Feel the Noise: Relating Individual Differences in Auditory Imagery to the Structure and Function of Sensorimotor Systems

Abstract

Humans can generate mental auditory images of voices or songs, sometimes perceiving them almost as vividly as perceptual experiences. The functional networks supporting auditory imagery have been described, but less is known about the systems associated with interindividual differences in auditory imagery. Combining voxel-based morphometry and fMRI, we examined the structural basis of interindividual differences in how auditory images are subjectively perceived, and explored associations between auditory imagery, sensory-based processing, and visual imagery. Vividness of auditory imagery correlated with gray matter volume in the supplementary motor area (SMA), parietal cortex, medial superior frontal gyrus, and middle frontal gyrus. An analysis of functional responses to different types of human vocalizations revealed that the SMA and parietal sites that predict imagery are also modulated by sound type. Using representational similarity analysis, we found that higher representational specificity of heard sounds in SMA predicts vividness of imagery, indicating a mechanistic link between sensory- and imagery-based processing in sensorimotor cortex. Vividness of imagery in the visual domain also correlated with SMA structure, and with auditory imagery scores. Altogether, these findings provide evidence for a signature of imagery in brain structure, and highlight a common role of perceptual-motor interactions for processing heard and internally generated auditory information.

Keywords: auditory imagery; auditory processing; fMRI; supplementary motor area; voxel-based morphometry.

Figure 1.

Association between gray matter volume and vividness of auditory imagery. (A) Cluster with peak in left SMA showing a significant positive correlation with vividness of auditory imagery in whole-brain analysis. Statistical maps were thresholded at P < 0.005 peak-level uncorrected, cluster corrected with a FWE correction (P < 0.05). (B) Scatterplot showing the association between vividness ratings and adjusted gray matter volume within the cluster depicted in (A).

Figure 2.

Brain regions in which BOLD responses were modulated by sound type during the processing of heard auditory information. The dotted dark red circle denotes a 12-mm sphere centered at the peak of the SMA cluster where the amount of gray matter was shown to correlate with auditory imagery (VBM study); this sphere was used for the representational similarity analysis looking at the links between representational specificity of heard sounds and vividness of imagery. For visualization purposes, activation maps were thresholded at P < 0.005 peak-level uncorrected (full details of activated sites are presented in Table 2).

Figure 3.

Association between lower representational similarity of functional responses to different types of heard sounds in SMA (i.e., higher specificity/fidelity) and higher reported vividness of auditory imagery.

Figure 4.

Association between vividness of visual and auditory imagery. Higher vividness corresponds to higher ratings for auditory and visual imagery.