scholarly journals No balance between glutamate+glutamine and GABA+ in visual and motor cortices of the human brain

2021 ◽  
Author(s):  
Reuben Rideaux
Keyword(s):  
Neural Activity ◽  
Brain Function ◽  
Theoretical Work ◽  
Aminobutyric Acid ◽  
Resonance Spectroscopy ◽  
Signal Quality ◽  
Tissue Composition ◽  
Inhibitory Neurotransmitters ◽  
Positive Correlation ◽  
Human Participants

ABSTRACTTheoretical work, supported by electrophysiological evidence, asserts that a balance between excitation and inhibition (E/I) is critical for healthy brain function. In magnetic resonance spectroscopy (MRS) studies, the ratio of excitatory (glutamate) and inhibitory (γ-aminobutyric acid, GABA) neurotransmitters is often used as a proxy for this E/I balance. Recent MRS work found a positive correlation between GABA+ and Glx (glutamate+glutamine) in medial parietal cortex, providing validation for this proxy and supporting the link between the E/I balance observed in electrophysiology and that detected with MRS. Here we assess the same relationship, between GABA+ and Glx, in primary visual and motor cortices of resting male and female human participants. We find moderate to strong evidence that there is no positive correlation between these neurotransmitters in either location. We show this holds true when controlling for a range of other factors (i.e., demographics, signal quality, tissue composition, other neurochemicals) and regardless of the state of neural activity (i.e., resting/active). These results show that there is no brain-wide balance between excitatory and inhibitory neurotransmitters and indicates a dissociation between the E/I balance observed in electrophysiological work and the ratio of MRS-detected neurotransmitters.

scholarly journals Imaging the Pathophysiology of Essential Tremor—A Systematic Review

2021 ◽  
Vol 12 ◽  
Author(s):  
Florian Holtbernd ◽  
N. Jon Shah
Keyword(s):  
Magnetic Resonance ◽  
Essential Tremor ◽  
Neurodegenerative Disorder ◽  
Aminobutyric Acid ◽  
Emission Computed Tomography ◽  
Resonance Spectroscopy ◽  
Gamma Aminobutyric Acid ◽  
Imaging Studies ◽  
Limited Evidence ◽  
Neurotransmitter System

Background: The pathophysiology underlying essential tremor (ET) still is poorly understood. Recent research suggests a pivotal role of the cerebellum in tremor genesis, and an ongoing controversy remains as to whether ET constitutes a neurodegenerative disorder. In addition, mounting evidence indicates that alterations in the gamma-aminobutyric acid neurotransmitter system are involved in ET pathophysiology. Here, we systematically review structural, functional, and metabolic neuroimaging studies and discuss current concepts of ET pathophysiology from an imaging perspective.Methods: We conducted a PubMed and Scopus search from 1966 up to December 2020, entering essential tremor in combination with any of the following search terms and their corresponding abbreviations: positron emission tomography (PET), single-photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), and gamma-aminobutyric acid (GABA).Results: Altered functional connectivity in the cerebellum and cerebello-thalamico-cortical circuitry is a prevalent finding in functional imaging studies. Reports from structural imaging studies are less consistent, and there is no clear evidence for cerebellar neurodegeneration. However, diffusion tensor imaging robustly points toward microstructural cerebellar changes. Radiotracer imaging suggests that the dopaminergic axis is largely preserved in ET. Similarly, measurements of nigral iron content and neuromelanin are unremarkable in most studies; this is in contrast to Parkinson's disease (PD). PET and MRS studies provide limited evidence for cerebellar and thalamic GABAergic dysfunction.Conclusions: There is robust evidence indicating that the cerebellum plays a key role within a multiple oscillator tremor network which underlies tremor genesis. However, whether cerebellar dysfunction relies on a neurodegenerative process remains unclear. Dopaminergic and iron imaging do not suggest a substantial overlap of ET with PD pathophysiology. There is limited evidence for alterations of the GABAergic neurotransmitter system in ET. The clinical, demographical, and genetic heterogeneity of ET translates into neuroimaging and likely explains the various inconsistencies reported.

scholarly journals Mixed-polarity random-dot stereograms alter GABA and Glx concentration in the early visual cortex

