Motor cortex excitability changes preceding voluntary muscle activity in simple reaction time task

Abstract

The effect of transcranial magnetic stimulation (TMS) on reaction time (RT) and motor cortex excitability in the premovement period was investigated. Single and paired-pulse TMS with 3 and 13 ms interstimulus intervals (ISI) were applied to the left motor cortex at different delays after a visual command for isometric right hand index finger abduction. Motor evoked potentials (MEPs) recorded from the right first dorsal interosseous (FDI) were analysed to assess cortex excitability. The MEPs in response to single pulse TMS were gradually increased in the premovement period in general, but strongly augmented in a period of 90-100 ms before the voluntary myoelectrical activity (EMG) onset. In paired-pulse TMS (13 ms ISI), the MEP augmentation was smaller but started earlier before the EMG burst, and a gradual increase of MEP amplitudes was not evident. In case of 3 ms ISI, the expected intracortical inhibition (ICI) was evident only when TMS preceded the voluntary EMG by an interval of more than 60 ms, but at shorter intervals, rather some MEP augmentation was observed. Generally, the augmentation of MEPs in the premovement period was more pronounced in single pulse TMS. Most strikingly, a dead band period without MEP occurrences was observed within an interval of 30-50 ms before the voluntary EMG. In conclusion, parallel action of intracortical facilitation (ICF) and ICI as well as different dynamic behaviour of ICF and pre movement facilitation may explain the earlier mentioned effects. Moreover, this leads to an extended description of the rather subtle TMS influence on RT.

Emotion and motor preparation: A transcranial magnetic stimulation study of corticospinal motor tract excitability

“…The TMS pulse was delivered simultaneously with the auditory cue. Accordingly, the shorter RTs during TMS, as compared with no-TMS, trials were consistent with the results of previous studies, which have demonstrated that shorter interstimulus intervals lead to shorter RTs (Masur, Schneider, Papke, & Oberwittler, 1996;Nikolova, Pondev, Christova, Wolf, & Kossev, 2006;Pascual-Leone et al, 1992). In the present study, the facilitation effect of the single TMS pulse was approximately 40 msec, and this effect was stable across pleasant, unpleasant, and neutral images.…”

Contribution of transcranial magnetic stimulation to the understanding of cortical mechanisms involved in motor control

“…Corticospinal and intracortical parameters can be assessed in the context of reaction time protocols, providing a picture of changing physiological interactions leading up to movement execution. Using single pulse TMS applied at a number of time points after a 'Go' cue (in a simple reaction time protocol), three studies have described a gradual increase in corticospinal excitability starting 80-120 ms prior to movement onset (Rossini et al 1988;Leocani et al 2000;Nikolova et al 2006). In the study of Leocani et al, this finding was accompanied by a suppression of MEPs in the contralateral resting hand (if the dominant right hand was being moved).…”

Interhemispheric interactions associated with unilateral ballistic motor tasks

“…For example, reaction time was shortened when stimuli were delivered to the M1 contra at early stage of movement preparation (Leocani, et al, 2000;McMillan, et al, 2006;Michelet et al, 2010;Nikolova, et al, 2006;Soto, et al, 2010;van Elswijk, et al, 2008). However, when TMS was applied close to the expected movement onset to the M1 contra , reaction time was delayed due to disruption of movement production (Leocani, et al, 2000;McMillan, et al, 2006;Michelet, et al, 2010;Nikolova, et al, 2006;Soto, et al, 2010;Ziemann, et al, 1997).…”

“…A large body of literature shows that corticospinal excitability for the agonist muscles of the responding hand increases only at approximately 100 ms prior to movement (Chen, et al, 1998;Evarts, 2011;Leocani, et al, 2000;Nikolova, et al, 2006).…”

“…A suprathreshold TMS applied over the M1 representation of hand muscles elicits muscle responses in the contralateral muscles, which can be recorded as motor evoked potentials (MEP) using surface electromyography (EMG). TMS studies of unilateral movement have reliably found that corticospinal excitability in M1 contra increases approximately 100 ms preceding voluntary movement (Chen et al, 1998;Hoshiyama et al, 1996;Leocani, et al, 2000;McMillan, et al, 2006;Nikolova et al, 2006;Sommer et al, 2001;Soto et al, 2010;van Elswijk, et al, 2008). In contrast, the activity in M1 ipsi during unilateral movement has received less attention and can either increase or decrease depending on the reaction time paradigm, such as simple vs choice reaction time tasks and pre-cued vs no pre-cued reaction time tasks (Duque et al, 2005;Leocani, et al, 2000;McMillan, et al, 2006).…”