Does alpha desynchronization reflect task demands and attentional processes?
It has been repeatedly shown that topographically widespread lower alpha desynchronization (in the range of about 7–10 Hz) could be obtained in response to almost any type of task. It has been suggested that this desynchronization reflects general task demands and attentional processes ( Pfurtscheller and Lopes da Silva, 1999 ).
What is the origin of alpha rhythms on EEG?
Moruzzi and Magoun in 1949 were the first to show that stimulation of the brain stem reticular formation activates the cortex and transfers the high voltage, low frequency EEG, that is, EEG with prominent alpha rhythms, into low voltage, high frequency EEG 22. In the normal brain alpha rhythms of EEG appear to be the largest in amplitude.
What is the frequency range of the alpha rhythm?
The rhythm is mostly defined by its frequency of 8 to 13 Hz and by its posterior distribution showing high amplitudes at occipital and parietal electrodes (in referential linkedear montages) ( Table 8-1 ). The alpha rhythm typically has a peak-to-peak amplitude of 20 to 60 μV.
Does the Alpha sub-band influence the activation of cognitive processes?
However, while in some cases, the activation of a certain cognitive process was suggested to be reflected by increased desynchronization in a specific alpha sub-band (e.g., Wise et al., 2011) as previously suggested ( Klimesch, 1999 ), in others, it was suggested to be indicated by increased alpha synchronization ( Knyazev et al., 2004).
What is Desynchronization in EEG?
n. in electroencephalography, the replacement of occipital alpha waves by the fast, low-amplitude, irregular waveforms characteristic of alert wakefulness, often because of an external stimulus, usually one that requires active attention.
What is the alpha rhythm of the brain?
The alpha rhythm refers to brain oscillations within a frequency range of 8–12 Hz. This rhythm was first observed when Hans Berger recorded electrical activity from the scalp (EEG) in 1929 (Berger, 1929).
Does desynchronization of the alpha rhythm decrease in amplitude occur when the eyes are open?
Does desynchronization of the alpha rhythm occur when the eyes are open? Yes because alpha waves happen when the eyes are closed and the person is relaxed. Opening the eyes increases external awareness which causes desynchronization as the wavelength transforms from alpha to beta.
What is alpha Desynchronisation?
Previous studies have identified a reduction in the number of connections when the eyes closed condition is compared to the eyes open condition, in the alpha band18,19. This is known as “alpha desynchronization”.
What do alpha brain waves indicate?
Non-Rapid Eye Movement Sleep. After one's eyes close, brainwaves become slower and more regular than when fully alert. They are called alpha waves, look like the teeth of a comb, and signify a relaxed yet still wakeful state, akin to meditation.
What do alpha brain waves do?
Alpha waves usually occur when you are engaged in activities such as daydreaming, meditating, or practicing mindfulness. Research suggests that this type of brain wave may play a role in reducing symptoms of depression and improving creativity.
Why do alpha waves increase when eyes are closed?
2.4. As one can see closing eyes dramatically increase EEG power in alpha frequency band in occipital areas. This synchronization is caused by blocking the visual input to occipital areas. That is one of the reasons why the occipital alpha rhythm is considered as an idling rhythm of the occipital cortex.
What pattern of EEG is affected by eye opening and closing?
The alpha rhythm, or alpha, is attenuated in amplitude and frequency and often completely ablated by eye opening.
What should be the result of hyperventilation on alpha rhythms and what is the mechanism behind it?
When a person hyperventilates (breathes rapidly and deeply), too much carbon dioxide is eliminated from the blood, causing the blood and the cerebrospinal fluid that bathes the brain to become too alkaline. These changes increase the overall electrical activity of the brain including the amplitude of alpha waves.
What is Desynchronization?
Desynchronization is a process inverse to synchronization, where initially synchronized oscillating systems desynchronize as parameters change or they do so under the influence of an external force or feedback.
What is alpha block in EEG?
Alpha blocking, a phenomenon where the alpha rhythm is reduced by attention to a visual, auditory, tactile or cognitive stimulus, is one of the most prominent features of human electroencephalography (EEG) signals.
What is synchrony and alpha block?
synchrony: when there is an alpha rhythm (patient is relaxed with eyes closed), the waves are uniform, in amplitude and frequency. Alpha block is when beta waves start to interfere with the alpha rhythm; the patient is stimulated by different kinds of stimuli from the environment.
How do you activate alpha brain waves?
Alpha brainwaves are produced by the brain in the frequency range of 8-12 Hz....Here are five ways to increase your alpha brainwaves:Meditate. ... Avoid alcohol. ... Avoid caffeine. ... Train your brain. ... Consider avoiding garlic and onions.
What are the 4 types of brain waves?
