Motor cortex neurovascular coupling: inputs from ultra–high-frequency ultrasound imaging in humans

OBJECTIVE Neurovascular coupling reflects the link between neural activity and changes in cerebral blood flow. De- spite many technical advances in functional exploration of the brain, including functional MRI, there are only a few re- ports of direct evidence of neurovascular coupling in humans. The authors aimed to explore, for the first time in humans, the local cerebral blood flow of the primary motor cortex using ultra–high-frequency ultrasound (UHF-US) Doppler imag- ing to detect low blood flow velocity (1 mm/sec). METHODS Four consecutive patients underwent awake craniotomy for glioma resection using cortical direct electro- stimulation for brain mapping. The primary motor cortical area eliciting flexion of the contralateral forearm was identified. UHF-US color Doppler imaging of this cortical area was acquired at rest, during repeated spontaneous forearm flexion, and immediately after the movement’s termination. In each condition, the surface areas of the detectable vessels were measured after extraction of non–zero-velocity colored pixels and summed. RESULTS During movement, local cerebral blood flow increased significantly by 14.4% (range 5%–30%) compared with baseline. Immediately after the termination of movements, the local hyperemia decreased significantly by 8.6% (range 1.9%–15.7%). CONCLUSIONS To the authors’ knowledge, this study is the first to provide a real-time demonstration of the neurovas- cular coupling in the human cortex by ultrasound imaging. They assume that UHF-US may be used to gather original and advanced data on brain functioning, which could be used to help in the identification of functional cortical areas dur- ing brain surgery.