Neuronal correlates of the BOLD signal during visual stimulations
Open Access
- Author:
- Zhang, Qingqing
- Graduate Program:
- Bioengineering (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 07, 2022
- Committee Members:
- Patrick Drew, Major Field Member
Bruce Gluckman, Major Field Member
Xiao Liu, Major Field Member
Nanyin Zhang, Chair & Dissertation Advisor
Thomas Neuberger, Outside Unit & Field Member
Daniel Hayes, Program Head/Chair - Keywords:
- Unanesthetized rat fMRI
visual stimulation
BOLD signal
neuronal signal - Abstract:
- The blood oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has been widely used to study brain functions with the assumption that it provides an indirect measurement of neuronal-related events. Despite its popularity, there are still important unresolved issues in BOLD-fMRI. First, it is well known that BOLD responses exhibit considerable variations to identical stimulation presentations. To quantitatively characterize this variability, the BOLD signal has been modeled as a linear summation of a stimulation-relevant and a stimulation-irrelevant (i.e., ongoing) component. However, a systematic investigation of the spatiotemporal features of the brain-wide ongoing BOLD component and how these features affect the trial-to-trial variability of BOLD responses are still lacking. To explore these questions, we collected the brain-wide BOLD response with fMRI and local neuronal response with fiber photometry during sustained light ON-OFF stimulations in unanesthetized rats. Our data for the first time revealed the BOLD responsive features to the visual stimulation onset and offset in unanesthetized rodents. Importantly, the cross-region BOLD responses were highly correlated at zero time lag. A linear model with the ongoing response estimated from the rest of the brain explained a large amount of the variance in the measured BOLD responses of visual regions, and removing this ongoing response improved the detection sensitivity of fMRI. Furthermore, in a significant portion of trials, negative BOLD ongoing activity was brain-wide and dominated over the stimulation-induced response, while populational neuronal firing measured by calcium-based fiber photometry remained unchanged. The second unresolved issue in BOLD-fMRI is that when the BOLD response is more complex than a stimulation-related monophasic impulse function, how BOLD signals in different phases relate to neural (or non-neural) signals has remained elusive. With the visual stimulation paradigms we developed, we observed reproducible multi-phase BOLD responses. Results from electrophysiological recordings in unanesthetized rats experiencing the same paradigms as in the fMRI experiments showed that the temporal evolution of the muti-unit activity (MUA) band (300 – 3000 Hz) power, rather than the gamma-band (30 – 100 Hz) power, highly resembled the BOLD dynamics. This result suggests that when populational neuronal spiking is dissociated from the gamma LFP, post-stimulus phases of the BOLD response can be better explained by the MUA signal.