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GABA, glutamatergic dynamics and BOLD contrast assessed concurrently using functional MRS during a cognitive task
Alexander R Craven1,2,3, Gerard Dwyer1,3, Lars Ersland2,3
1Department of Biological and Medical Psychology, University of Bergen, Bergen, Norway.
NMR in Biomedicine
|October 28, 2023
Summary
This study links brain activity (BOLD) to neurochemistry by simultaneously measuring glutamate and GABA with functional magnetic resonance spectroscopy (fMRS) during a cognitive task. Results show increased Glx levels during task performance, validating the new simultaneous measurement technique.
Area of Science:
- Neuroimaging
- Neurochemistry
- Cognitive Neuroscience
Background:
- Linking task-evoked hemodynamic responses (BOLD-fMRI) to synaptic neurochemistry remains a challenge.
- Neurotransmitters like glutamate and GABA are typically measured separately from fMRI and without cognitive tasks.
- Simultaneous measurement of BOLD and neurochemistry during tasks is needed to bridge this gap.
Purpose of the Study:
- To develop and validate techniques for simultaneously assessing GABA, glutamate/glutamine (Glx), and BOLD responses during a cognitive task at 3T.
- To resolve the disconnect between task-based fMRI and underlying neurochemical changes at the synaptic level.
Main Methods:
- Healthy participants (N=81) performed the Eriksen flanker task in a block design.
- Simultaneous functional magnetic resonance spectroscopy (fMRS) and BOLD-fMRI were acquired from the medial anterior cingulate cortex.
- An adapted MEGA-PRESS sequence with water-reference signals enabled continuous BOLD assessment via water linewidth changes.
- A novel linear model processed fMRS data to extract metabolite spectra linked to functional stimuli.
Main Results:
- fMRS-assessed BOLD activation correlated significantly with fMRI BOLD, localized to the region of interest.
- fMRS-assessed BOLD also correlated with increased response time in the incongruent flanker condition.
- A significant increase (~8.8%) in Glx levels was observed between task-OFF and task-ON periods; no significant task-related GABA+ changes were found.
Conclusions:
- The developed protocol and analysis pipelines are effective for simultaneously assessing metabolite dynamics and BOLD responses.
- This technique provides a robust foundation for future neuroimaging studies investigating neurochemical underpinnings of cognition.
- Identified areas for refinement will guide future improvements in simultaneous BOLD and metabolite measurement.
