Effects of aging on contact heat-evoked potentials: the physiological assessment of thermal perception

Age significantly influences the detection thresholds to noxious heat; such thresholds depend on responses in the cerebral cortex to thermal stimuli and the psychophysical perception of such responses. To understand the influence of age on cerebral responses, we used contact heat-evoked potentials (CHEPs) to investigate the physiology of cerebral responses to thermal stimuli in 70 healthy subjects (33 men and 37 women, 39.56 +/- 12.12 years of age). With heat stimulation of fixed intensity (51 degrees C) on the distal forearm and distal leg, CHEPs revealed consistent waveforms with an initial negative peak (N1 latency: 398.63 +/- 28.55 and 449.03 +/- 32.21 ms for upper and lower limbs) and a later positive peak (P1 latency: 541.63 +/- 37.92 and 595.41 +/- 39.24 ms for upper and lower limbs) with N1-P1 interpeak amplitude of 42.30 +/- 12.57 microV in the upper limb and 39.67 +/- 12.03 microV in the lower limb. On analyses with models of multiple linear regression, N1-P1 amplitudes were negatively correlated with age and N1 latencies were correlated with gender, with females having shorter latencies. The verbal rating scale (VRS) for pain perception was higher in females than males, and decreased with aging. In addition, VRS paralleled changes in N1-P1 amplitude and N1 latency; the higher the VRS, the shorter the N1 latency and the higher the N1-P1 amplitude. These results provide evidence that CHEPs are influenced significantly by aging, corresponding to aging-related changes in thermal pain perception.