title: Temporal patterns of uncoupling between oxidative metabolism and regional cerebral blood flow demonstrated by functional magnetic resonance imaging.
abstract: OBJECTIVE
  Brain activation can be detected by functional magnetic resonance imaging. Termination of stimulation can cause drop of postactivation signal below preactivation baseline; the nature of this "undershoot" remains controversial. The authors investigated postactivation signal after stimulation of the visual cortex with photic stimuli of different duration.
  
  
  METHODS
  Activation of visual cortex in 11 healthy subjects was studied. The authors underwent short and long stimulation. The relation between activation and postactivation signal was investigated after both durations of stimulation.
  
  
  RESULTS
  Average postactivation signal after short stimulation was -1.71 +/- 2.66% and after long stimulation 0.82 +/- 1.59% (P < or = 0.01). Significant "undershoot" was detected after short stimulation in the majority of cases, although this was typically absent after long stimulation.
  
  
  CONCLUSIONS
  The authors propose that "undershoot" is caused by decreased oxygen content in venous blood compared with the preactivation level and may reflect increased extraction of oxygen as a result of glycolytic metabolism. The absence of "undershoot" after longer stimulation suggests a gradual shift from uncoupling between regional cerebral blood flow and oxygen consumption toward a steady state.
authors.affiliation: Department of Neurology, University Hospitals of Cleveland, Ohio, USA.
authors.forename: P
authors.initials: P
authors.lastname: Hedera
authors.forename: D
authors.initials: D
authors.lastname: Wu
authors.forename: J S
authors.initials: JS
authors.lastname: Lewin
authors.forename: D
authors.initials: D
authors.lastname: Miller
authors.forename: A J
authors.initials: AJ
authors.lastname: Lerner
authors.forename: R P
authors.initials: RP
authors.lastname: Friedland
mesh_terms: D000328:Adult; D002550:Cerebral Veins; D002560:Cerebrovascular Circulation; D005260:Female; D006019:Glycolysis; D006801:Humans; D007089:Image Enhancement; D008279:Magnetic Resonance Imaging; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption; D010775:Photic Stimulation; D013997:Time Factors; D014793:Visual Cortex / Q000098:blood supply / Q000378:metabolism*
chemical_list: D010100:Oxygen