Reassessing referred sensations following peripheral deafferentation and the role of cortical reorganisation

Abstract

Background Some amputees have been prominently reported to perceive touch applied to their face as coming from their phantom hand. These referred sensations have been classically interpreted as the perceptual correlate of cortical remapping of the face into the neighbouring missing- hand territory in primary somatosensory cortex (S1). We investigated whether referred sensations reports are associated with S1 remapping or can instead be attributed to demand characteristics (e.g., compliance, expectation, and suggestion), which were uncontrolled in previous studies. Methods Unilateral upper-limb amputees (N=18), congenital one-handers (N=19), and two-handers (N=20) were repeatedly stimulated with PC-controlled vibrations on ten body-parts and asked to report on each trial the occurrence of any concurrent sensations on their hand(s). To further manipulate expectations, we gave participants the suggestion that some of these vibrations had a higher probability to evoke referred sensations. To evaluate remapping, we analysed fMRI data in S1 from two tasks involving movement of facial and whole-body parts, using univariate and multivariate approaches. Results The frequency and distribution of reported referred sensations were similar across groups, with higher frequencies in the high expectancy condition. In amputees, referred sensations were evoked by stimulation of multiple body-parts and reported in both the intact and phantom hand. The group profiles for referred sensations reports were not consistent with the observed patterns of S1 remapping. Conclusions These findings weaken the interpretation of referred sensations as a perceptual consequence of post-amputation S1 remapping and reveal the need to account for demand characteristics when evaluating anomalous perceptual and germane phenomena.

Beyond body maps: Information content of specific body parts is distributed across the somatosensory homunculus

“…As such, these clinical reports are not incompatible with the alternative eventuality that the latent activity, which comprises the information content we are reporting, might also be functionally relevant. For example, multiple reports of “referred sensations” across body parts have been documented, either under lab-based manipulations ( Badde et al., 2019 ; Amoruso et al., 2021 ) or spontaneously (e.g., Katz and Melzack, 1987 ; Ramachandran et al., 1992 ; Borsook et al., 1998 ; Moore et al., 2000 ; McCabe et al., 2003 ; Soler et al., 2010 ). Distributing the content of information throughout S1 could allow for an increased number of combinations and patterns throughout body parts ( Hoffmann et al., 2018 ), which might be more ecologically relevant, considering that we rarely use body parts independently from each other.…”

Should bionic limb control mimic the human body? Impact of control strategy on bionic hand skill learning

“…Comparing pre-to post-training scores, all trained participants reported a significant increase of embodiment in body ownership ( W =84.0, p <0.001), and agency ( W =12.0, p <0.001), but not visual appearance ( W =137.0, p =0.132; BF 10 =0.48; Figure 2B). As subjective reports are particularly malleable to task demands ( 19 ), we also compared the training group to the untrained group (responding to the statements one week apart). This allowed us to confirm increased embodiment (post-minus pre-training ratings) in the trained groups relative to the untrained group [body ownership: W =263.0, p =0.045; agency: W =81.0, p <0.001; visual appearance: W =169.50, p<0.001; Figure 2C].…”

Hypnotic suggestion versus sensory modulation of bodily awareness

“…Hypnotic suggestion has also been used to influence various dimensions of self-awareness, including the sense of agency [34][35][36], mirror self-recognition [37], sex change delusion [38], and the sense of body ownership [39]. Some of these studies specifically target bodily awareness [40][41][42] or have used expectation manipulation to modulate body perception [43] but to our knowledge, hypnotic suggestion has not yet been systematically used to modify the relatively low-level property of body metrics.…”