The brain, it is said, is the most complex organ in the human body. It produces our thoughts, actions, memories, feelings and experiences. This jelly-like mass of tissue, weighing about 1.4 kilograms, contains one hundred billion nerve cells, or neurons.
The complexity of the connectivity among these cells is mind-boggling. Each neuron can make contact with tens of thousands of other neurons, via tiny structures called synapses. In fact, our brains form a million new connections for each and every second of our lives. The pattern and strength of the connections is continuously changing and no two brains are identical.
In these changing connections, memories are stored, habits are learned and personalities are shaped, from reinforcement of certain brain activity patterns and losing others.
While most people know about “gray matter,” the brain also contains white matter. The gray matter is the cell bodies of the neurons, while the white matter is the branching network of thread-like tendrils, called dendrites and axons. They spread out from the cell bodies to connect to other neurons.
Another cell is the glial cells. These outnumber neurons ten times over. Once thought to be support cells, they are now known to amplify neural signals and to be as important as neurons in mental calculations. There are many different types of neurons, only one of which is unique to humans while the other is unique to great apes, the so-called spindle cells.
Brain structure is shaped in part by genes, but mostly by our experiences. In fact, via a process called neurogenesis, new brain cells are being created throughout our lives. The brain experiences bursts of growth and also periods of consolidation, when excess connections are pared. The most notable bursts are in the first two or three years of life, during puberty, and also a final burst during young adulthood.
Brain maturity also depends on genes and lifestyle. Exercising the brain and proper nutrition are just as important as it is for the rest of the body.
Our neurons communicate in various ways. Signals pass among them by the release and capture of neurotransmitter and neuromodulator chemicals, such as glutamate, dopamine, acetylcholine, noradrenalin, serotonin and endorphins.
Some neurochemicals work in the synapse, passing specific messages from release sites to collection sites, called receptors. Others also spread their influence more widely, like a radio signal, making whole brain regions more or less sensitive.
Deficiencies in certain neurochemicals are linked to disease. For example, a lack of dopamine in the basal ganglia (the part of the brain that controls movement) leads to Parkinson’s disease. It can also increase susceptibility to addiction because dopamine affects our sensations of reward and pleasure.
Similarly, a deficiency in serotonin, used by regions controlling the emotion, can be linked to depression or mood disorders, and the loss of acetylcholine in the cerebral cortex is characteristic of Alzheimer’s disease.
Within individual neurons, signals are formed by electrochemical pulses. This electrical activity can be detected by an electroencephalogram (EEG), placed outside the scalp . These signals have wave-like patterns, which scientists classify from alpha (common while we are relaxing or sleeping), to gamma (active thought). When this activity goes awry, it is called a seizure. Some researchers think that synchronizing the activity in different brain regions is important for perception.
There are other, indirect ways of imaging brain activity. Functional magnetic resonance imaging or positron emission tomography monitor blood flow. MRI scans, computed tomography scans and diffusion tensor images (DTI) use the magnetic signatures of different tissues, X-ray absorption, or the movement of water molecules in those tissues, to image the brain.
These and other scanning techniques have helped determine which parts of the brain are associated with which functions. For example, different parts of the brain govern activity related to sensations, movement, libido, choices, regrets and motivations. However, some experts argue that we put too much trust in these results, which also raise privacy issues.
Before scanning techniques, researchers relied on patients with brain damage caused by strokes, head injuries or illnesses, to determine which brain areas perform certain functions. This approach exposed the regions connected to emotions, dreams, memory, language, perception and to more enigmatic events, such as religious or “paranormal” experiences.
One famous example was the case of Phineas Gage, a 19th century railroad worker who lost part of the front of his brain when a 1-metre-long iron pole blasted through his head during an explosion. He recovered physically, but experienced permanent personality change, showing for the first time that specific brain regions are linked to different processes.
About the Author – Terry A. Rondberg, DC
Dr. Terry Rondberg is has been a champion of the chiropractic profession for decades. After receiving his Doctor of Chiropractic (DC), Dr. Rondberg founded The Chiropractic Journal, the industry’s first professionally edited source for chiropractic news and features.