Traditional test administration and proactive interference undermine visual-spatial working memory performance in schizophrenia-spectrum disorders

Dissociating the effects of distraction and proactive interference on object memory through tests of novelty preference

Encoding information into memory is sensitive to distraction while retrieving that memory may be compromised by proactive interference from pre-existing memories. These two debilitating effects are common in neuropsychiatric conditions, but modelling them preclinically to date is slow as it requires prolonged operant training. A step change would be the validation of functionally equivalent but fast, simple, high-throughput tasks based on spontaneous behaviour. Here, we show that spontaneous object preference testing meets these requirements in the subchronic phencyclidine rat model for cognitive impairments associated with schizophrenia. Subchronic phencyclidine rats show clear memory sensitivity to distraction in the standard novel object recognition task. However, due to this, standard novel object recognition task cannot assess proactive interference. Therefore, we compared subchronic phencyclidine performance in standard novel object recognition task to that using the continuous novel object recognition task, which offers minimal distraction, allowing disease-relevant memory deficits to be assessed directly. We first determined that subchronic phencyclidine treatment did not affect whisker movements during object exploration. Subchronic phencyclidine rats exhibited the expected distraction standard novel object recognition task effect but had intact performance on the first continuous novel object recognition task trial, effectively dissociating distraction using two novel object recognition task variants. In remaining continuous novel object recognition task trials, the cumulative discrimination index for subchronic phencyclidine rats was above chance throughout, but, importantly, their detection of object novelty was increasingly impaired relative to controls. We attribute this effect to the accumulation of proactive interference. This is the first demonstration that increased sensitivity to distraction and proactive interference, both key cognitive impairments in schizophrenia, can be dissociated in the subchronic phencyclidine rat using two variants of the same fast, simple, spontaneous object memory paradigm.

Comparison of the touch-screen and traditional versions of the Corsi block-tapping test in patients with psychosis and healthy controls

BACKGROUND

Working memory (WM) refers to the capacity system for temporary storage and processing of information, which is known to depend on the integrity of the prefrontal cortex. Impairment in working memory is a core cognitive deficit among individuals with psychotic disorders. The Corsi block-tapping test is a widely-used instrument to assess visuospatial working memory. The traditional version is composed of 9 square blocks positioned on a physical board. In recent years, the number of digital instruments has increased significantly; several advantages might derive from the use of a digital version of the Corsi test.

METHODS

This study aimed to compare the digital and traditional versions of the Corsi test in 45 patients with psychotic disorders and 45 healthy controls. Both groups completed a neuropsychological assessment involving attention and working memory divided into the two conditions.

RESULTS

Results were consistent between the traditional and digital versions of the Corsi test. The digital version, as well as the traditional version, can discriminate between patients with psychosis and healthy controls. Overall, patients performed worse with respect to the healthy comparison group. The traditional Corsi test was positively related to intelligence and verbal working memory, probably due to a more significant effort to execute the test.

CONCLUSIONS

The digital Corsi might be used to enhance clinical practice diagnosis and treatment.The digital version can be administered in a natural environment in real-time. Further, it is easy to administer while ensuring a standard procedure.