Facial-expression and gaze-selective responses in the monkey amygdala

Area of Science:

• Neuroscience
• Primate Social Behavior
• Facial Recognition

Background:

• Social behavior in primates depends on recognizing individuals, expressions, and gaze.
• The neural basis for processing combined facial cues (expression, gaze) remains unclear.

Purpose of the Study:

• To investigate whether facial expression and gaze direction are processed jointly or independently in the primate brain.
• To identify specific neural structures involved in processing these distinct facial dimensions.

Main Methods:

• Used functional Magnetic Resonance Imaging (fMRI) to measure brain activity (BOLD response) in awake macaques.
• Presented macaques with diverse monkey facial stimuli (expressions, gaze directions) and control images.
• Correlated neural activity with independent behavioral measures of arousal.

Main Results:

• Widespread activation in the superior temporal sulcus, inferotemporal cortex, and amygdala observed.
• Distinct activation patterns within the amygdala were linked to expression (threatening vs. appeasing) and gaze direction (averted vs. directed).
• Central nucleus and bed nucleus of the stria terminalis showed heightened activity for averted gaze, correlating with increased arousal.

Conclusions:

• Facial expression and gaze direction are processed by partially segregated neural pathways.
• The amygdala plays a crucial role in differentiating emotional expressions and gaze cues.
• Specific amygdalar nuclei are involved in processing threat-related expressions and attention/arousal related to gaze direction.