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  • Writer's pictureMatt Barraza

Can a barrier explain a connection between psychological and physiological health?

An important aspect in staying healthy can be maintaining a positive attitude. They seem to go hand in hand. When I have a good night's sleep, a quality meal and exercise, I feel energized. Maybe you have experienced the inverse, where skipping a snack or sitting on the couch all day left you feeling gross. Further, have you ever been sick and started to reminisce on times you did not have a stuffy nose or feel sore? Even after getting over a flu, you might feel tired or sad in the days that follow.

When the body is fighting an infection or out of balance, both external and internal stimuli can affect how you feel. During healthy times, you can interact with others and receive positive social cues. In contrast, social isolation can cause changes at the DNA level in immune cells and could cause unwanted inflammation. Researchers have found that leukocytes, the cells responsible for infection and foreign invasion in the body, turn on genes involved in activating your immune system during isolation. Given the pandemic we all just went through, this external cue example couldn’t be more relevant. Yet, connecting immune system function to how our brains work can be a black box. Like a puzzle, neuroscientists are trying to gain new insight from multiple angles.

One component related to neurologic health inside your body that is studied by neuroscientists is the Blood-Brain Barrier, or BBB for short. The BBB is a structure made up in the capillaries of your brain by multiple cell types. Together endothelial cells, pericytes and astrocytes form a barrier structure that insulates the tissue of your brain from anything circulating in your “outside”(peripheral) blood.

Figure 1: The components of the Blood-Brain Barrier (BBB). (Image: Lombardo et al., 2020)

When the BBB is leaky or has lost barrier integrity, outside molecules can cross when they aren’t supposed to (red to yellow in Figure 1). This is particularly a problem when those molecules can cause increased inflammation and dysfunction. Not surprisingly, across diseases (Alzheimer’s, Depression, Anxiety, COVID-19, Hypertension) there is evidence the BBB becomes more leaky.

Additionally, I think it’s also worth exploring how psychiatric disorders can cause behavioral changes often associated with a sick and immune activated state. Like when we have a cold, it’s thought we have an evolutionarily conserved response of physical isolation. Wanting to not go out when you're sick was a way we prevented spreading the infection to our peers long before vaccines existed. In comparison, when a person is suffering from depression, one symptom can also be self isolation. Interestingly, two brain regions commonly associated with reward and memory, the ventral striatum and hippocampus, may be less connected as a result of increased inflammation. Would this explain the altered connectivity also seen in psychiatric disorders? Could a leaky BBB be to blame for all this?

I think the main takeaway from this post should be the feedback mechanism at play within your body. When I take the time to take care of my mental health, I’m also making my body less susceptible to infection and inflammation. Conversely, when I get plenty of sleep, eat well and exercise, I can boost my mood. Finally, there is evidence that depression may be associated with patients battling long term diseases normally not thought of as having a cognition component, such as breast cancer. A literature review found multiple studies associated depression with cancer recurrence and mortality (both all-cause and cancer-specific). As evidence mounts, I think it’s important to convey the importance of mental health and to talk to a doctor if you or someone you know is experiencing any depressive symptoms, even if they may seem irrelevant to the current health status.

Matt Barraza is a neuroscientist and researcher at Northwestern University. He is currently pursuing his PhD in developmental neuroscience as part of Northwestern’s Driskill Graduate Program in Life Sciences.


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