Center-surround processing in psychosis
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Purpose
People with psychotic psychopathology (PwPP) often experience subtle variations in visual perception, which can be quantified experimentally. In the contrast surround suppression illusion, a central pattern appears to have lower contrast in the presence of a surrounding pattern. PwPP typically show weaker contrast suppression from the surround than controls, but the mechanisms underlying this difference are still poorly understood.
Methods
We assessed perceptual and neural surround suppression in 38 controls, 44 first-degree biological relatives of PwPP, and 64 PwPP as part of the Psychosis Human Connectome Project. To better understand neural mechanisms contributing to diminished surround suppression we quantified contrast discrimination thresholds and examined 7 tesla fMRI responses in the lateral geniculate nucleus (LGN), primary visual cortex (V1), and lateral occipital complex (LOC). Additionally, we measured the concentration of γ-aminobutyric acid (GABA; an inhibitory neurotransmitter) in occipital cortex using 7 T MR spectroscopy.
Results
Responses in LOC showed the expected effect of weaker surround suppression in PwPP and relatives versus controls. However, in V1 we found no differences in surround suppression strength between controls, relatives, and PwPP. Additionally, we saw no behavioral evidence for reduced surround suppression in PwPP. Suppression metrics were not significantly correlated with occipital GABA levels or symptom measures. Multi-voxel pattern analysis of V1 fMRI responses revealed a group difference in decoding Surround vs. No Surround, with a trend toward lower accuracy in PwPP vs. controls.
Conclusion
Our results suggest subtle differences in visual center-surround processing among people with schizophrenia. Possible explanations for the discrepancy with previous findings include differences in task design and the deployment of spatial attention across groups. Poorer decoding of center vs. surround may suggest neural representations of spatial context in V1 are less reliable in PwPP.
