Relating Eye Dominance to Neurochemistry in the Human Visual Cortex Using Ultra High Field 7Tesla MR Spectroscopy Although our view of the world looks singular, it is combined from each eyexe2x80x99s separate retinal image. If the balanced input between eyes is disrupted during early childhood, visual acuity and stereoscopic depth perception are impaired. This is because one eye dominates over the other, causing a neurological condition called xe2x80x98amblyopiaxe2x80x99 1. In the normal, healthy visual system, the balance between eyes can be determined using various methods to provide a measure of xe2x80x98eye dominancexe2x80x99. Eye dominance is the preference for using image from one eye over another 2, suggesting that the visual system applies different weights upon their input. Hence, eye dominance is relevant for understanding the mechanisms underlying binocular vision. As an investigative strategy to understand the binocular visual system in health in disease, we want to characterize eye dominance in the normal visual system. This information can then be used to serve as a baseline to compare to extreme eye dominance in xe2x80x98amblyopiaxe2x80x99. Specifically, we ask to which degree variations in eye dominance are related to visual cortex concentrations of major excitatory neurotransmitter and metabolite glutamate (xe2x80x98Gluxe2x80x99) and inhibitory neurotransmitter xcexb3aminobutyric acid (xe2x80x98GABAxe2x80x99). Their relationship is formalised as the xe2x80x98GluGABAxe2x80x99 ratio. 13 participants took part in a 1h psychophysical experiment to quantify eye dominance and a separate 1.5h 7Tesla MRI brain scan to measure hemodynamic and neurochemical responses during visual stimulation. The degree of eye dominance was predicted by the interocular difference in V1 GluGABA balance. Stronger eye dominance correlated with an increase in inhibition during dominant relative to nondominant eye viewing (r  xe2x88x920.647, p  0.023). In contrast the hemodynamic response, measured with functional magnetic resonance imaging, did not correlate with eye dominance. Our findings suggest that normally occurring eye dominance is associated with the balance of neurochemicals in the early visual cortex.

Brain GABA and glutamate levels across pain conditions: A systematic literature review and metaanalysis of 1HMRS studies using the MRSQ quality assessment tool Abstract   Background  A proposed mechanism of chronic pain is dysregulation between the main inhibitory (GABA) and excitatory (glutamate) neurometabolites of the central nervous system. The level of these neurometabolites appears to differ in individual studies of people with pain compared to painfree controls across different pain conditions. However, this has yet to be systematically investigated.    Aims  To establish whether GABA, glutamate, glutamine and Glx levels differ across pain conditions when compared to painfree controls.    Methods  Five databases were searched. Studies were included if they investigated: 1) A pain condition compared to control. 2) Reported GABA, glutamate, glutamine or glutamateglutamine level. 3) Used 1HMagnetic Resonance Spectroscopy (Prospero Project ID CRD42018092170). Data extracted included neurometabolite level, pain diagnosis, and spectroscopy parameters. Metaanalyses were conducted to establish the difference in neurometabolite level between participants with pain and painfree controls for different pain conditions. The MRSQ was developed from existing clinical consensus to allow for the assessment of quality in the included studies.    Results  Thirtyfive studies were included investigating combinations of migraine (nxe2x80xafxe2x80xaf11), musculoskeletal pain (nxe2x80xafxe2x80xaf8), chronic pain syndromes (nxe2x80xafxe2x80xaf9) and miscellaneous pain (nxe2x80xafxe2x80xaf10). Higher GABA levels were found in participants with migraine compared to controls (Hedgeu0027s G 0.499, 95%CI: 0.2 to 0.798). In contrast, GABA levels in musculoskeletal pain conditions (Hedgeu0027s G xe2x88x920.189, 95%CI: 0.530 to 0.153) and chronic pain syndromes (Hedgeu0027s G 0.077, 95%CI: 1.612 to 1.459) did not differ from controls. Results for other brain neurometabolites revealed significantly higher levels for glutamate in participants with migraine and Glx in chronic pain syndromes compared to controls.    Conclusion  These results support the theory that underlying neurometabolite levels may be unique in different pain conditions and therefore representative of biomarkers for specific pain conditions.