The Encoding of Aversive Memories
Post by Megan McCullough
The takeaway
The encoding of aversive memories depends on the amygdala modulating activity in the hippocampus. Theta phases in the amygdala coordinate gamma activity and neuronal firing in the hippocampus which is critical to the formation of memories associated with emotional, aversive events.
What's the science?
Humans tend to have a stronger recall of emotional events compared to neutral events. Previous research has implicated the amygdala and the hippocampus in encoding emotional memories. Data has shown that the amygdala modulates emotional memory storage processes in the hippocampus but the mechanism behind this is unclear. This week in Nature Communications, Webb and colleagues investigate the relationship between the amygdala and the hippocampus in encoding emotional memories by simultaneously recording brain activity in the two regions during memory tasks.
How did they do it?
The authors recorded neural activity in both the amygdala and the hippocampus in participants while they performed an emotional memory task. Participants consisted of individuals with drug-resistant epilepsy, and they were assigned to be in one of two cohorts. The participants in Cohort 1 had recording electrodes measuring oscillatory activity in both brain regions during the emotional memory task. The participants in Cohort 2 had microelectrodes recording single neuron activity in the brain regions during the task. The recording of both brain waves and single neuron activity allowed researchers to analyze how activity in one region affects the other during the formation of emotional memories. The emotional memory task involved the participants viewing both neutral and emotional scenes and then performing a recognition memory task for the shown events.
What did they find?
Across both cohorts, the authors found that recall was enhanced for the emotional stimuli compared to the neutral stimuli. First, the authors looked at the brain activity associated with successful recall in the amygdala and hippocampus separately. The encoding of emotional memories was associated with gamma activity in the amygdala. This high-frequency neural activity was not found for successful recall of neutral scenes. In the hippocampus, the authors found that gamma activity was associated with successful recall for both emotional and neutral events. Next, the authors examined how this activity was coupled during memory formation. It was found that the amygdala influenced hippocampal theta oscillations, leading to gamma activity and neuronal firing in the hippocampus. This relationship was correlated with the encoding of emotional visual stimuli. Theta oscillations were transmitted from the amygdala to the hippocampus during the presentation of emotional scenes.
What's the impact?
This study found that the formation of memories of emotional but not of neutral stimuli is dependent on the relationship between brain activity in the amygdala and hippocampus. Theta activity in the amygdala leads to subsequent gamma activity and neuronal firing in the hippocampus. This research suggests that theta burst stimulation in the amygdala could improve memory.