Event-related desynchronization reflects downregulation of intracortical inhibition in human primary motor cortex

Abstract

There is increasing interest in electroencephalogram (EEG)-based brain-computer interface (BCI) as a tool for rehabilitation of upper limb motor functions in hemiplegic stroke patients. This type of BCI often exploits mu and beta oscillations in EEG recorded over the sensorimotor areas, and their event-related desynchronization (ERD) following motor imagery is believed to represent increased sensorimotor cortex excitability. However, it remains unclear whether the sensorimotor cortex excitability is actually correlated with ERD. Thus we assessed the association of ERD with primary motor cortex (M1) excitability during motor imagery of right wrist movement. M1 excitability was tested by motor evoked potentials (MEPs), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) with transcranial magnetic stimulation (TMS). Twenty healthy participants were recruited. The participants performed 7 s of rest followed by 5 s of motor imagery and received online visual feedback of the ERD magnitude of the contralateral hand M1 while performing the motor imagery task. TMS was applied to the right hand M1 when ERD exceeded predetermined thresholds during motor imagery. MEP amplitudes, SICI, and ICF were recorded from the agonist muscle of the imagined hand movement. Results showed that the large ERD during wrist motor imagery was associated with significantly increased MEP amplitudes and reduced SICI but no significant changes in ICF. Thus ERD magnitude during wrist motor imagery represents M1 excitability. This study provides electrophysiological evidence that a motor imagery task involving ERD may induce changes in corticospinal excitability similar to changes accompanying actual movements.

Brain‐computer interfaces for post‐stroke motor rehabilitation: a meta‐analysis

“…The power decrease in SMR during an attempt to move the paralyzed limb was shown to be associated with; an increase in the excitability of the motor cortex,30, 31 a disinhibition of GABAergic inhibitory interneurons32 and an increased excitability of the corticospinal tract33 and of spinal motoneuron pools 34. An associated real‐time feedback system (e.g., a robotic orthosis, NMES or a virtual reality avatar) that reproduces the intended action (e.g., finger extension) allows patients to purposefully control sensorimotor oscillations 24.…”

“…Since then, an international effort has taken place to investigate whether repeated BCI training can lead to motor recovery. Several studies reported neurological and behavioral improvements, such as increased event‐related desynchronization (ERD) of SMR in the ipsilesional hemisphere,36, 37 changes of motor‐related functional connectivity assessed by functional magnetic resonance imaging;38 increased control of volitional electromyographic activity of the paralyzed muscles,37, 39 and learned control of the reanimated hand and arm 32, 34, 35, 36, 37, 40. These results have encouraged the use of BCI in post‐stroke motor rehabilitation, but however clinical efficacy is unknown so far.…”

Brain Activity During Motor Imagery

“…Abbruzzese and colleagues (1999) as well as Liepert and Neveling (2009) observed that during motor imagery, intracortical inhibition was decreased while intracortical facilitation remained unchanged. This finding suggests that the enhancement of corticospinal excitability that occurrs during motor imagery is caused by disinhibition (Takemi et al 2013).…”

“…During motor imagery (kinesthetic imagery) of hand movement, ERD of 8-13 Hz (alpha bands) and 14-30 Hz (beta bands) in the contralateral hemisphere was observed (Nam et al 2011). The ERD recorded from the MI associated with downregulation of intracortical inhibition during motor imagery (Matsumoto et al 2010;Takemi et al 2013).…”

Neuroscience-Based Rehabilitation for Stroke Patients

“…Electroencephalography (EEG) shows that the formation of MI, like ME, reduces the α-wave (Mu-rhythm) amplitude in the SMA (Refer to Section Interventions based on extraneous bottom-up processes), which is called event-related desynchronization (ERD). The degree of change rate in ERD that is associated with MI correlates with the motor-evoked potential increment, intracortical inhibition reduction, and F-wave frequency rate, and ERD is thought to reflect the excitability of the corticospinal tract [51].…”