The face-specific N170 component is modulated by emotional facial expression

Abstract

Background: According to the traditional two-stage model of face processing, the face-specific N170 event-related potential (ERP) is linked to structural encoding of face stimuli, whereas later ERP components are thought to reflect processing of facial affect. This view has recently been challenged by reports of N170 modulations by emotional facial expression. This study examines the time-course and topography of the influence of emotional expression on the N170 response to faces.

Methods: Dense-array ERPs were recorded in response to a set (n = 16) of fear and neutral faces. Stimuli were normalized on dimensions of shape, size and luminance contrast distribution. To minimize task effects related to facial or emotional processing, facial stimuli were irrelevant to a primary task of learning associative pairings between a subsequently presented visual character and a spoken word.

Results: N170 to faces showed a strong modulation by emotional facial expression. A split half analysis demonstrates that this effect was significant both early and late in the experiment and was therefore not associated with only the initial exposures of these stimuli, demonstrating a form of robustness against habituation. The effect of emotional modulation of the N170 to faces did not show significant interaction with the gender of the face stimulus, or hemisphere of recording sites. Subtracting the fear versus neutral topography provided a topography that itself was highly similar to the face N170.

Conclusion: The face N170 response can be influenced by emotional expressions contained within facial stimuli. The topography of this effect is consistent with the notion that fear stimuli exaggerates the N170 response itself. This finding stands in contrast to previous models suggesting that N170 processes linked to structural analysis of faces precede analysis of emotional expression, and instead may reflect early top-down modulation from neural systems involved in rapid emotional processing.

Figure 1

Sample stimuli used to elicit face N170 responses in (A) the neutral condition, and (B) the fear condition.

Figure 2

Polar presentation of channel locations in the 128 channel Geodesic sensor net. The 18 occipital-temporal channels used in the statistical analyses are highlighted in green for (A) the right hemisphere, and (B) the left hemisphere. Channels used to illustrate the time-course of the ERP effect (see Figure 3) are indicated in red.

Figure 3

Timecourse (in milliseconds) of the ERP face response (in microvolts) for the fear and neutral facial affect conditions, diplayed for (A) left occipital-temporal channel 65, and (B) right occipital-temporal channel 91.

Figure 4

Polar projections of spherical spline interpolations of the voltage topography (in microvolts) 170 milliseconds following the onset of the face stimulus for three conditions: (A) fear, (B) neutral, (C) fear minus neutral.