Abstract
Synchronized activity in ensembles of neurons recruited by excitatory afferents is thought to contribute to the coding information in the brain. However, the mechanisms by which neuronal ensembles are generated and modified are not known. Here we show that in rat hippocampal slices associative synaptic plasticity enables ensembles of neurons to change by incorporating neurons belonging to different ensembles. Associative synaptic plasticity redistributes the composition of different ensembles recruited by distinct inputs such as to specifically increase the similarity between the ensembles. These results show that in the hippocampus, the ensemble of neurons recruited by a given afferent projection is fluid and can be rapidly and persistently modified to specifically include neurons from different ensembles. This linking of ensembles may contribute to the formation of associative memories.
Highlights
In the brain features about the external world are represented by the activity of ensembles of neurons rather than by individual neurons [1,2,3]
We used imaging to visualize the activity of individual neurons within a population in order to understand how associative plasticity might reassign cells between different ensembles
We show that two different sets of afferents are represented by unique ensembles of cortical neurons, which become more similar following associative plasticity of the two inputs
Summary
In the brain features about the external world are represented by the activity of ensembles of neurons rather than by individual neurons [1,2,3]. The composition of an ensemble within a neuronal population is determined by the specific activity pattern of afferent inputs to that population and by the strength of the synapses between afferents and their target population. Experiencedependent changes in synaptic strength are likely to strongly modify the composition of neuronal ensembles, and critically affect the representation of a given afferent input. While the rules governing changes in synaptic strength at the cellular level are well established [8], how large ensembles of neurons are transformed by associative synaptic plasticity is unclear. In this study we address how associative plasticity modifies the composition of neuronal ensembles recruited by independent afferent pathways
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