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EEG characteristics of ASD

Brain activity assessment (qEEG) aims to identify the patterns in the brain that are related or can be the underlying reason for various disorders, such as ADHD, ADD, ASD, OCD etc.

While all brains share similar types of patterns, the combination of patterns that are out of balance and the degree to which they are differ.

Some patterns are more typical to a specific disorder. Here we will explore some of those that have been found more in Autistic brains compared to non-autistic brains. Autism Spectrum disorder (ASD) is a neuro-developmental disorder associated with deficits in executive function, language, emotions and social communication.

How is it measured?

There are few approaches to analysing brain patterns. One, that is also used in some research studies, is the Z score approach. Using this method, every brain activity of an individual is compared to a data base of “normal” brains that have been averaged. So, similar to the way blood tests are done, your results are checked against the averaged brain-data of a population and the abnormality is determined by how many standard deviations are you out of the average. The z score is the difference between the mean score of a population and the patient’s individual score divided by the standard deviation of the population. In the case of qEEG data, the Z-score indicates whether there is deficient or excessive activity in a given frequency for a given electrode (or group of electrodes).

Recent research highlights the association of autistic symptoms with information integration deficits resulting from under or over-connectivity within and between specialized areas of the brain. Few studies observed qEEG recurring patterns in children with ASD.

The EEG patterns found in ASD brains

Hyper- or hypo-functioning related activity

1. The presence of excess slow wave activity (delta, theta) and excess fast waves (alpha, beta) especially at the frontal lobe, relating to hyper- or hypo-functioning.

Slow wave activity

o High Delta/Theta activity corresponds to cortical slowing and inattention, impulsivity and hyperactivity (found in the study in 30-40% of participants with ASD).

o This excessive presence of slow wave activity (delta) was found at the frontal area (Fp1,Fp2 and F8)

o The lowest intensity of theta brainwave was at C3 area (left Hemisphere) among the ASD.

o Normal theta is important as it mediates and/or promotes adaptive activities such as learning and memory. Learning and memory reflected activity carried by the limbic system and hippocampus region located at the posterior temporal area.

Fast wave activity

o Excess of fast waves (beta) was found at Fp2

o Deficiency in beta activity was found at posterior regions at T5, T6, P3, P4, O1 and O2.

o Deficiency in beta brainwave were often associated with problem in attention, learning disabilities and brain injuries.

Alpha activity

2. The presence of particular rhythm called “mu, a characteristic waveform found in the 8-13 hz (alpha) range over the sensorimotor cortex (C3 Cz and C4), which corresponds to social skills.

o The presence of Alpha indicates the presence of mirror-neuron activity, the variant that

might explain the ASD children’s’ behavioural imitation impairment and inability to mimic an

instructed task (Oberman et al, 2005)

3. The brain wave pattern of ASD group is characterised by lower Alpha frequency.

o Sufficient alpha is needed for sensory processing and integration and insufficient of alpha

brainwave is associated with anxiety state. However, excess of alpha brainwave is

associated with attention problem, depression and memory deficiency

4. There are excessively high frequency of alpha wave in the left hemisphere temporal area (T3) of ASD children at which indicated hyperfunctioning and is linked to impairment in verbal memory, leading to language and communication impairments.

Connectivity patterns

5. General disruption in the overall connectivity of the different lobes to themselves and to each other known as hyper or hypoconnectivity.

6. Coherence Abnormalities (found in the study in 50-60% of participants with ASD). Coherence has especially been shown disrupted on the right hemisphere at sites involved in social and emotional recognition mechanisms.

Other patterns

7. High Beta activity which corresponds to obsessing, overfocusing and anxiety (found in the study in 50-60% of participants with ASD).

o High beta at FP1 and FP2 at the right frontal lobe area is associated with anxiety, irritability and also poor integration which might explain language impairment and anxiety of children with ASD.

8. Abnormal EEG/Seizure activity (found in the study in 33% of participants with ASD).

9. Metabolic/Toxic pattern of lower overall EEG activity (found in the study in 10% of participants with ASD).

*The findings mentioned in this article have been summarised and organised from the article by Norsiah Fauzan, 2015. To read this article click here.



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