigating whether a comparable inhibitory effect can be observed with MEPs elicited using double-coil1 ms TMS. To do so, we compared the amplitude as well as the coefficient of variation (CV) of MEPs produced by double-coil1 ms or single-coil TMS during action preparation. We observed that MEPs were suppressed (smaller amplitude) and often less variable (smaller CV) during the delay period compared to baseline. Importantly, these effects were equivalent whether single-coil or double-coil1 ms TMS was used. This suggests that double-coil1 ms TMS is a reliable tool to assess CSE, not only when subjects are at rest, but also when they are involved in a task, opening new research horizons for scientists interested in the corticospinal correlates of human behavior.

Graph-Based Transfer Learning for Managing Brain Signals Variability in NIRS-Based BCIs

One of the major limitations to the use of brain-computer interfaces (BCIs) based on near-infrared spectroscopy (NIRS) in realistic interaction settings is the long calibration time needed before every use in order to train a subject-specific classifier. One way to reduce this calibration time is to use data collected from other users or from previous recording sessions of the same user as a training set. However, brain signals are highly variable and using heterogeneous data to train a single classifier may dramatically deteriorate classification performance. This paper proposes a transfer learning framework in which we model brain signals variability in the feature space using a bipartite graph. The partitioning of this graph into sub-graphs allows creating homogeneous groups of NIRS data sharing similar spatial distributions of explanatory variables which will be used to train multiple prediction models that accurately transfer knowledge between data sets.

A Dynamical System Framework for Theorizing Preparatory Inhibition

During action preparation, the primary motor cortex (M1) and the spinal cord display considerable changes in neural activity. The functional role of this preparatory activity has been questioned for decades, motivating many investigations, from transcranial magnetic stimulation (TMS) to single-