Brain networks in human conscious visual perception

Abstract

Consciousness is not explained by a single mechanism, rather it involves multiple specialized neural systems overlapping in space and time. We hypothesize that synergistic, large-scale subcortical and cortical attention and signal processing networks encode conscious experiences. To identify brain activity in conscious perception without overt report, we classified visual stimuli as perceived or not using eye measurements. Report-independent event-related potentials and functional magnetic resonance imaging (fMRI) signals both occurred at early times after stimuli. Direct recordings revealed a novel thalamic awareness potential linked to conscious visual perception based on report. fMRI showed thalamic and cortical detection, arousal, attentional salience, task-positive, and default mode networks were involved independent of overt report. These findings identify a specific sequence of neural mechanisms in human conscious visual perception.

The neural activity of auditory conscious perception

“…By using this task in conjunction with large scale recordings from patients undergoing intracranial electroencephalography and through measuring neural activity by quantifying power in broadband gamma frequencies, we showed that a rapid progression of neural events closely followed a consciously perceived auditory stimulus; and that the scope of events associated with not-perceived stimuli is limited almost entirely to primary and other nearby early auditory cortex. Our findings expand the switch-and-wave model previously put forward by Herman, Smith 4 , and support more recent work done conducted with scalp EEG, fMRI and pupillometry 5 by adding two additional components: detect and pulse 47, 52, 56 . In this expanded model 6 , consciously perceived stimuli elicit a series of neural events: (1) detect : an initial activation of early sensory and other areas critical in the detection of incoming sensory stimuli (such as the frontal eye fields); (2) a pulse of activity originating from subcortical regions such as the thalamus; (3) a monophasic wave of activity that propagates from sensory regions to higher-order and association cortical regions and (4) the switch ing off of default-mode related regions.…”

“…Although the onset of this early sensory activity was consistent with the visual version of the task 4–5 , the dynamics of activation differed. Whereas in the visual task, gamma power in the primary visual areas showed an increase (<200 ms), followed by a decrease below baseline (200–600 ms), followed by a secondary increase (>600 ms), thus leading us to include the primary visual areas as a component of the ‘switch’, here we saw a sustained increase in early auditory regions.…”

“…This pulse began very shortly after the initial ‘detect’ signal in the early auditory regions and caudal middle frontal gyrus, and persisted until approximately 450 ms after stimulus onset. Previous work has shown that the intralaminar thalamus may be a key subcortical structure for arousal and consciousness 88, 89 ; and recent work in our lab has described an evoked potential in the thalamus (thalamic awareness potential [TAP]) and a BOLD signal consistent with TAP using the previously described visual analog of the current auditory task 5 . Our findings lend further evidence to a role of subcortical structures in conscious perception.…”

“…Although decades of research have studied the neural mechanisms underlying consciousness and perception 1 , the spatial and temporal dynamics of neural activity following consciously perceived sensory events remain incompletely understood. Previous findings from our laboratory and others have demonstrated that conscious perception is marked by activity in arousal and attention networks [2][3][4][5] and wide-spread activity that propagates from early sensory regions to higher order association regions of the cortex, as well as a downregulation of the default mode network 4,5 . Notably, the role of later, sustained activity in higher-order cortical regions is the subject of disagreement among consciousness researchers, and may be in part attributable to other task-related processes associated with perceptual report rather than conscious perception itself.…”

Decoding perceptual awareness across the brain with a no-report fMRI masking paradigm

“…66 In addition, although EEG and fMRI no-report paradigms have been previously used, the high spatial and temporal precision of intracranial recordings could provide valuable insights into the precise timing of conscious processing in the brain, including in the prefrontal cortex. 35,63,67 Specifically, methods with precise temporal resolution may help researchers differentiate between frontal activation associated with motor planning and execution, compared with other post-perceptual processes like decision-making, classification, memory, etc. Finally, other analysis methods, specifically representational similarity analysis, should be incorporated into no-report paradigms.…”