Baseline brain activity fluctuations predict somatosensory perception in humans

Abstract

In perceptual experiments, within-individual fluctuations in perception are observed across multiple presentations of the same stimuli, a phenomenon that remains only partially understood. Here, by means of thulium-yttrium/aluminum-garnet laser and event-related functional MRI, we tested whether variability in perception of identical stimuli relates to differences in prestimulus, baseline brain activity. Results indicate a positive relationship between conscious perception of low-intensity somatosensory stimuli and immediately preceding levels of baseline activity in medial thalamus and the lateral frontoparietal network, respectively, which are thought to relate to vigilance and "external monitoring." Conversely, there was a negative correlation between subsequent reporting of conscious perception and baseline activity in a set of regions encompassing posterior cingulate/precuneus and temporoparietal cortices, possibly relating to introspection and self-oriented processes. At nociceptive levels of stimulation, pain-intensity ratings positively correlated with baseline fluctuations in anterior cingulate cortex in an area known to be involved in the affective dimension of pain. These results suggest that baseline brain-activity fluctuations may profoundly modify our conscious perception of the external world.

Fig. 1.

Neural correlates of somatosensory stimuli awareness. Consciously perceived stimuli compared with unperceived intensity-matched stimuli were associated with greater activity in bilateral dorsolateral prefrontal (DLPF) and intraparietal sulcus/posterior parietal cortex (IPS) activity (yellow-red sections) (A) and less activity in a network encompassing bilateral posterior cingulate precuneas (Pr), mesiofrontal cortices (MF), temporoparietal junctions (TP), right inferior temporal (IT), and left superior frontal gyri (SF) (blue sections) (B). Results are of a 24-subject group analysis displayed at uncorrected P < 0.001.

Fig. 2.

Baseline brain activity predicting conscious perception of subsequent somatosensory stimuli. (A) Increased baseline brain activity in the medial thalamus (Th), dorsolateral prefrontal cortex (DLPF), intraparietal sulcus/posterior parietal cortex (IPS), and aACC 3 sec before stimulus presentation predicts perception of low-intensity sensory stimuli. (B) Decreased baseline activity in the default brain network encompassing posterior cingulate/precuneus (Pr) and bilateral temporoparietal junctions (TP) exerts a facilitatory effect upon perception of subsequent somatosensory stimuli. Contrasts are thresholded at an uncorrected P value of <0.001 on a canonical MR template. Color scales refer to T values of individual voxels. (C) Effect size (i.e., mean and standard deviation of the parameters estimates for baseline effect) in peak voxels of aACC, intraparietal sulcus (IPS), and middle frontal gyrus (DLPF) before stimuli subsequently rated as perceived (P1) or unperceived (P0). ∗, Significant difference between baseline effect sizes thresholded at a P value corrected for multiple comparisons of <0.05.

Fig. 3.

Baseline brain activity predicting subsequent pain-intensity ratings. High baseline activity in the pain-related pACC and insula (Ins) predicts a sensation of higher pain intensity in response to painful-range laser stimuli. Results reflect a 24-subject group analysis masked by pain-intensity-related areas contrasted with the first analysis, thresholded at an uncorrected P value of <0.001, and displayed on a canonical MR template. Color scale refers to T values of individual voxels.