Transcranial direct current stimulation modulates human color discrimination in a pathway-specific manner

Area of Science:

• Neuroscience
• Visual Perception
• Sensory Physiology

Background:

• Transcranial direct current stimulation (tDCS) is known to modulate visual cortex excitability.
• Previous research has not investigated the effects of tDCS on color perception.

Purpose of the Study:

• To investigate the effects of anodal, cathodal, and sham tDCS on color discrimination tasks.
• To explore the impact of tDCS on different color vision axes (protan, deutan, tritan) and spatial color contrast sensitivity.

Main Methods:

• Fifteen healthy subjects received anodal, cathodal, or sham tDCS over the Oz region for 22 minutes.
• Color discrimination was assessed using the Cambridge Color Test (Trivector and ellipses protocols).
• Spatial color contrast sensitivity was measured using a red-green sinusoidal grating task.

Main Results:

• Anodal tDCS significantly improved tritan sensitivity (p < 0.01), with effects returning to baseline within 15 minutes.
• Cathodal tDCS reduced deutan sensitivity and increased tritan sensitivity (p < 0.05).
• No significant effects of anodal tDCS were observed on protan, deutan, or red-green grating discrimination, potentially due to a ceiling effect.

Conclusions:

• tDCS differentially affects color discrimination pathways, specifically influencing tritan and deutan axes.
• Findings suggest distinct roles for Parvocellular (P) and Koniocellular (K) visual systems in color processing.
• Results support the segregation of P and K color-coding cells within the primary visual cortex (V1).