Individual Differences and Episodic Memory: Examining Behaviour, Genetics, and Brain Activity.

Dual-process models propose that two processes support recognition memory; familiarity, a general sense that something has been previously encountered; and recollection, the retrieval of details concerning the context in which a previous encounter occurred. Event-related potential (ERP) studies of recognition memory have identified a set of old/new effects that are thought to reflect these processes: the 300-500ms bilateral-frontal effect, thought to reflect familiarity and the 500-800ms left-parietal effect, thought to reflect recollection. Whilst the exact functional role of these effects remains unclear, they are widely viewed as reliable indices of retrieval. The ERP literature reviewed in this thesis suggests that the characteristics of these recognition effects vary with task specific details and individual participant differences, suggesting that the recognition effects purported to index retrieval may be conditional on both task and participant. This thesis examined the influence of individual differences on behavioural measures of recognition and the neural correlates of recognition memory, focusing on factors of stimulus material, task performance and participant genotype. Clear evidence of stimulus differences were found, with pictures eliciting more anteriorly distributed effects than words, and a late onsetting frontopolar old/new effect that was unique for voices. Furthermore, the pattern of ERP activity associated with successful recognition of faces appeared to vary as a function of general face recognition ability, with participants poorer at remembering faces exhibiting a 300-500ms old/new effect not present for those good at remembering faces. The data also suggested that activity over right-frontal electrodes, evident in some previous studies, may be participant specific and could reflect additional retrieval support processes. Contrary to expectations, behavioural task performance was not found to significantly modulate the ‘typical’ recognition memory effects. However, a number of genetic polymorphisms were found to significantly influence both behavioural scores and the pattern of ERP activity associated with recognition memory. These results therefore suggest that inherent participant differences influence the neural correlates of recognition memory, in a way that variations in task performance do not. Overall, the results from this thesis therefore suggest that the ‘typical’ bilateral-frontal and left-parietal effects thought to index retrieval are not universal. Furthermore the results suggest that the specific processes engaged during retrieval (as indexed by variations in ERP activity) may be dependent on specific task requirements, stimulus material and the genetic makeup of the individual

A functional electrical stimulation system for human walking inspired by reflexive control principles

This study presents an innovative multichannel functional electrical stimulation gait-assist system which employs a well-established purely reflexive control algorithm, previously tested in a series of bipedal walking robots. In these robots, ground contact information was used to activate motors in the legs, generating a gait cycle similar to that of humans. Rather than developing a sophisticated closed-loop functional electrical stimulation control strategy for stepping, we have instead utilised our simple reflexive model where muscle activation is induced through transfer functions which translate sensory signals, predominantly ground contact information, into motor actions. The functionality of the functional electrical stimulation system was tested by analysis of the gait function of seven healthy volunteers during functional electrical stimulation–assisted treadmill walking compared to unassisted walking. The results demonstrated that the system was successful in synchronising muscle activation throughout the gait cycle and was able to promote functional hip and ankle movements. Overall, the study demonstrates the potential of human-inspired robotic systems in the design of assistive devices for bipedal walking

Investigating the functional utility of the left parietal ERP old/new effect : brain activity predicts within but not between participant variance in episodic recollection

The work was funded by the United Kingdom Economic and Social Research Council (ESRC) grant PTA-030-2006-00337.A success story within neuroimaging has been the discovery of distinct neural correlates of episodic retrieval, providing insight into the processes that support memory for past life events. Here we focus on one commonly reported neural correlate, the left parietal old/new effect, a positive going modulation seen in event-related potential (ERP) data that is widely considered to index episodic recollection. Substantial evidence links changes in the size of the left parietal effect to changes in remembering, but the precise functional utility of the effect remains unclear. Here, using forced choice recognition of verbal stimuli, we present a novel population level test of the hypothesis that the magnitude of the left parietal effect correlates with memory performance. We recorded ERPs during old/new recognition, source accuracy and Remember/Know/Guess tasks in two large samples of healthy young adults, and successfully replicated existing within participant modulations of the magnitude of the left parietal effect with recollection. Critically, however, both datasets also show that across participants the magnitude of the left parietal effect does not correlate with behavioral measures of memory - including both subjective and objective estimates of recollection. We conclude that in these tasks, and across this healthy young adult population, the generators of the left parietal ERP effect do not index performance as expected. Taken together, these novel findings provide important constraints on the functional interpretation of the left parietal effect, suggesting that between group differences in the magnitude of old/new effects cannot always safely be used to infer differences in recollection.Publisher PDFPeer reviewe

