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Updated: Apr 16, 2026
07:29
A Novel Approach for Documenting Phosphenes Induced by Transcranial Magnetic Stimulation
Published on: April 1, 2010
12.7K
Phosphene Perception Relates to Visual Cortex Glutamate Levels and Covaries with Atypical Visuospatial Awareness
Devin B Terhune1, Elizabeth Murray1, Jamie Near2
1Department of Experimental Psychology, Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
Cerebral Cortex (New York, N.Y. : 1991)
|March 1, 2015
Summary
Phosphene thresholds, a measure of visual cortex excitability, are linked to glutamate levels. Lower thresholds indicate higher glutamate, suggesting a neurochemical basis for visual perception and synesthesia.
Area of Science:
- Neuroscience
- Visual Perception
- Neurochemistry
Background:
- Phosphenes, illusory visual percepts from transcranial magnetic stimulation, are used to assess cortical excitability.
- The underlying neural mechanisms of phosphene thresholds and their link to visual cognition remain unclear.
Purpose of the Study:
- To investigate the neurochemical basis of phosphene perception.
- To examine the relationship between phosphene thresholds and visual cortex neurotransmitter levels (GABA and glutamate).
- To explore the connection between phosphene thresholds and the visuospatial phenomenology of grapheme-color synesthesia.
Main Methods:
- Magnetic resonance spectroscopy was used to measure basal GABA and glutamate levels in the primary visual cortex.
- Phosphene thresholds were measured in controls and individuals with grapheme-color synesthesia (projector and associator types).
Main Results:
- Phosphene thresholds showed a negative correlation with glutamate concentrations in the visual cortex; lower thresholds were associated with higher glutamate.
- This relationship was consistent across control and synesthete groups and demonstrated specificity.
- Projector synesthetes had lower phosphene thresholds than associator synesthetes, who in turn had lower thresholds than controls.
Conclusions:
- Phosphene perception is influenced by individual differences in glutamatergic activity within the primary visual cortex.
- Phosphene thresholds are associated with cortical processes contributing to variations in visuospatial awareness.
- Glutamate levels in the visual cortex may represent a key neurochemical factor in phosphene perception and synesthetic experiences.
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