Multiplicative mechanism of lateral interactions revealed by controlling interhemispheric input

Area of Science:

• Neuroscience
• Visual Cortex Research
• Neural Connectivity

Background:

• Long-range horizontal connections, including interhemispheric projections, are crucial for modulating neuronal responsiveness by providing contextual information.
• Understanding the causal role of these connections, particularly callosal projections linking the cerebral hemispheres, is vital for deciphering visual processing.

Purpose of the Study:

• To causally investigate the functional impact of interhemispheric projections on neuronal activity in the cat primary visual cortex.
• To determine how stimulus properties influence the modulatory effects of callosal input on neuronal responses and selectivity.

Main Methods:

• Neuronal recordings were performed in the cat primary visual cortex.
• Corresponding contralateral regions were temporarily deactivated to isolate the effects of callosal projections.
• Stimuli included full-field gratings and random dot textures to assess responses to varying salient stimuli.

Main Results:

• Callosal projections modulated neuronal responses differently based on stimulus type: moderate rate decreases and some increases with gratings, but pronounced decreases with less salient random dot textures.
• Neuronal orientation and direction selectivity were minimally affected by callosal input, suggesting a gain control mechanism.
• The action of callosal input was quantified as primarily multiplicative scaling, with some additive scaling observed, particularly with grating stimuli.

Conclusions:

• The quantitative effect of long-range horizontal connections is stimulus-dependent, varying with the network's external input.
• Callosal projections adjust neuronal response gain, preserving feature selectivity, and their precise action (multiplicative vs. additive) depends on stimulus characteristics.