The cerebellum has been overlooked for its potential for neuromodulation for decades. Traditionally thought of as critical for motor coordination, anatomical, clinical and imaging evidence now indicate that the cerebellum also has central roles in cognition and emotion, and that cerebellar dysfunction impacts these functions. Consistent with these findings of cerebellar involvement in motor and non-motor functions, projections from the cerebellar nuclei (CN) target, via the thalamus, both motor and non-motor areas of the cortex and the basal ganglia. Thus, modulation of cerebellar outputs should be able to affect areas throughout the forebrain, and therefore has the potential to treat numerous disorders. Gap in Prior Research: Stimulation of the cerebellar cortex produced mixed results in clinical trials almost fifty years ago, which discouraged further attempts. Whereas stimulation of the CN, where the efferent axons from the cerebellar cortex converge, has recently been shown to have clinical benefits in patients and animal models, reviving interest in cerebellar stimulation as a therapeutic tool. However, direct stimulation of the CN requires surgical implantation of deep brain stimulation leads into the cerebellum. Research Opportunity: Focused Ultrasound (FUS) and Transcranial Electrical Stimulation (tES) are two non- invasive brain stimulation methods that have great potentials for clinical applications and provide ideal tools for cerebellar stimulation. FUS has the potential to stimulate the CN directly with its superior focusing and steering capabilities. tES would be the preferred method for stimulation of the cerebellar cortex due to its ease of application and the inexpensive equipment involved. Advances in the past two decades on functional imaging and anatomical mapping provide an improved understanding of the circuitry of the cerebellar cortex and its connections to the CN. Thus, we have novel tools and the knowledge base to develop effective protocols both for direct stimulation of the CN and indirect modulation of them via stimulation of the cerebellar cortex. Current Proposal: The overarching goal of this proposal is to develop effective modulation paradigms of cerebellar output both by direct stimulation of the CN using FUS and indirect CN modulation via electrical stimulation of the cerebellar cortex. Optimal stimulation parameters will be investigated for selective stimulation of neuronal subtypes in the cortex and the CN. Novel mechanisms of neuromodulation will also be investigated that can emerge from combined application of the two methods on the cerebellar circuits. The modulation paradigms developed should generalize to numerous motor and non-motor functions in which the cerebellum is involved.

The cerebellum is a primary center of motor coordination and its role in cognition is increasingly recognized, raising the possibility that cerebellar dysfunction contributes widely to symptoms of psychiatric and neurological disorders. Concurrent with the recognition of the cerebellum's expanded role in brain function, stimulation of the cerebellum has seen a surge of clinical studies in recent years reporting that it improves motor learning, cognitive and emotional processes. However, to date, very few studies have addressed the cellular and circuit level mechanisms by which the cerebellar activity can be modulated using non-invasive methods of stimulation such as transcranial electrical stimulation (tES) and focused ultrasound stimulus (FUS); this is the overarching goal of this proposal.