Oops, Turns Out… What Does the Brain Do?

Once people believed… that the brain’s role was to cool the blood in the body.

Today we understand that it is the center of the nervous system. The brain receives all the sensory information about what is happening around us and inside our bodies, processes it, makes decisions, and sends instructions to the body’s other systems.

The Greek philosopher Aristotle believed that the heart controls movement and sensation, while the brain’s job is to cool the heart. His ideas were based on several observations. First, Aristotle noticed that it was possible to cut into an animal’s brain while it was still alive without the animal showing any signs of resistance or pain. His observation was not incorrect—brain tissue does indeed lack pain receptors.

The idea that the brain plays an important role in cooling the blood arose, in part, from the enormous number of blood vessels that surround brain tissue and branch into extremely fine capillaries to supply brain cells with the nutrients and oxygen essential for their function. To Aristotle, this structure seemed particularly well suited to cooling the blood via the brain.

Although some of these arguments sound fairly convincing, Aristotle also relied on assumptions that had no scientific basis. In ancient Greece, it was believed that all matter was composed of four elements: air, water, earth, and fire. Each element was associated with certain properties: water is liquid, earth is cold and heavy, air is light, and fire is hot. Based on animal brains he dissected, Aristotle concluded that brain tissue—surrounded by cerebrospinal fluid and with a gel-like texture—appears moist and cold. He therefore linked it to “cold” elements such as water and earth. To support this idea, he noted that when a brain is boiled, water evaporates from the tissue. He believed that the substance remaining after the water evaporates was connected to earth, which he also regarded as having cold properties.

In contrast to brain tissue, which does not visibly respond to sensory or emotional stimuli, Aristotle observed that the heart reacts immediately to emotions and sensations, for example by changing its rate of beating. He also believed that the heart is the hottest organ in the body, because the fiery soul burns within it, and that cooling the heart and blood in the brain enables a person to think and act in a balanced way. For this reason, he believed there was a close connection between the brain and the heart. He did not deny the importance of the brain, but considered it secondary to the heart.

Aristotle’s ideas had a profound influence on many philosophers and scientists, but his view that the heart is the center of consciousness, the soul, and sensation—the cardiocentric view—did not endure. The Greek physician Hippocrates, who died when Aristotle was 14, promoted a cephalocentric view, placing the brain at the center and arguing that it controls thoughts and sensations. A few decades after Aristotle’s death, studies by Herophilus of the brain and the nervous system demonstrated unequivocally that the brain is the body’s control center.

Today, we know that the heart is a muscle whose function is to pump blood through the body, and that the brain is connected to the body’s organs via the nervous system. It controls movement, the senses, emotions, thoughts, and awareness, and also regulates physiological processes such as heart rate. Despite Aristotle’s error, there was a kernel of truth in his ideas: the brain is indeed the control center for regulating body temperature, a function carried out by a specific region within it known as the hypothalamus.

Come to the “Oops, We Made a Mistake” exhibition at the Clore Garden of Science this Hanukkah and discover scientific ideas we once believed — and were later shown to be wrong. Get tickets here.

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