Time course of superior temporal sulcus activity in response to eye gaze: a combined fMRI and MEG study

Abstract

The human superior temporal sulcus (STS) has been suggested to be involved in gaze processing, but temporal data regarding this issue are lacking. We investigated this topic by combining fMRI and MEG in four normal subjects. Photographs of faces with either averted or straight eye gazes were presented and subjects passively viewed the stimuli. First, we analyzed the brain areas involved using fMRI. A group analysis revealed activation of the STS for averted compared to straight gazes, which was confirmed in all subjects. We then measured brain activity using MEG, and conducted a 3D spatial filter analysis. The STS showed higher activity in response to averted versus straight gazes during the 150-200 ms period, peaking at around 170 ms, after stimulus onset. In contrast, the fusiform gyrus, which was detected by the main effect of stimulus presentations in fMRI analysis, exhibited comparable activity across straight and averted gazes at about 170 ms. These results indicate involvement of the human STS in rapid processing of the eye gaze of another individual.

Fig. 1

Illustrations of stimuli.

Fig. 2

(A) Statistical parametric map showing STS activity for averted vs straight gazes identified in a group analysis. The activation is overlaid on the spatially normalized anatomical MRI of the mean brain of the subjects. (B) The grand average current intensity of STS activity. The arrowhead indicates the peak of interest at about 170 ms. A shaded time zone with an asterisk indicates a significant difference in the mean intensity between averted and straight gazes (P < 0.05). (C) Mean (with SEM) peak amplitudes of STS at about 170 ms from stimulus onset.

Fig. 3

(A) Statistical parametric map showing FG activity for the main effect of stimulus presentations identified in a group analysis. The activation is overlaid on the spatially normalized anatomical MRI of the mean brain of the subjects. (B) The grand average current intensity of FG activity. The arrowhead indicates the peak of interest at about 170 ms. (C) Mean (with SEM) peak amplitudes of FG at about 170 ms from stimulus onset.

Fig. 4

(A) Statistical parametric map of a representative single subject showing STS and FG activity for averted vs straight gazes and main effect of stimulus presentations, respectively. The activation is overlaid on a corresponding spatially normalized anatomical MRI. (B) Representative current intensity of STS and FG activity in a single subject.