Pain processing within the primary somatosensory cortex in humans

Abstract

To investigate the processing of noxious stimuli within the primary somatosensory cortex (SI), we recorded magnetoencephalography following noxious epidermal electrical stimulation (ES) and innocuous transcutaneous electrical stimulation (TS) applied to the dorsum of the left hand. TS activated two sources sequentially within SI: one in the posterior bank of the central sulcus and another in the crown of the postcentral gyrus, corresponding to Brodmann's areas 3b and 1, respectively. Activities from area 3b consisted of 20- and 30-ms responses. Activities from area 1 consisted of three components peaking at 26, 36 and 49 ms. ES activated one source within SI whose location and orientation were similar to those of the TS-activated area 1 source. Activities from this source consisted of three components peaking at 88, 98 and 109 ms, later by 60 ms than the corresponding TS responses. ES and TS subsequently activated a similar region in the upper bank of the sylvian fissure, corresponding to the secondary somatosensory cortex (SII). The onset latency of the SII activity following ES (109 ms) was later by 29 ms than that of the first SI response (80 ms). Likewise, the onset latency of SII activity following TS (52 ms) was later by 35 ms than that of area 1 of SI (17 ms). Therefore, our results showed that the processing of noxious and innocuous stimuli is similar with respect to the source locations and activation timings within SI and SII except that there were no detectable activations within area 3b following noxious stimulation.

In vivo and in vitro Patch-clamp Recording Analysis of the Process of Sensory Transmission in the Spinal Cord and Sensory Cortex

“…We did not test whether the response showed adaptation or not. Unexpectedly, noxious pinch stimulation near a whisker did not produce any significant response in all neurons tested, in spite of the evidence that the primary sensory cortex responds to noxious stimuli revealed by imaging methods such as MEG, PET or fMRI (Inui, 2003). This discrepancy might be accounted for as follows: First, our patch-clamp recordings were made under anesthesia that presumably depressed nociceptive responses.…”

The old-but-new theories about human voluntary motor control

“…Although much attention has been given to sensorimotor interaction in SI, there is little evidence of such a phenomenon in the SII and the role of SII in motor execution has not been fully elucidated in humans. Compared with the SI, the SII is speculated to serve a higher level of cognitive function in somatosensory information processing, such as attention, decision-making, object recognition, and the integration of nociceptive and non-nociceptive inputs [60][61][62][63][64] . Our results show that these cortical areas play different roles in the function of sensorimotor integration.…”

Somatic Sensation and the Insular-Opercular Cortex: Relationship to Central Pain

“…A magnetoencephalographic study found that innocuous cold uniquely activates the posterior insular cortex, while noxious cold also excites SII [6]. Painful electrical stimulation of the first division of the trigeminal nerve in humans activates the SII but not the SI cortex [21]. The parietal operculum (SII) rather than the anterior insula was found to be involved with raised heat pain thresholds in 6 stroke patients with involvement of SII and/or anterior insula [22], while a patient with a tumour involving the parietal operculum and posterior insula (subsequently removed) had interference with both mechanical and thermal pain sensations [23].…”