Abstract
Visual cortical responses are known to be highly variable across trials within an experimental session. However, the long-term stability of visual cortical responses is poorly understood. Here using chronic imaging of V1 in mice we show that neural responses to repeated natural movie clips are unstable across weeks. Individual neuronal responses consist of sparse episodic activity which are stable in time but unstable in gain across weeks. Further, we find that the individual episode, instead of neuron, serves as the basic unit of the week-to-week fluctuation. To investigate how population activity encodes the stimulus, we extract a stable one-dimensional representation of the time in the natural movie, using an unsupervised method. Most week-to-week fluctuation is perpendicular to the stimulus encoding direction, thus leaving the stimulus representation largely unaffected. We propose that precise episodic activity with coordinated gain changes are keys to maintain a stable stimulus representation in V1.
Highlights
Visual cortical responses are known to be highly variable across trials within an experimental session
This session-to-session fluctuation raises an important question: Is there a stable representation of natural stimuli hidden in the unstable neural activity in V1? Stable stimulus representation is possible when neural fluctuations reside in a space orthogonal to the stimulus encoding dimensions[26]
To address the question of stable stimulus representation in unstable neural activity, we analyzed a dataset from longitudinal two-photon calcium imaging of excitatory neurons in the primary visual cortex of awake, head-fixed mice during visual stimulation with repeated identical natural movie clips across weeks
Summary
Visual cortical responses are known to be highly variable across trials within an experimental session. The random fluctuation in the highdimensional neural space would likely be perpendicular to the low-dimensional subspace of stimulus encoding, often referred to as the stimulus encoding dimension Clarification of these possibilities requires long-term recordings in response to repeated stimulation, identification of the stimulus encoding dimensions, and quantification of neural fluctuation within the highdimensional population activity. To address the question of stable stimulus representation in unstable neural activity, we analyzed a dataset from longitudinal two-photon calcium imaging of excitatory neurons in the primary visual cortex of awake, head-fixed mice during visual stimulation with repeated identical natural movie clips across weeks. Despite the unstable episodic activity, we extracted a low-dimensional stable representation of time in the natural movie from neuronal population activity across weeks. We propose that precise episodic activity with coordinated gain changes are keys to maintain a stable stimulus representation in V1
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