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Free keywords:
Perceptual awareness, conscious somatosensory perception, fMRI, neural network, graph theory
Abstract:
Does stimulus awareness modulate the brain’s functional network topology? If network topologies have explanatory power beyond BOLD signal contrasts, they will serve as promising candidates for a neural account of awareness as suggested by the global workspace theory (Baars, 1988). We acquired sub-second fMRI data (TR=0.75s) while participants (N=38) had to report the perception of near-threshold electrical pulses applied at their left index finger and their confidence about this yes/no decision. Additionally there were supra-threshold and catch trials. To evaluate BOLD signal differences, we calculated general linear models with AFNI including stimulus condition specific regressors and response onset regressors. Individual whole-brain functional networks were constructed with the generalized psychophysiological interaction (gPPI; McLaren et al., 2012) between 264 brain-wide nodes (Power et al., 2011). The gPPI tests for context-modulated functional connectivity changes beyond local BOLD signal changes and baseline functional connectivity. The graph theoretical analysis of the connectivity matrixes was performed with the Brain Connectivity Toolbox (Rubinov & Sporns, 2010) to test for global changes of integration and segregation metrics. The BOLD contrast for confident misses and hits revealed several brain areas with a positive signal change across a frontal-parietal network. Interestingly confident misses compared to correct rejections (~97% of catch trials) showed different patterns: (a) early sensory and frontal areas (S1, S2, insula, IFG, & MCC) showed a larger signal for confident misses than correct rejections while (b) parietal areas (precuneus, IPL, & cerebellum) showed a lower signal for confident misses than correct rejections. Despite these activation differences the accompanying functional network alterations showed no graph analytical differences between confident hits, misses and correct rejections. The data shows that the BOLD signal correlates with conscious somatosensory perception in early sensory as well as frontal and parietal areas. Different from Godwin et al. (2015) who reported that visual stimulus awareness is accompanied by a decreased brain’s functional network modularity, somatosensory awareness does not alter the functional connectivity of whole-brain networks.
