Introduction: Altered subjective visual sensitivity manifests as feelings of
discomfort or overload elicited by intense and irritative visual stimuli. This can
result in a host of visual aberrations including visual distortions, elementary visual hallucinations and visceral responses like dizziness and nausea, collectively referred to as “pattern glare.” Current knowledge of the underlying neural mechanisms has focused on overall excitability of the visual cortex, but the individual contribution of excitatory and inhibitory systems has not yet been
quantified.
Methods: In this study, we focus on the role of glutamate and γ-aminobutyric
acid (GABA) as potential mediators of individual differences in subjective
visual sensitivity, measured by a computerized Pattern Glare Test—a series of
monochromatic square-wave gratings with three different spatial frequencies,
while controlling for psychological variables related to sensory sensitivity with
multiple questionnaires. Resting neurotransmitter concentrations in primary
visual cortex (V1) and right anterior insula were studied in 160 healthy participants using magnetic resonance spectroscopy.
Results: Data showed significant differences in the perception of visual
distortions (VD) and comfort scores between men and women, with women
generally reporting more VD, and therefore the modulatory effect of sex was
considered in a further examination. A general linear model analysis showed a
negative effect of occipital glutamate on a number of reported visual distortions,
but also a significant role of several background psychological traits. When
assessing comfort scores in women, an important intervening variable was the
menstrual cycle.
Discussion: Our findings do not support that baseline neurotransmitter levels
have a significant role in overreactivity to aversive stimuli in neurotypical
population. However, we demonstrated that biological sex can have a significant
impact on subjective responses. Based on this additional finding, we suggest
that future studies investigate aversive visual stimuli while examining the role of
biological sex
