ADHD brain regions do not work well together

11 January 2010

Poor communication between the visual and attention centres

A study by Rubicon grant winner Ali Mazaheri has shown that a lack of communication between brain regions may result in ADHD symptoms. His conclusions add further support to the idea that ADHD is not due to a defect in the brain regions, but rather a deficit in interactions between the regions. The results of the study were published on 10 January in the journal Biological Psychiatry.

Using a simple test, Mazaheri and his colleagues studied whether the occipital lobe, responsible for visual observation, communicates well with the frontal lobe in children with ADHD (attention deficit hyperactivity disorder). The frontal lobe is responsible for activities such as attention, control of impulses and social behaviour.

During the experiment, the children first received a cue telling them what was going to happen: they then saw a figure or heard a sound. If they saw a V as the cue, the chance of a visual stimulus, the figure, was greatest and if they saw an inverted V (an A without the horizontal line), the chance of hearing a sound was greatest. Immediately after the cue, the picture appeared or the sound was heard. In the case of the former, the child had to state whether it saw a red or blue figure, and in the case of the latter whether it heard a low or high tone. All children were able to more quickly indicate what they heard or saw thanks to the prior warning. However, the children with ADHD were slower in all cases.

No reduction in activity

Mazaheri analysed the EEG activity in various brain regions to study why the children with ADHD responded slower. He first looked at whether there was a change in the activity of alpha waves at the back of the brain, where the lobe for visual observation is located. In “typical” children, brain activity in that region decreased once they had received the cue that they were to about to see something. The reduced activity was directly related to a rapid response. However, in children with ADHD, the level of activity did not change.

Front to back and back again

To find out how the visual cue was associated with the subsequent response – indicating whether a red or blue figure appeared or whether a low or high sound was heard – Mazaheri then examined activity in the front of the brain, where the frontal lobe is located. A previous study by him, also carried out with Rubicon funding, had shown that an increase in alpha wave activity at the back of the brain could predict future errors. After an error, there was a decrease in alpha wave activity at the back of the brain that was associated with an increase in activity at the front.

In the typical children, the test showed activity in the two regions to be linked, as expected: if activity fell in one region, it increased in the other. This indicated that the region controlling attention (anterior) and the region for observation (posterior) communicate with each other. However, this was not the case in children with ADHD. In these children, the level of activity in the two regions was not linked.

The EEG results obtained by Mazaheri showed that the activity in the attention-controlling region influenced the visual centre, thus preparing the brain to process the subsequent stimulus – the red or blue figure – properly. Normal children therefore see the cue, the information is passed on to the attention centre, which then prepares the visual centre so that it can respond quickly to the appearance of the figure. This preparation does not function optimally in children with ADHD, so they respond far slower. These results bring us a step closer to understanding the clinical picture of ADHD.

Ali Mazaheri was able to carry out his study thanks to funding from NWO’s Rubicon programme. Through Rubicon, NWO offers scientists who have recently obtained their doctorate degree the chance to carry out research at a top institute abroad. Mazaheri received his Rubicon award in 2007, and with it carried out research for two years at the University of California.

About NWO

The Netherlands Organisation for Scientific Research (NWO) is the principal Dutch science funding body and its mission is to facilitate excellent scientific research in the Netherlands by means of national competition. Each year NWO spends more than 700 million euro on grants for top researchers, on innovative instruments and equipment, and on institutes where top research is performed. NWO funds the research of more than 5300 talented researchers at universities and institutes. Independent experts select proposals by means of a peer review system. NWO facilitates the transfer of knowledge to society.

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Further information:

Publication details:
Functional Disconnection of Frontal Cortex and Visual Cortex in Attention Deficit Hyperactivity Disorder. A. Mazaheri, S. Coffey-Corina, G.R. Mangun, E.M. Bekker, A.S. Berry, B.A. Corbett

last modified on 12 February 2010