Abstract
We describe a mathematical model of learning and memory and apply it to the dynamics of forgetting and amnesia. The model is based on the hypothesis that the neural systems involved in memory at different time scales share two fundamental properties: (1) representations in a store decline in strength (2) while trying to induce new representations in higher-level more permanent stores. This paper addresses several types of experimental and clinical phenomena: (i) the temporal gradient of retrograde amnesia (Ribot’s Law), (ii) forgetting curves with and without anterograde amnesia, and (iii) learning and forgetting curves with impaired cortical plasticity. Results are in the form of closed-form expressions that are applied to studies with mice, rats, and monkeys. In order to analyze human data in a quantitative manner, we also derive a relative measure of retrograde amnesia that removes the effects of non-equal item difficulty for different time periods commonly found with clinical retrograde amnesia tests. Using these analytical tools, we review studies of temporal gradients in the memory of patients with Korsakoff’s Disease, Alzheimer’s Dementia, Huntington’s Disease, and other disorders.
Highlights
Since the 1950s, many models of long-term memory and retrograde amnesia have been published that are based on an abstraction of the neuroanatomy, giving a important role to the hippocampus and adjacent medial temporal lobe (MTL) structures
We have modeled this process in some detail using a neural network model (Murre, 1996; Meeter and Murre, 2005), demonstrating that such a model can explain many of the characteristics of amnesia and semantic dementia (Meeter and Murre, 2004b)
The model is tested on data from animals and human patients in the Section “Results.” In the Section “Discussion,” we evaluate the implications of the results for consolidation theory
Summary
Since the 1950s, many models of long-term memory and retrograde amnesia have been published that are based on an abstraction of the neuroanatomy, giving a important role to the hippocampus and adjacent medial temporal lobe (MTL) structures (see McClelland et al, 1995; Squire and Alvarez, 1995; Murre, 1996; Meeter and Murre, 2004a, 2005). These models postulate that memories show an initial dependence on the hippocampus that diminishes with time. In this paper we extend this model and apply it to a wider range of data
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