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. Author manuscript; available in PMC: 2013 Aug 1.
Published in final edited form as: NMR Biomed. 2012 Sep 4;26(8):987–1003. doi: 10.1002/nbm.2847

Figure 1.

Figure 1

The blood oxygenation level-dependent (BOLD) response is a complex signal. Basic sensory stimuli elicit an increase in neural activity, resulting in an increase in the cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMRO2). CBF increases to a larger degree than CMRO2, and also leads to a local increase in the cerebral blood volume (CBV). The amplitude of the resulting BOLD response is not only dependent on these changes, but also on the baseline physiological state. This baseline is determined by the blood haematocrit (Hct), resting oxygen extraction fraction (OEF) and CBV. An increase in CBF causes an increase in the BOLD signal, whereas increases in venous CBV (CBVv) and CMRO2 cause a decrease. Typically, the CBF effect is dominant, creating a positive BOLD response. The maximum BOLD signal change is determined by the baseline physiological state and increases with increasing Hct, OEF and CBV.