Functional near-infrared spectroscopy (fNIRS) of posterolateral cerebellum and prefrontal cortex for fNIRS-driven cerebellar tES � a case report

Background: Cerebellar transcranial direct current stimulation(ctDCS) has been shown to evoke brain responses that could be measured using functional near-infrared spectroscopy(fNIRS). Good general linear model fit was found between cerebellar electric field and brain responses at prefrontal cortex(PFC) and sensorimotor cortex in responders[1]. Recent work found that frontoparietal network is disproportionately expanded in the cerebellum compared to cortex[2], and found that cerebellar blood-oxygen-level-dependent imaging signals temporally lagged cortex where infra-slow activity(0.01�0.10 Hz) and delta band(0.5�4 Hz) activity propagated in opposite directions between cerebellum and cerebral cortex. Methods: We tested the feasibility of fNIRS of cerebellum and PFC where infra-slow(0.01�0.10 Hz) PFC oxyhemoglobin(HbO) fNIRS was used to drive(phase-amplitude-coupling, PAC) 4Hz cerebellar transcranial alternating current stimulation(ctACS) at right lobules VI-CrusI/II-VIIb. Ten young and healthy right-handed subjects(2 females, age: 21-25 years) volunteered for this case report. The session consisted of a block design of 2.5 min baseline, ctDCS/ctACS period of 5min, and 2.5 min post-intervention measures. Results: We found that 2mA ctDCS evoked similar HbO response in-the-range of 10-6M across cerebellum and PFC brain regions(a=0.01); however, 2mA PAC-driven ctACS evoked HbO was in-the-range of 10-7M. Increasing fNIRS-driven ctACS current to 4mA increased HbO response in-the-range 10-6M that was statistically different(a=0.01) across those brain regions. Discussion: Cerebellar modulation of the reward circuitry, via ventral tegmental area(VTA), where VTA-dopamine(DA) signaling in medial prefrontal cortex(mPFC) can play a key role in motivated behaviors and cognition. We showed the feasibility of fNIRS of cerebellum and fNIRS-driven ctACS at 4Hz, where higher 4mA tACS may facilitate cognitive function via the frontoparietal network in cerebellar cognitive affective/Schmahmann syndrome via the cerebello-thalamo-cortical pathway.