Development of Retinotopic Feedback: Layer 6 Pyramids to Lateral Geniculate Principal Cells

The development of many feedforward pathways in the brain, from sensory inputs to neocortex, have been studied and modeled extensively, but the development of feedback connections, which tend to occur after the development of feedforward pathways, have received less attention. The abundance of feedback connections within neocortex and between neocortex and thalamus suggests that understanding feedback connections is crucial to understanding connectivity and signal processing in the brain. It is well known that many neural layers are arranged topologically with respect to sensory input, and many neural models impose a symmetry of connections between layers, commonly referred to as reciprocal connectivity. Here, we are concerned with how such reciprocal, feedback connections develop so that the topology of the sensory input is preserved. We focus on feedback connections from layer 6 of visual area V1 to primary neurons in the Lateral Geniculate Nucleus (LGN). The proposed model is based on the hypothesis that feedback connections from V1-L6 to LGN use voltage-activated T-channels to appropriately establish and modify synapses in spite of unavoidable temporal delays. We also hypothesize that developmental spindling relates to synaptogenesis and memory consolidation.