Neurophysiological investigation of the basis of the fMRI signal

Abstract

Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trial-by-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.

Frontal theta EEG activity correlates negatively with the default mode network in resting state

“…A relative increase in theta oscillations could therefore lead to a decrease in the BOLD signal. Simultaneous recording of hemodynamic responses and intracortical electrophysiological responses in the visual cortex of cat (Niessing et al, 2005) and monkey (Logothetis et al, 2001;Shmuel et al, 2006) corroborate this notion. In the cat, Niessing et al (2005) reported negative correlations in between lower frequencies (delta and theta) and the hemodynamic responses, and strong positive correlations with gamma band activity during visual stimulation.…”

Abnormal oxygen homeostasis in the nucleus tractus solitarii of the spontaneously hypertensive rat

“…The post‐stimulus $P_{\mathrm{normalt}{\mathrm{O}}_2}$ overshoot is known to be uncoupled from metabolic demand (Leithner & Royl, 2014) and is determined by increases in local synaptic activity itself and the ability of the neurovascular unit to respond to increases in synaptic transmission (Logothetis et al . 2001). However, previous studies have shown that preconstriction of the cerebral vasculature can enhance the BOLD response evoked by somatosensory stimulation (Mulderink et al .…”

Maximizing sensitivity for fast GABA edited spectroscopy in the visual cortex at 7 T

“…The relationship between BOLD signals and excitatory neuro‐metabolic processes has been studied extensively; however, the relationship between BOLD signals and inhibitory neuro‐metabolic processes is less well understood 3, 4, 5. One of the key inhibitory metabolites is γ‐aminobutyric acid (GABA), which is the main inhibitory neurotransmitter of the brain and is believed to have a direct impact on BOLD contrast through regulation of neuronal firing rates 6, 7, 8. In the human brain in vivo , the relationship between GABA and BOLD signals has been investigated in studies that combined fMRI and MRS 7, 9, 10, 11, 12, 13, 14, 15…”