Proof! Narcolepsy does not significantly shrink your brain.
The latest issue of Sleep has looked at brain tissue changes in patients with narcolepsy and cataplexy. Dr Scherfler and his team from Innsbruck University used something called diffusion-tensor imaging to look at the brain. This included measurements of mean diffusivity (MD), which is a parameter of brain tissue integrity, fractional anisotropy (FA), which is a parameter of neuronal fibre integrity, and voxel-based morphometry, which is a measure of gray and white matter volume. All this was done to detect brain tissue changes in 16 patients with narcolepsy-cataplexy and a matched healthy control sample of 12.
The study looked at the whole brain but of course focussed on some areas where changes in the structure of the brain should be expected in people with narcolepsy. They were particularly interested in the volumes of white and grey matter compartments and these were analysed using statistical parametric mapping.
The report shows significant mean diffusivity (MD) increases and as expected fractional anisotropy (FA) decreases which were localised in the fronto-orbital cortex and the anterior cingulate in the narcolepsy-cataplexy patients. Additional MD increases without FA changes were detected in the ventral tegmental area, the dorsal raphe nuclei and of course the hypothalamus. FA signal decreases were observed in the white matter tracts of the inferior frontal and inferior temporal cortices of narcolepsy-cataplexy patients. They also discovered small brain volume loss in focal areas of the inferior and superior temporal cortices and the cingulated compared to the control sample
This all sounds so much alphabet soup so what does it mean? In terms of the cell loss this does seem to be contained within the hypothalamus and confirms what doctors have been suggesting for years. That whatever triggers the loss of hypocretinergeric cells, attacks just those cells and not other areas of the brain. They study also showed signal abnormalities that correspond to major synaptic targets of hypocretin neurons that were associated with the regulation of the sleep-wake cycle. Or that once again this study showed that reduced hypocretin does cause problems with the sleep-wake cycle. The final and possibly most interesting finding was the changes in tissue in the frontal cortex an area that is crucial in the maintenance of attention and reward-dependent decision making, both known to be impaired in narcolepsy-cataplexy.
We reported in 2011that research has shown that people with narcolepsy had a higher incidence of obesity and risk taking than the norm. This study does seem to show that there is a physical reason for this that is caused by the progress of the condition. Our suggestion that taking people with narcolepsy to Las Vegas was probably a bad idea remains – even though our American cousins had their conference there last year!