Abstract
The Müller-Lyer Illusion (MLI) has been suggested as a potential marker for the perceptual impairments observed in schizophrenia patients. Along with some positive symptoms, these deficits are not easily modeled in rodent experiments, and novel animal models are warranted. Previously, MK-801 was shown to reduce susceptibility to MLI in monkeys, raising the prospects of an effective perception-based model. Here, we evaluate the translational feasibility of the MLI task under NMDA receptor blockage as a primate model for schizophrenia. In Experiment 1, eight capuchin monkeys (Sapajus spp.) were trained on a touchscreen MLI task. Upon reaching the learning criteria, the monkeys were given ketamine (0.3 mg/kg; i.m.) or saline on four consecutive days and then retested on the MLI task. In Experiment 2, eight chronic schizophrenia patients (and eight matching controls) were tested on the Brentano version of the MLI. Under saline treatment, monkeys were susceptible to MLI, similarly to healthy human participants. Repeated ketamine administrations, however, failed to improve their performance as previous results with MK-801 had shown. Schizophrenic patients, on the other hand, showed a higher susceptibility to MLI when compared to healthy controls. In light of the present and previous studies, the MLI task shows consistent results across monkeys and humans. In spite of potentially being an interesting translational model of schizophrenia, the MLI task warrants further refinement in non-human primates and a broader sample of schizophrenia subtypes.
Highlights
In spite of being consistently associated with schizophrenia, sensory and perceptual deficits are not considered as core symptoms nor are they used to classify its subtypes
The results are discussed in light of using the Müller-Lyer Illusion (MLI) task as a translational model of perceptual changes in schizophrenia
For the percentage of correct responses on the ketamine test, the repeated measures analysis of variance (ANOVA) indicated a significant difference between the illusion conditions (‘‘neutral pairs’’ vs. ‘‘illusion pairs’’; F(1,12) = 80.96; p < 0.0001; Figure 3)
Summary
In spite of being consistently associated with schizophrenia, sensory and perceptual deficits are not considered as core symptoms nor are they used to classify its subtypes. There are several indications that the MLI may be influenced by top-down modulation from the anterior cingulate (Qiu et al, 2008) and posterior parietal cortex (Weidner and Fink, 2007; Maddaluno et al, 2019) These areas are subject to loss of volume or gray matter or even reduced connectivity in schizophrenia patients (Rimol et al, 2010; Roiser et al, 2013). The degree of sensitivity, measured in visual angle, seems to be quite similar between naïve monkeys and healthy humans (Tudusciuc and Nieder, 2010) These reports indicate that the MLI may be an illusory byproduct stemming from fundamental features of visual organization and/or processing. It translates into a stable parameter for cross-species comparisons using similar behavioral tasks. The results are discussed in light of using the MLI task as a translational model of perceptual changes in schizophrenia
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