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NJIT Mathematical Biology Seminar

Tuesday, September 27, 2011, 4:00pm
Cullimore Hall 611
New Jersey Institute of Technology

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Preserving tonotopy across feed-forward networks

Borja Ibarz

Center for Neural Science, New York University

Tonotopic representation of sound is maintained along all stages of the mammalian auditory pathway, from the cochlea, through midbrain and up to the primary auditory cortex (A1). The tonotopic representation preserves information about the frequency of the sound and its intensity. The manner in which precise tonotopy is preserved from structure to structure is yet unclear but is likely to depend on several variables, including the patterns of connections between excitatory and inhibitory neurons within and across the layers. We've performed computer simulations of networks of spiking excitatory pyramidal (P) and inhibitory fast-spiking (FS) neurons to investigate the conditions necessary for maintaining a tonotopic axis. In particular, we've looked for parameter values that optimize the estimation of sound frequency and intensity from the responses in successive stages, and the discrimination of pairs of tones. The trade-off between maximizing the sensitivity to individual stimuli and minimizing the interference between simultaneous inputs, and the degradation of frequency estimates with decreasing stimulus intensities, provide criteria for optimization and can be constrained by psychophysic requirements. We conclude that precise topographic mapping requires careful tuning of both circuit and input properties.