Sculpting Visual Cortex: How Recurrent Structure, Modulatory Signals, and Development Shape V1 Responses

Abstract

The primary visual cortex (V1) is the first cortical area to process retinal signals, and the classical picture featuring feedforward orientation-selective inputs and recurrent amplification is well established. However, this view is incomplete: V1 receives modulatory inputs from non-visual sources and orientation selectivity emerges even before visual experience. My thesis explores how modulation and development shape V1 responses across three complementary projects. In my first project, I show that optogenetic stimulation of macaque V1 excitatory neurons produces diverse single-cell responses yet preserves the population statistics of neurons whose feature preferences match the visual stimulus – a phenomenon we term "rate reshuffling." While randomly connected networks can reproduce this effect, they require strong coupling and tight excitatory-inhibitory cancellation inconsistent with observations. In contrast, I show that networks with feature-dependent structure generate reshuffling robustly under more biologically plausible conditions. My second project explores the underlying mechanisms by developing a mean-field framework for networks with feature-dependent structure in which decomposing global activity into tuned and untuned components reveals effective interactions between the visual-stimulus-matched and baseline populations. A linear response analysis then shows that strongly-coupled, feedback-inhibition-dominated networks exhibit suppressive baseline-to-matched interactions, robustly explaining the lack of matched responses to the optogenetic stimulus. In my final project, I characterize how endogenous mechanisms generate orientation selective and spatially organized visual responses in ferret V1 before the onset of vision. I propose that strong receptive field biases drive recurrent interactions to form phase-insensitive responses in layer 4, which are transformed into orientation-selective and spatially periodic activity in layers 2/3. This structure differs from the mature architecture but naturally emerges from activity-dependent plasticity driven by geniculate activity prior to eye-opening. My findings reveal mechanisms by which visually and behaviorally relevant signals can coexist in separate populations and demonstrate that structured visual representations can emerge without prior visual experience