Transcutaneous auricular VNS applied to experimental pain: a paired behavioral and EEG study using thermonociceptive CO2 laser

Transcutaneous Auricular taVNS is a non invasive treatment which was shown to modulate pain perception in humans, although with contrasting analgesic and pronociceptive effects. This study explores the behavioral and cerebral effects of taVNS on somatosensory evoked thermonociceptive CO2 laser pulses

How visual experience shapes body representation

We do not have a veridical representation of our body in our mind. For instance, tactile distances of equal measure along the medial-lateral axis of our limbs are generally perceived as larger than those running along the proximal-distal axis. This anisotropy in tactile distances reflects distortions in body-shape representation, such that the body parts are perceived as wider than they are. While the origin of such anisotropy remains unknown, it has been suggested that visual experience could partially play a role in its manifestation. To causally test the role of visual experience on body shape representation, we investigated tactile distance perception in sighted and early blind individuals comparing medial-lateral and proximal-distal tactile distances of stimuli presented on the ventral and dorsal part of the forearm, wrist, and hand. Overestimation of distances in the medial-lateral over proximal-distal body axes were found in both sighted and blind people, but the magnitude of the anisotropy was significantly reduced in the forearms of blind people. We conclude that tactile distance perception is mediated by similar mechanisms in both sighted and blind people, but that visual experience can modulate the tactile distance anisotropy

Do you get what you expect? Studying the effect of expectations on high-frequency electrical stimulation-induced pain and pinprick hypersensitivity.

This study investigated whether expecting more pain increases high-frequency electrical stimulation (HFS)-induced pain and pinprick hypersensitivity. Fifty healthy volunteers were randomly allocated to either a control group (N=25) or a nocebo group (N=25). Participants in both groups received a patch containing water on the right forearm. The nocebo group was told that the patch contained capsaicin that sensitized their skin, while the control group was told that the patch contained water that had no effect on skin sensitivity. Before and after patch attachment, single electrical stimuli were delivered to the area of the patch to measure the perceived intensity to these stimuli. After patch removal, and after the participant rated expected pain and fear for HFS, HFS was delivered to the same skin site. To assess changes in pinprick sensitivity, pinprick stimuli were delivered before and after HFS. The nocebo group rated the perceived intensity for the single electrical stimulus after removal of the patch as more intense compared to the control group, indicating that our manipulation worked. Yet, this effect did not transfer to expected pain for HFS, nor did it affect pain intensity ratings during HFS. HFS increased pinprick sensitivity but no group differences were found. Because of the lack of differences in expected pain and pain intensity ratings for HFS between groups, no firm conclusions can be drawn regarding their effect on pinprick hypersensitivity. Nevertheless, exploratory analyses showed a significant and moderate correlation between the expected pain for HFS and the actual pain intensity reported during HFS

Perceptual correlates of homosynaptic long term potentiation in human nociceptive pathways: a replication study

Animal studies have shown that high-frequency stimulation (HFS) of peripheral C-fibers induces long-term potentiation (LTP) within spinal nociceptive pathways. The aim of this replication study was to assess if a perceptual correlate of LTP can be observed in humans. In 20 healthy volunteers we applied HFS to the left or right volar forearm. Before and after applying HFS we delivered single electrical test stimuli through the HFS electrode while a second electrode at the contralateral arm served as control condition. Moreover, to test the efficacy of the HFS protocol we quantified changes in mechanical pinprick sensitivity before and after HFS of the skin surrounding both electrodes. The perceived intensity was collected for both electrical and mechanical stimuli