A new method for demonstration of central effects of analgesic agents in man.

A new method of eliciting experimental pain in man is described. Microelectrodes are inserted percutaneously into the peripheral nerves of awake subjects, and are positioned close to nociceptive fibres in order to elicit pain during intraneural electrical stimulation. Under fixed stimulation conditions the estimated magnitude of evoked pain remains relatively stable, unless a high stimulus frequency is used, which may lead to excitation failure of nociceptive fibres. This method can be employed to test for possible central modulation of pain, for instance by analgesic agents, since peripheral receptors are bypassed.