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Concept
Coincidence detection in neurobiology
Résumé
Coincidence detection is a neuronal process in which a neural circuit encodes information by detecting the occurrence of temporally close but spatially distributed input signals. Coincidence detectors influence neuronal information processing by reducing temporal jitter and spontaneous activity, allowing the creation of variable associations between separate neural events in memory. The study of coincidence detectors has been crucial in neuroscience with regards to understanding the formation of computational maps in the brain.
Coincidence detection relies on separate inputs converging on a common target. For example (Fig. 1), in a basic neural circuit with two input neurons—A and B—that have excitatory synaptic terminals converging on a single output neuron (C), if each input neuron's EPSP is sub-threshold for an action potential at C, then C cannot fire unless the two inputs from A and B are temporally close. The synchronous arrival of these two inputs may push the membrane potential of a target neuron over the threshold required to create an action potential. Conversely, if the two inputs temporally arrive too far apart, the depolarization of the first input may have time to drop significantly, preventing the membrane potential of the target neuron from reaching the action potential threshold. Hence, the function of coincidence detection is to reduce the jitter caused by spontaneous neuronal activity, and while random sub-threshold stimulations from cells may not often fire coincidentally, coincident synaptic inputs derived from a unitary external stimulus ensure that a target neuron will fire as a result of the stimulus.
The above description applies well to feedforward inputs to neurons, which provide inputs from either sensory nerves or lower-level regions in the brain. About 90% of interneural connections are, however, not feedforward but predictive (or modulatory, or attentional) in nature. These connections receive inputs mainly from nearby cells in the same layer as the receiving cell, and also from distant connections which are fed through Layer 1.
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