Neurodegenerative disorders such as Alzheimer's disease (AD) are increasingly threatening public health. Most animal models of AD consist of transgenic mice that are usually housed singly or in unisexual groups in small barren cages. Such restricted environments, however, prevent the mice from showing a variety of speciesspecific behaviors and consequently may constrain comprehensive behavioral phenotyping. On the other hand, allowing the animals to freely organize their lives in a spacious physically and socially enriched environment makes behavioral phenotyping laborious and time consuming. Radio frequency identification (RFID) using a network of antennae and small glass-coated transponders labeling each individual allows for gathering spatiotemporal information about a large number of individuals in parallel. The aim of this project was to use the RFID technique to facilitate the characterization of mice carrying a genetic disposition to develop AD-like pathology and of their wild-type conspecifics in a spacious seminaturalistic environment.

Several studies have investigated the eff ects of amyloid ␤ protein (A ␤ ) in the pathogenesis of Alzheimer ' s disease (AD). A ␤ accumulates as amyloid in senile plaques, in the walls of cerebral blood vessels, and in more diff use immunoreactive deposits in the brains of patients with AD. This accumulation has been implicated in a pathological cascade that ultimately results in neuronal dysfunction and cell death ( 1, 2 ). Multiple A ␤ species with varying N and C termini are generated from the amyloid ␤ protein precursor (APP) through sequential proteolytic cleavages by the ␤ -and ␥ -secretases ( 3 ). The 40-aa form (A ␤ 40) is the most abundantly produced A ␤ peptide, whereas a slightly longer and less abundant 42-aa form (A ␤ 42) has been implicated as the more pathogenic species ( 4 ). A ␤ 42 forms aggregate much more readily than A ␤ 40 and other shorter A ␤ peptides, and these aggregates are toxic to a variety of cells in culture. Despite being a minor A ␤ species, A ␤ 42 is deposited earlier and more consistently than A ␤ 40 in the AD brain.Recent studies suggest that soluble A ␤ peptide " oligomers " (aggregates and/or protofibrils) play an important role in the neuronal atrophy and/or disruption of neural circuits in the cerebral cortex and hippocampus during AD ( 5, 6 ). Moreover, the severity of human AD correlates closely with the accumulation of A ␤ oligomers rather than other clinical parameters (e.g., senile plaque density) ( 7 -9 ). Recently, the existence of such A ␤ oligomers in human AD brain was demonstrated by use of a specifi c

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