We don’t think about spleens much these days, but ancient Greeks viewed the spleen as the arbiter of melancholy and happiness. Today’s scientists know that the spleen is an important part of the immune system, an armory where immune cells pick up antigens. If an antigen is recognized as an enemy (like a previously encountered virus), antibodies are sent off to battle. 

The spleen is controlled by the autonomic nervous system, which also triggers the fight-or-flight response. But it’s also getting commands from higher up: the brain itself.

In a recent study, scientists identified the “brain-spleen axis,” a pathway linking the midbrain to the spleen that enables the brain to directly regulate immune function.

Researchers removed nerves from the spleens of mice, then injected the mice with antigens that should produce the immune cells that trigger antibody release. Without brain-spleen communication, immune cell production shut down. Two brain regions sent the bulk of these signals: the central nucleus of the amygdala, and the paraventricular nucleus of the thalamus. 

Both regions activate when we’re stressed and regulate production of stress-related hormones. When mice were placed in stressful situations (like standing on a high, transparent platform), stress hormones released from the brain slowed down antibody production in the spleen.

If this brain-spleen axis also exists in humans, it raises an exciting possibility: by strategically activating certain brain regions through behavioral intervention or noninvasive stimulation, we may be able to boost immune function. 

Ancient Greek physicians weren’t quite right, but they were on to something: the brain and the body (yes, even the spleen) are in constant communication, and we’re just beginning to understand their language.