Increased evoked potentials and behavioral indices in response to pain among individuals with intellectual disability

Objective. Previous studies on the sensitivity and reactivity to pain of individuals with intellectual disability (ID) are inconsistent. The inconsistency may result from the reliance on self-reports and facial expressions of pain that are subject to internal and external biases. The aim was therefore to evaluate the reactivity to pain of individuals with ID by recording painevoked potentials (EPs), here for the first time, and testing their association with behavioral pain indices. Subject. Forty-one healthy adults, 16 with mildmoderate ID and 25 controls. Methods. Subjects received series of phasic heat stimuli and rated their pain on self-report scales. Changes in facial expressions and in pain EPs were recorded and analyzed offline. Results. Pain self-reports, facial expressions, and the N2P2 amplitudes of the EPs exhibited stimulusresponse relationship with stimulation intensity in both groups. The facial expressions and N2P2 amplitudes of individuals with ID were increased and N2P2 latency prolonged compared with controls. N2P2 amplitudes correlated with self-reports only in controls. Conclusions. Individuals with ID are hypersensitive/ reactive to pain, a finding bearing clinical implications. Although pain EPs may reflect a somewhat different aspect of pain than the behavioral indices do, there is evidence to support their use to record pain in noncommunicative individuals, pending further validation.