MONTREAL – Volumetric measurement of the brains of children with learning disabilities of unknown etiology has revealed subtle abnormalities in regions associated with the anterior thalamocortical tract that correlate with the severity of the learning disability, according to a report that merited the Best Abstract Award in a Clinical Topic at the 10th International Child Neurology Congress.
This Finnish study examined 122 children (average age, 12 years) who had learning problems that ranged from mild specific disabilities to severe intellectual limitations. A group of 43 children in mainstream education served as controls, said Dr. Taina Autti, who is with the Helsinki Medical Imaging Center and Helsinki University Central Hospital.
The children underwent conventional magnetic resonance imaging with a 1.5-tesla magnet.
Three-dimensional images were then generated for volumetric analyses, and fluid-attenuated inversion recovery (FLAIR) and T2-weighted coronal images were examined for possible abnormalities. Voxel-based morphometry was used to compare local volumes of gray matter, white matter, and cerebrospinal fluid between study groups. Each voxel was 1 mm
Thirteen children were found to have structural abnormalities, such as optic glioma, enlarged ventricles, enlarged sulci, and vermis atrophy, and were eliminated from further analysis. For the remaining 152 participants, conventional MRI showed no apparent gross structural abnormalities.
When the investigators searched for brain areas where local volume correlated with degree of learning disability, several regions stood out:
▸ In the anterior cingulate cortex, a significant positive correlation was found with gray matter volume (Tmax = 5.50, P < .001). (See images.)
▸ In the left frontoparietal lobe, a significant positive correlation was found with white matter volume (Tmax = 5.34, P < .001).
▸ In the left thalamus, a significant negative correlation was found with gray matter volume (Tmax = 5.26, P < .001).
▸ In the posterior internal capsules, a significant negative correlation was found with white matter volume (TmaxRight = 5.57, P < .001; TmaxLeft = 5.20, P < .001).
The study findings indicate dysfunction of the anterior thalamocortical tracts, which begin in the anterior mediodorsal nucleus of the thalamus, pass through the anterior internal capsule, and terminate in the anterior cingulate gyrus or prefrontal cortex, according to Dr. Autti.
The anterior cingulate cortex plays a central role in many cognitive tasks–functions that are often disturbed in children with learning disabilities, Dr. Autti said. These include cognitive flexibility, initiation of appropriate behaviors, suppression of inappropriate behaviors, attentiveness, adaptability, alertness, motivation, fluid thought transfer, and the ability to evaluate options and make choices. “The greater gray volume in the anterior cingulate cortex may be the unifying feature in learning disabilities of unexplained, familial etiology,” Dr. Autti said.