REGIONAL BRAIN BLOOD-FLOW IN THE OVINE FETUS DURING TRANSITION TO THELOW-VOLTAGE ELECTROCORTICAL STATE

Sequential changes in cerebral blood flow and regional distribution we re studied in nine chronically catheterized fetal sheep during the tra nsition to the low-voltage ECOG (REM) state to determine the time cour se for blood flow change within the brain and whether executive centre s for REM state generation might thus be identified. Blood flows were measured during the first, second and third minutes after the transiti on to the low-voltage ECOG state and during the third minute of the su bsequent high-voltage ECOG (NREM) state using the radioactive labelled microsphere technique. Blood now to the brain was increased during th e low-voltage REM state when compared to that of the high-voltage NREM state, with the increase evident when measured during the first minut e after the state transition and with no sequential change thereafter. Regional blood flow increases during the low-voltage state were great est to those areas variously associated with the generation of REM sta te activity, but were again remarkably stable through the first 3 minu tes after the state transition. This rapid increase in blood flow with in the brain and the regional hierarchy for such, supports the partici pation of multiple anatomical areas which are highly integrated and ac t in concert to give rise to what is known as the REM state.