How do animals initiate voluntary behavior? A key phenomenon in neuroscience is the readiness or preparatory neural activity in specific regions of the animal brain. The neurons and synaptic mechanisms mediating this activity are unknown. We found that the readiness discharge is shaped by sequential synaptic excitation and inhibition in the brain of crayfish (Procambarus clarkii). The readiness discharge neurons extended axon collaterals that appeared to activate recurring local interneurons. Therefore, we propose that the readiness discharge is formed by sequential synaptic events within the brain without feedback signals from downstream ganglia. The circuit involved is suited for signal processing for self-generated voluntary initiation of behavior.