Visual response properties of neurons in the LGN of normally reared and visually deprived macaque monkeys

It is now well appreciated that parallel retino-geniculo-cortical pathways exist in the monkey as in the cat, the species in which parallel visual pat hways were first and most thoroughly documented. What remains unclear is pr ecisely how many separate pathways pass through the parvo- and magnocellula r divisions of the macaque lateral geniculate nucleus (LGN), what relations hips-homologous or otherwise-these pathways have to the cat's X, Y, and W p athways, and whether these are affected by visual deprivation. To address t hese issues of classification and trans-species comparison, we used achroma tic stimuli to obtain an extensive set of quantitative measurements of rece ptive field properties in the parvo- and magnocellular laminae of the LGN o f nine macaque monkeys: four normally reared and five monocularly deprived of vision by lid suture near the time of birth. In agreement with previous studies, we find that on average magnocellular neurons differ from parvocel lular neurons by having shorter response latencies to optic chiasm stimulat ion, greater sensitivity to luminance contrast, and better temporal resolut ion. Magnocellular laminae are also distinguished by containing neurons tha t summate luminance over their receptive fields nonlinearly (Y cells) and w hose temporal response phases decrease with increasing stimulus contrast (i ndicative of a contrast gain control mechanism). We found little evidence f or major differences between magno- and parvocellular neurons on the basis of most spatial parameters except that at any eccentricity, the neurons wit h the smallest receptive field centers tended to be parvocellular. All para meters were distributed unimodally and continuously through the parvo- and magnocellular populations, giving no indications of subpopulations within e ach division. Monocular deprivation led to clear anatomical effects: cells in deprived-eye laminae were pale and shrunken compared with those in nonde prived eye laminae, and Cat-301 immunoreactivity in deprived laminae was es sentially uniformly abolished. However, deprivation had only subtle effects on the response properties of LGN neurons. Neurons driven by the deprived eye in both magno- and parvocellular laminae had lower nonlinearity indices (i.e., summed signals across their receptive fields more linearly) and wer e somewhat less responsive. In magnocellular laminae driven by the deprived eye, neuronal response latencies to stimulation of the optic chiasm were s lightly shorter than those in the nondeprived laminae, and receptive field surrounds were a bit stronger. No other response parameters were affected b y deprivation, and there was no evidence for loss of a specific cell class as in the cat.