A groundbreaking study from Harvard Medical School has uncovered a previously unknown role of thyroid hormone in shaping brain circuits and driving exploratory behavior. This research, published in the journal Cell, provides new insights into how this crucial hormone influences both the brain and body, potentially shedding light on certain psychiatric conditions.
The study, conducted in mice, demonstrates that thyroid hormone alters brain wiring in a way that motivates animals to explore their environment. This discovery could help explain the link between thyroid disorders and mood changes in humans, offering new avenues for understanding and treating conditions like depression and bipolar disorder.
Unraveling the Brain-Body Connection
Thyroid hormone has long been known to regulate various bodily functions, including metabolism, heart rate, and growth. However, its effects on the brain have remained largely mysterious until now.
Lead author Daniel Hochbaum, a research fellow in neurobiology at Harvard Medical School, explained the significance of their findings: “It’s well known that thyroid hormone modulates metabolism, and now we’ve shown that it also modulates exploratory behaviors through direct action on the brain.”
The researchers found that thyroid hormone acts on neuronal circuits in the cortex by activating various genes, effectively rewiring brain cells. When they increased thyroid hormone levels in the mouse cortex, the animals became more willing to explore their environment and take risks. Conversely, blocking the hormone’s action in the cortex prevented changes in exploratory behavior based on thyroid hormone levels.
Synchronizing Brain and Body for Survival
This discovery raises an intriguing question: Why would a hormone that controls metabolism also alter brain circuits affecting behavior? To answer this, the team examined field studies of various mammals, including lemurs and squirrel monkeys.
These studies revealed that thyroid hormone levels and metabolic rates tended to be higher during warmer seasons when food and resources were more abundant. Coincidentally, animals also explored more during these periods.
Bernardo Sabatini, senior author of the study and professor of neurobiology at Harvard Medical School, summarized their conclusion: “It seems like thyroid hormone prompts the body to tell the brain to go explore and capture resources.”
This coordination between brain and body could be an evolutionary adaptation, allowing animals to maximize their chances of survival and reproduction when conditions are favorable.
Why it matters: Understanding the link between thyroid hormone, brain function, and behavior could have significant implications for human health and well-being. Thyroid disorders affect millions of people worldwide, often leading to mood disturbances and cognitive issues. This research provides a potential explanation for these symptoms and could pave the way for new treatment approaches.
Moreover, the study’s findings might help explain the biological basis of certain psychiatric conditions. As Hochbaum noted, “The thought is that these conditions are also shaping exploratory activity, so perhaps manipulating thyroid hormone to change brain circuits will reveal relevant points of entry for treatment.”
The research team is now exploring the potential long-term effects of psychological trauma on thyroid hormone levels in humans. They are studying individuals in Indonesia who experienced the 2004 tsunami to investigate whether the trauma led to lasting changes in thyroid function.
While the study was conducted in mice, the researchers believe that a similar brain-body connection likely exists in humans. In fact, a 2024 study by the same team found a correlation between higher thyroid hormone levels and increased employment rates and work hours in U.S. adults.
As research in this area continues, it may open up new possibilities for treating mood disorders and other psychiatric conditions by targeting thyroid hormone pathways in the brain. However, it’s important to note that more studies, particularly in humans, will be needed to fully understand the implications of these findings and develop potential therapies.
The study was supported by various funding sources, including the Burroughs Wellcome Fund, the Baszucki Brain Research Fund, and the National Institutes of Health, underscoring the importance of this research in the scientific community.
