Social inclusion enhances biological motion processing: a functional near-infrared spectroscopy study

Abstract

Humans are especially tuned to the movements of other people. Neural correlates of this social attunement have been proposed to lie in and around the right posterior superior temporal sulcus (STS) region, which robustly responds to biological motion in contrast to a variety of non-biological motions. This response persists even when no form information is provided, as in point-light displays (PLDs). The aim of the current study was to assess the ability of functional near-infrared spectroscopy (fNIRS) to reliably measure brain responses to PLDs of biological motion, and determine the sensitivity of these responses to interpersonal contextual factors. To establish reliability, we measured brain activation to biological motion with fNIRS and functional magnetic resonance imaging (fMRI) during two separate sessions in an identical group of 12 participants. To establish sensitivity, brain responses to biological motion measured with fNIRS were subjected to an additional social manipulation where participants were either socially included or excluded before viewing PLDs of biological motion. Results revealed comparable brain responses to biological motion using fMRI and fNIRS in the right supramarginal gyrus. Further, social inclusion increased brain responses to biological motion in right supramarginal gyrus and posterior STS. Thus, fNIRS can reliably measure brain responses to biological motion and can detect social experience-dependent modulations of these brain responses.

Figure 1

Visual depiction of the experimental paradigm for the fNIRS session (top) and fMRI session (bottom). Each block of biological (bio) and scrambled motion consisted of a 24-second point-light video clip. The fNIRS session consisted of three runs of 10 PLD videos, presented at baseline, post-inclusion, and post-exclusion. The fMRI session consisted of one run of 12 PLD videos.

Figure 2

Activation to biological > scrambled motion measured with functional MRI (top left) and functional NIRS (collapsed across conditions; top right) in an identical group of 12 participants. Functional MRI activation is displayed on a Talairach-transformed template brain depicting functional activation in the plane x = 54 projected onto a smoothed surface map. Functional NIRS activation is displayed on a template brain normalized to MNI space. Functional MRI results were assessed at a corrected threshold of α < .05. Functional NIRS results were assessed at a threshold of p < .05. An example of normalized recording channel placement in MNI space for one participant is shown on the bottom left, while the outline of pixels used in the group analysis (where 11 or more participants had functional data) is shown on the bottom right.

Figure 3

Activation to biological > scrambled motion in each experimental condition and in the contrast of post-inclusion > post-exclusion, measured with functional NIRS. Activation is displayed on a template brain normalized to MNI space, and assessed at a threshold of p < .05.

Figure 4

Activation in participant-specific structurally defined regions of superior temporal sulcus measured with functional NIRS. Average responses to biological motion in each condition 6-16 seconds post-stimulus onset are depicted in the top bar graph. Waveforms depict brain responses to biological motion (middle panel, top) and scrambled motion (middle panel, bottom) in each condition. Average responses to biological > scrambled motion (calculated for each participant, then averaged across the group) in each condition 6-16 seconds post-stimulus onset are depicted in the bottom bar graph. All bars depict standard error, stimulus onset and offset are at 3 and 27 seconds, respectively. * denotes significance at p < .01, while † denotes significance of p = .05.