Game-based movement facilitates acute priming effect in stroke.

OBJECTIVE: Cortical priming is an emerging strategy to enhance motor recovery after stroke, however, limited information exists on the neuromodulatory effects of lower limb movement-based priming to facilitate corticomotor excitability after stroke. In this study, we investigated the feasibility and effectiveness of game-based ankle movement priming using the DIG-I-PRIME™ on corticomotor excitability and motor performance in chronic stroke survivors. METHODS: Nineteen stroke survivors participated in a 20-min session of game-based priming. A period of rest served as a control for the priming condition. Transcranial magnetic stimulation (TMS) was used to measure corticomotor excitability of the paretic and non-paretic tibialis anterior (TA) muscle representations. Motor performance was quantified by assessing the accuracy to track a sinusoidal target wave with paretic dorsiflexion and plantarflexion. RESULTS: Ipsilesional corticomotor excitability increased by 25% after game-based movement priming (p = 0.02) while changes were not observed after the control condition. No change in motor performance was noted. CONCLUSION: Game-based ankle movement priming demonstrated a significant acute priming effect on the ipsilesional lower limb M1. These data provide preliminary evidence for the potential benefits of game-based priming to promote functional recovery after stroke.

Characterization of stimulus response curves obtained with transcranial magnetic stimulation from bilateral tibialis anterior muscles post stroke.

BACKGROUND: Stimulus response curves (SR curves), measured using transcranial magnetic stimulation (TMS) induced motor evoked potentials (MEP), yield important information regarding corticomotor connectivity. Limited understanding of SR curve analyses techniques for leg muscles after stroke may limit the utility of TMS data for walking recovery. OBJECTIVE: To compare linear and non-linear curve fitting for MEP responses from the non-paretic and paretic tibialis anterior (TA) muscles. METHODS: Accuracy of fit was measured using coefficient of determination (R2). Similarities of the fit were compared using slopes and area under the curve (AUC). RESULTS: The non-linear function demonstrated higher R2 and slopes. The AUC was not significantly different between the two analyses approaches. The non-linear non-paretic SR slopes and paretic AUC had significant associations with walking speed. CONCLUSION: Our results highlight the differences between non-linear and linear approaches to best fit the SR curves from bilateral TA muscles in stroke survivors. Although the linear function can appropriately fit the SR curve of the paretic and non-paretic TA, the non-linear function estimated a higher slope. We found the AUC to be a more robust measure that was not affected by the type of curve-fitting approach and only the AUC of the paretic TA showed significant association with walking speeds. A better understanding of SR curve fitting approaches for the TA muscles in individuals with chronic stroke allows for their optimal use in interpretation of TMS data and literature.

Influence of neurovascular mechanisms on response to tDCS: an exploratory study.

The beneficial effects of transcranial direct current stimulation (tDCS) for stroke rehabilitation are limited by the variability in changes in corticomotor excitability (CME) after tDCS. Neuronal activity is closely related to cerebral blood flow; however, the cerebral hemodynamics of neuromodulation in relation to neural effects have been less explored. In this study, we examined the effects of tDCS on cerebral blood velocity (CBv) in chronic stroke survivors using transcranial Doppler (TCD) ultrasound in relation to changes in CME and described the neurovascular characteristics of tDCS responders. Middle cerebral artery (MCA) CBv, cerebrovascular resistance (CVRi) and other cerebral hemodynamics-related variables were continuously measured before and after 15 min of 1 mA anodal tDCS to the lesioned lower limb M1. tDCS did not modulate CBv in the whole group and upon TMS-based stratification of responders and non-responders. However, at baseline, responders demonstrated lower CME levels, lower CBv and higher CVRi as compared to non-responders. These results indicate a possible difference in baseline CME and CBv in tDCS responders that may influence their response to neuromodulation. Future trials with a large sample size and repeated baseline measurements may help validate these findings and establish a relationship between neuromodulation and neurovascular mechanisms in stroke.

Non-invasive brain stimulation in the modulation of cerebral blood flow after stroke: A systematic review of Transcranial Doppler studies.

OBJECTIVE: Non-invasive brain stimulation (NIBS), such as repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS), are promising neuromodulatory priming techniques to promote task-specific functional recovery after stroke. Despite promising results, clinical application of NIBS has been limited by high inter-individual variability. We propose that there is a possible influence of neuromodulation on cerebral blood flow (CBF), as neurons are spatially and temporally related to blood vessels. Transcranial Doppler (TCD), a clinically available non-invasive diagnostic tool, allows for evaluation of CBF velocity (CBFv). However, little is known about the role of neuromodulation on CBFv. METHODS: A systematic review of literature to understand the effects of NIBS on CBFv using TCD in stroke was conducted. RESULTS: Twelve studies fit our inclusion criteria and are included in this review. Our review suggested that CBFv and/or vasomotor reactivity maybe influenced by rTMS dosage (intensity and frequency) and the type of tDCS electrode montage. CONCLUSION: There is limited evidence regarding the effects of NIBS on cerebral hemodynamics using TCD and the usefulness of TCD to capture changes in CBFv after NIBS is not evident from this review. We highlight the variability in the experimental protocols, differences in the applied neurostimulation protocols and discuss open questions that remain regarding CBF and neuromodulation. SIGNIFICANCE: TCD, a clinically accessible tool, may potentially be useful to understand the interaction between cortical neuromodulation and CBFv.