Fascinating. I had no idea that the brain stores glycogen. Depletion of these stores could be another mechanism - alongside the known ones - whereby lack of carbohydrate availability can induce depression.
Although the amounts stored are small, turnover is very slow (3-5 days for depletion - see Human brain glycogen content and metabolism: implications on its role in brain energy metabolism). Hence, as well as protecting the brain from hypoglycaemia in times of stress, could the level of brain glycogen be used as a sensitive indicator of glycogen levels in the muscles and possibly the liver? I also note that the 3-5 days depletion corresponds with good results from carbing up or calorie cycling about once a week.
I like the idea that sprinting in workouts could help the brain load more glycogen to enable it to sprint when it's problem-solving.
F 5 ft 3. HW: 196 lbs. Primal SW (May 2011): 182 lbs (42% BF)... W June '12: 160 lbs (29% BF) (UK size 12, US size 8). GW: ~24% BF - have ditched the scales til I fit into a pair of UK size 10 bootcut jeans. Currently aligning towards 'The Perfect Health Diet' having swapped some fat for potatoes.