Blue-on cells are part of the third geniculocortical pathway in a new world monkey, the marmoset caluthrix jacchus

Purpose. To compare the distribution of cells receiving input from shortwavelength sensitive (SWS), or medium-long (ML) wavelength sensitive cone mechanisms in the primate lateral geniculate nucleus (LGN). Methods. Extracellular responses were recorded in the LGN of six female marmosets. Animals were anaesthetised with 1-4% Fluothane in 70% N20/Ü2, Stimuli were presented through a Maxwellian view s>stem with Red (638 nm), Green (545 nm) and Blue (470 nm) LEDs as light sources. The amplitude and phase of the LEDs was adjusted as required to provide selective modulation of the SWS or ML opsins as described (Yeh et al., J. Neurosci, 1995). Time averaged illuminance was close to 1000 Human Td. The position of each recorded cell was recovered histologically. Results. Cells exhibUirg ML cone opponent responses (n=15) were evenly distributed within the m£in parvocellular laminae. The receptive fields of ML opponent cells were all located within 15 degrees of the fovea. By contrast, cells showing evidence of exciatory input from SWS cones ("blue-ON", n=13) were located at the ventral bonier of the parvocelluar layers and in the interlaminar zones between the main Liyers. Non-opponent ML cells (n > 200) were also encountered throughout the LGN. CojcJunions: These results give evidence that opponent signals are segregated so that ML opponent cells form part of the main parvocellular pathway, but blue-ON cells are part of the koniocellular/interlaminar pathway in piimates.