Subcortical correlates of consciousness with human single neuron recordings

Summary Current methods to investigate the neural correlates of consciousness aim at contrasting the neural activity associated with different percepts under constant sensory stimulation to identify the minimal set of neuronal events sufficient for a specific conscious percept to occur (1–2). Much of this research has relied on subjective reports from humans to define conscious percepts (3), but only very few studies have found such contrasts at the single neuron level (4–8) and only in cortical regions of the human brain. The role of subcortical structures for perceptual consciousness is theoretically relevant (2,9,10) with some empirical support from detection studies in non-human primates (11,12), as well as functional imaging or local field potentials in humans (13,14). Nonetheless, it remains unknown whether and how the firing rate of subcortical neurons changes when a stimulus is consciously perceived. Here, we recorded individual neurons from the subthalamic nucleus (STN) and thalamus of human participants during 36 deep brain stimulation surgeries. While participants detected vibrotactile stimuli provided at the perceptual threshold, we found that neurons in both subcortical structures were modulated by the onset of the task or of the stimulus. Importantly, we found that 23% of the recorded neurons changed their activity when a stimulus was consciously perceived. Our results provide direct neurophysiological evidence of the involvement of subcortical structures in conscious detection with subjective reports, thereby calling for a less cortico-centric view of the neural correlates of consciousness.