Features of Referred Sensation Areas for Artificially Generated Sensory Feedback - A Case Study

Phantom limb pain (PLP) is a frequent consequence of amputation. Recent evidence suggests that the pathophysiological mechanisms of PLP are related to neuroplastic changes in the cortex, as consequence of the lost sensory feedback. Formation of referred sensation areas (RSAs) may follow amputation. Sensations may be evoked in the lost body part upon stimulation of RSAs that may be exploited as artificial sensory feedback. The RSAs, however, have also shown to change over time. Features of RSAs in the case of a 36 year old male with right arm amputation aiming to identify placement of electrodes for sensory feedback are reported in this paper. The arm was amputated at shoulder level following patient's request five years after a vehicle accident that resulted in brachial plexus injury and consequent severe arm paralysis with residual sensory functionality up to 20 %. RSAs were characterized over five sessions within 27 days using mechanical stimuli (brushing over the area or applying light pressure). Tests of electrical stimuli were applied hrough two surface electrodes covering one or multiple RSAs to generate evoked sensations. Location and extent of RSAs as well as the type and location of sensations evoked in the phantom limb were stable within the session (tested up to 30 minutes) and dynamic between sessions. Partial overlapping of RSAs with associated evoked sensation of same or different type was observed for different sessions. Various painful and non-painful sensations were evoked by both mechanical and electrical stimuli dependent on location of the applied stimulus and assessment time. Mechanical andelectrical stimuli applied at the same location evoked the same or different types of sensation in the phantom limb. RSAs may be a promising pathway for delivering sensory feedback for PLP treatment. Features, however, of RSAs may highly influence the efficiency of the PLP treatment.