Synaptic physiology of horizontal connections in the cat's visual cortex

Area of Science:

• Neuroscience
• Cortical circuitry
• Visual processing

Background:

• Horizontal connections are crucial for integrating visual information across cortical columns.
• These connections link neurons with similar orientation preferences, extending up to 8 mm.

Purpose of the Study:

• To investigate the synaptic physiology of the horizontal pathway in the cat's striate cortex.
• To understand how lateral fiber activation influences pyramidal cell responses.

Main Methods:

• Recorded postsynaptic potentials in pyramidal cells (layer 2+3, area 17) after electrical stimulation.
• Stimulation sites included the home column (layers 2+3, 4) and lateral sites (0.9-3 mm).
• Used pharmacological agents like QX-314 and APV to probe synaptic mechanisms.

Main Results:

• Lateral fiber activation produced both excitation (EPSPs) and inhibition (IPSPs).
• Horizontally evoked EPSPs were voltage-dependent, amplified by Na+ channels, and too small to spike at resting potential.
• Disynaptic GABAAergic inhibition could truncate EPSPs and modulate responses.

Conclusions:

• Horizontal connections modulate activity within receptive fields via voltage-dependent excitation.
• Lateral input can facilitate responses to stimuli within the receptive field.
• The influence of horizontal input is state-dependent, varying with converging inputs.