Mirror Neurons (MNs) constitute a system for matching action observation and execution and for recognising socially meaningful gesticulation. Here we explored the possibility that this system also contributes to emotional processing. To test this hypothesis, a novel affective startle paradigm was developed to investigate MNs and emotional processing.

Fifty healthy participants completed a startle experiment where they were presented with 36 emotionally valenced pictures equally split into positive, negative and neutral categories. All pictures were preceded by emotionally congruent primes, half of which consisted of a videoclip showing a biologically meaningful hand-object interaction and half that consisted of a control stimulus showing static images of the interaction. Acoustic startle probes were presented during picture viewing at 2.5, 3, 3.5, 4 and 4.5 second intervals and startle eyeblink responses were recorded.

Startle amplitude was magnified only for emotionally negative pictures. This effect was present when the images were preceded by a prime containing biological motion but not a static prime. This result was found for startle probes presented at 2.5s, but not at longer intervals.

The MN system is involved in emotional processing, as shown by modulation of the startle reflex when a negative picture is primed with emotionally congruent biological motion. Further, this modulation occurs only when the time interval between picture presentation and startle probe is relatively short, suggesting that the MN system may provide an early warning of threat-related actions.