Stimulus awareness is associated with secondary somatosensory cortex activation in an inattentional numbness paradigm.

Inattentional numbness, the somatosensory equivalent of inattentional blindness or deafness, was studied with fMRI in 44 participants who received weak electrical stimulation on the left hand while performing a demanding visual task. Half were told the tactile stimuli would be above detection threshold, half below. Ten participants did not consciously perceive the stimuli. Prior information did not significantly affect awareness. Awareness of stimuli increased activation in the contralateral secondary somatosensory cortex but not in the primary somatosensory cortex or frontoparietal areas. The results suggest that somatosensory awareness relies on higher somatosensory cortex areas and does not require strong activation in extended anterior or posterior networks seen when stimuli are task-relevant.

Study at a glance

Abstract

While inattentional blindness and deafness studies have revealed neural correlates of consciousness (NCC) without the confound of task relevance in the visual and auditory modality, comparable studies for the somatosensory modality are lacking. Here, we investigated NCC using functional magnetic resonance imaging (fMRI) in an inattentional numbness paradigm. Participants (N = 44) received weak electrical stimulation on the left hand while solving a demanding visual task. Half of the participants were informed that task-irrelevant weak tactile stimuli above the detection threshold would be applied during the experiment, while the other half expected stimuli below the detection threshold. Unexpected awareness assessments after the experiment revealed that altogether 10 participants did not consciously perceive the somatosensory stimuli during the visual task. Awareness was not significantly modulated by prior information. The fMRI data show that awareness of stimuli led to increased activation in the contralateral secondary somatosensory cortex. We found no significant effects of stimulus awareness in the primary somatosensory cortex or frontoparietal areas. Thus, our results support the hypothesis that somatosensory stimulus awareness is mainly based on activation in higher areas of the somatosensory cortex and does not require strong activation in extended anterior or posterior networks, which is usually seen when perceived stimuli are task-relevant.