  The amygdala is assumed to contribute to a bottom-up attentional bias during
visual processing of emotional faces. Still, how its response to emotion
interacts with top-down attention is not fully understood. It is also unclear
if amygdala activity and scalp EEG respond to emotion and attention in a
similar way. Therefore, we studied the interaction of emotion and attention
during face processing in oscillatory gamma-band activity (GBA) in the amygdala
and on the scalp. Amygdala signals were recorded via intracranial EEG (iEEG) in
10 patients with epilepsy. Scalp recordings were collected from 19 healthy
participants. Three randomized blocks of angry, neutral, and happy faces were
presented, and either negative, neutral, or positive expressions were denoted
as targets. Both groups detected happy faces fastest and most accurately.
During attention to negative faces, low GBA (< 90 Hz) increased specifically
for angry faces both in the amygdala and over posterior scalp regions, albeit
earlier on the scalp (60 ms) than in the amygdala (130 ms). From 220 ms,
amygdala high GBA (117.5-145 Hz) was additionally persistently increased for
both angry and neutral compared to happy faces. When neutral faces served as
targets, amygdala high GBA (105-122.5 Hz) was higher for emotional than neutral
faces from 160-320 ms. Attention to positive faces did not result in a
differentiation between facial expressions. Present data reveal that
attention-independent emotion detection in amygdala high GBA may only occur
during a neutral focus of attention. Top-down threat vigilance coordinates
widespread GBA, biasing stimulus processing in favor of negative faces. These
results are in line with a multi-pathway model of emotion processing and help
specify the role of GBA in this process by revealing how attentional focus can
tune timing and amplitude of emotional GBA responses.
