Long before the prefrontal cortex gave humans the ability to express ourselves and engage in complex decision-making processes, our early ancestors were guided by a much simpler, more primitive brain. Today, we can still find evidence of this early brain buried deep beneath more recently-evolved structures like the parietal and temporal lobes of the cerebrum.
The oldest part of our brain, the brainstem, is so ancient that it predates the first appearance of mammals on earth. This structure, together with the cerebellum, constitute our “reptilian brain,” which governs vital body functions such as breathing, body temperature and heart rate. In addition to regulating these functions, the brainstem also connects the rest of the brain and the spinal cord to the peripheral nervous system, which includes billions of sensory and motor neurons.
The brainstem might be the oldest hardware in our skulls, but it remains essential to proper brain function in modern humans.
In essence, the brainstem serves as the foundation upon which all the other more complex structures of our brain have been built. When the brainstem is damaged by an injury or stroke, it can have debilitating effects on a person’s ability to write, walk and even eat. Brainstem trauma can also cause partial paralysis and contribute to problems with breathing, hearing and speech.
In this illustration, you can see the humble brainstem nestled beneath the deep folds of the cerebrum and in front of the smaller, tightly-woven structure of the cerebellum. The spinal cord, meanwhile, begins at the base of the brainstem, stretching down the back and branching out into the rest of the nervous system. It might not look like much, but this prehistoric bundle of brain cells has been downright fundamental to our evolution as a species.