Do wholes become more than the sum of their parts in the rodent (Rattus Norvegicus) visual system? A test case with the configural superiority effect.

The rodent has been used to model various aspects of the human visual system, but it is unclear to what extent human visual perception can be modelled in the rodent. Research suggests rodents can perform invariant object recognition tasks in a manner comparable to humans. There is further evidence that rodents also make use of certain grouping cues, but when performing a shape discrimination they have a tendency to rely much more on local image cues than human participants. In the current work, we exploit the fact that humans sometimes discriminate better between whole shapes, rather than the parts from which they are constructed, to ask whether rodents show a classic Configural Superiority Effect. Using touchscreen-equipped operant boxes, rats were trained to discriminate 'part' or 'whole' images based off of those used by J. R. Pomerantz et al. () J Exp Psychol Hum Percept Perform, 3, 422-435. Here, we show that rats show no advantage for wholes and that they perform better when presented with simpler image parts, a pattern of effect opposite to what was seen in humans when highly comparable stimuli were used. These results add to our understanding of the similarities and differences between the human and rodent visual system, and suggest that the rodent visual system may not compute part whole relationships in a way comparable to humans. These results are significant from both a comparative anatomy perspective, and of particular relevance for those wishing to use rodents to model visuo-perceptual deficits associated with human psychiatric disorders.

Dissociable effects of NR2A and NR2B NMDA receptor antagonism on cognitive flexibility but not pattern separation.

RATIONALE: N-methyl-D-aspartate (NMDA) receptors play crucial roles in learning and memory, but the role of each NMDA receptor subtype in a specific cognitive process is unclear. Non-selective blockers of NMDA receptor are used to model the cognitive impairment in schizophrenia and Alzheimer's disease. Counter-intuitively selective NR2A and 2B NMDA receptor antagonists are thought to have pro-cognitive properties. These seemingly contrasting findings might in part be the result of different compounds and behavioral measures used across studies. OBJECTIVE: We compared the effect of NVP-AAM077 (NR2A antagonist), CP 101-606 (NR2B antagonist), and MK-801 (non-selective antagonist) in a series of touch screen tasks that can be used to measure spatial cognition and cognitive flexibility. METHODS: NVP-AAM077, CP 101-606, and MK-801 were administered prior to testing, in adult male Lister-hooded rats trained in tasks of location discrimination, paired associate learning (PAL), and trial unique non-match to location (TUNL). RESULTS: Results showed that MK-801 impaired performance on all the tasks. In contrast, CP 101-606 only impaired reversal learning in location discrimination and had minimal effect on working memory in TUNL and caused a modest improvement in accuracy in PAL and acquisition of a spatial discrimination. NVP-AAM077 had little effect on performance across tasks, although these data allude to a potential enhancement of acquisition of a spatial location and impairments in spatial reversal learning in a separation-dependent manner. CONCLUSIONS: These data demonstrated that non-selective NMDA antagonism will disrupt numerous aspects of cognitive function. However, selective antagonism is capable of impairing or enhancing cognitive function in a task-dependent fashion.

Opposing effects of glutamatergic and GABAergic pharmacological manipulations on a visual perception task with relevance to schizophrenia.

RATIONALE: Numerous psychiatric disorders and neurodegenerative diseases have been associated with differences in visual perception, and it has been proposed that the treatment of these differences may represent a novel means to treat disorders like schizophrenia. Unfortunately, few methods exist to study visual perception in pre-clinical species. OBJECTIVE: The purpose of the present study was to adapt a task of visual integration by proximity with relevance to schizophrenia to a rodent touchscreen environment to determine the effects of glutamatergic and GABAergic compounds. In this way, we could evaluate the effects of common models of cognitive impairment, as well as the effects of net excitation versus inhibition, on a task of visual integration. METHOD: Rats were trained to perform a visual discrimination where the stimuli were composed of rows of dots differing only in there horizontal and vertical proximity. Once stable performance had been achieved, animals were tested under the influence of glutamatergic or GABAergic drugs (ketamine, MK-801, PCP, memantine, chlordiazepoxide, or diazepam) while attempting to perform a visual discrimination with altered stimuli. RESULTS: Ketamine appeared to impair perceptual grouping in this paradigm, while the GABA agonist chlordiazepoxide enhanced grouping even in the presence of non-selective effects. CONCLUSIONS: In general, these findings support the theory that NMDA antagonists may disrupt visual grouping by proximity and highlight a potential beneficial effect of enhanced GABA activity in perception. However, additional research will be required to confirm the stimulus selectivity of this effect, and the clinical significance of this approach.