Partial claims were made here: http://www.naturalnews.com/023880.html
Following claim can be found at Sirsasana wikipedia page:
Practitioners of yoga believe that, like most inverted positions, the practice of sirsasana may increase the flow of blood to the brain, improve memory and other functions of the cerebrum. Included in the physiological benefits are the drainage of blood and lymph which are held in reserve in the legs. Any inversion, when the legs are held over the heart, helps to move stored fluids into the core for oxygenation, filtration and elimination of metabolic/cellular wastes.
Is it true? if yes - how many minutes?