Pain processing is faster than tactile processing in the human brain

Abstract

Pain signals threat and drives the individual into a behavioral response that significantly depends on a short stimulus-response latency. Paradoxically, the peripheral and spinal conduction velocities of pain are much slower than of tactile information. However, cerebral processing times and reaction times of touch and pain have not yet been fully assessed. Here we show that reaction times to selective nociceptive cutaneous laser stimuli are substantially faster than expected from the peripheral conduction velocities. Furthermore, by using magnetoencephalography, we found that latencies between earliest stimulus-evoked cortical responses and reaction times are approximately 60 ms shorter for nociceptive than for tactile stimuli. These findings reveal that cerebral processing of pain is substantially faster than processing of tactile information and relatively compensates for the slow peripheral and spinal conduction velocities of pain. Our observation shows how the cerebral organization of pain processing enhances motor responses to potentially harmful stimuli and thereby subserves the particular behavioral demands of pain.

Figure 1.

Paradigm and analysis. Stimuli were painful and tactile stimuli randomly applied to the right hand. Reaction times were button presses with the index finger of the left hand. Central processing time was defined as latency between earliest stimulus-evoked cortical responses and reaction times.

Figure 2.

Cortical responses, reaction times, and central processing times to painful and tactile stimuli. Left and right show individual and group mean results, respectively. Cortical responses are global stimulus-evoked responses detected by all 122 magnetoencephalographic sensors over the whole head. Lines in the bottom left connect data points from the same individual. Shaded areas in the top right time course panels depict ±SEM. Error bars refer to SEM. **p < 0.01, Wilcoxon's signed-rank test.

Figure 3.

Local cortical responses, reaction times, and latencies between local cortical responses and reaction times. Locations of responses to painful and tactile stimulation were calculated as group mean normalized dipole locations. Mean coordinates of responses to painful stimuli are as follows: S1, −30, −34, 65; contralateral S2, −52, −4, 18; ipsilateral S2, 50, −8, 15. Mean coordinates of responses to tactile stimuli are as follows: S1, −46, −23, 58; contralateral S2, −56, −14, 21; ipsilateral S2 49, −10, 20. The latency difference between earliest local responses (S1, contralateral S2, and ipsilateral S2) and reaction times represents the local equivalent of the central processing time of Figure 2, which refers to global cortical responses. Shaded areas in the time course panels depict ±SEM. Error bars refer to SEM. cl, Contralateral; il, ipsilateral. *p < 0.05, Wilcoxon's signed-rank test.