Neuronal correlates of spontaneous fluctuations in fMRI signals in monkey visual cortex: Implications for functional connectivity at rest

Abstract

Recent studies have demonstrated large amplitude spontaneous fluctuations in functional-MRI (fMRI) signals in humans in the resting state. Importantly, these spontaneous fluctuations in blood-oxygenation-level-dependent (BOLD) signal are often synchronized over distant parts of the brain, a phenomenon termed functional-connectivity. Functional-connectivity is widely assumed to reflect interregional coherence of fluctuations in activity of the underlying neuronal networks. Despite the large body of human imaging literature on spontaneous activity and functional-connectivity in the resting state, the link to underlying neural activity remains tenuous. Through simultaneous fMRI and intracortical neurophysiological recording, we demonstrate correlation between slow fluctuations in BOLD signals and concurrent fluctuations in the underlying locally measured neuronal activity. This correlation varied with time-lag of BOLD relative to neuronal activity, resembling a traditional hemodynamic response function with peaks at approximately 6 s lag of BOLD signal. The correlations were reliably detected when the neuronal signal consisted of either the spiking rate of a small group of neurons, or relative power changes in the multi-unit activity band, and particularly in the local field potential gamma band. Analysis of correlation between the voxel-by-voxel fMRI time-series and the neuronal activity measured within one cortical site showed patterns of correlation that slowly traversed cortex. BOLD fluctuations in widespread areas in visual cortex of both hemispheres were significantly correlated with neuronal activity from a single recording site in V1. To the extent that our V1 findings can be generalized to other cortical areas, fMRI-based functional-connectivity between remote regions in the resting state can be linked to synchronization of slow fluctuations in the underlying neuronal signals.

Mesoscale infraslow spontaneous membrane potential fluctuations recapitulate high-frequency activity cortical motifs

“…In agreement with these studies, advancements permitting simultaneous localized neurophysiological measurements alongside fMRI indicate that changes in low-frequency (2-15 Hz) LFP and the slow modulation of gamma frequency LFP signals are strong neurophysiological correlates of activity for both evoked-and resting-state BOLD signal fluctuations in nonhuman primates 45,47,48 . Similar correlative findings between spontaneous infraslow (o0.1 Hz) frequency activity in LFP and resting-state BOLD signal have also been observed in anaesthetized rats 38 .…”

“…Neuroimaging of spontaneous infraslow activity has been the focus of tremendous research interest, but has typically relied upon imaging modalities that indirectly reflect neuronal activity [45][46][47][48] and have thus raised questions about the underlying nature and interpretation of these data 22,36 . Innovative efforts to directly assess the neurophysiological basis of fMRI BOLD signal fluctuations have revealed much about the best electrophysiological correlates of these signals, but these approaches require specialized recording equipment and technical analysis to remove electrical artifacts and are limited in their spatial coverage.…”

Local synchronization and amplitude of the fluctuation of spontaneous brain activity in attention-deficit/hyperactivity disorder: a resting-state fMRI study

“…It seems that the neurophysiology of ALFF is more straightforward than that of ReHo. LFFs are associated with activity of the gamma band in monkeys [26] , the delta band in rats [27] , and the alpha band in humans [28,29] . High local synchronization was revealed between the local field potentials from multiple cortical electrodes with a physical distance ranging from 2.6 mm to 10.6 mm in an electrophysiological study, and such local synchronization could be modulated by stimulation [30] .…”

Europe's green billions

“…It was, however, published online 2 Officials at the Department of the Interior say the request will be considered by the committee that reviews the return of remains and artefacts when it meets in Seattle, Washington, on 23-24 May.…”