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BackgroundOngoing, pre-stimulus oscillatory activity in the 8-13 Hz alpha range has been shown to correlate with both true and false reports of peri-threshold somatosensory stimuli. However, to directly test the role of such oscillatory activity in behaviour, it is necessary to manipulate it. Transcranial alternating current stimulation (tACS) offers a method of directly manipulating oscillatory brain activity using a sinusoidal current passed to the scalp.ObjectiveWe tested whether alpha tACS would change somatosensory sensitivity or response bias in a signal detection task in order to test whether alpha oscillations have a causal role in behaviour.MethodsActive 10 Hz tACS or sham stimulation was applied using electrodes placed bilaterally at positions CP3 and CP4 of the 10-20 electrode placement system. Participants performed the Somatic Signal Detection Task (SSDT), in which they must detect brief somatosensory targets delivered at their detection threshold. These targets are sometimes accompanied by a light flash, which could also occur alone.ResultsActive tACS did not modulate sensitivity to targets but did modulate response criterion. Specifically, we found that active stimulation generally increased touch reporting rates, but particularly increased responding on light trials. Stimulation did not interact with the presence of touch, and thus increased both hits and false alarms.ConclusionstACS stimulation increased reports of touch in a manner consistent with our observational reports, changing response bias, and consistent with a role for alpha activity in somatosensory detection.

Objective High symptom reporting (HSR) and medically unexplained symptoms (MUS) are associated with considerable distress, disability, healthcare utilization and costs, but are poorly understood, and current treatments are of limited benefit. Most models of HSR and MUS implicate cognitive-perceptual factors, such as increased body-focused attention, reduced perceptual thresholds and a tendency to experience somatic misperception, but little is known about the causal role of these variables. We investigated this issue by studying whether there is a longitudinal relationship between perceptual-attentional variables and later clinical outcomes in primary care patients. Method Primary care patients (N = 102) completed clinical (physical symptom reporting, health anxiety and healthcare utilization) and perceptual-attentional (body-focused attention, perceptual threshold, somatic misperception) measures at baseline and then again six months later (N = 72). Hierarchical regression was used to examine cross-lagged relationships between baseline and follow-up scores. Results Contrary to expectation, attending away from the body at baseline predicted increased not decreased symptom reporting six months later. Neither perceptual threshold nor somatic misperception predicted clinical outcomes at six months. Conclusions These findings suggest that body avoidance, rather than increased body focus, contribute to the development of HSR. Future studies should consider the potential clinical benefits of reducing bodily avoidance, via techniques that promote adaptive engagement with bodily sensations.

Fluctuations of pre-stimulus oscillatory activity in the somatosensory alpha band (8-14 Hz) observed using human EEG and MEG have been shown to influence the detection of supra- and peri-threshold somatosensory stimuli. However, some reports of touch occur even without a stimulus. We investigated the possibility that pre-stimulus alpha oscillations might also influence these false reports of touch known as tactile misperceptions. We recorded EEG while participants performed the Somatic Signal Detection Task (SSDT), in which participants must detect brief, peri-threshold somatosensory targets. We found that pre-stimulus oscillatory power in the somatosensory alpha range exhibited a negative linear relationship with reporting of touch at electrode clusters over both contralateral and ipsilateral somatosensory regions. As pre-stimulus alpha power increased, the probability of reporting a touch declined; as it decreased, the probability of reporting a touch increased. This relationship was stronger on trials without a somatosensory stimulus than on trials with a somatosensory stimulus, although was present for both trial types. Spatio-temporal cluster-based permutation analysis also found that pre-stimulus alpha was lower on trials when touch was reported irrespective of whether it was present over contralateral and ipsilateral somatosensory cortices, as well as left frontocentral areas. We argue that alpha power may reflect changes in response criterion rather than sensitivity alone. Low alpha power relates to a low barrier to reporting a touch even when one is not present, while high alpha power is linked to less frequent reporting of touch overall. © 2017 Elsevier Ltd

Mood can bias the judgements people make about themselves and how people compare themselves to others. However, it is not yet clear whether mood also affects appearance-based self-evaluations and social comparisons. Given the importance of perceived health status for well-being, we investigated the effect of mood on self-image and social comparisons of healthiness during two versions of a face health judgement task. Thirty participants judged how they felt compared to healthy and unhealthy looking versions of their own (self version) and a stranger's face (stranger version), after a positive, negative and neutral mood induction. The effect of mood was dependent on self/stranger task order. Although mood did not affect face health judgement for participants who initially judged themselves against their own face, it did affect face health judgement for participants who initially judged themselves in comparison to a stranger's face. After the positive and negative mood inductions, these participants judged themselves as equivalent to healthier/unhealthier looking versions of their own and stranger's faces, respectively. Thus, social comparisons of facial healthiness could provide a perceptual measure of state well-being.