Temporal Information Processing in Short- and Long-Term Memory of Patients with Schizophrenia

Cognitive deficits of patients with schizophrenia have been largely recognized as core symptoms of the disorder. One neglected factor that contributes to these deficits is the comprehension of time. In the present study, we assessed temporal information processing and manipulation from short- and long-term memory in 34 patients with chronic schizophrenia and 34 matched healthy controls. On the short-term memory temporal-order reconstruction task, an incidental or intentional learning strategy was deployed. Patients showed worse overall performance than healthy controls. The intentional learning strategy led to dissociable performance improvement in both groups. Whereas healthy controls improved on a performance measure (serial organization), patients improved on an error measure (inappropriate semantic clustering) when using the intentional instead of the incidental learning strategy. On the long-term memory script-generation task, routine and non-routine events of everyday activities (e.g., buying groceries) had to be generated in either chronological or inverted temporal order. Patients were slower than controls at generating events in the chronological routine condition only. They also committed more sequencing and boundary errors in the inverted conditions. The number of irrelevant events was higher in patients in the chronological, non-routine condition. These results suggest that patients with schizophrenia imprecisely access temporal information from short- and long-term memory. In short-term memory, processing of temporal information led to a reduction in errors rather than, as was the case in healthy controls, to an improvement in temporal-order recall. When accessing temporal information from long-term memory, patients were slower and committed more sequencing, boundary, and intrusion errors. Together, these results suggest that time information can be accessed and processed only imprecisely by patients who provide evidence for impaired time comprehension. This could contribute to symptomatic cognitive deficits and strategic inefficiency in schizophrenia

Performance on the script-generation task separately for patients with schizophrenia and healthy controls.

<p>Note. N = number of subjects; SZ = chronic schizophrenia patients; C = healthy controls; in brackets = standard errors;</p><p>* = groups differ; p = .05.</p

Example of a script card in the script-generation task.

<p><i>Note.</i> The heading indicated the theme of the script. The upper event was always a starting item, the lower event was the ending item of the script. The arrow indicates how the participant had to generate the script: downward direction = chronological order (as shown); upward direction = inverse temporal order (not shown). Cards remained visible during script generation. A sample answer of the depicted script “buying groceries” in chronological order could have been: 1) going to the grocery store by car, 2) getting a shopping cart and entering the grocery store, 3) putting groceries into the shopping cart, 4) looking for a register, 5) getting in line, 6) paying at the register, 7) putting the groceries into shopping bags, 8) putting bags into the car, 9) driving home, 10) unloading shopping bags from the car.</p

Demographic information of the two groups.

<p>Abbreviations: N = number of subjects; SZ = chronic schizophrenia patients; C = healthy controls; F = females; R = right-handed; L = left-handed; M = mixed-handed; years of study = 12 years of study corresponding to a high school diploma (Bacheleaureat); PANSS = Positive and Negative Syndrome Scale <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026140#pone.0026140-Kay1" target="_blank">[75]</a>; CPZ = Chlorpromazine equivalent of daily medication intake; numbers in brackets = standard deviations.</p

Performance measures of the patient and healthy control group for the temporal-order reconstruction task.

<p>a) Overall performance depicted as the Pearson product moment correlation (on the left) and sum of absolute difference deviations (on the right). b) Serial organization depicted as the number of reproduced item pairs. c) Semantic clustering depicted as correct clustering and clustering errors.</p