Grant: Project Grant

Nerve cells in the brain communicate with each other via chemical synapses. Generally, each nerve cell releases either an excitatory or an inhibitory neurotransmitter onto its postsynaptic partner. Excitatory neurotransmitters activate postsynaptic neurons, increasing the probability that they fire action potentials; while inhibitory neurotransmitters do the opposite. The efficiency of most computations rely on 'balanced' excitation/inhibition (E/I), where on the gross scale these opposing forces are always in competition. It is the fine imbalances in E/I that in fact controls the level of neural activity. Despite its central importance, measuring the fine balance between E and I is not easy. This is inhibitory and excitatory inputs are made throughout the neurons dendritic tree, where they interact. Current methods do not allow us to easily measure electrical activity in the dendritic trees. Instead, electrodes are usually placed at the soma, which collects the average I/E throughout the dendritic tree. While, results from such measurements have provided a framework for understanding E/I balance, the lack of insights of how E/I interacts in the dendritic tree strongly limits our understanding how neural computations occur in the brain. In this proposal, we aim to understanding how E/ I shape a specific computation that underlies our ability to compute the direction of moving objects, performed by neural circuit that lies at the back of the eye, in the retina. Our experiments will use a multidisciplinary approach including molecular, electrophysiological and two-photon Ca2+ imaging techniques, which allow us to view synaptic activity throughout the intricate dendritic trees of neurons. We hypothesize that the E/I is finely modulated in space and in time, which enables the circuit to compute direction with speed and extreme precision. This allows us to accurately perceive the direction of rapidly moving objects, which of course, is crucial for our survival.