PSYCH 013: Immune–Brain Interactions in Psychiatry

The brain does not operate in isolation from the body’s defence systems. This chapter explores the evolving understanding of how the immune system and the brain interact - not only in illness, but as part of normal regulation of mood, behaviour, and cognition.In this episode, we examine how immune signalling molecules, particularly cytokines, influence brain function. These signals can alter neurotransmission, neural plasticity, and circuit activity - effectively shifting how the brain processes information.We explore the concept of “sickness behaviour” - a coordinated response to inflammation characterised by fatigue, low mood, reduced motivation, and social withdrawal. While adaptive in acute illness, similar patterns may become maladaptive when immune activation is prolonged or dysregulated.This provides a powerful framework for understanding aspects of depression, as well as emerging links between inflammation and other psychiatric conditions. The boundary between physical and mental illness becomes increasingly blurred - revealing shared biological pathways.This chapter invites a reframing of psychiatric symptoms: not solely as disorders of the brain, but as states influenced by systemic processes - where the immune system becomes an active participant in shaping experience.Key Takeaways* The immune system and brain interact through signalling molecules such as cytokines.* Immune activation can influence neurotransmission, plasticity, and neural circuits.* “Sickness behaviour” reflects adaptive responses that can resemble depressive symptoms.* Chronic or dysregulated inflammation may contribute to psychiatric disorders.* The distinction between physical and mental illness is increasingly blurred.* Immune–brain interactions offer new perspectives on mechanisms and treatment targets.* Psychiatry must consider systemic biology, not just brain-specific processes. This is a public episode. If you'd like to discuss this with other subscribers or get access to bonus episodes, visit drmanaankarray.substack.com/subscribe