Sustained Working Memory Research Articles

Disentangling Some Conceptual Knots.

Disentangling Some Conceptual Knots.

Transcranial Direct Current Stimulation Does Not Counteract Cognitive Fatigue, but Induces Sleepiness and an Inter-Hemispheric Shift in Brain Oxygenation.

Sustained cognitive demands may result in cognitive fatigue (CF), eventually leading to decreased behavioral performance and compromised brain resources. In the present study, we tested the hypothesis that transcranial direct current stimulation (tDCS) would counteract the behavioral and neurophysiological effects of CF. Twenty young healthy participants were tested in a within-subject counterbalanced order across two different days. Anodal tDCS (real vs. sham) was applied over the left prefrontal cortex. In the real tDCS condition, a current of 1.5 mA was delivered for 25 min. Cortical oxygenation changes were measured using functional Near Infrared Spectroscopy (fNIRS) on the frontal cortices. CF was triggered using the TloadDback task, a sustained working memory paradigm that allows tailoring task demands according to each individual’s maximal cognitive capacity. Sustained cognitive load-related effects were assessed using pre- versus post-task subjective fatigue and sleepiness scales, evolution of performance accuracy within the task, indirect markers of dopaminergic activity (eye blinks), and cortical oxygenation changes (fNIRS) both during the task and pre- and post-task resting state periods. Results consistently disclosed significant CF-related effects on performance. Transcranial DCS was not effective to counteract the behavioral effects of CF. In the control (sham tDCS) condition, cerebral oxygen exchange (COE) levels significantly increased in the right hemisphere during the resting state immediately after the induction of CF, suggesting a depletion of brain resources. In contrast, tDCS combined with CF induction significantly shifted interhemispheric oxygenation balance during the post-training resting state. Additionally, increased self-reported sleepiness was associated with brain activity in the stimulated hemisphere after recovery from CF during the tDCS condition only, which might reflect a negative middle-term effect of tDCS application.

Facing the Future: Face-Emotion Processing Deficits as a Potential Biomarker For Various Psychiatric and Neurological Disorders

Facing the Future: Face-Emotion Processing Deficits as a Potential Biomarker For Various Psychiatric and Neurological Disorders

Evaluative processing of ambivalent stimuli in patients with schizophrenia and depression: A [15O] H2O PET study

Decision making in an emotionally conflicting situation is important in social life. We aimed to address the similarity and disparity of neural correlates involved in processing ambivalent stimuli in patients with schizophrenia and patients with depression. Behavioral task-related hemodynamic responses were measured using [15O]H2O positron emission tomography (PET) in 12 patients with schizophrenia and 12 patients with depression. The task was a modified word-stem completion task, which was designed to evoke ambivalence in forced and non-forced choice conditions. The prefrontal cortex and the cerebellum were found to show increased activity in the healthy control group. In the schizophrenia group, activity in these two regions was negligible. In the depression group, the pattern of activity was altered and a functional compensatory recruitment of the inferior parietal regions was suggested. The prefrontal cortex seems to be associated with the cognitive control to resolve the conflict toward the ambivalent stimuli, whereas the cerebellum reflects the sustained working memory to search for compromise alternatives. The deficit of cerebellar activation in the schizophrenia group might underlie the inability to search and consider compromising responses for conflict resolution.

