Rythme alpha

Alpha waves, or the alpha rhythm, are neural oscillations in the frequency range of 8–12 Hz likely originating from the synchronous and coherent (in phase or constructive) electrical activity of thalamic pacemaker cells in humans. Historically, they are also called "Berger's waves" after Hans Berger, who first described them when he invented the EEG in 1924. Alpha waves are one type of brain waves detected by electrophysiological and closely related methods, such as by electroencephalography (EEG) or magnetoencephalography (MEG), and can be quantified using quantitative electroencephalography (qEEG). They can be predominantly recorded from the occipital lobes during wakeful relaxation with closed eyes and were the earliest brain rhythm recorded in humans. Alpha waves are reduced with open eyes and sleep, while they are enhanced during drowsiness. Occipital alpha waves during periods of eyes closed are the strongest EEG brain signals. Historically, alpha waves were thought to represent the activity of the visual cortex in an idle state. More recently, research suggests that they inhibit areas of the cortex not in use, or alternatively that they play an active role in network coordination and communication. Whether they are inhibitory or play an active role in attention links to their direction of propagation, with top-down rearward waves being inhibitory, and forward bottom-up ones aiding visual attentional processes. An alpha-like variant called a mu wave can be found over the primary motor cortex. Some researchers posit that there are at least two forms of alpha waves, which may have different functions in the wake-sleep cycle. Alpha waves are present at different stages of the wake-sleep cycle. The most widely researched is during the relaxed mental state, where the subject is at rest with eyes closed, but is not tired or asleep. This alpha activity is centered in the occipital lobe, although there has been speculation that it has a thalamic origin. This wave begins appearing at around four months, and is initially a frequency of 4 waves per second.