Question No.  19931 :
What are the values of frequencies and voltages that occur in the brain during thought processes, emotions, etc., and how are they both measured and interpreted?

Brain waves are rhythmic pulsations of low voltage electrical current passing from one part of the brain to another. A biofeedback machine known as electroencephalograph (EEG) is normally used to measure brain waves of different frequencies associated with various states of cortical arousal (thinking, learning, relaxing, recuperating etc.). An electroencephalogram is performed with 16 to 64 electrodes (or passive sensors) gently placed on the lateral border of the scalp, from anterior to posterior on top of the head. The potential differences between pairs of electrodes are measured. These potential differences range from 20-100 microvolts in a normal subject. They are characterized by frequencies from 0.5-30Hz. There are four main types of brain waves: Beta (13-30 Hz), Alpha (8-12 Hz), Theta (4-8 Hz) and Delta (0.5-4 Hz). Beta brain wave indicates that your conscious mind is in control. It indicates a mental state of logical thought, analysis, and action. You are alert and awake talking, speaking, doing, solving problems, etc. Alpha brain wave indicates relaxation and meditation. It is a state of relaxed alertness good for inspiration, learning facts fast. Theta brain wave indicates deep meditation. This is associated with life-like imagination and is best for suggestibility and inspiration. This brain wave is dominant in children of age 2 to 5. Delta brain wave is associated with deep dreamless sleep and deep relaxation. When we lie down to sleep, the brain waves gradually slow down. The more excited we become, the faster the cycles of waves. These brain waves also show us the brain's response to a particular stimulus or external event, such as a picture or sound. Brain activity before, during, and after a stimulus presentation is recorded. This allows us to observe where, when, and how the brain responds to a given stimulus. The EEG reflects the summed activity of neurons in the cerebral cortex, perhaps with small contributions from deep brain structures. While the resistance of a single cell can be hundreds of megaohms to gigaohms, giving large voltage deflections, the resistance of extracellular fluids is very low and thus causes very small voltage drops. An extracellular recording only has access to these small signals. Even with an electrode inside the brain, you will not be able to see these signals unless the electrode is right next to a cell. They are only discernable when a population of cells of similar orientation is synchronously active. That way, their very small extracellular signals can sum in space and time. It is these signals, which have been attenuated and filtered by the tissues between the neurons and your electrodes, that you measure in the EEG. Since the EEG depends so much on spatial and temporal summation of very small signals in an organ as geometrically complicated as the brain, it is exceedingly difficult to interpret. Question Asked By:

Name: Eric

Age Group: 30 and above

Occupation Type: Others

Education Level: Post Graduate