Introduction from Dr Markus Reuber, editor-in-chief of Seizure
The epilepsies are disorders of brain, an organ we know a lot about, but one that also harbours many known, and even more unkown unknowns. Of course, at the personal level some of this lack of knowledge is simply due to not having learned things about the brain (or having forgotten them again). My editor’s choice feature from the current issue of Seizure “Corpus callosum and epilepsies” by Iris Unterberger et al. can help to address this problem, at least with respect to one of the brain’s largest white matter tracts. The reader will learn that this fibre bundle carries around 190 million axons, and that it’s congenital agenesis is one of the commonest malformations of the brain. Although about two third of patients with congenital agenesis of the corpus callosum (AGCC) have epilepsy, epilepsy does not seem to be caused by AGCC as such but by other associated structural abnormalities of the brain. The review also discusses corpus callosotomy, which continues to be a surgical treatment option, especially for epileptic drop attacks.
My own interest in the corpus callosum goes back to coming across research carried out on illiterate adults who underwent brain imaging before and after a programme intended to teach them to read and write (2). An increase in the size of the corpus callosum was seen in those who had successfully acquired these new complex skills. This research is quite “old hat” now, but like the study demonstrating structural changes in the brains of London cab drivers taking “the Knowledge” (an examination in which they have to demonstrate their knowledge of London’s network of over 25000 streets) (3), it had a significant influence on our understanding of the plasticity of the brain.
Whilst the review by Iris Unterberger et al. will bring the reader’s knowledge of known knowns about the corpus callosum and the epilepsies up-to-date, it can only make us wonder about the answers to some bigger questions about the brain in general and the largest connection between the two hemispheres of the brain in particular. Why is there no closer relationship between structural integrity of this important fibre bundle and brain function? How (and in which cases) does callosotomy cause functional effects (deficits or benefits) which are only temporary? Could the high degree of plasticity evident from the observations above be used therapeutically – for instance with interventions inhibiting callosal transmission or treatments facilitating callosal connectivity?
(1) Unterberger I, Bauer R, Walser R, Bauer G. Corpus callosum and epilepsies, Seizure 2016; 37: 55-60.
(2) A. Castro-Caldas, P. Cavaleiro Miranda, I. Carmo et al., Influence of learning to read and write on the morphology of the corpus callosum, European Journal of Neurology 1999; 6: 23–28.
(3) Woollett K and Maguire EA. Acquiring “the Knowledge” of London’s Layout Drives Structural Brain Changes. Curr Biol 2011; 21: 2109–2114.