Fig. 3. Activation at the nerve entrance (N) following a 10°C temperature drop, as determined by blood oxygenation level-dependent-weighted (BOLD) functional magnetic resonance images (fMRI). (A) T₂-weighted high-resolution spin echo image showing the complex (N) of trigeminal, facial, acoustic and anterior lateral line nerve extending from the brain. The image resolution does not allow for separate identification of the cranial nerves. tel, telencephalon. (B) Average of the color-coded percentual BOLD difference maps within the first 5 min after the onset of the temperature drop overlaid on the high-resolution image. The brain region surrounding the entrance of the cranial nerves is transiently activated (blue, reduced BOLD signal intensities). Some increase in BOLD signal intensities (red) can sometimes be observed in other brain regions. Scale bar, 2.5 mm. (C) The transient decrease of BOLD signal intensity measured in the region surrounding the entrance of the cranial nerves is not accompanied by any substantial change in cerebral blood volume (CBV; D) from which it is concluded that the decreased BOLD signal is a result of increased cellular activity. (D) CBV signal intensity changes in the region surrounding the entrance of the cranial nerves. Values are means ± s.d. (N=3).