Model-Based Approach Shows ON Pathway Afferents Elicit a Transient Decrease of V1 Responses.

Area of Science:

• Neuroscience
• Computational Neuroscience
• Visual Processing

Background:

• Neurons in the primary visual cortex (V1) process visual information through parallel ON (light) and OFF (dark) pathways.
• V1 neurons typically exhibit a stronger response to dark stimuli compared to light stimuli, a phenomenon known as 'dark-dominance'.

Purpose of the Study:

• To investigate the underlying mechanisms responsible for the observed dark-dominance in V1 neurons.
• To determine whether dark-dominance arises from increased excitation in the OFF pathway or reduced inhibition in the ON pathway.

Main Methods:

• Electrophysiological recordings were performed on individual simple-type V1 neurons in anesthetized cats.
• Neurons were stimulated with natural image stimuli to analyze their response patterns.
• Biologically inspired convolutional neural networks were trained to predict neuronal responses, aiding in mechanism analysis.

Main Results:

• V1 neuronal responses were confirmed to be more driven by dark than light stimuli.
• The dark-dominance was found to be primarily caused by slower inhibitory responses to light stimuli, rather than stronger excitation from the OFF pathway.
• Dark-dominance was most pronounced at early response latencies, and strongly dark-dominated neurons showed reduced orientation selectivity.

Conclusions:

• The asymmetry in V1 neuronal responses to light and dark stimuli is mainly attributed to differential inhibitory pathway dynamics.
• Slower inhibition to light stimuli is the key mechanism driving the 'dark-dominance' phenomenon in early visual processing.
• These findings offer new insights into excitatory-inhibitory integration and the emergence of response asymmetries in cortical neurons.