Opposite Dynamics of GABA and Glutamate Levels in the Occipital Cortex during Visual Processing

• Published in: The Journal of neuroscience 2018-11, Vol.38 (46), p.9967-9976
• Main Authors: Kurcyus, Katarzyna, Annac, Efsun, Hanning, Nina M, Harris, Ashley D, Oeltzschner, Georg, Edden, Richard, Riedl, Valentin
• Format: Article
• Language: English
• Subjects: Brain; Brain mapping; Darkness; Eye; Eye (anatomy); Functional magnetic resonance imaging; Information processing; Magnetic resonance imaging; Magnetic resonance spectroscopy; Metabolites; Neurotransmitters; Occipital lobe; Resonance; Spectroscopy; Spectrum analysis; Variation; Visual cortex; Visual discrimination; Visual signals; Visual stimuli; Visual system; γ-Aminobutyric acid
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/jneurosci.1214-18.2018

Magnetic resonance spectroscopy (MRS) measures the two most common inhibitory and excitatory neurotransmitters, GABA and glutamate, in the human brain. However, the role of MRS-derived GABA and glutamate signals in relation to system-level neural signaling and behavior is not fully understood. In this study, we investigated levels of GABA and glutamate in the visual cortex of healthy human participants (both genders) in three functional states with increasing visual input. Compared with a baseline state of eyes closed, GABA levels decreased after opening the eyes in darkness and Glx levels remained stable during eyes open but increased with visual stimulation. In relevant states, GABA and Glx correlated with amplitude of fMRI signal fluctuations. Furthermore, visual discriminatory performance correlated with the level of GABA, but not Glx. Our study suggests that differences in brain states can be detected through the contrasting dynamics of GABA and Glx, which has implications in interpreting MRS measurements. GABA and glutamate are the two most abundant neurotransmitters in human brain. Their interaction, known as inhibitory-excitatory balance, plays a crucial role in establishing spontaneous and stimulus-driven brain activity. Yet, the relationship between magnetic resonance spectroscopy (MRS)-derived levels of both metabolites and fMRI is still a matter of dispute. In this work, we study GABA and glutamate in three states of visual processing and in relation to fMRI and visual discriminatory performance in healthy people. We found that states of visual processing can be detected through the contrasting dynamics of GABA and glutamate and their correlation with fMRI signals. We also demonstrated that GABA, but not glutamate, in the visual system predicts visual performance. Our results provide insights into MRS-derived GABA and glutamate measurements.