Contrast gain control is drift-rate dependent: an informational analysis

Area of Science:

• Neuroscience
• Computational Neuroscience
• Visual System Physiology

Background:

• Visual cortex neurons adapt to ambient light levels by adjusting their contrast response functions (CRFs).
• Contrast gain control optimizes neuronal sensitivity but its effect at non-optimal visual drift rates is not well understood.

Purpose of the Study:

• To investigate how contrast gain control influences the accuracy of contrast representation in the visual cortex across different drift rates.
• To determine the optimal contrast coding strategy for maximizing Fisher information under varying visual conditions.

Main Methods:

• Calculated Fisher information from neuronal contrast response functions (CRFs) in halothane-anesthetized cats.
• Analyzed the relationship between adapting contrast, drift rate, and the contrast at which maximal Fisher information (C(MFI)) occurs.

Main Results:

• Maximal Fisher information (C(MFI)) consistently occurred at a fixed level above the adapting contrast.
• The relationship between C(MFI) and adapting contrast was linear (slope ~1) for adapting contrasts up to 0.32.
• The offset of C(MFI) was dependent on drift rate, increasing at higher drift rates, while the slope remained constant.

Conclusions:

• Visual cortex employs a contrast coding strategy that prioritizes accuracy for contrasts exceeding the prevailing environmental level.
• This strategy optimizes visual perception for natural scenes by enhancing sensitivity to changes above the average illumination.