Blue-off Cells show Suppressed-by-Contrast Properties in Lateral Geniculate Nucleus of Anesthetized Marmosets

Abstract

Purpose : We previously reported that neurons in the intercalated (koniocellular, K) layers of the lateral geniculate nucleus (LGN) show brain state-related variability in spike rate, in absence of visual stimulation (Cheong et. al., P.N.A.S. 2011). Here we show that this variability can give a unified account of two types of LGN receptive field. Suppressed-by-contrast (SBC) cells are characterised by high baseline spike rate which is transiently suppressed by stimulus presentation (Solomon et al., J Nphys 2010). In contrast, blue-OFF cells are characterised by low spike rates, and they respond to short wavelength (S) cone decrement and medium-long (ML) wavelength increment stimuli. We found that either signature can appear if the same cell is recorded during different brain states.

Methods : Extracellular spike activity of K cells in the LGN provisionally classified as ‘blue-OFF’ (n=19) or SBC (n=9) were recorded in Sufentanil-anaesthetised marmosets (Callithrix jacchus). Visual stimuli (achromatic and cone-isolating, uniform fields and gratings) were presented against a uniform grey background near 50 Cd / m^2. Responses were analysed as a function of baseline spike rate in the 200 ms before stimulus onset.

Results : Cone opponent signature (S-, ML+) was found in 89% of cells (25/28). When baseline spike rate is low, S cone decrements cause excitation (n=13 cells) or no change in spike rate (n=13 cells) whereas ML+ stimuli are ineffective and ML- stimuli are suppressive. When baseline spike rate is high the ML+ and ML- stimuli become suppressive, and therefore the blue-OFF cells acquire an SBC response profile.

Conclusions : We propose that blue-Off and SBC cells are a single cell type in which blue-Off characteristic is present at low baseline spike rates, and SBC characteristic dominates at high baseline spike rates.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.