Luminance invariant encoding in visual cortex: The visual system adapts to maintain sensitivity and selectivity over a large range of luminance intensities. One way the retina maintains sensitivity across night and day is by switching between rod and cone photoreceptors, which alters the receptive fields and interneuronal correlations of retinal ganglion cells (RGCs). While these adaptations allow the retina to transmit visual information to the brain across environmental conditions, the code used for that transmission varies. To determine how downstream targets encode visual scenes across light levels, I measured the effects of luminance adaptation on thalamic and cortical population activity. While changes in the retinal output are evident in the lateral geniculate nucleus (LGN), selectivity in primary visual cortex (V1) is largely invariant to the changes in luminance. I used a model to show that the visual system could maintain sensitivity across environmental conditions without altering cortical selectivity through the convergence of parallel functional pathways from the thalamus to cortex.

Thalamic burst and tonic firing modes are disrupted in Fragile X: Burst and tonic firing modes in the thalamus may underlie the selective and flexible relay of sensory information to cortex, a capacity which is dysregulated in Fragile X (FX) syndrome. Here we show that typical thalamic firing dynamics are disrupted in FX mutant mice. We show that a shift in the voltage sensitivity of the cellular mechanism for generating bursts contributes to reduced burst frequency and duration in FX thalamus.