Conclusions

So, what did we learn from this study?

Our question was, which networks are affected when a brain injury causes REM sleep behavior disorder? Or, in other words, what areas of the brain are part of a "team" within the brain that includes the injured area?

In discussing this, we will call the area of a patient's brain that received a brain injury "area A". When talking about the same area of the brain on a healthy individual, we will also call that area of the brain "area A". Each patient with RBD has a different injured area, but all correspond with an area of the brain that is also found on healthy, non-injured individuals.

We found that the areas highlighted in green are positively functionally connected to the areas of the brain that received the injury ("area A"). That means, in a healthy brain, when "area A" is active, all the green areas are also active. However, in the brains of the individuals with RBD that we studied, "area A" was injured, which will affect all the other areas that are green.

Additionally, the areas highlighted in red are negatively functionally connected to the areas of the brain that received the injury ("area A"). That means, in a healthy brain, when "area A" is active, all the red areas are not active. However, in the brains of the individuals with RBD that we studied, "area A" was injured, which will affect all the other areas that are red.

So, we found that three main areas were also active when "area A" was active: namely, the brainstem and cerebellum (bottom of the brain), the anterior cingulate gyrus (front/middle of the brain), and the left insula. This is interesting because previous studies have connected unusual activity in the anterior cingulate gyrus to other disorders, such as depression (Lichenstein et al., 2016), insomnia (Yan et al., 2018), and anorexia nervosa (Kaye et al., 2000). Since RBD is a disorder that, like insomnia and many cases of depression, involves sleep disturbance, it makes sense that it would also be related to this region (American Psychiatric Association, 2013).

The front half of the insula allows us to pay attention to our internal processes, such as focusing on our breathing, our heart beating, or the feeling of food in our belly (Price & Carole, 2018; Wang et al., 2019). Finally, the brainstem and cerebellum, responsible for basic bodily processes such as breathing, sleep, posture, and walking, were also highly connected to the "area A" of the individuals with RBD (Basinger & Hogg, 2022; Jimsheleishvili & Dididze, 2022).

Additionally, we found that two areas that were not active when "area A" was active were the primary sensory and motor cortices, which are situated right on the top of the brain (where one might pat their head). These areas are mainly responsible for controlling our movements and sensing the world around us, especially through touch (Yip & Lui, 2022; Raju & Tadi, 2021). It makes sense that these areas would be negatively related to "area A", because, in a healthy individual, there is little movement during deep sleep. That means that the brain has to "turn off" our motor control to keep us still while we sleep. It is likely that "area A" is involved in "turning off" motor control during sleep. So, in REM behavior disorder, when "area A" is damaged, there is no one around to turn off the motor control, and so motor control stays on, making these individuals very active during their deep sleep.

Cover photo by Kelly Sikkema on Unsplash