Animals fed a high-protein diet (50% casein) are hyperactive and more responsive to nociceptive stimuli than those fed either a normal- or low-protein diet. The mechanisms mediating dietary protein-induced behavior are unknown and may include both central and peripheral neural effects. Adult, Sprague-Dawley rats were fed 50% casein (treatment group) and 24% casein (control group) ad lib for 36-40 weeks. The animals were anesthetized with alpha-chloralose and urethane (50 mg/kg and 1.5 mg/kg, IP). EEG recordings were averaged while the anesthetized animal was conditioned using an alerting stimulus-imperative stimulus (AS-IS) paradigm. AS consisted of a 1.5 kHz, 90 dB tone cue. This was followed 2 seconds later by IS, an electrical tail stimulation (11 V, 1.4 s duration). Two negative deflections (N1 and N2) were generated by the frontal cortex during the AS-IS interstimulus interval. N1, an alerting response, was not different between the two groups. N2 amplitude and peak latency were significantly increased in the high-protein group (205% and 117% of control, respectively; p less than 0.05). N2 represents the activation of cells in the motor cortex. Brainstem auditory-evoked responses and somatosensory-evoked potentials also were recorded, but no differences were observed between the two diet groups. These data suggest that consumption of a high-protein diet results in an increase in central arousal mechanisms (measured by cortical negativity response), specifically involving increased excitability of the motor cortex, that is not associated with a disorder of information processing in the cerebral cortex (measured by brainstem auditory-evoked responses and somatosensory-evoked potentials).