2019 ◽  
Author(s):  
Reuben Rideaux ◽  
Nuno Goncalves ◽  
Andrew E Welchman
Keyword(s):  
Visual Cortex ◽  
Three Dimensional ◽  
Theoretical Work ◽  
Dimensional Structure ◽  
Resonance Spectroscopy ◽  
Gaba Concentration ◽  
Recent Theoretical Work ◽  
Random Dot Stereograms ◽  
Mixed Polarity ◽  
Early Visual Cortex

ABSTRACTThe offset between images projected onto the left and right retinae (binocular disparity) provides a powerful cue to the three-dimensional structure of the environment. It was previously shown that depth judgements are better when images comprise both light and dark features, rather than only dark or only light elements. Since Harris and Parker (1995) discovered the “mixed-polarity benefit”, there has been limited evidence supporting their hypothesis that the benefit is due to separate bright and dark channels. Goncalves and Welchman (2017) observed that single- and mixed-polarity stereograms evoke different levels of positive and negative activity in a deep neural network trained on natural images to make depth judgements, which also showed the mixed-polarity benefit. Motivated by this discovery, here we seek to test the potential for changes in the balance of excitation and inhibition that are produced by viewing these stimuli. In particular, we use magnetic resonance spectroscopy to measure Glx and GABA concentration in the early visual cortex of adult humans while viewing single- and mixed-polarity random-dot stereograms (RDS). We find that observers’ Glx concentration is significantly higher while GABA concentration is significantly lower when viewing mixed-polarity RDS than when viewing single-polarity RDS. These results indicate that excitation and inhibition facilitate processing of single- and mixed-polarity stereograms in the early visual cortex to different extents, consistent with recent theoretical work (Goncalves & Welchman, 2017).

scholarly journals GABA Levels in Left and Right Sensorimotor Cortex Correlate across Individuals

Biomedicines ◽  
2018 ◽  
Vol 6 (3) ◽  
pp. 80 ◽  
Author(s):  
Nicolaas Puts ◽  
Stefanie Heba ◽  
Ashley Harris ◽  
Christopher Evans ◽  
David McGonigle ◽  
...  
Keyword(s):  
Sensorimotor Cortex ◽  
Resonance Spectroscopy ◽  
Behavioral Performance ◽  
Gaba Level ◽  
Tissue Composition ◽  
Mr Images ◽  
Left And Right ◽  
Highly Correlated ◽  
Cortical Regions ◽  
Bulk Tissue

Differences in γ-aminobutyric acid (GABA) levels measured with Magnetic Resonance Spectroscopy have been shown to correlate with behavioral performance over a number of tasks and cortical regions. These correlations appear to be regionally and functionally specific. In this study, we test the hypothesis that GABA levels will be correlated within individuals for functionally related regions—the left and right sensorimotor cortex. In addition, we investigate whether this is driven by bulk tissue composition. GABA measurements using edited MRS data were acquired from the left and right sensorimotor cortex in 24 participants. T1-weighted MR images were also acquired and segmented to determine the tissue composition of the voxel. GABA level is shown to correlate significantly between the left and right regions (r = 0.64, p < 0.03). Tissue composition is highly correlated between sides, but does not explain significant variance in the bilateral correlation. In conclusion, individual differences in GABA level, which have previously been described as functionally and regionally specific, are correlated between homologous sensorimotor regions. This correlation is not driven by bulk differences in voxel tissue composition.

NMR spectroscopy and imaging of the neonatal brain

2000 ◽  
Vol 28 (2) ◽  
pp. 121-126 ◽  
Author(s):  
C. E. Cooper ◽  
J. S. Wyatt
Keyword(s):  
Blood Flow ◽  
Brain Function ◽  
Blood Oxygenation ◽  
Cell Swelling ◽  
Resonance Spectroscopy ◽  
Neonatal Brain ◽  
Cellular Processes ◽  
Nmr Techniques ◽  
The Brain ◽  
Ischaemic Insult

Magnetic resonance spectroscopy and imaging provide unique information about the brain to the biochemist and the clinician. In particular, the ability to image metabolites other than water and to get detailed information about dynamic cellular processes (such as blood flow, blood oxygenation and cell swelling) is leading to many new insights into brain function and dysfunction. This review describes the use of old and new NMR techniques which demonstrate that mitochondrial dysfunction plays an important role in the cell death that occurs following an hypoxic-ischaemic insult to the neonatal brain.

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