Learning and consolidation

At the University of Liege, the group Ageing and Memory, which brings together two teams, one working on normal ageing (headed by neuropsychologist Fabienne Colette) and the other on dementia (headed by neuropsychologist Christine Bastin), conducted various experiments aimed at better understanding how memories function and the dysfunctions which affect them in Alzheimer’s.

In clinic, learning a list of words constitutes a traditional assessment of episodic memory. In the California Verbal Learning Test, a list of words is verbally given to the participants five times. After each trial, they are asked to repeat the words they remember. “In this way we can precisely analyze the learning capacity of the subjects from one trial to another by calculating the percentage of new words learned during each recollection”, explains Professor Salmon. The neuroscientists of the University of Liege offered this test to normal elderly people and also to Alzheimer’s patients (1). What were the results of this? Firstly, they observed that learning capacity was damaged not only in the Alzheimer’s patients but in a fraction of people complaining of isolated memory impairment which did not have a great impact on their daily lives (“mild cognitive impairments”). This fraction of people affected by isolated memory impairment concerns individuals who are likely to develop Alzheimer’s at some point in the future.

The researchers then used the PET scan (see article Positron Emission Tomography using FDG 18-fluorodeoxyglucose) in order to correlate these results with the brain function of subjects in the resting state, which is a situation where the patient is awake, with their eyes closed, and does not carry out any tasks. It emerged that in the normal-aged subjects, learning capacity is related to the metabolic activity of an anterior parietal area which is involved in attention. “It is therefore the attention capacity which underlies the differences in performance between the healthy subjects”, comments Professor Salmon. However, the situation changes in Alzheimer’s patients. Indeed their learning capacity is shown to be directly related to the hippocampal region which is a structure that is greatly involved in episodic memory and which is particularly affected in patients with Alzheimer’s disease.

In addition to the learning capacities of the subjects, the neuroscientists were interested in the consolidation of the knowledge acquired during the tests. In this area too, Alzheimer’s patients are defective - their scores do not improve and they forget words which they had previously remembered. Which areas of the brain are involved in the loss of information from one test to another? For the moment, the answer remains unknown. “The phenomenon cannot be imputed to a critical region; on the contrary, it is probable that it stems from dysfunctions in the relations between several regions”, indicates Eric Salmon. The team from the University of Liege is also trying to develop new analysis techniques which fall into the category of multivariate analysis, in order to create a model of how certain regions of the brain condition the performance of memory-loss consolidation by means of a Functional Magnetic Resonance Imaging (IRMf) examination (Read The channels of memory loss).

(1) Genon S. et al., Verbal learning in Alzheimer's disease and mild cognitive impairment: fine-grained acquisition and short-delay consolidation performance and neural correlates, Neurobiological Ageing (in press).