Mid-Cingulate Cortex Degeneration in ALS

By: Lorna Poplak

A study published in the February 2011 edition of the American Journal of Neuroradiology adds to the growing body of pathologic and imaging evidence that there is degeneration of the brain beyond the primary motor area in ALS. A team of researchers from the University of Alberta embarked on the study to assess neurodegeneration in three regions of the brain — the motor cortex, the mid-cingulate cortex (MCC), a region that plays a role in the cognitive control of movements, and the thalamus, a subcortical relay station for both sensory and motor information. The study was conducted in vivo through the use of magnetic resonance spectroscopic imaging (MRSI). The researchers hypothesized that the spectroscopic marker of neuronal integrity, N-acetylaspartate, expressed in the study as an N-acetylaspartate/choline (NAA/Cho) ratio, would be reduced in these regions.

MRSI was performed on 14 patients with ALS and 14 healthy controls. The results corroborated previous studies that have shown reduced NAA/Cho in the motor cortex. Where this study broke new ground was in establishing that NAA/Cho was reduced by 14 per cent in the MCC of patients with ALS as compared with the controls. There was, however, no difference in NAA/Cho in the thalamus.

Furthermore, the researchers found specific relationships between the NAA/Cho values of each of the three regions studied in healthy subjects. These relationships were lost in patients with ALS, suggesting that degeneration in these regions is not dependent on the connections between them.

Sanjay Kalra, MD, associate professor of neurology and co-director of the multidisciplinary ALS clinic at the University of Alberta, and the senior author of the study, explains: “If degeneration in a region, say, the mid-cingulate cortex, was linked to the deleterious effects in another, such as the motor cortex, then one would have expected the relationship of NAA/Cho to be retained between these two areas. Because it was not, it is likely that the two regions degenerate independently due to local processes.” He adds that longitudinal studies and studies with other imaging modalities such as diffusion tensor imaging would help to improve our understanding of altered neurochemistry and connectivity between regions in the brain, as well as their significance with regard to degeneration and clinical effects.

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