title: 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.
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany, Max-Planck-Institute for Human Cognitive and Brain Sciences, Department of Neurology, 04303 Leipzig, Germany, Mind-Brain Institute and Berlin School of Mind and Brain, Charité and Humboldt-University, 10117 Berlin, Germany, till.nierhaus@charite.de.
authors: Till
authors: http://orcid.org/0000-0003-0906-592X
authors: T
authors: Nierhaus
authors: Max-Planck-Institute for Human Cognitive and Brain Sciences, Department of Neurology, 04303 Leipzig, Germany, Department of Psychology, University of Leipzig, 04109 Leipzig, Germany, and.
authors: Norman
authors: http://orcid.org/0000-0003-2525-7059
authors: N
authors: Forschack
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors: Sophie K
authors: http://orcid.org/0000-0002-0147-8992
authors: SK
authors: Piper
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors: Susanne
authors: S
authors: Holtze
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany, Center for Stroke Research Berlin, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors: Thomas
authors: T
authors: Krause
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany, Center for Stroke Research Berlin, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors: Birol
authors: B
authors: Taskin
authors: Max-Planck-Institute for Human Cognitive and Brain Sciences, Department of Neurology, 04303 Leipzig, Germany.
authors: Xiangyu
authors: X
authors: Long
authors: Max-Planck-Institute for Human Cognitive and Brain Sciences, Department of Neurology, 04303 Leipzig, Germany.
authors: Johannes
authors: J
authors: Stelzer
authors: Max-Planck-Institute for Human Cognitive and Brain Sciences, Department of Neurology, 04303 Leipzig, Germany, Mind-Brain Institute and Berlin School of Mind and Brain, Charité and Humboldt-University, 10117 Berlin, Germany.
authors: Daniel S
authors: DS
authors: Margulies
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany, Center for Stroke Research Berlin, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors: Jens
authors: http://orcid.org/0000-0002-8632-6225
authors: J
authors: Steinbrink
authors: Berlin Neuroimaging Center and Department of Neurology, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany, Max-Planck-Institute for Human Cognitive and Brain Sciences, Department of Neurology, 04303 Leipzig, Germany, Mind-Brain Institute and Berlin School of Mind and Brain, Charité and Humboldt-University, 10117 Berlin, Germany, Center for Stroke Research Berlin, Charité Universitätsmedizin Berlin, 10117 Berlin, Germany.
authors: Arno
authors: A
authors: Villringer
mesh_terms: D000328:Adult; D000344:Afferent Pathways / Q000098:blood supply* / Q000502:physiology; D001931:Brain Mapping; D004558:Electric Stimulation; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood; D010507:Periodicity; D011930:Reaction Time; D013003:Somatosensory Cortex / Q000098:blood supply* / Q000502:physiology*; D055815:Young Adult
chemical_list: D010100:Oxygen
keywords: EEG background rhythms; fMRI; functional connectivity; somatosensory evoked potentials; subthreshold electrical stimulation; unconscious