High resolution focused non-invasive electrical stimulation of motor cortex in rodent model

Transcranial electrical stimulation (TES), a technique for stimulating the brain without surgical intervention, has potential applications for therapeutic interventions as well as brain-computer interfaces. One of the known limitations of conventional TES is that the stimulation volume is very large, due to the size and placement of electrodes typically used, which does not allow accurate targeting and results in large off-target activation. This work demonstrates a novel method for high resolution transcranial stimulation of motor cortex in mouse models using a flexible ultra-high-density electrode array. An electrode array was designed with ring-shaped electrodes having a hole in the middle, allowing simultaneous transcranial stimulation and intracortical recording using a commercial silicon neural probe. Intracortical recordings performed during transcranial stimulation, at both the stimulation target and at adjacent locations spaced at a 650 μm pitch, demonstrate the spatial localization of the evoked neural activity. Significant multi-unit activity was recorded at the center of the stimulation zone in the 15ms following stimulation, while low off-target activity is measured 650 μm away from the center. The locus of the stimulation was moved at four different locations in the cortex, with similar localized intracortical response obtained at all locations. Simultaneous stimulation of multiple sites was also demonstrated.