Rapid Processing of Invisible Fearful Faces in the Human Amygdala.
Level 4 - case-series / case-control
Observational intracranial electrophysiological study in human surgical patients
PubMed 36690451 · doi:10.1523/JNEUROSCI.1294-22.2022
What was done
Researchers recorded intracranial electroencephalography (iEEG) responses directly from the amygdala and multiple cortical regions (early visual areas, fusiform gyrus, and parahippocampal gyrus) in human subjects of both sexes. Participants viewed backward-masked, consciously invisible faces displaying fearful, happy, or neutral emotions, as well as spatial-frequency-filtered face stimuli (low spatial frequency components).
What was found
The amygdala showed a short-latency intracranial event-related potential (iERP) beginning 88 ms post-stimulus that was selectively evoked by invisible fearful faces compared to invisible happy or neutral faces. This iERP demonstrated selectivity for the low spatial frequency (LSF) component of fearful faces. Time-frequency analysis identified an even earlier amygdala low-gamma band response to LSF fearful faces starting at 45 ms post-stimulus. In contrast, these rapid responses were absent in early visual areas, fusiform gyrus, and parahippocampal gyrus.
Why it matters
This provides direct human electrophysiological evidence for a rapid subcortical visual pathway to the amygdala that processes threat-related facial signals independently of conscious awareness and preceding cortical activation.
Limits
The abstract does not state the sample size (n is unspecified) or clinical details of the patient population (typically individuals with drug-resistant epilepsy). The anatomical subcortical route itself is inferred from response latencies rather than directly mapped or recorded.