Alpha rhythms of 8 to 12 Hz were first observed over the occipital cortex when human subjects were relaxed or closed their eyes. Midrange oscillations include theta and alpha waves. In Fundamentals of Cognitive Neuroscience, 2013 Alpha and theta rhythms The rhythm in delta waves are usually between 0.1 and 3.9 Hz. Additionally, they are present in adults who are awake, when areas of the brain have been damaged by inflammation, a tumor, or vascular blockage. They are also present in infant brains that are still developing. In all ages of patients, they normally occur during deep sleep. Delta wavesĭelta waves are low-frequency waves.
The neurologist sometimes refers to this as “slow background,” which indicates a “nonspecific” dysfunction of the brain in that area. For example, in a coma caused by sedative medications or severe infection, the background EEG becomes “slow” and mostly consists of theta and delta waves. The rhythm of theta waves is usually between 4 and 7.9 Hz. If theta waves occur at other times, they may indicate cerebral dysfunction. However, theta waves are most common in children.
Theta waves in normal adults may appear transiently during sleep. Beta waves from different sites that are out of phase are called desynchronized. If a patient opens the eyes or begins the mental activity, the alpha waves decrease or attenuate, to be replaced by beta waves all over the scalp. Beta waves are present over the remaining frontocentral areas of the scalp besides the regions described under the alpha waves. The rhythm of beta waves is usually between 13 and 40 Hz. They are common while concentrating, or when a person is under stress or experiencing psychological tension. Beta wavesīeta waves replace alpha waves during attention to tasks or stimuli and are of higher frequency. In most cases, a neurologist measures the alpha rhythm in the back of the head while the patient's eyes are closed. Alpha waves are maximal over the occipital region. The rhythm of alpha waves may have a frequency between 8 and 13 Hz. They disappear during sleep and vanish when there is concentration on a specific task. Alpha wavesĪlpha waves in healthy, awake adults occur while resting with the eyes closed. Brain waves help in the diagnosis of certain neurologic disorders, including brain lesions and the likelihood of having a seizure. These are similar and relatively stable in all normal individuals. There are four types of typical brain waves: alpha, beta, theta, and delta. Brain wavesĪny number of patterns of rhythmic electric impulses are produced in different parts of the brain. This is called focal seizure with secondary generalization. The changes may begin in one cortical area and then spread across the entire cortical surface. Regardless of type, all seizures involve a significant change in electrical activities, which can be seen on an EEG. If the auditory cortex is affected, the patient may hear odd sounds. If the primary motor cortex is affected by a seizure, movements of the contralateral side will occur. Based on the involved cortex area, the symptoms are different. Seizure disorders, or epilepsies, are characterized by seizures that happen more than once. A seizure is a temporary cerebral disorder that involves abnormal movements, inappropriate behavior, unusual sensations, or a combination of these, as a result of electrical discharges. When there is a lack of this synchronization, there may be localized damage or a cerebral abnormality, such as a tumor or an injury to just one hemisphere. In the two hemispheres, electrical activity is usually synchronized via a pacemaker mechanism involving the thalamus. A neural function is based on the electrical events of the plasma membrane of neurons. The billions of brain neurons and their activities generate a measurable electrical field that changes constantly when areas are stimulated or reduce their activities. A positron emission tomography (PET) scan allows visualization of activities in specific brain regions, as does functional magnetic resonance imaging ( fMRI).īrain activity is assessed using EEG by placing electrodes on the brain or outer skull surface. The brains of people undergoing brain surgery, and changes that follow localized strokes or injuries, have been studied to better understand the brain's electrical activities. The observed electrical patterns are called brain waves. Jahangir Moini, Pirouz Piran, in Functional and Clinical Neuroanatomy, 2020 ElectroencephalogramĪn electroencephalogram (EEG), is a printed recording of the electrical activity of the brain.