Abstract
Neuroimaging studies commonly associate dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex with conscious perception. However, such studies only investigate correlation, rather than causation. In addition, many studies conflate objective performance with subjective awareness. In an influential recent paper, Rounis and colleagues addressed these issues by showing that continuous theta burst transcranial magnetic stimulation (cTBS) applied to the DLPFC impaired metacognitive (subjective) awareness for a perceptual task, while objective performance was kept constant. We attempted to replicate this finding, with minor modifications, including an active cTBS control site. Using a between-subjects design for both DLPFC and posterior parietal cortices, we found no evidence of a cTBS-induced metacognitive impairment. In a second experiment, we devised a highly rigorous within-subjects cTBS design for DLPFC, but again failed to find any evidence of metacognitive impairment. One crucial difference between our results and the Rounis study is our strict exclusion of data deemed unsuitable for a signal detection theory analysis. Indeed, when we included this unstable data, a significant, though invalid, metacognitive impairment was found. These results cast doubt on previous findings relating metacognitive awareness to DLPFC, and inform the current debate concerning whether or not prefrontal regions are preferentially implicated in conscious perception.
Highlights
Many studies support the view that the lateral prefrontal cortex, as well as the posterior parietal cortex (PPC), are associated with conscious processes [1,2,3,4,5,6,7,8,9,10,11](See Bor & Seth, 2012; Dehaene & Changeux, 2011; Koch et al, 2016 for reviews)
In the Rounis paradigm no participants were excluded, in our study, for each group, subjects were excluded from the analysis if: i) in either of the two main experimental metacontrast masking blocks there were extreme signal detection theory (SDT) values for type I or 2 HR and FAR (0.95); ii) in either of the two main experimental metacontrast masking blocks accuracy was significantly below the 75% required: or iii) because of problems with the Transcranial Magnetic Stimulation (TMS) administration, for instance that the experimenter was unable to find an accurate active motor threshold (AMT)
We carried out two experiments to attempt to replicate Rounis and colleagues’ key finding that theta-burst TMS to dorsolateral prefrontal cortex (DLPFC) reduced metacognitive sensitivity [19]
Summary
Many studies support the view that the lateral prefrontal cortex, as well as the posterior parietal cortex (PPC), are associated with conscious processes [1,2,3,4,5,6,7,8,9,10,11](See Bor & Seth, 2012; Dehaene & Changeux, 2011; Koch et al, 2016 for reviews). The vast majority of these studies, employing neuroimaging techniques, are correlational, and are unable to test whether the prefrontal parietal network is causally implicated in conscious perception. Prefrontal and parietal lesion studies could in contrast demonstrate a causal relationship between this cortical network and consciousness. Such studies have produced more equivocal results, and tend to show at best subtle impairments in conscious detection [12, 13]. It is PLOS ONE | DOI:10.1371/journal.pone.0171793 February 13, 2017
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