8 Since then, fMRI has been widely used in both healthy subjects and patients with neurologic and psychiatric disorders to analyze synchronous, spontaneous fluctuations of various resting-state networks. 8 When the subjects were asked to perform bilateral finger tapping in that experiment, researchers identified a highly correlated BOLD time course between the left somatosensory cortex and the homologous areas in the contralateral hemisphere. The biologic significance of the neural activity fluctuations was first described by Biswal et al in 1995. The frequencies of neural activity fluctuations measured by fMRI (which are low-frequency and indirectly measured using BOLD signal) and of neural firing measured in neurophysiologic studies (which are high-frequency and are directly measured) are different. 3 The change in the BOLD signal is the cornerstone of functional MR imaging, 4, 5 which is traditionally used to construct maps indicating subspecialized brain regions that are activated by certain tasks or reacting to a stimulus at a low frequency (0.01–0.1Hz). More recent research suggests that BOLD signal is determined by both the arterial partial pressure of O 2 and CO 2, rather than CO 2 alone. Conventionally, BOLD signal change has been known to be modulated by the arterial partial pressure of CO 2 level. This imaging approach is called blood oxygen level–dependent (BOLD) contrast imaging. 1, 2 This process results in a change in terms of the relative levels of oxyhemoglobin and deoxyhemoglobin that can be detected by MR imaging on the basis of their differential magnetic susceptibilities.
When activated, they are provided with more energy by the adjacent capillaries through a process called the hemodynamic response, which supplies them with increased regional cerebral blood flow and an increase in oxygen supply, usually even greater than their needs. Neurons do not contain any internal reserves of energy, either in the form of glucose or oxygen.
Working in concert, these subspecialized areas orchestrate complex bodily functions and allow human behavior. Structurally, the brain is organized grossly into different regions specialized for processing and relaying neural signals functionally, the brain is subspecialized for perceptual and cognitive processes. The brain controls all the complex functions in the human body.