Subcortical orientation biases explain orientation selectivity of visual cortical cells

Area of Science:

• Neuroscience
• Visual System Research
• Sensory Processing

Background:

• The primary visual cortex in carnivores and primates exhibits organized domains of neurons selective to specific visual stimulus orientations.
• Cortical cells display remarkable orientation selectivity, but its origin remains a key question in visual neuroscience.

Purpose of the Study:

• To investigate whether the orientation sensitivity of single-thalamic afferent fibers could underlie the orientation selectivity observed in cortical cells.
• To determine the contribution of subcortical inputs to the functional organization of the primary visual cortex.

Main Methods:

• Optical imaging of intrinsic signals was used to map orientation domains in the cat's area 17.
• Electrophysiological recordings identified orientation preferences of single neurons and geniculate afferents.
• Pharmacological inactivation (kainic acid or muscimol) of cortical neurons isolated the activity of afferent terminals.

Main Results:

• A strong correlation was found between the orientation preferences of geniculate afferents and the neurons within their termination domains (Pearson's r = 0.633, P = 0.002).
• Pharmacological silencing of the cortex allowed for the recording of afferent fiber responses, confirming their orientation tuning.

Conclusions:

• The findings suggest a significant subcortical contribution to the orientation selectivity of primary visual cortex neurons.
• Orientation tuning in thalamic afferents provides a potential basis for the orientation maps observed in the visual cortex.