N170 sensitivity to facial expression: A meta-analysis.

The N170 component is the most important electrophysiological index of face processing. Early studies concluded that it was insensitive to facial expression, thus supporting dual theories postulating separate mechanisms for identity and expression encoding. However, recent evidence contradicts this assumption. We conducted a meta-analysis to resolve inconsistencies and to derive theoretical implications. A systematic revision of 128 studies analyzing N170 in response to neutral and emotional expressions yielded 57 meta-analyzable experiments (involving 1645 healthy adults). First, the N170 was found to be sensitive to facial expressions, supporting proposals arguing for integrated rather than segregated mechanisms in the processing of identity and expression. Second, this sensitivity is heterogeneous, with anger, fear and happy faces eliciting the largest N170 amplitudes. Third, we explored some modulatory factors, including the focus of attention - N170 amplitude was found to be also sensitive to unattended expressions - or the reference electrode -common reference reinforcing the effects- . In sum, N170 is a valuable tool to study the neural processing of facial expressions in order to develop current theories.