Neuroanatomical correlates of the perception of body axis orientation during body tilt: a voxel-based morphometry study

Abstract

Accurate perception of the orientations of the body axis and gravity is essential for actions. The ability to perceive these orientations during head and body tilt varies across individuals, and its underlying neural basis is unknown. To address this, we investigated the association between inter-individual differences in local gray matter (GM) volume and inter-individual differences in the ability to estimate the directions of body longitudinal axis or gravity during whole-body tilt using voxel-based morphometry (VBM) analysis in 50 healthy adults (20-46 years, 25 men and 25 women). Although no anatomical regions were identified relating to performance requiring estimates of gravitational direction, we found a significant correlation between the GM volume in the right middle occipital gyrus and the ability to estimate the body axis orientation. This finding provides the first evidence on neuroanatomical substrates of the perception of body axis orientation during body tilt.

Figure 1

Adjustment errors in the No-OKS conditions at each tilt position for the subjective visual body axis (SVBA) and subjective visual vertical (SVV) tasks. Gray-colored lines represent the averaged error of each participant, and black-colored lines represent errors averaged across all participants. LSD left-side-down, RSD right-side-down.

Figure 2

Effect of optokinetic stimulation (OKS-effect) on adjustment errors in the SVBA or SVV tasks. Gray-colored lines represent averaged values of each participant, and black-colored bars represent errors averaged across all participants. As illustrated, both SVBA and SVV were biased toward the rotation direction of OKS. CW clockwise, CCW counterclockwise.

Figure 3

Brain region showing the significant correlation between gray matter (GM) volume and SVBA performance. The significant clusters are superimposed on the axial (left), coronal (center), and sagittal slices (right) of the standardized anatomical image. A color bar represents the t value. The GM volume in the right middle occipital gyrus (peak MNI coordinate x = 35, y =  − 86, z = 6; t = 5.85; cluster size = 31 voxels) was significantly positively correlated with the TE values in the SVBA task (p < 0.05 FWE-corrected at the voxel and cluster levels).

Figure 4

Schematic illustration of each spatial orientation task and visual stimuli. (A) Participants were asked to align the visual line (denoted as red lines) along the perceived direction of the body longitudinal axis (SVBA task) or gravitational vertical (SVV task). Adjustment errors in each task (denoted as arrows) were calculated as the angular bias of the subjective directions of body longitudinal axis or vertical (solid lines) from the objective directions (dotted lines). (B) Illustration of the visual stimuli on the display as seen by the participants in the optokinetic stimulation (OKS) conditions. Many dots were randomly positioned around the visual line, and they rotated uniformly clockwise (CW) or counterclockwise (CCW) around the center of the display during the SVBA or SVV tasks.