Abstract
Purpose: :
To compare spatial and temporal tuning properties of blue–off, blue–on, and parvocellular (PC) cells in the lateral geniculate nucleus (LGN) of marmosets.
Methods: :
Extracellular single–unit recordings were made from blue–off cells (n=15) in the LGN of sufentanil anaesthetised marmosets (n=9). Stimuli were luminance modulated (yellow–black) or S–cone selective (S–cone contrast >60%, ML cone contrast <5%) drifting sinusoidal gratings of variable spatial and temporal frequency.
Results: :
Blue–off cells respond to S–cone modulation in approximately opposite temporal phase to blue–on cells (mean phase difference: 162 deg). Regression of response phase on temporal frequency showed greater equivalent latency for blue–off (95.8 S.D. 33.8 ms, n=8) than PC cells (55.2 S.D. 7.9 ms, n=24). Receptive field center radius (rc) of blue–off cells (n=15) was larger than those of blue–on (n=36) or PC (n=87) cells (< 2 deg eccentricity, blue–off: mean 0.48 S.D. 0.34 deg; blue–on: 0.11 S.D. 0.04 deg; PC: 0.04 S.D. 0.02 deg; 2–20 deg, mean rc, blue–off: 0.96 S.D. 0.68 deg; blue–on: 0.38 S.D. 0.45 deg; PC: 0.08 S.D. 0.05 deg). Histological reconstruction of some electrode tracks showed all blue–off cells (4/4) recovered were in koniocellular layers.
Conclusions: :
The large receptive field size, sluggish temporal characteristic and location of blue–off cells are consistent with the idea that they form part of the third (koniocellular) retino–geniculo–cortical pathway.
Keywords: color vision • electrophysiology: non-clinical • receptive fields