Recovery of the 20 Hz Rebound to Tactile and Proprioceptive Stimulation after Stroke

Abstract

Sensorimotor integration is closely linked to changes in motor-cortical excitability, observable in the modulation of the 20 Hz rhythm. After somatosensory stimulation, the rhythm transiently increases as a rebound that reflects motor-cortex inhibition. Stroke-induced alterations in afferent input likely affect motor-cortex excitability and motor recovery. To study the role of somatosensory afferents in motor-cortex excitability after stroke, we employed magnetoencephalographic recordings (MEG) at 1–7 days, one month, and 12 months in 23 patients with stroke in the middle cerebral artery territory and 22 healthy controls. The modulation of the 20 Hz motor-cortical rhythm was evaluated to two different somatosensory stimuli, tactile stimulation, and passive movement of the index fingers. The rebound strengths to both stimuli were diminished in the acute phase compared to the controls and increased significantly during the first month after stroke. However, only the rebound amplitudes to tactile stimuli fully recovered within the follow-up period. The rebound strengths in the affected hemisphere to both stimuli correlated strongly with the clinical scores across the follow-up. The results show that changes in the 20 Hz rebound to both stimuli behave similarly and occur predominantly during the first month. The 20 Hz rebound is a potential marker for predicting motor recovery after stroke.

β-Oscillations Reflect Recovery of the Paretic Upper Limb in Subacute Stroke

“…As expected, the motor outcome could be predicted by early motor scores at the subacute timepoint, while the neuroplastic mechanisms underlying motor recovery were reflected by MEG markers including the ipsilesional β-ERD and β-ERS peak amplitudes. Our results were in line with earlier studies by Parkkonen et al who utilized both tactile stimulation and passive movement in acute stroke survivors with longitudinal follow-up 22,34 .…”

“…A similar phenomenon was observed in the TMS study that the SICI also decreased in contralesional M1 particularly in subacute stroke. 54,55 Parkkonen et al 22,34 also discovered that the β-rebound decreased after somatosensory stimulation in both paretic and nonparetic hands when compared with healthy controls, and only the β-rebound of the paretic hand correlated with concurrent motor scores. Subacute stroke constitutes a unique, highly sensitive period for motor recovery, 10 and the bihemispheric changes in β-ERS featured the global disinhibition status in this period.…”

“…33 Somatosensory stimulation studies in acute stroke demonstrated decreased β-band rebound in either paretic or nonparetic hand stimulation, with subsequent increase during recovery. 22,23,34 However, most of these were cross-sectional studies providing inconsistent evidence influenced by the heterogeneity in stroke survivor enrolment (poststroke time, stroke severity, mixed ischemic and hemorrhagic stroke, mixed arterial territories, mixed subcortical and cortex involvement). 9,33,[35][36][37] Here, we have studied longitudinal MEG changes in a relatively homogeneous cohort of first-time subcortical ischemic stroke in the middle cerebral artery (MCA) territory at weeks 3, 5, and 12 after stroke to test a number of hypotheses.…”

CMC is more than a measure of corticospinal tract integrity in acute stroke patients

“…Indeed, a dissociation between cortical oscillations and CMC has already been shown earlier in healthy subjects: doubling of cortical 20-Hz activity by administering diazepam did not change the strength of CMC ( Baker and Baker, 2003 ). In line, although the modulation of 20-Hz oscillations to tactile or proprioceptive stimulation has shown to be altered after stroke, no changes in resting-state beta oscillations were observed ( Laaksonen et al, 2012 , Parkkonen et al, 2018 ). Hence, changes in resting state oscillations are not sufficient to explain the observed slowing of CMC peak frequency.…”

The effect of alertness and attention on the modulation of the beta rhythm to tactile stimulation

“…These findings support the reliability of group-level findings of changes in beta suppression/ rebound, that is, in different clinical conditions. Especially the minimal effect of reduced alertness on the strength of beta rebound is important, as the beta rebound has been suggested as a biomarker of the functional state of the SMI cortex after stroke (Laaksonen et al, 2012;Parkkonen et al, 2017Parkkonen et al, , 2018Tang et al, 2020). However, at the individual level, alterations in alertness may affect beta rhythm modulation, especially beta suppression, which should be taken into account in longitudinal experiments to avoid misinterpretations.…”