There is a significant unmet need for new approaches to treat migraine and post-traumatic headache (PTH) in Veterans who have suffered traumatic brain injury (TBI). The major aim of this proposal is to modulate cerebello-thalamic circuits to treat migraine and PTH. Headache reduces quality of life and can coincide with disabling sensory abnormalities including photophobia and pain. Migraine alone is estimated to affect 18% of women and 6% of men (12% overall). However, this prevalence is even greater in Veterans (50% overall) who have served in Iraq and Afghanistan and have experienced TBI and/or post-traumatic stress disorder. To date, nearly half of patients who have either migraine or PTH receive no beneficial outcomes with current treatments. This proposal will test the hypothesis that inhibition of cerebello-thalamic circuits can be used to treat migraine- like behaviors in mice. In the first aim, the plan is to inhibit the posterior thalamic area and the fastigial nucleus of the cerebellum to treat mice that are in a headache-like state. To model headache, we will use calcitonin gene-related peptide (CGRP) (a neuropeptide that is necessary and sufficient to induce migraine) and a TBI model involving mild closed head impact. We will test mice in three translatable behavior paradigms that measure light aversion, touch hypersensitivity and grimace. We will modulate the posterior thalamic area and fastigial nuclei of the cerebellum using a chemogenetic strategy with an inhibitory ligand-activated designer receptor. Our preliminary data indicate that stimulation of those two brain regions is sufficient to induce migraine-like behaviors in mice. Successful completion of this aim will provide translatable targets for direct brain modulation to treat headache disorders. In the second aim of this proposal, we will use blood-oxygen- level-dependent functional magnetic resonance imaging (BOLD fMRI) to identify downstream targets of the posterior thalamic area and cerebellum during a migraine-like or post-traumatic headache-like state. We will perform imaging in mice after they are given CGRP, pituitary adenylate cyclase-activating polypeptide (PACAP) (a peptide that is also reported to cause migraine in patients), or mild TBI. We will also optogenetically stimulate the posterior thalamic area and cerebellum fastigial nucleus to map functional connectivity changes of downstream targets in the brain. The goal is to identify additional brain targets that are more accessible for modulation. The significance of this study is the potential translation of these pre-clinical studies to the clinic. With large populations of Veterans suffering from headache disorders the need for new therapeutics is critical. This study has the potential to provide a road map for new therapeutic approachs to treating migraine and PTH.