Limits on activation-induced temperature and metabolic changes in the human primary visual cortex

• Published in: Magnetic resonance in medicine 2006-08, Vol.56 (2), p.348-355
• Main Authors: Katz-Brull, Rachel, Alsop, David C., Marquis, Robert P., Lenkinski, Robert E.
• Format: Article
• Language: English
• Subjects: Adult; Algorithms; Analysis of Variance; Aspartic Acid - analogs & derivatives; Aspartic Acid - metabolism; Body Temperature; brain activation; cerebral blood flow; Cerebrovascular Circulation; Choline - metabolism; Female; Glutamic Acid - metabolism; Humans; Inositol - metabolism; Lactates - metabolism; Magnetic Resonance Imaging; magnetic resonance spectroscopy; Magnetic Resonance Spectroscopy - methods; Male; Middle Aged; N-acetylaspartate; Photic Stimulation; temperature; Visual Cortex - metabolism
• ISSN: 0740-3194; 1522-2594
• DOI: 10.1002/mrm.20972

Changes in cerebral blood flow (CBF) and metabolism are now widely used to map and quantify neural activity, although the underlying mechanism for these changes is still incompletely understood. Magnetic resonance spectroscopy (MRS) at 3T, synchronized with a 32‐s block design visual stimulation paradigm, was employed to investigate activation‐induced changes in temperature and metabolism in the human primary visual cortex. A marginally significant increase in the local temperature of the visual cortex was found (0.1°C, P = 0.09), excluding the possibility of a temperature decrease (95% confidence interval (CI) = 0.0–0.2°C), which was previously suggested. A comparison with models of thermal equilibrium in the presence of blood flow suggests that an increase in heat production during activation, greater than or at least equal to that produced by the complete oxidative metabolism of the elevated glucose (Glc) utilization accompanying activation, would be required to offset the cooling effects of the increased blood flow. The total pools of glutamate (Glu), glutamine (Gln), myo‐Inositol (mI), N‐acetylaspartate (NAA), choline (Cho), and lactate (Lac) were not significantly affected by activation. Limits on Lac concentration changes were too weak to constrain theories of the metabolic use of elevated Glc consumption during stimulation, and emphasize the challenges of measuring even large Lac changes accompanying stimulation. Magn Reson Med, 2006. © 2006 Wiley‐Liss, Inc.