The medial prefrontal cortex (mPFC) is thought to be an essential brain region for sensorimotor gating. The exact neuronal mechanisms, however, have not been extensively investigated yet by delicate single unit recording methods Prepulse inhibition (PPI) of the startle response is a broadly used important tool to investigate the inhibitory processes of sensorimotor gating. The present study was designed to examine the neuronal mechanisms of sensorimotor gating in the mPFC in freely moving rats. In these experiments, the animals were subjected to both pulse alone and prepulse+pulse stimulations. Head acceleration and the neuronal activity of the mPFC were simultaneously recorded. To adequately measure the startle reflex, a new headstage with 3D-accelerometer was created. The duration of head acceleration was longer in pulse alone trials than in prepulse+pulse trial conditions, and the amplitude of head movements was significantly larger during the pulse alone than during the prepulse+pulse situations. Single unit activities in the mPFC were recorded by means of chronically implanted tetrodes during acoustic stimulation evoked startle response and PPI. High proportion of medial prefrontal cortical neurons responded to these stimulations by characteristic firing patterns: short duration equal and unequal excitatory, medium duration excitatory, and long duration excitatory and inhibitory responses were recorded. The present findings, first time in the literature, demonstrated the startle and PPI elicited neuronal activity changes of the mPFC, and thus, provided evidence for a key role of this limbic forebrain area in sensorimotor gating process.