BOLD signal sign and transient vessels volume variation

Near-infrared study of the underlying physiology of the functional magnetic resonance signal in humans during hypoxia

“…However, other experimental paradigms such as breath holding, may produce different cerebral hemodynamic responses, and therefore they can be used to further investigate the physiological basis of the BOLD signal. Cerebrovascular reactivity to the hypoxia was previously separately studied both by NIRS [2] and fMRI [3,4]. Studying cerebral vasomotor responses to altered CO 2 tension is clinically important because they can be used to determine the cerebrovascular reserve capacity and to access the autonomic disturbance in a number of clinical syndromes, including neuropathies, sleep disorders, and other diseases.…”

“…Studying cerebral vasomotor responses to altered CO 2 tension is clinically important because they can be used to determine the cerebrovascular reserve capacity and to access the autonomic disturbance in a number of clinical syndromes, including neuropathies, sleep disorders, and other diseases. In fMRI study [3] the authors…”

Identification of activated regions during a language task

“…While these positive signal changes reflect an increase in task-induced functional activity, in general, a substantial fraction of the signal does not correlate with the task, and an important observation in fMRI studies is the prolonged negative BOLD signal change, the so-called negative BOLD response (NBR), found in some brain regions during stimulation [21][22][23][24]. Several researchers already account for it when assigning a meaning to functional activation maps, particularly when more complicated stimuli and experimental paradigms, like a language task, are used.…”