Modulation of Working Memory

Visual working memory, a limited temporary storage system for relevant information, is a critical contributor to many essential cognitive functions. In this thesis, I aimed to investigate some of the mechanisms underlying working memory in healthy humans and neurological patients, as well as its modulation by processes attributed to attention and the neurotransmitter dopamine. There currently is an important controversy regarding models of working memory. I investigated whether a resource model of memory (which argues for a limited resource distributed amongst to-be-remembered items) might be extended to the domain of visual motion. The results suggest that this is indeed be the case, supporting the utility of this model as a general conceptual framework for understanding working memory across a range of visual features and modes of presentation (Chapter 2). A comprehensive model of working memory should consider its relationship with attention. My findings point to an intimate yet highly specific relationship between these two processes, demonstrating that attention is essential for maintenance of integrated features within working memory (Chapters 2 and 4). Further, evidence for a causal role of early visual areas in maintenance of items in focus of attention, compared to the full content of working memory, is provided using transcranial magnetic stimulation (Chapter 3). Finally, I investigated neuromodulation of working memory processes by dopamine in patients with dopamine dysfunction (Parkinson’s disease) and using the dopamine agonist, Cabergoline, in healthy controls. The results demonstrate that dopamine can modulate working memory precision (Chapter 5 and 6). Furthermore, deficits in working memory were also observed in individuals with glucocerebrosidase mutations who have a significantly raised risk of developing Parkinson’s disease (Chapter 7). I discuss the possibility that specific deficits in working memory might provide a cognitive marker of risk for neurodegeneration and development of Parkinson’s disease

Prioritization of noise abatement methods for controlling hospital noise pollution

Noise pollution in hospitals has increased over the last few years to a level that can threaten the health and productivity of staff and patient safety. There are many control measures to reduce hospital noise. However, there is still no consensus on the best measures. This study aims to prioritize the control measures for reducing hospital noise. The work is divided into three phases. The first phase identifies and categorizes noise sources in hospitals through a review of the state-of-the art literature using Scopus®, ProQuest, PubMed, Google Scholar, Embase,™ and Web of Science™. The second phase identifies possible strategies for reduction of hospital noise and the best criteria for their adoption using findings from the literature review and interviews with corresponding experts. The third phase uses Fuzzy Analytic Hierarchy Process (FAHP) method and the Technique for Order of Preference by Similarity to Ideal Solution (fuzzy TOPSIS) method to weigh the criteria and to prioritize the control measures. Based on the results, hospital noise sources were classified into four groups: outdoor noise sources (29.7%), noise produced by domestic facilities (20.8%), indoor noise from human activities (27.5%), and noise produced by diagnostic and treatment equipment (22%). The study further arrives at a set of 9 criteria and 22 alternatives ranked using FAHP and fuzzy TOPSIS. The criteria’s weights were determined using the FAHP method, with feasibility (0.175), effectiveness (0.143), and interference with staff activities (0.140) being the most important criteria. It was found that engineering controls such as substitution of noisy equipment (rank = 1), using acoustic enclosures (rank = 2), using double-glazed windows (rank = 2), and soundproofing walls, doors, and windows (rank = 3) have priority for reducing hospital noise

Development of visual working memory precision in childhood

Visual working memory (VWM) is the facility to hold in mind visual information for brief periods of time. Developmental studies have suggested an increase during childhood in the maximum number of complete items that can simultaneously be stored in VWM. Here, we exploit a recent theoretical and empirical innovation to investigate instead the precision with which items are stored in VWM, where precision is a continuous measure reflecting VWM resolution. Ninety boys aged 7 to 13 years completed one-item and three-item VWM tasks in which stimuli were coloured bars varying in orientation. On each trial, participants used a rotating dial to reproduce the probed stimulus from memory. Results show linear age-related improvement in recall precision for both one-item and three-item VWM tasks. However, even the youngest age group stored a significant amount of information about all three items on the difficult 3-item VWM task. Importantly, the development of VWM precision was not accounted for by development on a sensorimotor control task. Whereas storage of a single complete item was previously thought to be well within the capacity limitations of the current age range, these results suggest protracted development during childhood and early adolescence in the resolution with which single and multiple items are stored in VWM. Probabilistic modelling of response distribution data suggests that improvement in VWM performance is attributable to a specific decrease in variability of stored feature representations, rather than to a decrease in misbinding or random noise. As such, we highlight a novel, potentially developmentally plausible mechanism that may underlie developmental improvement in VWM performance, independent of any alterations in the maximum number of complete items which can be stored

Binding deficits in visual short-term memory in patients with temporal lobe lobectomy.

