Working Memory Control Processes Research Articles

Verbal learning in frontal patients: area 9 is critical for employing semantic strategies

Abstract Background Learning is a long-term memory process, influenced by working memory control processes, including recognition of semantic properties of items by which subjects generate a semantic structure of engrams. Aim The aim of the study is to investigate the verbal learning strategies of Parkinson’s disease patients. Methods Thirty patients with idiopathic Parkinson’s disease and thirty normal control subjects were tested with a multi-trial word list learning, under two conditions: without cue and then with an explicit cue suggesting the categories in the list, respectively. Results and conclusions In comparison to healthy control subjects, parkinsonian patients recalled fewer words and achieved a reduced number of categorical clusters; strategical cue did not improve their performance. This suggests, besides a difficulty in identifying the correct learning strategy, a deficit in working memory, which undermines the strategy implementation. We hypothesize that this function pertains to the dorsolateral cognitive circuit of the extrapyramidal system.

Visuospatial bootstrapping: Binding useful visuospatial information during verbal working memory encoding does not require set-shifting executive resources.

Immediate serial recall of digits is better when the digits are shown by highlighting them in a familiar array, such as a phone keypad, compared with presenting them serially in a single location, a pattern referred to as "visuospatial bootstrapping." This pattern implies the establishment of temporary links between verbal and spatial working memory, alongside access to information in long-term memory. However, the role of working memory control processes like those implied by the "Central Executive" in bootstrapping has not been directly investigated. Here, we report a study addressing this issue, focusing on executive processes of attentional shifting. Tasks in which information has to be sequenced are thought to be heavily dependent on shifting. Memory for digits presented in keypads versus single locations was assessed under two secondary task load conditions, one with and one without a sequencing requirement, and hence differing in the degree to which they invoke shifting. Results provided clear evidence that multimodal binding (visuospatial bootstrapping) can operate independently of this form of executive control process.

Inefficient executive cognitive control in schizophrenia is preceded by altered functional activation during information encoding: An fMRI study

Working memory deficits are a core feature of schizophrenia. Previous working memory studies suggest a load dependent storage deficit. However, explicit studies of higher executive working memory processes are limited. Moreover, few studies have examined whether subcomponents of working memory such as encoding and maintenance of information are differentially affected by these deficits. Therefore, the aim of the present study was to examine the neural substrates of working memory subprocesses requiring stimulus encoding, maintenance and higher executive processing. Using functional magnetic resonance imaging a modified Sternberg working memory task involving verbal stimulus material was applied. The event-related design enabled the segregation of encoding, active maintenance and executive manipulation of information. Forty-one patients with schizophrenia and 41 healthy subjects were included. Relative to normal controls, schizophrenic patients demonstrated a significantly stronger activation pattern in a fronto-parietal network during executive information manipulation. Additionally, significant relative hypoactivity was detectable in the thalamus. Conversely, during stimulus encoding the patients demonstrated lower activation relative to controls in the prefrontal cortex and the anterior cingulate gyrus. The present findings indicate a pronounced prefrontal functional hyperactivation within the neural network subserving higher executive working memory control processes in schizophrenia. Moreover, they suggest that these altered activations during executive control are related to a preceding abnormality of information encoding. During encoding, a reduced activation in mainly dorsolateral prefrontal and anterior cingulate regions was observed. These results could be explained by increased top-down control processing from prefrontal cortex as a compensation for functional deficits occurring during encoding.

Working memory control in patients with schizophrenia: a PET study during a random number generation task.

The authors' goal was to investigate brain regions involved in the deficiency of working memory control processes in patients with schizophrenia. Regional cerebral blood flow was measured with positron emission tomography in eight men with stabilized schizophrenia and eight healthy men while they were performing a graded random number generation task. Twelve scans were made for each subject. Covariations between randomness of responses and regional activation were analyzed. The pattern of covariation between randomness of responses and activation in the anterior cingulate and superior parietal regions differed between patients and healthy subjects. These results suggest a cinguloparietal dysfunction underlying the impairment of working memory control processes during a random number generation task in patients with schizophrenia.