L-/M-cone opponency in visual evoked potentials of human cortex

Area of Science:

• Neuroscience
• Visual Perception
• Ophthalmology

Background:

• L- and M-cones transmit signals via chromatic (parvocellular, blue-yellow koniocellular) and luminance (magnocellular) pathways.
• These pathways include ON and OFF subpathways for excitation increments and decrements, respectively.

Purpose of the Study:

• To investigate L- and M-cone driven increment and decrement activity using visually evoked potentials (VEP).
• To provide electrophysiological evidence for antagonistic L/M signal processing in the visual cortex.

Main Methods:

• VEP recordings were conducted on 12 trichromats and 4 dichromats (2 protanopes, 2 deuteranopes).
• Analysis focused on responses to L- and M-cone increments (LI, MI) and decrements (LD, MD).

Main Results:

• LI responses closely matched MD responses; LD and MI responses were highly similar.
• Dichromats showed a dominance of the ON pathway for the remaining photoreceptor type when one type was absent.
• VEP data align with psychophysical findings on perceived brightness changes.

Conclusions:

• Electrophysiological evidence supports antagonistic L/M signal processing in the visual cortex, extending retinal and LGN findings.
• VEP is a noninvasive tool suitable for diagnosing color vision deficiencies.