Classical views of the medial temporal lobe (MTL) have established that it plays a crucial role in long-term memory (LTM). Here we demonstrate, in a sample of patients who have undergone anterior temporal lobectomy for the treatment of pharmacoresistant epilepsy, that the MTL additionally plays a specific, causal role in short-term memory (STM). Patients (n=22) and age-matched healthy control participants (n=26) performed a STM task with a sensitive continuous report measure. This paradigm allowed us to examine recall memory for object identity, location and object-location binding, independently on a trial-by-trial basis. Our findings point to a specific involvement of MTL in object-location binding, but, crucially, not retention of either object identity or location. Therefore the MTL appears to perform a specific computation: binding disparate features that belong to a memory. These results echo findings from previous studies, which have identified a role for the MTL in relational binding for LTM, and support the proposal that MTL regions perform such a function for both STM and LTM, independent of the retention duration. Furthermore, these findings and the methodology employed here may provide a simple, sensitive and clinically valuable means to test memory dysfunuction in MTL disorders

Attention and binding in visual working memory : two forms of attention and two kinds of buffer storage

We review our research on the episodic buffer in the multicomponent model of working memory (Baddeley, 2000), making explicit the influence of Anne Treisman’s work on the way our research has developed. The crucial linking theme concerns binding, whereby the individual features of an episode are combined as integrated representations. We summarize a series of experiments on visual working memory that investigated the retention of feature bindings and individual features. The effects of cognitive load, perceptual distraction, prioritization, serial position, and their interactions form a coherent pattern. We interpret our findings as demonstrating contrasting roles of externally driven and internally driven attentional processes, as well as a distinction between visual buffer storage and the focus of attention. Our account has strong links with Treisman’s concept of focused attention and aligns with a number of contemporary approaches to visual working memory

Working memory in Alzheimer's disease and Parkinson's disease

Working memory impairments are frequently observed in patients with Alzheimer's disease (AD) and Parkinson's disease (PD). Recent research suggests that the mechanisms underlying these deficits might be dissociable using sensitive tasks, specifically those that rely on the reproduction of the exact quality of features held in memory.In patients with AD, working memory impairments are mainly due to an increase in misbinding errors. They arise when patients misremember which features (e.g., color, orientation, shape, and location) belong to different objects held in memory. Hence, they erroneously report features that belong to items in memory other than the one they are probed on. This misbinding of features that belong to different objects in memory can be considered a form of interference between stored items. Such binding errors are evident even in presymptomatic individuals with familial AD (due to gene mutations) who do not have AD yet. Overall, these findings are in line with the role of the medial temporal lobes, and specifically the hippocampus, in retention of feature bindings, regardless of retention duration, i.e., in both short- or long-term memory.Patients with PD, on the other hand, do not show increased misbinding. Their working memory deficits are associated with making more random errors or guesses. These random responses are not modulated by manipulations of their dopaminergic medication and hence may reflect involvement of non-dopaminergic neurotransmitters in this deficit. In addition, patients with PD demonstrate impairments in gating of information into relevant vs. irrelevant items in memory, a cognitive operation that is modulated by dopaminergic manipulation in line with a frontal executive effect of this neurotransmitter. Thus, although AD and PD are both associated with working memory impairments, these surface manifestations appear to be underpinned by very different mechanisms

Assessment of the costs of fatal occupational accidents in Tehran

Background: Occupational accidents are major health problems in both developed and developing countries. The most important aspect is death leading to loss of years of life and work. The objective of this study is evaluation of human costs of fatal occupational accidents in the insured employees by Human Capital method in Tehran. Materials and Methods: Data for this study were collected through specific checklists filled in by referring to the branches of the Social Security Organization. Human costs were calculated by determination of the lost years of life, years of active economic function as well as annual income of the deceased people. Results: In the three years of the study 7552 years of life and 3656 years of work have been lost because of the occupational accidents. Findings also showed that human cost for each occupational accident was 3.36 billion Rials. Human costs of fatal occupational accidents for each year of study was found to be equal to 0.03 percent of Iran's GDP. Conclusion: Very high expenses of occupational accidents mandates more attention to the occupational health and safety services

Causes and consequences of limitations in visual working memory.

Recent methodological and conceptual advances have led to a fundamental reappraisal of the nature of visual working memory (WM). A large corpus of evidence now suggests that there might not be a hard limit on the number of items that can be stored. Instead, WM may be better captured by a highly limited––but flexible––resource model. More resource can be allocated to prioritized items but, crucially, at a cost of reduced recall precision for other stored items. Expectations may modulate resource distribution, for example, through neural oscillations in the alpha band increasing inhibition of irrelevant cortical regions. Our understanding of the neural architecture of WM is also undergoing radical revision. Whereas the prefrontal cortex has previously dominated research endeavors, other cortical regions, such as early visual areas, are now considered to make an essential contribution, for example holding one or more items in a privileged state or “focus of attention” within WM. By contrast, the striatum is increasingly viewed as crucial in determining why and how items are gated into memory, while the hippocampus, it has controversially been argued, might be critical in the formation of temporally resilient conjunctions across features of stored items in WM