Motor activity including locomotion and other movement types influence neuronal activity in many brain areas across animal species, including worms, flies, and mice. Yet the origin of these neural representations of ongoing behavior remain elusive. We posit that in extreme cases, activity could arise from two opposite sources: neural activity could originate in superior decision-making areas and then spread across the brain (“top-down”). Alternatively, neural activity could be initiated by motor activity and proprioception, and then distributed to higher brain areas (“bottom-up”). To distinguish between these two informational flows, we used fast, in vivo light field microscopy to image whole brain activity of head-fixed flies during spontaneous and forced behavior. We used unsupervised methods (PCA and ICA) to generate activity maps and obtain functional associated with locomotor activity. We assigned neuronal activities to different brain regions or neuron types by aligning activity maps to a comprehensive set of anatomical images widely available within the Drosophila community. We found that walking elicits global activity across the brain, regardless of whether flies were spontaneously walking or forced to walk. Furthermore, this global neural activity is not due to disinhibition of specific motor pathways, since excitatory and inhibitory neurons were both activated during behavior. In addition, neuromodulatory neurons (i.e. dopamine, serotonin and octopamine) differentially encode walk. Lastly, activity signatures of walking are different from those of grooming or flailing, indicating that the observed global upregulation of neuronal activity is not simply due to leg movements. We propose that specific locomotion patterns activates the brain by sending proprioceptive information to the base of the brain, from where it spreads over all brain regions. Ascending neurons, which carry information from the motor to higher brain centers, are promising candidates involved in this global activity upregulation.