# Impairment of unconscious emotional processing after unilateral medial temporal structure resection

## TL;DR

The study shows that removing one side of the brain's medial temporal structures, including the amygdala, impairs unconscious emotional processing.

## Contribution

The study provides behavioral evidence for the amygdala's causal role in unconscious emotional processing.

## Key findings

- Positive emotional primes enhanced target valence ratings more when presented to the intact hemisphere.
- Emotional processing was impaired when stimuli were presented to the hemisphere with the resected amygdala.
- Results support the amygdala's role in unconscious emotional processing.

## Abstract

The role of the amygdala in unconscious emotional processing remains a topic of debate. Past lesion studies have indicated that amygdala damage leads to impaired electrodermal activity in response to subliminally presented emotional stimuli. However, electrodermal activity can reflect both emotional and nonemotional processes. To provide behavioral evidence highlighting the critical role of the amygdala in unconscious emotional processing, we examined patients (n = 16) who had undergone unilateral resection of medial temporal lobe structures, including the amygdala. We utilized the subliminal affective priming paradigm in conjunction with unilateral visual presentation. Fearful or happy dynamic facial expressions were presented in unilateral visual fields for 30 ms, serving as negative or positive primes. Subsequently, neutral target faces were displayed, and participants were tasked with rating the valence of these targets. Positive primes, compared to negative ones, enhanced valence ratings of the target to a greater extent when they stimulated the intact hemisphere (i.e., were presented in the contralateral visual field of the intact hemisphere) than when they stimulated the resected hemisphere (i.e., were presented in the contralateral visual field of the resected hemisphere). These results suggest that the amygdala is causally involved in unconscious emotional processing.