The spatial extent over which neurons in macaque striate cortex pool visual signals.

Area of Science:

• Neuroscience
• Visual Neuroscience
• Computational Neuroscience

Background:

• The primary visual cortex (V1) is crucial for initial visual processing.
• Understanding the spatial extent of neuronal receptive fields in V1 is key to comprehending visual perception.

Purpose of the Study:

• To define the retinotopic extent of visual inputs driving or modulating macaque monkey V1 neuron responses.
• To investigate the spatial summation and surround suppression properties of V1 neurons in parafoveal and peripheral cortex.

Main Methods:

• Recorded single-unit activity in macaque monkey V1.
• Utilized high-contrast drifting grating stimuli to map receptive field summation and surround extent.
• Analyzed laminar differences and sources of surround suppression.

Main Results:

• Most V1 cell responses summed over approximately 1 degree.
• A suppressive surround, typically twice the summation area diameter, was observed.
• Some cells, including those in parafoveal V1, exhibited surrounds exceeding 13 degrees.
• No significant laminar differences were found in summation extent or surround suppression strength.
• Surround suppression primarily originated from both the sides and ends of the receptive field.
• Strongest modulatory input came from regions adjacent to the excitatory summation area.

Conclusions:

• The high-contrast summation field of V1 neurons is largely explained by lateral geniculate nucleus (LGN) inputs.
• Monosynaptic lateral connections within V1 contribute to larger summation fields and near surrounds.
• The largest surrounds likely result from feedback connections from extrastriate visual areas.