The human amygdala parametrically encodes the intensity of specific facial emotions and their categorical ambiguity.
Level 4 - case-series / case-control
Small observational study combining case-series (lesion patients), exploratory fMRI, and invasive single-unit recordings in surgical patients
PubMed 28429707 · doi:10.1038/ncomms14821
What was done
Investigated amygdala processing of emotional facial expressions using three converging methods: behavioural assessment of 3 patients with focal amygdala lesions, fMRI BOLD neuroimaging in 19 healthy adults, and intracranial single-neuron recordings in 9 neurosurgical patients evaluated on facial expressions ranging in fear, happiness, and categorical ambiguity.
What was found
The abstract reports no numerical values or statistical effect sizes. Patients with amygdala lesions demonstrated a shift in behavioural sensitivity to fear. Amygdala BOLD responses in healthy adults were modulated by both fear intensity and emotion ambiguity. Single-unit recordings revealed two distinct neuronal populations: one whose firing correlated with the degree of fear or happiness, and another whose firing decreased linearly as categorical ambiguity increased.
Why it matters
Provides single-neuron evidence in humans that the amygdala independently tracks both the graded intensity of specific facial emotions and the categorical uncertainty of the expression.
Limits
Sample sizes were very small across all subgroups (n = 3 lesion patients, n = 9 intracranial recording patients, n = 19 neuroimaging participants). The abstract provides no quantitative statistical metrics, confidence intervals, or effect sizes. Electrophysiological findings were obtained from neurosurgical patients, whose underlying clinical conditions could potentially affect neural function.