Neurologists carry out detailed studies of how humans think, how we are aware of our own being, using special scientific instruments.
Their studies show that our ability to perceive, to think about things, and to act is associated with a special kind of cell called neurons.
Our brains are vast cities of these creatures. They range in size from about 0.5 mm in diameter for large motor cells of the cerebral cortex to 0.005 mm in diameter. The brain has more than 10 billion of them. Neurons have tentacles. Lots of tentacles. Some brain cells have 10,000 tentacles. The dendrites bring electrical impulses toward the cell body. A long single tentacle, called an axon, carries signals away from the cell body to other cells. The axon terminates with a bushy network of tentacles.
Neurons communicate with each other, and with other cells of the body, where their tentacles touch. The message travels along the body of the neuron as an electric pulse generated by an ionic pump. The pump operates by moving sodium and potassium ions in and out of the neuron's membrane. This happens quickly, and the nerve impulse travels along the neurons at rates ranging from one meter per second for a thin nerve fiber to 150 meters per second for a major nerve fiber.
The longest neuron has its body in our brain and has an axon that reaches to the tip of our big toe. If something touches the tip of our big toe, it takes about 0.03 seconds for that neuron to relay a message to other brain cells indicating that the event has happened (and somewhat longer until we process that information to become aware of something touching our toe).
When the ionic pulse arrives at the tips of the tentacles, nodes in small pads secrete special proteins, called neurotransmitters. These molecules migrate from the tentacle tip to receptors on the next cell to relay the message. The first cell then secretes a second protein, an enzyme, that destroys the neurotransmitter and clears the way for the next signal. This process takes time (not very much) and determines our interval of awareness; how rapidly we can respond to changes in our environment. It is the reason, for example, we see a movie when in actuality we view a series of 24 still photographs flashed on the screen in one second.
Neurons are active creatures. Their tentacles move about, touching other neuron tentacles. All of the brain cells are in place before birth. As humans grow older, their neurons form patterns, holding onto tentacles of other neurons when messages are repeatedly sent along the same pathways. When we "learn" to behave a certain way and repeat that skill again and again, the neurons get more and more efficient at passing messages in the required pattern to make our muscles perform the task. Practice makes perfect and repeated efforts on our part make the complex muscular movements easier and easier to do.
A new born baby has a difficult time learning muscular coordination of its eyes, facial movements, hand and arm movements, and so on. The first few attempts to learn to balance on two legs is a very wobbly experience. But each process becomes easier as the neurons get the messages straight. Eventually, our bodies do what we want them to do with hardly any conscious effort at all. Walking becomes totally "automatic." The process of creating the pathways of our mind is becoming clearer each year. For the latest information on this, read about the birth of mind.
Most of the early information on brain function came from studies of the behavior of people with brain damage of various kinds. Tests on mental processes before and after neurosurgery also provides information on what parts of the brain do what. Studies about how the brain functions in relationship to what we call mind or consciousness has become progressively less invasive. Today, researchers ask patients to do specific mental tasks and track the parts of the brain that receive more blood (heat up or increase amounts of radioactive tracers in the blood), become electrically active, or change their magnetic resonance. We know our brains consume about 20 watts of energy and generate a composite surging electrical pulsing of 8 to 10 cycles per second. Above and below a narrow band of energy limits, consciousness vanishes.
The most obvious feature of the brain is bilaterally symmetry. It is divided right and left into two major lobes, each with some 5 billion neurons.
There are connections between these two cell cities. The largest connection, by far, is the corpus collosum. Some optic fibers also link the two sides of the brain, as if each hemisphere needs some information from both eyes. Otherwise the two hemispheres operate separately and do different tasks.
The left hemisphere operates the right side of the body, the right hemisphere operates the left side. The left hemisphere, the one looking out of the right eye and working the right side of the body, has (in most Europeans, anyway) the speech center. The left hemisphere does not speak, but is actively involved in music, poetry and other forms of communication. This relationship does not hold true for other language types. Japanese language, researchers believe, is linked with the right hemisphere. Perhaps because it is more tonal, poetic, less digital than European language. Bilingual Japanese process English and Japanese in opposite hemispheres.
People have (some of them) continued to function and lead seemingly normal lives even after having one whole hemisphere of the brain removed.
The brain has grown, evolutionarily, by adding structures onto older structures. Layer upon layer. The deeper levels of the brain, near the brain stem leading to the spinal chord, are the most "primitive."
They are involved with basic states of mind, such as emotional context, through secretion of hormones.
The pineal gland, for example, located adjacent to the optic nerves at the base of the brain, controls waking and sleeping states by the secretion of seretonin.
The hippocampus produces enzymes essential to changing perceptions into long term memories.
Emotional feelings of hate, anger, love, fear, joy, are linked to hormones produced by the ancient limbic system.
Early investigators pointed out that the limbic system is almost unchanged from our reptilian ancestors. Which brings us full circle, so to speak, back to the mind conspiracy theory.
Beyond such measurements and tests, the question of how the brain manages to produce mind is still in hot debate and vigorous investigation. Neuroscientists who have initiated the science of cognition now have a new model that turns this whole question around.