Abstract
Ongoing, 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. We 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. Active 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. Active 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. TACS 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.
Highlights
There is a wide range of evidence across multiple sensory modalities that spontaneous, ongoing neural oscillations in the alpha band – 8–13 Hz – have a direct role in perception and determining which stimuli are detected and which missed (e.g., Busch et al, 2009; Chaumon and Busch, 2014; Craddock et al, 2017; Ergenoglu et al, 2004; Neuling et al, 2012)
We found that detection of peri-threshold tactile stimuli was predicted from alpha power in a period shortly before stimulus onset
We examined the effects of 10 Hz transcranial alternating current stimulation over centro-parietal regions on performance of the Somatic Signal Detection Task
Summary
There is a wide range of evidence across multiple sensory modalities that spontaneous, ongoing neural oscillations in the alpha band – 8–13 Hz – have a direct role in perception and determining which stimuli are detected and which missed (e.g., Busch et al, 2009; Chaumon and Busch, 2014; Craddock et al, 2017; Ergenoglu et al, 2004; Neuling et al, 2012). Much of this evidence is necessarily correlative, based on observations recorded using magneto- or electroencephalography (M/ EEG). Modulation of alpha oscillations using tACS influences detection of visual targets phasically (Helfrich et al, 2014), consistent with the pattern found previously in the absence of tACS stimulation (e.g., Mathewson et al, 2009, 2011; VanRullen et al, 2011)
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