PRKCA polymorphism changes the neural basis of episodic remembering in healthy individuals

This work was primarily funded by the Economic and Social Research Council (http://www.esrc.ac.uk) through award reference PTA-030-2006-00337. Funding for the DNA analysis was provided by the University of Stirling Department of Psychology Resources Committee.Everyday functioning relies on episodic memory, the conscious retrieval of past experiences, but this crucial cognitive ability declines severely with aging and disease. Vulnerability to memory decline varies across individuals however, producing differences in the time course and severity of memory problems that complicate attempts at diagnosis and treatment. Here we identify a key source of variability, by examining gene dependent changes in the neural basis of episodic remembering in healthy adults, targeting seven polymorphisms previously linked to memory. Scalp recorded Event-Related Potentials (ERPs) were measured while participants remembered words, using an item recognition task that requires discrimination between studied and unstudied stimuli. Significant differences were found as a consequence of a Single Nucleotide Polymorphism (SNP) in just one of the tested genes, PRKCA (rs8074995). Participants with the common G/G variant exhibited left parietal old/new effects, which are typically seen in word recognition studies, reflecting recollection-based remembering. During the same stage of memory retrieval participants carrying a rarer A variant exhibited an atypical pattern of brain activity, a topographically dissociable frontally-distributed old/new effect, even though behavioural performance did not differ between groups. Results replicated in a second independent sample of participants. These findings demonstrate that the PRKCA genotype is important in determining how episodic memories are retrieved, opening a new route towards understanding individual differences in memory.Publisher PDFPeer reviewe

Who, What, Where: an analysis of private sector family planning provision in 57 low- and middle-income countries.

OBJECTIVE: Family planning service delivery has been neglected; rigorous analyses of the patterns of contraceptive provision are needed to inform strategies to address this neglect. METHODS: We used 57 nationally representative Demographic and Health Surveys in low- and middle-income countries (2000-2013) in four geographic regions to estimate need for contraceptive services, and examined the sector of provision, by women's socio-economic position. We also assessed method mix and whether women were informed of side effects. RESULTS: Modern contraceptive use among women in need was lowest in sub-Saharan Africa (39%), with other regions ranging from 64% to 72%. The private sector share of the family planning market was 37-39% of users across the regions and 37% overall (median across countries: 41%). Private sector users accessed medical providers (range across regions: 30-60%, overall mean: 54% and median across countries 23%), specialised drug sellers (range across regions: 31-52%, overall mean: 36% and median across countries: 43%) and retailers (range across regions: 3-14%, overall mean: 6% and median across countries: 6%). Private retailers played a more important role in sub-Saharan Africa (14%) than in other regions (3-5%). NGOs and FBOs served a small percentage. Privileged women (richest wealth quintile, urban residents or secondary-/tertiary-level education) used private sector services more than the less privileged. Contraceptive method types with higher requirements (medical skills) for provision were less likely to be acquired from the private sector, while short-acting methods/injectables were more likely. The percentages of women informed of side effects varied by method and provider subtype, but within subtypes were higher among public than private medical providers for four of five methods assessed. CONCLUSION: Given the importance of private sector providers, we need to understand why women choose their services, what quality services the private sector provides, and how it can be improved. However, when prioritising one of the two sectors (public vs. private), it is critical to consider the potential impact on contraceptive prevalence and equity of met need

Bipedal robotic walking control derived from analysis of human locomotion

This paper presents a human-inspired approach to the design of bipedal robotic walking control, using information that appears to be intrinsic to human walking. We first investigated the correlation between ground contact information from the feet and leg muscle activity (EMG) in human walking. From this relationship filter functions were created which relate the sensory input to motor actions producing a minimal, nonlinear and robust robotic controller which incorporates hip, knee and ankle control. The developed control system was subsequently analysed by applying it to our bipedal robot "RunBot III", a minimalistic robotic walker designed without any central pattern generators (CPGs) or precise trajectory control. Our results demonstrated that this controller, which regards the function between the sensory input and motor output as a black box derived from human data, can generate stable robotic walking. This indicates that complex locomotion patterns can result from a simple model based on reflexes and supports the premise that human-inspired methods have the potential for use in the control of robotics or in the development of assistive devices for gait

Development and validation of a low-cost, portable and wireless gait assessment tool

