Abstract
Accumulating evidence indicates that control mechanisms are not tightly bound to conscious perception since both conscious and unconscious information can trigger control processes, probably through the activation of higher-order association areas like the prefrontal cortex. Studying the modulation of control-related prefrontal signals in a microscopic, neuronal level during conscious and unconscious neuronal processing, and under control-free conditions could provide an elementary understanding of these interactions. Here we performed extracellular electrophysiological recordings in the macaque lateral prefrontal cortex (LPFC) during monocular physical alternation (PA) and binocular flash suppression (BFS) and studied the local scale relationship between beta (15–30 Hz) oscillations, a rhythmic signal believed to reflect the current sensory, motor, or cognitive state (status-quo), and conscious or unconscious neuronal processing. First, we show that beta oscillations are observed in the LPFC during resting state. Both PA and BFS had a strong impact on the power of this spontaneous rhythm with the modulation pattern of beta power being identical across these two conditions. Specifically, both perceptual dominance and suppression of local neuronal populations in BFS were accompanied by a transient beta desynchronization followed by beta activity rebound, a pattern also observed when perception occurred without any underlying visual competition in PA. These results indicate that under control-free conditions, at least one rhythmic signal known to reflect control processes in the LPFC (i.e., beta oscillations) is not obstructed by local neuronal, and accordingly perceptual, suppression, thus being independent from temporally co-existing conscious and unconscious local neuronal representations. Future studies could reveal the additive effects of motor or cognitive control demands on prefrontal beta oscillations during conscious and unconscious processing.
Highlights
According to a traditionally held view suggesting that control functions are bound to consciousness (Norman and Shallice, 1986), it is reasonable to assume that conscious perception of sensory cues is a prerequisite for their integration into a control function
We examined the temporal dynamics of beta oscillatory power in the lateral prefrontal cortex (LPFC) during conscious and unconscious stimulus processing using binocular flash suppression (BFS), a paradigm of rivalrous visual stimulation that dissociates conscious perception from purely sensory stimulation, and compared it with the respective dynamics during monocular physical alternation (PA) of the same visual patterns
Since such peaks or bumps in the Local field potential (LFP) power spectrum are indicative of dominant, frequency-specific, intrinsic rhythmic activity, these results show that beta oscillations represent a dominant resting-state rhythm in the LPFC
Summary
According to a traditionally held view suggesting that control functions are bound to consciousness (Norman and Shallice, 1986), it is reasonable to assume that conscious perception of sensory cues is a prerequisite for their integration into a control function. The impact of these subliminal stimuli in control is rather small compared to conscious signals, the observed effects suggest that control processes are not strictly conscious but can be detected across a wide spectrum of conscious and unconscious processing. These observations suggest that control and consciousness are, to a considerable degree, separable functions (Hommel, 2007, 2013; van Gaal et al, 2012) and a similar dissociation should be expected for their respective neuronal correlates. The source of the N2 ERP component has a frontal origin (van Gaal et al, 2008) which is in accordance with the activation of inferior frontal gyrus during unconscious inhibitory control and other control-related tasks affected by unconscious information as determined by functional magnetic resonance imaging (fMRI) or intracranial EEG www.frontiersin.org
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