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 SK et. al., P.N.A.S. 2011). 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). ‘Blue-OFF’ cells are characterised by low spike rate and respond to short wavelength (S) cone decrement and medium-long (ML) wavelength increment stimuli. We here show 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. Results: Cone opponent signature (S−, ML+) was found in 89% of cells (25/28). In 93% (26/28) 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+ are ineffective and ML- stimuli 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. Conclusion: We propose that blue-Off and SBC cells are a single cell type in which response signature depends on the baseline spike rate.