http://hdl.handle.net/2144/2705 Fri, 24 May 2013 13:23:05 GMT 2013-05-24T13:23:05Z http://hdl.handle.net/2144/3445 The Influence of Markov Decision Process Structure on the Possible Strategic Use of Working Memory and Episodic Memory Zilli, Eric A.; Hasselmo, Michael E. Researchers use a variety of behavioral tasks to analyze the effect of biological manipulations on memory function. This research will benefit from a systematic mathematical method for analyzing memory demands in behavioral tasks. In the framework of reinforcement learning theory, these tasks can be mathematically described as partially-observable Markov decision processes. While a wealth of evidence collected over the past 15 years relates the basal ganglia to the reinforcement learning framework, only recently has much attention been paid to including psychological concepts such as working memory or episodic memory in these models. This paper presents an analysis that provides a quantitative description of memory states sufficient for correct choices at specific decision points. Using information from the mathematical structure of the task descriptions, we derive measures that indicate whether working memory (for one or more cues) or episodic memory can provide strategically useful information to an agent. In particular, the analysis determines which observed states must be maintained in or retrieved from memory to perform these specific tasks. We demonstrate the analysis on three simplified tasks as well as eight more complex memory tasks drawn from the animal and human literature (two alternation tasks, two sequence disambiguation tasks, two non-matching tasks, the 2-back task, and the 1-2-AX task). The results of these analyses agree with results from quantitative simulations of the task reported in previous publications and provide simple indications of the memory demands of the tasks which can require far less computation than a full simulation of the task. This may provide a basis for a quantitative behavioral stoichiometry of memory tasks. Wed, 23 Jul 2008 00:00:00 GMT http://hdl.handle.net/2144/3445 2008-07-23T00:00:00Z http://hdl.handle.net/2144/3444 Coincidence Detection of Place and Temporal Context in a Network Model of Spiking Hippocampal Neurons Katz, Yael; Kath, William L; Spruston, Nelson; Hasselmo, Michael E Recent advances in single-neuron biophysics have enhanced our understanding of information processing on the cellular level, but how the detailed properties of individual neurons give rise to large-scale behavior remains unclear. Here, we present a model of the hippocampal network based on observed biophysical properties of hippocampal and entorhinal cortical neurons. We assembled our model to simulate spatial alternation, a task that requires memory of the previous path through the environment for correct selection of the current path to a reward site. The convergence of inputs from entorhinal cortex and hippocampal region CA3 onto CA1 pyramidal cells make them potentially important for integrating information about place and temporal context on the network level. Our model shows how place and temporal context information might be combined in CA1 pyramidal neurons to give rise to splitter cells, which fire selectively based on a combination of place and temporal context. The model leads to a number of experimentally testable predictions that may lead to a better understanding of the biophysical basis of information processing in the hippocampus. Author Summary. Understanding how behavior is connected to cellular and network processes is one of the most important challenges in neuroscience, and computational modeling allows one to directly formulate hypotheses regarding the interactions between these scales. We present a model of the hippocampal network, an area of the brain important for spatial navigation and episodic memory, memory of "what, when, and where." We show how the model, which consists of neurons and connections based on biophysical properties known from experiments, can guide a virtual rat through the spatial alternation task by storing a memory of the previous path through an environment. Our model shows how neurons that fire selectively based on both the current location and past trajectory of the animal (dubbed "splitter cells") might emerge from a newly discovered biophysical interaction in these cells. Our model is not intended to be comprehensive, but rather to contain just enough detail to achieve performance of the behavioral task. Goals of this approach are to present a scenario by which the gap between biophysics and behavior can be bridged and to provide a framework for the formulation of experimentally testable hypotheses. Fri, 14 Dec 2007 00:00:00 GMT http://hdl.handle.net/2144/3444 2007-12-14T00:00:00Z http://hdl.handle.net/2144/3154 Validity and Reliability of a Fijian Translation and Adaptation of the Eating Disorder Examination Questionnaire Becker, Anne E; Thomas, Jennifer J; Bainivualiku, Asenaca; Richards, Lauren; Navara, Kesaia; Roberts, Andrea L; Gilman, Stephen E; Striegel-Moore, Ruth H OBJECTIVE: Assessment of disordered eating has uncertain validity across culturally diverse populations. This study evaluated Eating Disorder Examination Questionnaire (EDE-Q) performance in an ethnic Fijian study population. METHOD: The EDE-Q was translated, adapted, and administered to school-going Fijian adolescent females (N = 523). A subsample (n = 81) completed it again within ∼1 week. We assessed feasibility, internal consistency, and test-retest reliability; evaluated construct validity through factor analysis and correlation with similar constructs; and examined the marginal utility of an additional question on traditional purgative use. RESULTS: Internal consistency reliability was adequate for the global scale and subscales (Cronbach's alpha = 0.66–0.91); retest reliability was adequate for both the languages (range of ICCs, 0.50–0.79, and of kappas, 0.46–0.81, excluding purging items). Construct validity was supported by significant correlations with measures of similar constructs. Factor analysis confirms multiple dimensions of eating disorder symptoms but suggests possible culture-specific variation in this population. The majority of respondents endorsing traditional purgative use (58%) did not endorse conventional EDE-Q items assessing purging. DISCUSSION: The EDE-Q is a valid measure of eating disorder pathology for ethnic Fijian adolescent females and measures a unitary underlying construct. Copyright 2009 by Wiley Periodicals, Inc. Int J Eat Disord, 2010 Mon, 23 Mar 2009 00:00:00 GMT http://hdl.handle.net/2144/3154 2009-03-23T00:00:00Z http://hdl.handle.net/2144/3155 Adaptation and Evaluation of the Clinical Impairment Assessment to Assess Disordered Eating Related Distress in an Adolescent Female Ethnic Fijian Population Becker, Anne E; Thomas, Jennifer J; Bainivualiku, Asenaca; Richards, Lauren; Navara, Kesaia; Roberts, Andrea L; Gilman, Stephen E; Striegel-Moore, Ruth H OBJECTIVE: Measurement of disease-related impairment and distress is central to diagnostic, therapeutic, and health policy considerations for eating disorders across diverse populations. This study evaluates psychometric properties of a translated and adapted version of the Clinical Impairment Assessment (CIA) in an ethnic Fijian population. METHOD: The adapted CIA was administered to ethnic Fijian adolescent schoolgirls (N = 215). We calculated Cronbach's α to assess the internal consistency, examined the association between indicators of eating disorder symptom severity and the CIA to assess construct and criterion validity, and compared the strength of relation between the CIA and measures of disordered eating versus with measures of generalized distress. RESULTS: The Fijian version of the CIA is feasible to administer as an investigator-based interview. It has excellent internal consistency (α = 0.93). Both construct and criterion validity were supported by the data, and regression models indicated that the CIA predicts eating disorder severity, even when controlling for generalized distress and psychopathology. DISCUSSION: The adapted CIA has excellent psychometric properties in this Fijian study population. Findings suggest that the CIA can be successfully adapted for use in a non-Western study population and that at least some associated distress and impairment transcends cultural differences. Copyright 2009 by Wiley Periodicals, Inc. Int J Eat Disord, 2010 Mon, 23 Mar 2009 00:00:00 GMT http://hdl.handle.net/2144/3155 2009-03-23T00:00:00Z