Activation of neurones in the prefrontal cortex by brain-stimulation reward in the rat

To investigate reward pathways in the brain, recording were made from neurones while electrical stimulation was applied to brain-stimulation reward sites in the rat. Single units in most areas of the neocortex were not activated by the stimulation. In the sulcal prefrontal cortex (which forms the dorsal bank of the rhinal sulcus) and in the medial prefrontal cortex (which forms the medial pregenual wall of the hemisphere) single units were activated by the stimulation. This indication that prefrontal neurones are involved in brain-stimulation reward received support from the observation that the neurones were activated in self-stimulation of many different sites — the lateral hypothalamus, the midbrain tegmentum ventrolateral to the central grey, the nucleus accumbens, and the medial prefrontal cortex. Many of the prefrontal units were directly (probably antidromically) excited, with short latencies (1–10 msec), by stimulus pulses applied to self-stimulation sites other than the nucleus accumbens. Many prefrontal units were trans-synaptically activated with longer latencies (2–30 msec) by stimulus pulses applied to the self-stimulation sites. Further evidence that the prefrontal neurones are involved in brain-stimulation reward is that units in the prefrontal cortex were in general not activated from non-reward sites in the midbrain tegmentum. Also neurones in many other areas of the neocortex did not appear to be activated by the brain-stimulation reward.