Hyperacuity in the Auditory System

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Reed0109872 Certain cells in the mammalian auditory brainstem (threeneurons from the periphery) show exceptionally small standarddeviations in the microsecond range of the timing of the firstaction potential response under repeated trials of the samesound. Moreover, the latency and its standard deviation arequite independent of frequency and decibel level over largeranges. This behavior is exceptional since the inputs to thesecells come from octopus and other cells in the contralateralcochlear nucleus, a nucleus which is ennervated by auditory nervefibers that have much larger standard deviations and highdependence on frequency and decibel level. Thus, this system isan example of how the brain can use relatively sloppy andvariable devices (neurons) to perform surprisingly accuratecalculations. Professor Michael Reed, with colleague physiologistJoseph Blum, investigates this system with three researchprojects: (i) They create and investigate by machine computationa large scale mathematical model of the whole system using knownphysiological properties of auditory nerve fibers and recentlydiscovered properties of octopus cells; (ii) They usemathematical analysis investigate of the improvement of thestandard deviation of latency in converging networks where thetarget cells require coincident inputs within time windows inorder to fire; (iii) They use partial differential equations tounderstand the special properties of dendritic informationprocessing in octopus cells. Using mathematics and machine computation, Professor MichaelReed continues to study how groups of cells (neurons) in theauditory brainstem perform calculations that individual cells cannot do by themselves. Neurons are inherently sloppy and variabledevices that perform differently even under (apparently) the sameconditions with the same inputs. Nevertheless, large groups ofthese neurons are able to perform together, reliably, highlyaccurate calculations. This project tries to understand thisapparent paradox. The project sheds light on how and why humanbrains are organized the way they are and it suggests newmechanisms for the development of man-made thinking devices.