Behavioral (reaction time) and prefrontal cortex response revealed differences in grief vs. sadness perception

Research on basic emotions has expanded beyond the traditional six categories, identifying over 20 distinct emotional states. However, differentiating some emotions remained challenging due to partially overlapping facial expressions. Grief and sadness are two such emotions that are difficult to distinguish. This study investigated the behavioral and neural mechanisms of grief perception in the prefrontal cortex (PFC), comparing it with sadness. Participants categorized and rated emotional facial images in grief and sadness conditions on valence, arousal, and dominance scales. While participants perceiving emotional facial images prefrontal cortex (PFC) hemodynamic activities were measured using functional near-infrared spectroscopy (fNIRS). Explicit behavioral responses showed no significant differences, however implicit measures (reaction times) revealed distinctions between grief and sadness perception. Further fNIRS results indicated increased oxy-Hb in the right dorsolateral PFC for grief condition images compared to sadness condition images. Additionally, cultural differences were observed, with Asian participants showing higher oxy-Hb responses in the dorsal PFC for unpleasant facial stimuli in grief conditions. These findings support cultural variability in emotion perception and regulation. The combination of behavioral reaction time and neuroimaging data suggests distinct implicit perceptual and neural processing mechanisms for grief and sadness. This indicates separate automatic implicit mechanisms for these emotions.