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Brain Wave

Brain Wave Brain wave is not electromagnetic radiation (e.g., visible light, radio wave, ...). The action potential in individucal neuron is too weak for detection (by current technology). It is the coherent oscillation of ionic charges in million neurons that is detected by the electroencephalogram (EEG). Figure 15 shows the simulation of neural oscillations at 10 Hz. Upper panel shows spiking (action potential) of individual neurons with each dot representing an individual action potential within the population of neurons, and the lower panel the macroscopic potential reflecting their summed activity. It illustrates how synchronized patterns of action potentials may result in macroscopic oscillations that can be measured on the scalp.

Figure 15 Brain Wave [view large image]

EEG Seizure EEG Just as it is possible to record the electrical activity of the heart cells from electrodes attached to the chest, activities inside the brain can be measured by multiple electrodes stuck to the scalp with conductive jelly (Figure 16). Since such signals are measured only from the surface layer of the brain and they are the sum of individual signal from millions of nerve cells, the data are very difficult to interpret. Thus, it has rather limited value as a research tool. Nevertheless, it does provide a glimpse

Figure 16 EEG
[view large image]

Figure 17 Seizure EEG [view large image]

of what the brain is doing and it has been particularly useful in studies of sleep and epilepsy with convulsive seizure (Figure 17).

Types of Brain Wave Figure 18 is produced by an EEG (ElectroEncephaloGraph) chart recorder to show the different kind of brain wave according to the different state of the brain. Beta wave rhythms appear to be involved in higher mental activity, including perception and consciousness. It seems to be associated with consciousness, e.g., it disappears with general anesthesia. Other waves that can be detected are Alpha, Theta, and Delta. When the hemispheres or regions of the brain are producing a wave synchronously, they are said to be coherent. Alpha waves are generated in the Thalamus (the brain within the brain), while Theta waves occur mainly in the parietal and temporal regions of the cerebrum. The Alpha and Theta waves seem to be associated with creative, insightful thought. When

Figure 18 Types of Brain Wave [view large image]

an artist or scientist has the "aha" experience, there's a good chance he or she is in Alpha or Theta.

Integration of Brain Waves 2 These two kinds of brain waves are also associated with relaxation and, stronger immune systems. Therefore, many people try to train themselves to enter such states through various biofeedback techniques (with varying degree of success). Delta Waves occur during sleep. They originate from the cerebral cortex when it is not being activated by the reticular formation. In slow-wave sleep, the entire brain oscillates in a gentle rhythm quite unlike the fragmented oscillations of normal consciousness. The neocortical activity is often modulated by a rhythm of 40-80 Hz, called the Gamma wave (not shown in Figure 18). When there are strong gamma oscillations in certain parts of the neocortex, human subjects do better on learning and memory tasks.A 2010 study indicates that brainwaves are for integrating various sensations to ensure all the relevant signals for one event arrive at the binding site at exactly the same time. This allows the receiving neurons to process the signals together, recombining them into a single sensation. For example, we see an apple as red and round, not one red thing and another round thing

Figure 19 Integration of Brain Waves [view large image]

although red and round are processed by different neuron cells. Figure 19 shows the brain experiences simultaneously many types of brainwaves within its various regions, each performing different functions.
Brain Death The EEG is also used to monitor the depth of anaesthesis, and to distinguish between whether an individual is in a coma or is dead. In most countries, death is defined as the cessation of brain electrical activity. The person is legally dead when no brain wave is detected. This is in conformity with "brain death" as defined by a group of physicians and bioethicists at Harvard University in 1968. These include, among other criteria, lack of consciousness (coma), lack of reflexes associated with the brain stem (no response to pain, loss of pupillary reflexes, loss of gag and cough reflexes) and apnea (the inability to breathe). Figure 20 shows the EEG at the moment of the cessation of brain electrical activity. When all these criteria are present, it is no doubt that the person will never regain brain

Figure 20 Brain Death
[view large image]

function, the consensus is to declare death. Such definition has the benefit for organ transplantation as other parts of the body may survive for many minutes, or even hours, after brain death and it can be used to save another person's life.

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