Oscillatory neural dynamics play an important role in the coordination of large-scale brain networks. High-level cognitive processes depend on dynamics evolving over hundreds of milliseconds, so measuring neural activity in this frequency range is important for cognitive neuroscience. However, current noninvasive neuroimaging methods are not able to precisely localize oscillatory neural activity above 0.2 Hz. Electroencephalography and magnetoencephalography have limited spatial resolution, whereas fMRI has limited temporal resolution because it measures vascular responses rather than directly recording neural activity. We hypothesized that the recent development of fast fMRI techniques, combined with the extra sensitivity afforded by ultra-high-field systems, could enable precise localization of neural oscillations. We tested whether fMRI can detect neural oscillations using human visual cortex as a model system. We detected small oscillatory fMRI signals in response to stimuli oscillating at up to 0.75 Hz within single scan sessions, and these responses were an order of magnitude larger than predicted by canonical linear models. Simultaneous EEG-fMRI and simulations based on a biophysical model of the haemodynamic response to neuronal activity suggested that the blood oxygen level-dependent response becomes faster for rapidly varying stimuli, enabling the detection of higher frequencies than expected. Accounting for phase delays across voxels further improved detection, demonstrating that identifying vascular delays will be of increasing importance with higher-frequency activity. These results challenge the assumption that the haemodynamic response is slow, and demonstrate that fMRI has the potential to map neural oscillations directly throughout the brain.
Functional magnetic resonance imaging (fMRI) is a powerful tool for understanding both brain structure and activity. fMRI measures brain activity very indirectly, by tracking blood oxygenation, which is thought to lag activity by a few seconds. fMRI measures slow changes in blood oxygenation rather than directly recording brain activity.
fMRi scans every second or so, but ultra fast MRI can scan the brain once every 200 milliseconds (200 thousandth of a scecond) , which should acquire data faster. Using ultra-fast MRI scans, it was possible to track rapid oscillations in brain activity that before would have gone undetected and may open the door to understanding fast-occurring cognitive processes .
In this study they placed volunteers in scanners, then rapidly flashed images on a screen. It was found that the researchers were easily able to track the signals of brain activity, even when images were flashed once every two seconds.Many of the things by fMRI are the complicated things people do, like using language or high-level cognition, and these happen in hundreds of millisecond timescales. Fast fMRI studies potentially could resolve the spatial distribution of these dynamics across the entire cortex and in subcortical structures simultaneously, yielding new insight into the role of oscillatory neural dynamics in human cognition.