Imperceptible Somatosensory Stimulation Alters Sensorimotor Background Rhythm and Connectivity

Abstract

Most sensory input to our body is not consciously perceived. Nevertheless, it may reach the cortex and influence our behavior. In this study, we investigated noninvasive neural signatures of unconscious cortical stimulus processing to understand mechanisms, which (1) prevent low-intensity somatosensory stimuli from getting access to conscious experience and which (2) can explain the associated impediment of conscious perception for additional stimuli. Stimulation of digit 2 in humans far below the detection threshold elicited a cortical evoked potential (P1) at 60 ms, but no further somatosensory evoked potential components. No event-related desynchronization was detected; rather, there was a transient synchronization in the alpha frequency range. Using the same stimulation during fMRI, a reduced centrality of contralateral primary somatosensory cortex (SI) was found, which appeared to be mainly driven by reduced functional connectivity to frontoparietal areas. We conclude that after subthreshold stimulation the (excitatory) feedforward sweep of bottom-up processing terminates in SI preventing access to conscious experience. We speculate that this interruption is due to a predominance of inhibitory processing in SI. The increase in alpha activity and the disconnection of SI from frontoparietal areas are likely correlates of an elevated perception threshold and may thus serve as a gating mechanism for the access to conscious experience.

Evidence‐based source modeling of nociceptive cortical responses: A direct comparison of scalp and intracranial activity in humans

“…The PCC activity observed here developed concomitantly, and peaked after the conscious detection of nociceptive stimuli by participants (i.e., later than their motor responses), and this was also the case in intracranial EEG studies (Bastuji et al, ), which is consistent with a possible contribution to stimulus awareness, or to its modulation and further cognitive processing such as memory encoding. Concordant with this view, subjective reports of touch in the absence of actual somatosensory stimulation were shown to result in activation of a network comprising the posterior cingulate and precuneus together with medial frontal cortex (Lloyd et al, ), while subliminal, imperceptible somatosensory stimulation resulted in decreased functional connectivity between somatosensory and PCC cortices as compared to rest (Nierhaus et al, ). However, PCC activation is absent from many neuroimaging studies of pain, and PCC deactivations (i.e., a decrease in BOLD signal) have been reported, for example, in response to painful punctate stimuli, in the context of hyperalgesia (Iannetti et al, ), or in the development of wind‐up pain (Perrotta et al, ).…”

Effect of imperceptible vibratory noise applied to wrist skin on fingertip touch evoked potentials - an EEG study

“…; Nierhaus et al. ) and is representative of stimulation strength which in this study was constant between the vibration‐on and ‐off conditions. While perithreshold stimuli can evoke varying amplitudes of the early component potentially due to variability in neuronal firing and the amplitudes are associated with awareness (Auksztulewicz and Blankenburg ), the present study used a suprathreshold stimulus that may be less affected by variability in neuronal firing.…”

Sensorimotor Rhythm Neurofeedback Enhances Golf Putting Performance

“…Differences between these two levels of cognitive processing are reflected at the neurophysiological level: participants who were in the automatic stage exhibited weaker activity of the bilateral cerebellum, presupplementary motor area, premotor cortex, parietal cortex, and prefrontal cortex compared with novices (Wu, Chan, & Hallett, 2008). In addition, the somatosensory cortex has been related to conscious perception of somatosensory stimuli (Nierhaus et al, 2015), such that lower activity in the somatosensory cortex might be a signature of reduced conscious involvement in movement execution, as is frequently observed in highly skilled performers.…”