Donguibogam's view of the heart as the monarch of the mind and its statement that excessive thinking damages the heart and spleen offer a remarkably insightful explanation from the perspective of modern neuroscience and endocrinology. When we commonly feel that we have too many thoughts, what is actually happening in the brain?
It enters a state of cognitive overload. The frontal lobe of the brain, particularly the prefrontal cortex, oversees higher-order cognitive functions such as thinking, planning, decision-making, and emotional regulation. When rumination—the phenomenon of constantly repeating negative thoughts or anxious scenarios—intensifies, this prefrontal cortex becomes excessively activated, just like a factory operating relentlessly even in the middle of the night.
Such hyperactivation continuously stimulates our body's stress response system, namely the hypothalamic-pituitary-adrenal axis. When the hypothalamic-pituitary-adrenal axis is activated, the stress hormone cortisol is secreted in excess. While cortisol may enhance concentration in the short term, chronic secretion can exert toxicity on the brain. In particular, it can induce atrophy of neurons in the hippocampus, which is responsible for memory and learning, and fuel hyperactivation of the amygdala, which plays an important role in emotional regulation, thereby deepening anxiety and depression.
Furthermore, excessive thinking disrupts the balance of neurotransmitters such as serotonin, dopamine, and GABA. Serotonin regulates mood and sleep, dopamine is involved in reward and motivation, and GABA functions to calm brain activity. An imbalance among them can lead to impaired concentration, sleep disorders, emotional instability, and even physical fatigue. The part in Donguibogam about damaging the spleen can be explained in modern terms via the gut-brain axis, the close connection between the brain and the gut. Stress directly affects intestinal motility and the gut microbiota environment, which can trigger symptoms such as indigestion or irritable bowel syndrome.
Consequently, the state of having too many thoughts is an important issue that goes beyond mere fatigue to cause structural and functional changes in the brain and adversely affect systemic health. The symptoms referred to as mental fatigue or burnout in modern society can be seen as occurring precisely within this context. This is why the wisdom of Donguibogam deeply resonates with the lives of modern people across thousands of years.
