Why Do We Remember Emotional Events Better?
Columbia Engineering neuroscientists have identified a neural mechanism in the human brain that tags information with emotional associations, enhancing memory. Their study, published on January 16, 2023, in Nature Human Behaviour, demonstrates that high-frequency brain waves in the amygdala (involved in emotional processes) and the hippocampus (involved in memory processes) are essential for enhancing memory for emotional stimuli. Disruptions to this neural mechanism, caused by either electrical brain stimulation or depression, impair memory specifically for emotional stimuli.
The Prevalence of Memory Disorders
The rising prevalence of memory disorders such as dementia has highlighted the damaging effects of memory loss on individuals and society. Disorders like depression, anxiety, and PTSD can also feature imbalanced memory processes and have become increasingly prevalent during the COVID-19 pandemic. Understanding how the brain prioritizes certain information for storage could provide critical insight into developing new therapeutic approaches for memory enhancement or normalization.
Investigating Neural Mechanisms in Humans
Most studies of neural mechanisms are conducted on animals due to the need for direct brain access to record activity and perform experiments. However, studying complex cognitive phenomena like emotional memory enhancement is difficult in animals. To address this, researchers analyzed data from epilepsy patients undergoing intracranial brain recording for seizure localization and treatment. During these recordings, patients memorized lists of words while electrodes placed in their hippocampus and amygdala recorded brain activity.
Brain-Wave Patterns and Emotional Memory
The researchers systematically characterized the emotional associations of each word using crowd-sourced emotion ratings. They found that participants remembered emotional words (e.g., “dog,” “knife”) better than neutral words (e.g., “chair”). High-frequency neural activity (30-128 Hz) was more prevalent in the amygdala-hippocampal circuit when participants remembered emotional words. This pattern was absent when participants remembered neutral words or failed to remember a word. Analyzing data from 147 patients, researchers found a clear link between enhanced memory for emotional words and the prevalence of high-frequency brain waves across the amygdala-hippocampal circuit.
Electrical Stimulation and Emotional Memory
To establish causality, the researchers analyzed a subset of patients who performed the memory task while direct electrical stimulation was applied to the hippocampus for half of the words. They found that electrical stimulation consistently impaired memory specifically for emotional words and diminished high-frequency activity in the hippocampus. This provided causal evidence that stimulation selectively diminished emotional memory by disrupting the brain activity pattern correlated with it.
Depression and Emotional Memory
The researchers also hypothesized that depression, which involves dysregulated emotional memory, might act similarly to brain stimulation. They analyzed patients’ emotional memory in parallel with mood assessments and observed that patients with depression showed a concurrent decrease in emotion-mediated memory and high-frequency activity in the hippocampus and amygdala.
Future Research Directions
Qasim, now a postdoctoral researcher at the Icahn School of Medicine at Mt. Sinai, is investigating how individual neurons fire during emotional memory processes. Qasim and Jacobs hope their work will inspire further research exploring how high-frequency activity is linked to norepinephrine, a neurotransmitter related to attentional processes. Future research may target high-frequency activity in the amygdala-hippocampal circuit to strengthen and protect memory, particularly emotional memory.
Conclusion
“Our emotional memories are one of the most critical aspects of the human experience, informing everything from our decisions to our entire personality,” said Qasim. “Any steps we can take to mitigate their loss in memory disorders or prevent their hijacking in psychiatric disorders is hugely exciting.”
Story Source: Materials provided by Columbia University School of Engineering and Applied Science [Link]. Original written by Holly Evarts. Content may be edited for style and length.