Effect of acute hyperglycemia on visual cortical activation as measured byfunctional MRI

To determine whether acute hyperglycemia changes the hyperemic response to functional activation of brain, the area and magnitude of the activation we re measured in healthy volunteers maintained at euglycemia and then at hype rglycemia using the hyperglycemic clamp technique. Activation of the visual cortex (8-16 Hz) was assessed by functional MRI with blood oxygenation lev el dependent (BOLD) contrast using a 4 Tesla magnet and a multi-slice echo- planar imaging sequence (TE = 30 msec, TR = 1.5 sec). At euglycemia (4.8 +/ - 0.2 mM, mean +/- SEM, n = 6), the number of activated pixels in the occip ital lobe was 79 +/- 10 and the intensity of activation was 4.5 +/- 0.5%. D uring hyperglycemia (plasma glucose 300% of control), the number of activat ed pixels was 90 +/- 20% of control and the BOLD activation was 3.5 +/- 0.3 %, respectively. The change in BOLD signal was below 0.2%/mM plasma glucose . This study demonstrates that acute hyperglycemia is without substantial e ffect on the size and intensity of activation of the occipital cortex. The results further suggest that fluctuations in blood glucose within the physi ologic range are without effect on the functional activation of the cerebra l cortex measured by BOLD fMRI. (C) 2000 Wiley-Liss, Inc.