Abstract
Neuronal ensembles, coactive groups of neurons found in spontaneous and evoked cortical activity, are causally related to memories and perception, but it is still unknown how stable or flexible they are over time. We used two-photon multiplane calcium imaging to track over weeks the activity of the same pyramidal neurons in layer 2/3 of the visual cortex from awake mice and recorded their spontaneous and visually evoked responses. Less than half of the neurons remained active across any two imaging sessions. These stable neurons formed ensembles that lasted weeks, but some ensembles were also transient and appeared only in one single session. Stable ensembles preserved most of their neurons for up to 46 days, our longest imaged period, and these 'core' cells had stronger functional connectivity. Our results demonstrate that neuronal ensembles can last for weeks and could, in principle, serve as a substrate for long-lasting representation of perceptual states or memories.
Highlights
Using two-photon calcium imaging, ensembles have been found in visual cortex during spontaneous activity and after visual stimulation
We performed longitudinal calcium imaging experiments using two-photon volumetric microscopy and tracked the responses of same neurons for up to 46 days in the visual cortex of awake mice
Functional connectivity based on neuronal coactivity was used to detect neuronal ensembles and we examined if ensembles were preserved in the following days
Summary
Neuronal ensembles, defined as a group of neurons which tend to fire together, are thought to underlie the neural representations of memories, perceptions, thoughts, motor. Ensembles can be optogenetically imprinted (Carrillo-Reid et al, 2016) and their activation can lead to behavioral effects, consistent with the hypothesis that they represent perceptual states (Carrillo-Reid et al, 2019; Marshel et al, 2019). If this is the case, one would expect those representations to be preserved over time, to retain learned memories or perception. It still unknown how stable neuronal ensembles are. Our results reveal long-term stability over several weeks of ensembles constituted mainly by neurons that are more functionally connected
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