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Related Experiment Video

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Optrode Array for Simultaneous Optogenetic Modulation and Electrical Neural Recording

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Published on: September 1, 2022

Internal Gain Modulations, But Not Changes in Stimulus Contrast, Preserve the Neural Code.

Sangkyun Lee^1,2, Jiyoung Park³, Stelios M Smirnakis^1,2

¹Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, and slee@bwh.harvard.edu smsmirnakis@bwh.harvard.edu.

The Journal of Neuroscience : the Official Journal of the Society for Neuroscience

|January 17, 2019

Summary

Neural population codes are preserved during internal input fluctuations but not by stimulus contrast changes. This suggests the brain prioritizes stable neural coding despite varying internal signals.

Keywords:

brain states mouse visual cortex population codes two-photon calcium imaging visual contrast

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Area of Science:

Neuroscience
Computational Neuroscience
Visual System

Background:

Neurons in the primary visual cortex respond to both external stimuli (like contrast) and internal input fluctuations.
Understanding how these factors affect neural population codes is crucial for deciphering brain function.
Previous assumptions suggested population codes remain invariant to contrast changes, but the impact of internal modulations was unknown.

Purpose of the Study:

To investigate whether the neural population code for direction-of-motion is preserved under varying stimulus contrast and internal input fluctuations.
To compare the effects of stimulus contrast versus internal gain modulations on population coding in the primary visual cortex.

Main Methods:

Studied the encoding of oriented grating direction-of-motion in mouse layer 2/3 primary visual cortex.
Analyzed neuronal responses to changes in stimulus contrast and internal input fluctuations.
Assessed population code invariance under different modulation conditions.

Main Results:

Heterogeneous contrast gain responses across neurons led to a violation of population code invariance with changing stimulus contrast.
Internal input fluctuations, causing commensurate single-cell firing rate changes, resulted in more homogeneous gain responses.
Population code invariance was maintained during internal input fluctuations, unlike during contrast changes.

Conclusions:

The brain actively maintains the stability of the neural population code despite fluctuating internal inputs.
Internal input fluctuations promote population code invariance, whereas stimulus contrast changes disrupt it due to heterogeneous neuronal gain.
These findings highlight the brain's strategy for robust information processing in the face of internal variability.