Effects of electrical stimulation of periaqueductal gray matter on evoked potentials recorded in the primary somesthetic cortical areas of the rat.

The influence of focal electrical stimulation of PGM on primary cortical evoked potentials elicted by nociceptive peripheral stimulation was studied in anaesthetized and conscious rats. This analgesic electrical stimulation produces an abolition of cortical responses during its application and a significant decrease of the positive and negative amplitude waves after interruption of PGM electrical stimulation. Since these effects were observed in animals under barbiturate anesthesia and in conscious rats, they are interpreted as a supraspinal action on the primary pain pathway.