Physiological Basis of BOLD fMRI Decreases

Recent studies suggest that positive functional magnetic resonance imaging (fMRI) signal changes in the cortex under normal physiological conditions are closely related to increased neuronal activity. However, the physiological basis of negative blood oxygen level-dependent (BOLD) fMRI signal changes in the cortex as well as in subcortical structures are less well understood. Animal models that employ combined neuroimaging and direct electrophysiological measurements provide a powerful avenue for studying the complex relationships between negative fMRI changes and neuronal activity under normal and abnormal conditions (such as epilepsy). Several animal studies have shown that fMRI decreases do not necessarily translate to decreased electrophysiological signals. Here, we review three such scenarios: (1) increased local field potentials (LFP) occur during cortical slow oscillations despite reduced mean neuronal firing, resulting in decreased BOLD, cerebral blood flow (CBF) and cerebral blood volume (CBV); (2) massive increases in neuronal activity during hippocampal seizures exceed the ability of CBF to meet metabolic demands leading to decreased local BOLD fMRI signals; (3) reverse coupling of neuronal activity and CBF in the basal ganglia leads to increased neuronal firing and LFP during normal somatosensory stimulation and spike-wave seizures, along with a paradoxical decrease in BOLD fMRI, CBF, and CBV. A better understanding of the physiological basis underlying BOLD fMRI ...
Source: Springer protocols feed by Neuroscience - Category: Neuroscience Source Type: news