Scientists have identified an ingeniously elegant brain circuit consisting of just five nerve cells that allows female crickets to automatically identify the chirps of males from the same species through the rhythmic pulses hidden within the mating call. The circuit uses a time delay mechanism to match the gaps between pulses in a species-specific chirp - gaps of just few milliseconds. The circuit delays a pulse by the exact between-pulse gap, so that, if it coincides with the next pulse coming in, the same species signal is confirmed. It's one of the first times a brain circuit consisting of individual neurons that identifies an acoustic rhythm has been characterised. The results are reported were reported online on September 11, 2015 in the journal Science Advances. The article is titled “An Auditory Feature Detection Circuit for Sound Pattern Recognition.” Using tiny electrodes, scientists from Cambridge University's Department of Zoology explored the brain of female crickets for individual auditory neurons responding to digitally-manipulated cricket chirps (even a relatively simple organism such as a cricket still has a brain containing up to a million neurons). Once located, the nerve cells were stained with fluorescent dye. By monitoring how each neuron responded to the sound pulses of the cricket chirps, scientists were able to work out the sequence the neurons fired in, enabling them to unpick the time delay logic of the circuit. Sound processing starts in hearing organs, but the temporal, rhythmic features of sound signals - vital to all acoustic communication from birdsong to spoken language - are processed in the central auditory system of the brain.
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