Working memory encoding and false memory in schizophrenia and bipolar disorder in a spatial delayed response task.

Abstract

Working memory (WM) impairment is a core feature of schizophrenia, but the contributions of different WM components are not yet specified. Here, we investigated the potential role of inefficient encoding in reduced WM performance in patients with schizophrenia (PSZ). Twenty-eight PSZ, 16 patients with bipolar disorder (PBP), 16 unaffected and unmedicated relatives of PSZ (REL), and 29 demographically matched healthy controls (HC) performed a spatial delayed response task with either low or high WM demands. The demands on attentional selection were also manipulated by presenting distractor stimuli during encoding in some of the trials. After each trial, participants rated their level of response confidence. This allowed us to analyze different types of WM responses. WM was severely impaired in PSZ compared to HC; this reduction was mainly due to an increase in the amount of false memory responses (incorrect responses that were given with high confidence) rather than an increase in the amount of incorrect and not-confident responses. Although PBP showed WM impairments, they did not have increased false memory errors. In contrast, reduced WM in REL was also accompanied by an increase in false memory errors. The presentation of distractors led to a decline in WM performance, which was comparable across groups indicating that attentional selection was intact in PSZ. These findings suggest that inefficient WM encoding is responsible for impaired WM in schizophrenia and point to differential mechanisms underlying WM impairments in PSZ and PBP.

Failure to benefit from target novelty during encoding contributes to working memory deficits in schizophrenia

“…This provides some evidence that the increased rate of false memory errors likely reflects difficulties in deploying attention, which then may lead to inefficient WM encoding. This is consistent with our previous findings indicating that the impairments in spatial WM observed in PSZ as well as healthy first-degree relatives of PSZ can be attributed at least to some degree, to deficits in processes associated with WM encoding such as less precise encoding (Lee & Park, 2005; Mayer & Park, 2012). This finding is also consistent with the results from neuroimaging studies that compared true memory and false memory responses in PSZ and observed similar activation patterns in the prefrontal cortex for both types suggesting that the mechanisms that support the maintenance of the internal representation were intact whether that representation was correctly or incorrectly encoded (Lee et al, 2008).…”

“…If an incorrect response was giving with confidence, this was classified as false memory, in contrast to an incorrect response that was given without confidence (incorrect/ not confident response). We were particularly interested in the rate of false memory responses because false memory errors most likely reflect a problem at the encoding stage such as less precise encoding of the stimuli as demonstrated previously in PSZ (Mayer & Park, 2012). If one successfully transfers imprecisely encoded information into WM, it is possible to maintain and retrieve this information from WM, resulting in an error response that is coupled with a high degree of confidence concerning the veracity of the response.…”

Impairments of Working Memory in Schizophrenia and Bipolar Disorder: the Effect of History of Psychotic Symptoms and Different Aspects of Cognitive Task Demands

“…Although WM impairments were previously probed in SZ and BPD, comparisons across disorders have yielded inconsistent findings and the relationships between cognitive and clinical symptom domains across the psychotic variations of the disorders remain unclear (Hamilton et al, 2009;Mayer and Park, 2012;Milanovic and Vangel, 2012;Zhang et al, 2012). Discrepancy in previous studies may be due to a heterogeneous patient group and/or differences in specific task demands of the cognitive measures employed.…”

Serotonergic modulation of spatial working memory: predictions from a computational network model

“…In a previous study we argued that one way to distinguish error types would be by separating errors based on the declared confidence of the subjects in their responses (Cano-Colino et al, 2013). While confidence reports are increasingly being used in behavioral studies of SWM (Pessoa and Ungerleider, 2004; Middlebrooks and Sommer, 2011; Mayer and Park, 2012; Rademaker et al, 2012; Tanaka and Funahashi, 2012), interpretations suffer from our limited understanding of metacognition mechanisms. Here, we sought to explore other possible strategies to distinguish errors without using metacognition, in order to control for possible confounds and to provide simpler behavioral protocols that can be implemented more easily in animal studies.…”

“…In particular, the confidence declared by subjects after erroneous responses could distinguish the behavioral effects of increased and reduced 5-HT activations, and thus lead to detecting a robust serotonergic effect on SWM. These predictions are experimentally testable, since confidence reports are being increasingly used in both human (Pessoa and Ungerleider, 2004; Mayer and Park, 2012; Rademaker et al, 2012) and animal (Middlebrooks and Sommer, 2011, 2012; Tanaka and Funahashi, 2012) studies of working memory. However, there are limitations in relying only on the confidence report to test the computational model.…”