A key problem with neuroprostheses and brain monitoring interfaces is that they need extreme energy efficiency. One way of lowering energy is to use the low power modes available on the processors embedded in these devices. We present a technique to predict when neuronal activity of interest is likely to occur, so that the processor can run at nominal operating frequency at those times, and be placed in low power modes otherwise. To achieve this, we discover that branch predictors can also predict brain activity. By performing brain surgeries on awake and anesthetized mice, we evaluate several branch predictors and find that perceptron branch predictors can predict cerebellar activity with accuracies as high as 85%. Consequently, we co-opt branch predictors to dictate when to transition between low power and normal operating modes, saving as much as 59% of processor energy. !"#$ !%#$ Figure 1: (a) The cerebellum, shown in red, is located behind the top of the brain stem and has two hemispheres [47]; (b) a major cerebellar neuron is the Purkinje neuron, imaged here from a mouse brain [48].Figure 2: (a) Block diagram of cerebellar implant (dimensions not drawn to scale) and compared against a coin [2]; (b) the Utah array is used to collect intracellular Purkinje recordings [53, 54].studies on using other branch predictors beyond the ones we study [37,[44][45][46] for neuronal prediction.2 We model a cerebellar monitoring implant. Using architectural, RTL, and circuit modeling, we use the branch predictor to not only predict branches but to also guide energy management. We place the processor in idle low power mode but leave the predictor on to predict brain activity. When the predictor anticipates interesting future cerebellar behavior, it brings the processor back to normal operating mode (where the predictor goes back to being a standard branch predictor). Overall, we save up to 59% of processor energy.An important theme of this work is to ask -since machine learning techniques inspired by the brain have been distilled into hardware predictors (e.g., like the perceptron branch predictor), can we now close the loop and use such predictors to anticipate brain activity and manage resources on neuroprostheses? Our work is a first step in answering this question. Ultimately, this approach can guide not only management of energy, but also other scarce resources.