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Why can’t a scarecrow make correct decisions?
Adrenaline is a hormone secreted in the human body when one is under threat. It causes breathing and heart rate to increase, preparing the body for “fight or flight.” In The Da Vinci Code, Professor Langdon, who suffers from claustrophobia, occasionally feels surges of adrenaline when he is in an elevator. After reading Dan Brown’s novel, what I remember most clearly is this word—adrenaline. At the time, it was a completely new concept to me, representing science and knowledge. Since then, whenever I read literary works, I often encounter the term “adrenaline,” which shows how much writers, like myself, are drawn to it.
From cutting-edge scientific research to everyday language, there is always a time lag. Adrenaline took more than a century—from its discovery and synthesis in the late 19th century—to enter popular literature such as Dan Brown’s works. That is quite a long time. While we were still excited by the novelty of the word “adrenaline,” science had already moved on to a close relative—dopamine—which began to appear frequently and gain prominence in the latter half of the 20th century. This time, I vowed not to let dopamine take another hundred years to be widely understood. So I decided to write about dopamine.
Dopamine is a neurotransmitter in the brain that helps transmit signals and regulate emotions. Although its discoverer, the Swedish scientist Arvid Carlsson, along with two other scientists, was awarded the Nobel Prize in Physiology or Medicine, dopamine’s philosophical significance may be even greater than its scientific one.
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1. Emotion and reason: what distinguishes humans from other primates
As a child, before I understood the definitions of reason and emotion, I once wrote in my notebook: emotion is a wild horse, and reason is the reins that guide it. Only later did I realize that this metaphor originates from Western philosophers.
Plato believed that emotion and reason were like two horses pulling a chariot side by side. The horse of reason is noble and refined, while the horse of emotion is wild and unruly. The charioteer—the human mind—must constantly restrain the wild horse so that the chariot can move forward properly. According to Plato and other classical thinkers, what distinguishes humans from animals is reason. In this framework, reason and emotion form a binary opposition, with reason at the center, while emotion is suppressed or marginalized.
This line of thought continued through later philosophers. Although Aristotle, Plato’s student, often disagreed with his teacher on other matters—emphasizing observation and experience over abstract forms—he largely shared a similar view on emotion and reason: that human flourishing depends on reason guiding and regulating emotion.
Descartes introduced a dualistic framework, proposing that humans consist of mind and body, with the mind governing the body. As the “father of modern philosophy,” he advocated using mathematical reasoning in philosophy, believing that rationality is more reliable than emotion.
Later thinkers such as Bacon, Jefferson, and Kant largely followed this rationalist tradition. However, philosophers like Hegel and Nietzsche introduced new perspectives, arguing against strict dualism and emphasizing that opposing elements are interconnected and interdependent rather than separable.
Freud, however, in some sense returned to a dualistic view. In his theory, the mind is composed of conflicting parts. At the center lies the id, representing human desires; above it is the ego, representing conscious self-awareness and rational control. The ego suppresses the impulses of the id, channeling instinctual drives into socially acceptable behavior. In this sense, the relationship between the id and the ego resembles Plato’s charioteer and wild horse. The goal of psychoanalysis, in Freud’s view, is to strengthen the ego and enhance its ability to control the id.
Only Heidegger and Derrida clearly broke away from this tradition, arguing that our understanding of the world arises from the integration of reason and emotion rather than their separation.
Freudian psychoanalysis once flourished and gained great popularity, but over time it gradually declined in influence because many of its core ideas lacked empirical scientific support. Concepts such as the id, ego, and the Oedipus complex have been largely replaced by modern neuroscience studies of specific brain regions.
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In the 1980s, a patient underwent surgery to remove a tumor near the cortex of the frontal lobe. After the operation, he seemed like a completely different person. He began to meticulously consider every detail without end, yet still could not make decisions. Tasks that once took minutes now required hours and still remained unfinished. He had previously held a good job but ultimately lost his career, finances, and family due to his inability to make decisions. Another notable characteristic was that he behaved like a scarecrow—emotionless and unresponsive to stimuli.
Before this, rooted in traditional philosophical views, scientists explained the human brain in layers:
1. The brainstem at the base controls vital functions such as heartbeat, breathing, and body temperature.
2. Above it, the diencephalon regulates hunger and sleep cycles.
3. The limbic system governs emotions such as desire, aggression, and impulsive behavior.
4. At the top lies the prefrontal cortex, considered the seat of reason, intelligence, and moral judgment. This final layer was thought to represent rational control over the lower layers.
However, more recent research shows that this hierarchical model is overly simplistic. The expansion of the frontal cortex in human evolution did not simply suppress animal instincts. On the contrary, much of the frontal cortex is closely involved in emotional processing. In other words, reason is deeply intertwined with emotion.
In the case of the patient mentioned earlier, damage to the orbitofrontal cortex disrupted the integration of emotion into decision-making. The orbitofrontal cortex connects internal emotional signals from the more primitive parts of the brain with conscious awareness. When a person is choosing from a menu, for example, the brain evaluates options unconsciously and translates the results into emotional preferences. These signals guide decisions without deliberate reasoning. When we smell or see something we dislike, it is the orbitofrontal cortex that helps steer us toward alternative choices. Many everyday decisions rely on this emotional guidance.
When this connection is damaged, as in the patient’s case, individuals lose the emotional feedback necessary for decision-making. They may struggle to choose even simple options—what to eat, whether to work overtime, or how to respond to a client. The result is a profound inability to make decisions.
This is also why the human orbitofrontal cortex is significantly larger than that of other primates. Contrary to Plato and Freud’s assumption that reason suppresses emotion, neuroscience suggests the opposite: emotion is essential for rational decision-making. From the perspective of brain function, humans are highly emotional creatures.
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