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Anouk M. van Loon, H. Steven Scholte, Victor A. F. Lamme; Lorazepam reduces stimulus visibility by impairing recurrent processing in visual cortex. Journal of Vision 2010;10(7):927. doi: 10.1167/10.7.927.
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© ARVO (1962-2015); The Authors (2016-present)
It is becoming increasingly accepted that reentrant processing in the visual cortex plays a crucial role in perceptual organization and visual awareness. It is however unclear what the fundamental differences are between reentrant and feedforward processing. Therefore, we investigate the contribution of specific neurotransmitters to these types of processing, and study the effects of pharmacological interventions on conscious visual perception. Here, we use EEG measurements to determine what happens in the human visual cortex during the detection of a texture-defined square under nonmasked (seen) and masked (unseen) conditions. The strength of the masks was varied spanning the range from not visible to visible. Previous research has demonstrated that masking disrupts reentrant processing in the human visual cortex, while leaving feedforward processing relatively untouched. In a within-subject design, subjects were given the benzodiazepine Lorazepam (1,5 mg) or a placebo, to study the effect of GABAergic neurotransmission on reentrant processing and stimulus visibility. Our behavioral results show that detection rate decreased with increasing masking strength and that the detection rate decreased even more in the Lorazepam condition compared to the control condition. The subtracted ERP signal (figure - homogeneous) showed: (1) an early posterior occipital and temporal component (90-125 ms), not influenced by Lorazepam and (2) a later recurring bilateral occipital component (168-203 ms), which was influenced by Lorazepam. The period between 90-125 ms is related to boundary detection and was not influenced by masking strength. The second period represents recurrent processing and was modulated by masking strength; the stronger the mask, the smaller the difference wave. Furthermore, this modulation was correlated with detection behavior; the poorer the detection, the larger the decrease of the ERP deflection. Lorazepam deteriorates this correlation with behavior. These results give more insight in the role of GABAergic neurotransmission in visual processing and perception.
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