Synaptic and dendritic mechanisms mediating direction-selective signaling in the retina

Understanding how information is integrated and processed in single neurons and small circuits is crucial for comprehending information processing in neural circuits, and will help elucidate the biophysical basis of cognition and cognitive dysfunction. The direction selective circuit of the retina has been an archetypical model for understanding how neural circuits process information in the brain since the direction selective ganglion cell (DSGC) was first discovered more than 40 years ago. Much progress has been made towards understanding how the direction selective circuits extracts information from moving stimuli on the retina and computes the direction of motion; however, several key questions have remained unanswered. While it had been shown that directional inhibitory inputs to the DSGC are crucial to forming directional responses, the mechanisms underlying the integration of synaptic inputs to produce directional spiking in the DSGC are unknown. Furthermore, the cell that mediates the crucial directional inhibition, the starburst amacrine cell (SBAC) has been identified, yet we do not have a complete understand how the SBAC generates this directional inhibitory signal. Using In-vitro patch-clamp recordings and two-photon calcium imaging, we show that DSGCs employ orthograde spikes originating in the dendrites to locally integrate excitatory and inhibitory synaptic inputs and signal the direction of motion, which enhances the directional selectivity of the circuit. This represents the first demonstration of how dendritic action potentials contribute to direction selectivity and more generally it is one of the first demonstrations of a