The amygdala (magenta) connects to other regions deep within the brain (brown, green). These overlap with nerve fibres of other regions regulating hormones, movement and vision (orange, pink, dark blue, light blue). The connection between these pathways is stronger in people who are better at processing and recognising fearful faces. Image credit: McFadyen et al. 2019 (CC BY 4.0)
Being able to quickly detect and respond to potential threats is essential for survival. Fear and threat trigger a range of responses in the body, which are controlled by different regions in the brain. For example, a structure located deep within the brain called the amygdala is connected to other parts of the brain that regulate hormones, senses and muscles. The amygdala is highly responsive to signs of threat, and research in rodents has shown that it plays a role in transmitting sounds that indicate danger. However, so far it has remained unclear if this was also the case for visual information.
This is particularly challenging to study in humans because it has been difficult to image the deeper regions in the human brain. Now, McFadyen et al. reconstructed the pathways between the deeper brain regions important for processing vision and the amygdala using the brain scans of 622 participants. Then, they tested whether there was any connection between these pathways and the ability to recognise emotional expressions. To do so, fMRI brain scanning was used to measure the blood flow in the brain of volunteers looking at 40 faces that were either happy, sad, angry, fearful or neutral.
The results showed that when people were looking at pictures of fearful and angry faces, the blood flow between visual areas and the amygdala increased, especially in individuals with stronger connections, such denser nerve fibres, between the involved regions. The denser those fibres were, the better the people were at recognising when a face was fearful.
These discoveries suggest that the amygdala also plays a role in transmitting signals from deep-brain visual areas indicating danger and is likely to be one of the first areas to trigger a fear response in the brain. People with autism respond less to fearful faces, while people with anxiety respond more. Future research could investigate if the pathways to the amygdala differ in these people.