Performing gait analysis in a clinical setting can often be challenging due to time, cost and the availability of sophisticated three-dimensional (3D) gait analysis systems. This study has developed and tested a portable wireless gait assessment tool (wi-GAT) to address these challenges. Methods: Ten healthy volunteers participated in the study (age range 23–30 years). Spatio-temporal gait parameters were recorded simultaneously by the Vicon and the wi-GAT systems as each subject walked at their self-selected speed. Results: The stride length and duration, cadence, stance duration and walking speed recorded using the wi-GAT showed strong agreement with those same parameters recorded by the Vicon (ICC of 0.94–0.996). A difference between the systems in registering “toe off” resulted in less agreement (ICC of 0.299–0.847) in gait parameters such as %stance and %swing and DST. Discussion and conclusion: The study demonstrated good concurrent validity for the wi-GAT system. The wi-GAT has the potential to be a useful assessment tool for clinicians

Two decades of antenatal and delivery care in Uganda: a cross-sectional study using Demographic and Health Surveys.

BACKGROUND: Uganda halved its maternal mortality to 343/100,000 live births between 1990 and 2015, but did not meet the Millennium Development Goal 5. Skilled, timely and good quality antenatal (ANC) and delivery care can prevent the majority of maternal/newborn deaths and stillbirths. We examine coverage, equity, sector of provision and content of ANC and delivery care between 1991 and 2011. METHODS: We conducted a repeated cross-sectional study using four Uganda Demographic and Health Surveys (1995, 2000, 2006 and 2011).Using the most recent live birth and adjusting for survey sampling, we estimated percentage and absolute number of births with ANC (any and 4+ visits), facility delivery, caesarean sections and complete maternal care. We assessed socio-economic differentials in these indicators by wealth, education, urban/rural residence, and geographic zone on the 1995 and 2011 surveys. We estimated the proportions of ANC and delivery care provided by the public and private (for-profit and not-for-profit) sectors, and compared content of ANC and delivery care between sectors. Statistical significance of differences were evaluated using chi-square tests. RESULTS: Coverage with any ANC remained high over the study period (> 90% since 2001) but was of insufficient frequency; < 50% of women who received any ANC reported 4+ visits. Facility-based delivery care increased slowly, reaching 58% in 2011. While significant inequalities in coverage by wealth, education, residence and geographic zone remained, coverage improved for all indicators among the lowest socio-economic groups of women over time. The private sector market share declined over time to 14% of ANC and 25% of delivery care in 2011. Only 10% of women with 4+ ANC visits and 13% of women delivering in facilities received all measured care components. CONCLUSIONS: The Ugandan health system had to cope with more than 30,000 additional births annually between 1991 and 2011. The majority of women in Uganda accessed ANC, but this contact did not result in care of sufficient frequency, content, and continuum of care (facility delivery). Providers in both sectors require quality improvements. Achieving universal health coverage and maternal/newborn SDGs in Uganda requires prioritising poor, less educated and rural women despite competing priorities for financial and human resources

Family planning, antenatal and delivery care: cross-sectional survey evidence on levels of coverage and inequalities by public and private sector in 57 low- and middle-income countries.

OBJECTIVE: The objective of this study was to assess the role of the private sector in low- and middle-income countries (LMICs). We used Demographic and Health Surveys for 57 countries (2000-2013) to evaluate the private sector's share in providing three reproductive and maternal/newborn health services (family planning, antenatal and delivery care), in total and by socio-economic position. METHODS: We used data from 865 547 women aged 15-49, representing a total of 3 billion people. We defined 'met and unmet need for services' and 'use of appropriate service types' clearly and developed explicit classifications of source and sector of provision. RESULTS: Across the four regions (sub-Saharan Africa, Middle East/Europe, Asia and Latin America), unmet need ranged from 28% to 61% for family planning, 8% to 22% for ANC and 21% to 51% for delivery care. The private-sector share among users of family planning services was 37-39% across regions (overall mean: 37%; median across countries: 41%). The private-sector market share among users of ANC was 13-61% across regions (overall mean: 44%; median across countries: 15%). The private-sector share among appropriate deliveries was 9-56% across regions (overall mean: 40%; median across countries: 14%). For all three healthcare services, women in the richest wealth quintile used private services more than the poorest. Wealth gaps in met need for services were smallest for family planning and largest for delivery care. CONCLUSIONS: The private sector serves substantial numbers of women in LMICs, particularly the richest. To achieve universal health coverage, including adequate quality care, it is imperative to understand this sector, starting with improved data collection on healthcare provision