Is the frontal lobe involved in conscious perception?

Abstract

When studying the neural mechanisms underlying conscious perception we should be careful not to misinterpret evidence, and delineate these mechanisms from activity which could reflect the prerequisites or consequences of conscious experiences (Aru et al., 2012; de Graaf et al., 2012). However, at the same time, we need to be careful not to exclude any relevant evidence about the phenomenon. Recently, novel paradigms have attempted to dissociate activity related to conscious perception from activity reflecting its prerequisites and consequences. In particular, one of these studies focused on resolving the role of frontal lobe in conscious perception (Frassle et al., 2014). Through a clever experimental design that contrasted blood-oxygen-level-dependent (BOLD) activity elicited during binocular rivalry with and without behavioral reports, Frassle et al. (2014) suggested that frontal lobe, or a large part of it, may not be necessary for conscious perception per se. Rather frontal areas are involved in processing the consequences of conscious perception like monitoring the perceptual content in order to elicit the appropriate report of the subjective experience. In particular, Frässle et al. showed that behavioral reports of conscious experiences resulted in increased and more widespread activity of the frontal lobe compared to a condition without behavioral reports, where spontaneous transitions in the content of consciousness were estimated through the objective measures like optokinetic nystagmus (OKN) and pupil dilation. The authors of this study concluded that ldquo;frontal areas are associated with active report and introspection rather than with rivalry per serdquo;. Therefore activity in prefrontal regions could be considered as a consequence rather than a direct neural correlate of conscious experience. However, a previous study (Panagiotaropoulos et al., 2012) that measured directly neural activity in the macaque lateral prefrontal cortex (LPFC) using extracellular electrophysiological recordings could help to narrow down the role of frontal activity in conscious perception and exclude the contribution of cognitive or motor consequences in prefrontal neural activity during visual awareness. Specifically, the activity of feature selective neurons in the macaque LFPC was shown to be modulated in accordance with the content of subjective perception, without any confound from motor action (i.e. behavioral reports). Using binocular flash suppression (BFS), a paradigm of robust, externally induced perceptual suppression and without any requirement of behavioral reports, neurons in the LPFC were found to increase or decrease their discharge activity when their preferred stimulus was perceptually dominant or suppressed, respectively. Therefore, since neuronal discharges in the LPFC follow the content of conscious perception even without any motor action, the conclusion of Frassle et al. (2014) about the role of frontal lobe activity in rivalrous perception needs to be refined. Prefrontal activity can indeed reflec...

What Is Wrong with the No-Report Paradigm and How to Fix It

“…This result led to a flurry of controversy [17,18] in which different types of experiments seemed to differ in whether they showed prefrontal differences in perceptual transitions in a paradigm closely related to binocular rivalry. These results presented serious challenges to the conclusion just described.…”

“…These results presented serious challenges to the conclusion just described. In particular, prefrontal reflections of perceptual contents were decoded in a noreport experiment with monkeys using electrophysiological methods (electrodes inserted in cortical regions) that are known to be more sensitive to neural activations than the fMRI used in the result mentioned in the last paragraph [17]. Impressively, these results used monkeys that had not been trained on a discrimination task, ruling out covert decision-making that would have been expected to make a prefrontal difference (personal communication from Theofanis Panagiotaropoulos, the corresponding author of [17].).…”

“…In particular, prefrontal reflections of perceptual contents were decoded in a noreport experiment with monkeys using electrophysiological methods (electrodes inserted in cortical regions) that are known to be more sensitive to neural activations than the fMRI used in the result mentioned in the last paragraph [17]. Impressively, these results used monkeys that had not been trained on a discrimination task, ruling out covert decision-making that would have been expected to make a prefrontal difference (personal communication from Theofanis Panagiotaropoulos, the corresponding author of [17].). Later work in the same lab has been devoted to recording from grids of micro-electrodes ("Utah" arrays) placed in the prefrontal cortex of monkeys in a binocular rivalry setup with gratings in different directions, suggesting decoding of direction from prefrontal cortex [19,20].…”

Decoding the contents of consciousness from prefrontal ensembles

“…Its proponents among others have suggested that the neural substrates underlying conscious perception can be traced to a "posterior cortical hot zone", with PFC being primarily critical for processing the behavioral and cognitive consequences of conscious perception (24)(25)(26) like task demands and monitoring, introspection and motor reports, rather than consciousness per se (26)(27)(28)(29). For example, frontal cortex was found to be dramatically more active during motor reports, when blood-oxygen-level-dependent (BOLD) fMRI signal modulation was compared between reported and unreported spontaneous changes in the content of consciousness (27,30,31). Additionally, reduced frontal activation accompanied inconspicuous and unreportable switches in perception, when contrasted against a condition, where perceptual changes were easily discernible (29).…”

Can skeletomotor action integration occur without consciousness? Evidence from unconscious action inhibition

“…In conclusion, regarding neuroanatomy, our primary hypothesis is that consciousness is associated with what has traditionally been regarded as "perceptual" regions of the brain, a hypothesis that challenges some accounts of consciousness in which consciousness is associated with executive processes in frontal cortex (e.g., Boly et al 2011;Dehaene & Naccache 2001;Lau 2008;Panagiotaropoulos et al 2012;Safavi et al 2014;Velly et al 2007). Our secondary hypothesis is that olfactory consciousness can be constituted entirely by cortical circuits.…”