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In 1890 Roy and Sherrington's paper 'On the regulation
of blood supply of the brain' suggested that neural activity was accompanied
by a regional increase in cerebral blood flow. Until 1990 there was
no way of non-invasively measuring the flow of blood in cortical areas.
Ogawa and Lee at the AT and T Bell Laboratories working on rodents discovered
that the oxygenation level of blood acts as a contrast agent in MR images.
They demonstrated that signals received from vessels were altered by drug-induced
changes in blood flow from the brain. It was suggested that
this is a consequence of changing the content of deoxyhemoglobin in the
blood.
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