Brain regions affected by ADHD
1. Brain regions affected by ADHD
ADHD is associated with changes in various regions of the brain:
- Nucleus caudates
- Largest reductions in gray matter in:
Frontal-parietal brain regions
- Limbic system
- Corpus mamillare
- Memory formation, in the context of the Papez neuron circle
- Sexual functions
- Cingulate gyrus
- Vegetative functions
- Psychomotor and locomotor drive
- Parahippocampal gyrus
- Primarily transmits information from the limbic system to the hippocampus
- Memory formation
- Memory formation
- Vegetative and emotional functions
- Storage of emotionally moving memory content
- Vegetative and sexual functions
Significant hypoactivation in
- Several frontal-temporal brain regions
- Right postcentral gyrus
- Left insula
An analysis of car accidents in unaffected people found a correlation between percuneus volume and car accidents that is consistent with changes in ADHD.
2. Volume changes in brain regions with ADHD
In ADHD, the volume of various brain regions is altered.
In children with ADHD, MRI studies found that compared to those not affected
- Total brain volume reduced
- Caudates downsized
Anterior PFC reduced
- Orbital PFC reduced, predominantly on the right
Inferior dorsolateral frontal region
Striatum reduced in size
- Globus pallidus reduced in size
- Central vermis area, predominantly reduced on the right
- Reduced, mostly underactivated
- Splenium (beam bulge) reduced
- Thalamus changes or hypoactive
The effects are stronger in boys than in girls, which correlates with the Polygenic Risk Score.
One study investigated structural and functional changes in the glymphatic system in treatment-free children with ADHD. The cerebral volume of the Virchow-Robin spaces was increased by 32 % (15.514 mL vs. 11.702 mL).
Interestingly, the reduction in the size of certain brain regions that is usually observed from the age of 60 appears to be less pronounced in ADHD. This is discussed as a neuroprotective factor of ADHD. It remains to be seen whether this is a consequence of ADHD itself or of stimulant treatment.
This is particularly significant in brain regions in which a strong loss of volume correlates with cognitive impairment and Alzheimer’s, such as the hippocampus and amygdala.
3. White substance
The white matter consists mainly of neurons and their extensions (axons). Myelinated axons look white.
A meta-analysis of 129 studies with n = 6739 ADHD sufferers and n = 6476 controls found conspicuous changes in the posterior interhemispheric connections responsible for the cognitive and motor functions affected by ADHD:
- reduced fractional anisotropy (FA) in the projection, commissural and association pathways, which correlated with symptom severity and cognitive deficits
- consistently reduced FA in the splenium and corpus callosum, extending to the cingulum
- lower FA was only found in old age, not in children
- possibly due to the late development of the callosal fibers
In ADHD, a significantly increased axial diffusivity was found in the right cingulum bundle.
Children with ADHD showed microstructural changes and alterations in long-range white matter connections. Learning problems and hyperactivity/impulsivity correlated negatively with the mean FA value in the right forceps major (the occipital part of the fibers of the corpus callosum), the left IFOF and the left genu capsulae internae.
One study found no differences in ADHD with regard to myelin content in the entire brain.
ADHD correlated with
- a higher mean myelin volume fraction in
bilateral inner capsule
- outer capsule
- Corona radiata
- left tapetum
- left superior fronto-occipital fascia
- right cingulum
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