Dark adaptation and receptive field organisation of cells in the cat lateral geniculate nucleus

Abstract

The receptive fields of LGN cells were investigated with stationary light and dark spot and annulus stimuli. Stimulus size and background intensity were varied while stimulus/background contrast was kept constant. The speed of dark adaptation vaired considerably from cell to cell. Dark adaptation made responses more sustained in all neurones and eliminated the oscillatory on-responses evoked under some conditions in the light-adapted cells. Dark adaptation led also to a disappearance of early phasic inhibition in on-responses, and increased response rise time and latency. The power of surround responses to inhibit centre responses decreased slightly at low levels of light adaptation in LGN cells but much less than in retinal ganglion cells. Some other traces of changing retinal surround effects also appeared inthe LGN on dark adaptation. For example, the functional size of receptive fields increased at low levels of illuminance as has been observed in retinal ganglion cells and the receptive fields as estimated from response peaks were larger than those estimated from sustained components.

Effects of dark adaptation on spatial and temporal properties of receptive fields in cat lateral geniculate nucleus.

“…To increase the sensitivity of our measurement, we decided to measure the response of the cells to bars of various widths and to use the reduction in effectiveness of diffuse light stimulation (when compared to a bar of optimal width) as a measure of the surround strength. This approach is similar to the one taken by others (EnrothCugell & Lennie, 1975;Virsu et al 1977). with the peak of the response-width function is the measure we chose for the antagonistic strength of the surround.…”

“…It is more difficult to compare our results with those reported by Virsu et al (1977), since they used a different method to quantify the neural responses. They used square-wave modulated stimuli with a modulation depth as high as 2 log units above the background.…”

“…Both Maffei & Fiorentini (1972) and Virsu et al (1977) reported that the surround of l.g.n. neurones remained effective at low luminance levels.…”

“…Virsu et al (1977) used Nembutal in their experiments. Therefore, we performed several experiments with Nembutal but the results obtained from these animals were identical to those obtained from urethane anaesthetized cats.…”

“…Some variability can also be seen in previously published data from l.g.n. cells (Virsu et al 1977) and optic tract neurons (Enroth-Cugell & Lennie, 1975; allowed us to study only a few cells per cat. It is important to note that both we and others observed variability in data from the optic tract fibres.…”