1.4: Neuroscience is ever changing

One of the most exciting and satisfying aspects of modern science is the rapidity of new discoveries in the field. New findings are often communicated by publishing academic studies in scientific journals. More neuroscience studies were published between 2015 and 2020 than in the previous seventy years! But, advancements in neuroscience haven’t always moved so quickly.

The ritualistic funerary rites of the ancient Egyptians around 2500 BCE provide a glimpse into how humankind’s understanding of the brain has changed over time. When important Egyptians died, major organs including their stomach, lungs, and liver, were removed and stored in canopic jars in preparation for immortality in the afterlife. The fate of the brain, however, was much messier: Using a pair of sticks up the nose, the brain was blended up into a mush and flushed out of the skull using palm wine. The brain, apparently, wasn’t needed for the afterlife.

Figure 1.11 The ancient Egyptians preserved some of the important internal organs after death (top), while the brain was scrambled using tools (bottom) and discarded.

Around 2,000 years later, ancient Greek physicians had a different understanding of the function of the brain. Aristotle developed a theory that the heart was the seat of the soul, and that blood was the life force that dictated a person’s behavior. When a person was “hot blooded,” they acted impulsively with no regard for consequences. In his view, the function of the brain was to cool the blood as the blood passed through it, which calmed the temper.

For the hundreds of years that followed, physicians attempted to correlate behaviors with changes in the brain. In the mid 1800s, Paul Broca was one of the first to suggest that specific areas of the brain were responsible for carrying out specific functions, which came to be called localization theory. Much evidence favors this line of thinking, such as the idea that language comprehension starts in a small patch of cells in the left hemisphere (Chapter 14), perception of faces relies on a set of cells at the base of the brain (Chapter 7), and balance and motor coordination depends on the cerebellum (Chapter 10). On the other hand, the opposing view, called the distributive processing theory, suggests that behavioral functions require activation of cells across several different areas of the brain. Complex behaviors such as emotion, consciousness, or cognition (the act of generating knowledge through a combination of senses, memories, and thoughts) require coordinated action across distinct brain areas. Most likely, some behaviors are more localized than others, but still rely on signals from across many other brain areas. As with most fields of biology, absolutes are rare in neuroscience.

Figure 1.12 Paul Broca (left), through his study of the brains of patients with the language disorder aphasia (right), was a proponent of the localization theory of brain function.

While anatomists and physicians tried to define the gross anatomical workings of the brain, they missed out on a layer of understanding at the level of cells until microscopy was widely adopted by the scientific community. In the early 1900s, a heated debate between two anatomists, Camillo Golgi and Santiago Ramon y Cajal, prompted researchers to look more closely at the neurons. Through careful drawings of their observations, they concluded that neurons had different shapes and therefore carried out different functions. This microscopic level analysis laid the foundation for understanding the cells that make up the nervous system and the way they communicate with one another (Chapter 2).

Today, we have a clearer understanding of the function of the brain, largely due to the advancements brought to us by a better understanding of animal biology and new technology. In 1954, the electron microscope was aimed at the space between neurons for the first time, allowing us to see a tiny anatomical component about 20 nanometers across - a thousand times smaller than the width of a human hair (Chapter 5). A medical diagnostic tool, the functional magnetic resonance imaging device (fMRI), made its debut to the neuroscience world in 1991, which allowed us to visualize brain changes while a person is actively engaged in behaviors, such as a decision making task, or while observing visual stimuli (Chapter 6). Today, much excitement revolves around visualization strategies like CLARITY, a method to render an entire brain transparent, which helps us to map out the nature of the connections that span the nervous system.

Figure 1.13 An electron microscope (top) gives us the resolution to visualize the synapse (bottom), the tens of nanometer distance between two neurons.

The ever-changing landscape of scientific inquiry presents a challenge. Our current understanding of the brain, as described here, is only a snapshot along the timeline of scientific discoveries. As we look to the future, many new discoveries will continue to reinforce what knowledge we have already amassed. But some discoveries, with help from not-yet-invented technology, will push the frontiers of knowledge and find compelling evidence against longstanding accepted theories in the field, prompting a shift in the paradigm.