All vertebrate creatures have a central nervous system operated by the brain, a highly complex organ that acts as central command for the entire body. The brain is the center for sensory, motor, arousal, and neurotransmitting functions in the body. Brain activity is literally the electricity caused by the firing of neurons as the brain goes about its constant routine. As internal and external stimuli change, brain activity may also change.
Brain activity can be changed by ingestion or exposure to certain drugs. Most drugs used to treat psychological problems will affect brain activity in some way, but so do many other substances. Caffeine, heroin, antidepressants, and sedatives all can affect how quickly and frequently neurotransmitters fire. While this effect may be temporary, some studies show that prolonged use of a drug can have extended effects.
Disruption of normal sleeping habits can have a serious effect on brainwave activity, according to some studies. Although it might seem logical that brain activity drops with sleep deprivation, some evidence shows that activity in certain parts of the brain actually increases, as if the brain is compensating for the lack of rest. Unfortunately, sleeplessness also disrupts cognitive and motor functions, usually defeating the attempts of the brain to keep up normal performance levels.
Hormones in the body can also cause significant alternations to activity in the brain. In one study, post-menopausal women were given small doses of estrogen and monitored for brain activity changes. In many cases, women treated with the hormone showed increased memory function. Studies such as this have lead to additional research in menstruating women, as hormonal levels fluctuate during a monthly menstrual cycle. New research suggests that mate preference and sexual attraction, both partially controlled by brain activity, may alter depending on the subject's menstrual cycle.
The brain controls sensory perception, such as touch, smell, taste, and hearing. Certain sensory external stimuli may cause activity in the brain to alter out of self-preservation. For instance, if a deer picks up the scent of a predator, its brain may activate a flight response to get it out of danger.
Levels of brainwaves also appear to be influenced to some degree by lifestyle choices. Stress, religious devotion, and even culture have all been shown to have some level of influence on how the brain functions. Some experts believe that lowering stress levels and focusing on a healthy lifestyle can lead to improved levels of brain activity.
The study of brain activity is done mostly through a type of observational research called electroencephalography. This method employs the use of sensors that can measure and map the amount of activity in the brain. By measuring the patterns in different brain waves, neurologists and researchers can detect the brain's ability to respond to stimuli, as well as see any developing areas of affected activity that may indicate neural-related problems such as epilepsy.