Two Routes to Better Control
A research team has identified two distinct neural mechanisms that improve brain-computer interface performance when specific brain regions receive targeted stimulation. The findings address a persistent challenge in BCI rehabilitation: many stroke survivors cannot generate sufficient brain activity during motor imagery to reliably control these systems.
The study tested intermittent theta burst stimulation (iTBS), a non-invasive brain stimulation technique, on 25 healthy subjects across four separate sessions. Each session targeted different brain regions: the primary motor cortex (M1), the dorsolateral prefrontal cortex (DLPFC), both regions simultaneously, or neither (sham stimulation).
When researchers stimulated M1, they observed a significant increase in corticospinal excitability (P = 0.016). The degree of this increase directly predicted improvements in BCI performance (P = 0.013). This pathway operates through the brainโs motor execution system, essentially priming the neural circuits that translate imagined movement into detectable signals.
DLPFC stimulation worked differently. Rather than affecting the motor cortex directly, it strengthened functional connectivity within the frontoparietal network. This network governs attention, working memory, and the cognitive aspects of motor planning. The magnitude of connectivity changes correlated positively with BCI performance improvements across multiple measurements.
When Combination Fails
The simultaneous stimulation of both regions produced no significant effects. This null result carries weight because it suggests the two mechanisms may interfere when activated concurrently, or that the brain cannot effectively integrate both enhancement strategies at once. The finding complicates assumptions about therapeutic optimization through simple addition.
Clinical Implications
These results matter because motor imagery BCIs remain unreliable for a substantial portion of stroke patients. Current estimates suggest 15-30% of users cannot achieve functional control, often due to diminished brain activity in damaged motor regions. The identification of two independent enhancement pathways creates options for personalized intervention.
Patients with preserved motor cortex function but impaired cognitive control might benefit from DLPFC stimulation. Those with intact planning abilities but weakened motor output could respond better to M1 targeting. The research provides a framework for matching stimulation protocols to individual neural profiles rather than applying uniform approaches.
The study used functional near-infrared spectroscopy to track brain activation patterns and single-pulse TMS to measure corticospinal changes. This multimodal approach allowed researchers to separate performance improvements from their underlying neural causes, establishing causal rather than merely correlative relationships between stimulation and control enhancement.