What are Brainwaves?Delta waves (. 5 to 3 Hz) ... Theta waves (3 to 8 Hz) Theta brainwaves occur most often in sleep but are also dominant in deep meditation. ... Alpha waves (8 to 12 Hz) ... Beta waves (12 to 38 Hz) ... Gamma waves (38 to 42 Hz)
What are alpha beta theta and delta waves?
In a nutshell, Alpha brainwaves relate to creativity and daydreaming, Beta waves are produced in the middle of deep thinking, Delta/Theta waves can be found during deep sleep, and Gamma waves are associated with problem solving, happiness, and compassion.
How do you know if you are in alpha state?
You likely know the feeling. Alpha, on the other hand, is characterized by being clear-headed, present, and fully in the moment. Alpha waves create a sense of peace and well-being in your mind and body. When people are in this state, they seem to exude charisma as their mind focuses only on the here and now.
What is alpha desynchronization?
Alpha suppression is produced by an influx of light, other afferent stimuli and mental activity 41. Alpha rhythm is the EEG correlate of relaxed wakefulness, best obtained while the eyes are closed 20.
What frequency is a signal filtered online?
Signals were filtered online using a high-pass (0.1 cutoff fre quency) and an anti-aliasing low-pass filter. Offline filtering using Matlab in house-scripts, consisted of a high-pass and low-pass filter at 0.5–70 Hz and a notch filter applied at 60 Hz to remove electrical line noise.
Where were electroencephalography recordings collected?
The intracranial electroencephalography recordings were collected at the Toronto Western Hospital (Toronto ON, Canada). Our research protocol was approved by the University Health Network Research Ethics Board and informed consent was obtained from the participants. All methods were performed in accordance with the relevant guidelines and regulations. Informed consent was obtained from all patients. Eleven participants (6 female) with pharmacologically-refractory mesial temporal lobe epilepsy underwent a surgical procedure, in which electrodes were implanted subdurally on the temporal lobe and stereotaxic depth electrodes were implanted in the hippocampi or other deep structures (Fig. 1 ). For each patient, electrode placement was determined to best pinpoint the origin of seizure activity. In addition to electrodes implanted in the temporal lobe, including depth electrodes in the hippocampi, some patients had electrodes implanted in frontal, interhemisphic and the cortical convexity (see Table 1 ). The electrode implants are thus not identical for all participants, though they tend to overlap in the mesial temporal lobe epilepsy (MTLE) sensitive regions. This limits the ability to directly compare the wiring cost or other network properties among participants. However, we can still compare and generalize from participants by examining the difference between the two conditions. For example, in order to compare the functional connectivity pattern of two participants, one with a grid in the left cortex and another with depth electrodes in the hippocampus and temporal areas, we calculate the difference between network parameters from eyes closed to eyes open, within each participant.
Can correlation matrices be converted to adjacency matrices?
The correlation matrices can be converted into adjacency matrices and then into undirected graphs with the direct application of a threshold. The choice of the threshold specifies the relationship between two electrodes, two electrodes are connected when the correlation is within a certain threshold. Thus, two electrodes are connected when the correlation is larger than the threshold.
What is the alpha rhythm?
Alpha Rhythm. The alpha rhythm (Fig. 8-12), is one of the most prominent normal adult brain rhythms and is identified by its frequency, spatial topography , behavioral correlates, and reactivity to stimuli. 17–22 The alpha rhythm is fully present only when a subject is mentally inactive, yet alert, with eyes closed.
What is the function of alpha rhythm?
An important functional characteristic of the alpha rhythm is its disruption by visual attentiveness. Just opening the eyes is generally sufficient to cause alpha blocking, which is a significant decrease in the signal versus an eyes-closed state (often by more than a factor of two).
What is the change in activity?
The change of activity is a well-known phenomenon due to the synchronization of the groups of neurons in the motor cortex region. When the limbs are inactive, the μ rhythms presents activity, whereas when a subject moves his limbs, the rhythms present a decrease of amplitude, which is termed as α desynchronization.
What is the frequency of theta rhythm?
Theta rhythm: The frequency in the range of 4–8 Hz; it appears on both sides of the parietal and temporal lobes in the brains of younger people; and it appears when drowsiness or the central nervous system is in a state of inhibition. (3) Alpha rhythm: The frequency range is 8–13 Hz.
Where is the alpha rhythm found?
It is most obvious in the occipital region of the human brain, and its amplitude ranges from 20 to 100 uV. The alpha rhythm can reflect a lot of thinking information of the human body and is easy to discover, so the alpha rhythm is a common rhythm of EEG research.
Where are gamma power changes greatest?
Gamma power changes are greatest in the superficial layers, where most recordings are made. Recordings in the deep layers show greater alpha effects and smaller gamma effects, but with the same attentional contingency, that is, a reduction in alpha and an enhancement of gamma.
Where is theta wave located?
It is located in the prefrontal part of the cortex.
