Study objectives: In this study, we test the hypothesis that when REM-state activation (which impinges upon all lateral geniculate nucleus laminae irrespective of stimulating eye) is deprived, the monocular segment (MS) that is cut off from visual input and also deprived of REM-state activation will exhibit smaller cells, owing to the loss of extrinsic as well as intrinsic activation.
Design: We carried out a study comparing soma sizes in the MSs of kittens subjected to monocular deprivation (MD) + REM deprivation (RD) to two age-matched nonRD groups, MD ONLYs and MD MOMS (MD kittens living in their home cages).
Measurements and results: Perikaryal outlines of 100 cells in each of the bilateral MSs were measured. As predicted, mean cell size in the MS connected to the patched eye of MD + RD kittens, but in neither of the control groups, was significantly smaller than in the MS afferented by the nonpatched eye. One-way ANOVAs comparing MS cell-size means from the same sides across groups were also significant, but the two MSs showed different results on post hoc tests. The ordering of MS cell-size means correlated significantly with a measure that aggregates the sources of activation reaching a particular MS and their durations.
Conclusions: These results reveal that removal of REM-state activation during CNS development amplifies the plasticity processes generated when normal visual afferentation to central visual areas is interrupted. Our findings in the MS of the LGN indicate that during the usual operation of REM sleep, central visual-sensory sites receive intrinsic activation that, in the visual system, is additive and complementary to the stimulation obtained from extrinsic sources. In the course of early development, normative symmetrical activation of central visual areas during REM sleep may counterbalance plasticity changes caused either by absent or aberrant sensory stimulation.