The study investigates the neural basis of global resting-state fMRI activity in monkeys, revealing that spontaneous fluctuations in local field potentials (LFPs) measured from a single cortical site are strongly correlated with fMRI signals across nearly the entire cerebral cortex. This correlation is particularly evident in the upper gamma frequency range (40–80 Hz), where the hemodynamic signal lags the neural signal by 6–8 seconds. A weaker but still positive correlation is observed in lower frequencies (2–15 Hz), with a lag closer to zero. The global pattern of correlation remains consistent regardless of whether the LFP signal is measured in occipital, parietal, or frontal electrodes. However, the coupling is dependent on the monkey's behavioral state, being stronger and anticipatory when the animals' eyes are closed. These findings suggest that the global component of fMRI fluctuations, often discarded in resting-state studies, is tightly coupled with underlying neural activity. The cerebral cortex is divided into specialized regions for various cognitive functions, yet the brain continues to show dynamic activity even in the absence of cognitive or sensory stimulation. Spontaneous activity has been observed in various species under different behavioral states, and fMRI allows visualization of large-scale spatial patterns of intrinsic activity. The temporal correlation between fluctuations in different regions is often taken as a measure of functional connectivity. These fluctuations typically exhibit highest intervoxel coherence at low temporal frequencies and can be observed during alertness, sleep, light sedation, and general anesthesia. In humans, spontaneous activity is typically investigated in the resting state, a condition where subjects lie in the scanner without explicit stimuli or tasks. Analysis of spatiotemporal coherence of fMRI activity reveals distinct domains of correlated activity, sometimes described as networks. These include the default-mode network, attentional networks, and networks in visual, auditory, and somatomotor cortex, as well as networks involving the thalamus, cerebellum, and basal ganglia. Global signal fluctuations in resting-state fMRI are often removed to focus on functional networks, but this process can affect the spatial pattern and polarity of measured correlations. However, some aspects of spontaneous fMRI fluctuations appear to arise from underlying neural activity. Electrophysiological studies in humans and animals suggest that slow fluctuations in high-frequency gamma LFP power exhibit spatial coherence over long timescales. A recent study directly demonstrated a strong link between spontaneous fMRI fluctuations and neural activity, including gamma-range LFP and spiking, in anesthetized monkeys. The study shows that spontaneous neural and fMRI signals are not only correlated but that the neural signal from a single cortical site is coupled to global fMRI fluctuations over large parts of the cerebral cortex. This coupling was observed in electrodes in the occipital, parietal, and frontal lobes, with consistent correlation found in the upper gamma frequency range (40–80 Hz). These findings demonstrate that global signal fluctuations commonly observed in human resting-state fThe study investigates the neural basis of global resting-state fMRI activity in monkeys, revealing that spontaneous fluctuations in local field potentials (LFPs) measured from a single cortical site are strongly correlated with fMRI signals across nearly the entire cerebral cortex. This correlation is particularly evident in the upper gamma frequency range (40–80 Hz), where the hemodynamic signal lags the neural signal by 6–8 seconds. A weaker but still positive correlation is observed in lower frequencies (2–15 Hz), with a lag closer to zero. The global pattern of correlation remains consistent regardless of whether the LFP signal is measured in occipital, parietal, or frontal electrodes. However, the coupling is dependent on the monkey's behavioral state, being stronger and anticipatory when the animals' eyes are closed. These findings suggest that the global component of fMRI fluctuations, often discarded in resting-state studies, is tightly coupled with underlying neural activity. The cerebral cortex is divided into specialized regions for various cognitive functions, yet the brain continues to show dynamic activity even in the absence of cognitive or sensory stimulation. Spontaneous activity has been observed in various species under different behavioral states, and fMRI allows visualization of large-scale spatial patterns of intrinsic activity. The temporal correlation between fluctuations in different regions is often taken as a measure of functional connectivity. These fluctuations typically exhibit highest intervoxel coherence at low temporal frequencies and can be observed during alertness, sleep, light sedation, and general anesthesia. In humans, spontaneous activity is typically investigated in the resting state, a condition where subjects lie in the scanner without explicit stimuli or tasks. Analysis of spatiotemporal coherence of fMRI activity reveals distinct domains of correlated activity, sometimes described as networks. These include the default-mode network, attentional networks, and networks in visual, auditory, and somatomotor cortex, as well as networks involving the thalamus, cerebellum, and basal ganglia. Global signal fluctuations in resting-state fMRI are often removed to focus on functional networks, but this process can affect the spatial pattern and polarity of measured correlations. However, some aspects of spontaneous fMRI fluctuations appear to arise from underlying neural activity. Electrophysiological studies in humans and animals suggest that slow fluctuations in high-frequency gamma LFP power exhibit spatial coherence over long timescales. A recent study directly demonstrated a strong link between spontaneous fMRI fluctuations and neural activity, including gamma-range LFP and spiking, in anesthetized monkeys. The study shows that spontaneous neural and fMRI signals are not only correlated but that the neural signal from a single cortical site is coupled to global fMRI fluctuations over large parts of the cerebral cortex. This coupling was observed in electrodes in the occipital, parietal, and frontal lobes, with consistent correlation found in the upper gamma frequency range (40–80 Hz). These findings demonstrate that global signal fluctuations commonly observed in human resting-state f