Individual Variation in Amygdala Connectivity

Post by Deborah Joye

What's the science?

The amygdala is a part of the brain most known for its role in aggression and fear. Amygdala function is affected in many psychiatric illnesses including post-traumatic stress disorder, anxiety, depression, and phobias. Most in-depth studies of the amygdala in humans measure brain signals averaged across a group of individuals to determine the location and connections of the amygdala. While this approach has helped us to better understand the amygdala in general, it has limited our ability to tailor treatment of amygdala dysfunction to individual patients. This week in PNAS, Sylvester and colleagues use extensive functional magnetic resonance imaging (fMRI) of individuals to characterize three functional subdivisions of the amygdala and their specific patterns of connectivity with other networks in the brain.

How did they do it?

The authors analyzed over 5 hours of fMRI data per individual from 10 individuals to determine different amygdala subdivisions based on activity patterns within the amygdala and associated activity in other cortical regions. The authors then used both group-averaged and individualized data to demonstrate that group-averaged analyses can obscure the specific locations of amygdala regions and mask their functional patterns. The authors compared their amygdala subregions from the individualized dataset against a much larger independent dataset to understand whether amygdala subdivisions and their connectivity patterns were roughly consistent across people. Finally, the authors investigated possible differences in the timing of activity across the amygdala and other cortical networks to investigate whether individual differences exist in the timing of amygdala-cortex connectivity.

What did they find?

The authors characterized three subdivisions of the amygdala that are roughly consistent across individuals with some differences in spatial location. The authors also found that each subdivision of the amygdala had its own unique connections to other brain networks and that the magnitude of these connections varied from person to person. One subdivision was anatomically superior and preferentially connected to the default mode network, a widespread neural network important for reflecting on the self and others, as well as thinking of the past and future. This amygdala connection’s role could be to integrate important environmental information with an individual’s past history regarding the emotional significance of that stimuli. Another subdivision was anatomically medial in most people and preferentially connected to the dorsal attention network which is active during attention-demanding tasks. This amygdala connection’s role might be the top-down modulation of attention networks.

The last subdivision was anatomically ventral and did not show a preferential connection to a specific neural network but had connectivity properties that were shared across the rest of the amygdala. When the authors compared these findings with a larger, publicly available dataset they found similar amygdala subdivisions, but the selectivity of each subdivision for particular neural networks was much weaker compared to individual analyses. Lastly, the authors found that the timing of activity between amygdala subdivisions and other neural networks was consistent across both datasets, suggesting that though location and magnitude of amygdala connections may vary from person to person, the networks themselves are consistent.

What's the impact?

This study is the first to use extensive fMRI from individuals to demonstrate that three distinct subdivisions of the amygdala are roughly consistent across people, but with important individual variation in location and magnitude of connectivity. The study also revealed that subdivisions of the amygdala can have preferential connectivity with specific neural networks, providing a framework for a more detailed understanding of how the amygdala interacts with other brain regions in individual patients. These findings could lead to improvements in personalized psychiatry and potential therapeutics for amygdala dysfunction.

Sylvester et al., Individual-specific functional connectivity of the amygdala: A substrate for precision psychiatry, PNAS (2020). Access the original scientific publication here.