A model of V1 for visual working memory using cortical and interlaminar feedback

Event Abstract Back to Event A model of V1 for visual working memory using cortical and interlaminar feedback Thorsten Hansen1* and Heiko Neumann2 1 Justus Liebig University, Department of General Psychology, Germany 2 University of Ulm, Institute of Neural Information Processing, Germany Early visual areas can store specific information about visual features held in working memory for many seconds in the absence of a physical stimulus (Harrison & Tong 2009, Nature 458 632-635). We have developed a model of V1 using recurrent long-range interaction that enhances coherent contours (Hansen & Neumann 2008, Journal of Vision 8(8):8 1-25) and robustly extracts corners and junctions points (Hansen & Neumann 2004, Neural Computation 16(5) 1013-1037). Here we extend this model by incorporating an orientation selective feedback signal from a higher cortical area. The feedback signal is nonlinearly compressed and multiplied with the feedforward signal. The compression increases the gain for decreasing input, such that the selection of the orientation to be memorized is realized by a selective decrease of feedback for this orientation. As a consequence, the model predicts that the overall activity in the network should decrease with the number of orientations to be memorized. Model simulations reveal that the feedback results in sustained activity of the orientation to be memorized over many recurrent cycles after stimulus removal. The pattern of activity is robust against an intervening, irrelevant orthogonal orientation shown after the orientation to be memorized. We suggest that the prolonged activation for sustained working memory in V1 shares similarities with the finding that different processing stages map onto different temporal episodes of V1 activation in figure-ground segregation (Roelfsema, Tolboom, & Khayat 2007, Neuron 56 785-792). Unlike previous approaches that have modeled working memory with a dedicated circuit, we show that a model of recurrent interactions in a sensory area such as V1 can be extended to memorize visual features by incorporating a feedback signal from a higher area. Conference: Bernstein Conference on Computational Neuroscience, Frankfurt am Main, Germany, 30 Sep - 2 Oct, 2009. Presentation Type: Poster Presentation Topic: Dynamical systems and recurrent networks Citation: Hansen T and Neumann H (2009). A model of V1 for visual working memory using cortical and interlaminar feedback. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference on Computational Neuroscience. doi: 10.3389/conf.neuro.10.2009.14.055 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 26 Aug 2009; Published Online: 26 Aug 2009. * Correspondence: Thorsten Hansen, Justus Liebig University, Department of General Psychology, Giessen, Germany, thorsten.hansen@psychol.uni-giessen.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Thorsten Hansen Heiko Neumann Google Thorsten Hansen Heiko Neumann Google Scholar Thorsten Hansen Heiko Neumann PubMed Thorsten Hansen Heiko Neumann Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Circuitry underlying temporally extended spatial working memory

Extended maintenance delays decrease the accuracy of information stored in spatial working memory. In order to elucidate the network underlying sustained spatial working memory, 16 subjects were scanned using fast event-related fMRI as they performed an oculomotor delayed response task containing trials with “short” (2.5 s) or “long” (10 s) delay periods. Multiple cortical and subcortical regions were common to both delay trial types indicating core task regions. Three patterns of activity were found in a subset of core regions that reflect underlying processes: maintenance-related (e.g., left FEF, right supramarginal gyrus (SMG)), response planning-related (e.g., right FEF, SEF), and motor response-related (e.g., lateral cerebellum (declive)) activation. Several regions were more active during long than short delay trials, including multiple sites in DLPFC (BA 9, 46), indicating a circuitry dynamically recruited to support sustained working memory. Our results suggest that specialized brain processes support extended periods of working memory.

Prefrontal cortical involvement in visual working memory

Studies of human amnesia provide evidence for a short-term memory store with information transfer to long term memory occurring within 60 s of sensory encoding. Human and nonhuman primate research has shown that maintenance of this short-term or working memory store is dependent upon frontal cortical activation, although the critical temporal parameters of frontal involvement throughout this 60-s window are undetermined. We examined prefrontal contributions to rapid (under 2 s) and sustained (over 4 s) visual working memory by recording behavioral performance and event-related potentials (ERPs) in patients with lesions in dorsolateral frontal cortex and age-matched control subjects. Prefrontal lesioned patients generated a reduced sustained frontal positivity at all delays. At short delays, patients generated reduced performance to stimuli presented in the contralesional field. Patients generated a negative potential (N400), greatest to contralesionally presented stimuli, that was observed in the control subjects only at long delays. The results indicate that prefrontal lesions impair the frontal component of an anterior–posterior working memory network activated during rapid and sustained visual memory processing. Frontal patients may require activation of limbic cortex, indexed by N400, for maintenance of both rapid and sustained working memory.