Within-session sensitization and between-session habituation: a robust physiological response to repetitive painful heat stimulation.

Habituation and sensitization are important behavioural responses to repeated exposure of painful stimuli. Whereas within-session response dynamics to nociceptive stimuli is well characterized, little is known about long-term behaviour due to repetitive nociceptive stimulation. We used a standardized longitudinal heat pain paradigm in 66 healthy participants, 21 patients with chronic low back pain and 22 patients with depression who received daily sessions of 60 suprathreshold heat stimuli (48 °C each) for eight consecutive days. All three groups showed the same response: Repeated painful stimulation over several days resulted in substantially decreased pain ratings to identical painful stimuli. The decreased perception of pain over time was associated with a very robust increase in pain ratings in each single pain session, i.e., all participants sensitized within sessions and habituated between sessions. This uniform pattern was equally present in all examined groups. Chronic pain and depression do not seem to interfere with short-term sensitization and long-term habituation in this model of repetitive phasic heat pain.