Why do brain injuries have so many different symptoms?

parts of the brain

Some of the many parts of the brain. Image source: Wikimedia Commons

If you have a broken leg or a strained neck, your doctor can usually tell you exactly where your injury is in your body, what symptoms you can expect, and how long recovery should take. With brain injuries, patients face a long list of potential symptoms, with no guarantee that they will experience most of them. They also face an uncertain path to recovery, with some symptoms lasting months or years after the initial injury.

This is because the brain isn't just a homogeneous organ. Different areas of the brain regulate complex functions, which means that symptoms are dependant on the area of the brain that was injured.

The cerebrum is the largest part of the brain and is divided into two hemispheres. This area is responsible for higher functions such as vision, hearing, interpreting touch, speech, emotions, and fine motor control. The surface of the cerebrum has a folded appearance, which allows the structure to contain approximately 70 billion of the brain’s total 100 billion nerve cells. This folded material is called grey matter and is made of nerve cell bodies. Beneath the grey matter is white matter, a lighter tissue that affects how the brain learns and functions.

The cerebrum is also divided into distinct lobes, which are mirrored on each hemisphere. Scientists believe that each love controls a different function, with some areas of each lobe serving very specific functions. The frontal lobe controls many of the functions that make us “who we are”: judgement, speech, writing, personality, behavior, emotions, self-awareness, concentration, and some body movements. The parietal lobe interprets pain, temperature, touch, language, sounds, sensory and memory information, and spatial and visual perception. The occipital lobe interprets signals from vision, such as movement, color, and light. The temporal lobe is also involved in understanding language, hearing, memory, and sequencing and organizing information.

The cerebellum is a smaller structure located under the cerebrum. It controls muscle movements, posture, and balance.

The brainstem connects the brain to the spinal cord. This area of the brain controls automatic functions—that is, the activities your body performs that you are not consciously in control of, such as regulating body temperature, controlling the heart rate, sneezing, coughing, breathing, swallowing vomiting, digesting food, and wake and sleep cycles.

The short and long-term effects of a brain injury vary depending on the part of the brain that was injured. Injuries to some areas of the brain are almost always fatal, since those areas control vital life functions. Other parts of the brain may control higher-level functions such as speech, memory, and decision-making. In some cases, when one part of the brain is damaged, the brain may eventually “rewire” itself, creating new neural pathways that serve the same functions, in a phenomenon called neuroplasticity. This is why a brain injury patient may experience some, but not all, symptoms of a brain injury: the area that was injured can vary from patient to patient, and their recovery from a brain injury is a very complex internal process.