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How General Are Neural Codes In Sensory Systems?

Explore how neural codes in sensory systems, such as inter-aural level difference (ILD), inter-aural time difference (ITD), inter-aural phase difference (IPD), and inhibitory input, play a role in distinguishing spatial differences and recognizing spatial information. Discover the tonotopic arrangement difference and different patterns of inhibitory input in avian and mammalian species. Also, explore new models for understanding neural coding in sensory systems.

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How General Are Neural Codes In Sensory Systems?

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  1. How General Are Neural Codes In Sensory Systems? • Presenter: 유승범 • (Department of Brain and Cognitive Sciences)

  2. 1. Inter- aural Level Difference(ILD) • ILD is the detecting the difference of • intensity reaching each sides of the ear. • Since head works like low frequency • filter, ILD is more related with • distinguishing spatial difference of • higher frequency. • [ Shorter width: higher cut-off]

  3. 2. Inter- aural Time Difference(ITD) ITD and Coincidence Detection • * ITD is the time difference of signal reaching to both ears. • * Since ITD is works recognizing the spatial difference by temporal • information, then how can it be re-perceived as spatial information? • * Place of coincidence detectors transforms the temporal to spatial information.

  4. 3. Inter- aural Phase Difference(IPD) IPD and Phase Ambiguity(Phantom Phenomena) • When lagging signal’s phase is equivalent to ITD±T of leading signal and ITD±T • exist within physiological range, it causes phase ambiguity. • (T is cycle of stimuli tone)

  5. 4. Inhibitory Input • There are systematic shifts of post-synaptic pulses due to IPSP gradient. • As inhibition increases(GI max increase), the ITD shifts into the leftward.

  6. 1. Tonotopic arrange difference • Avians have ITD map running orthogonal to • frequency tonotopic map. Thus,within iso-frequency • layer, full representation of ITD is available! • However, mammals have parallel ITD maps to • primary frequency tonotopic map.

  7. 2. ITD Utilizing Strategies Characteristic Delay Avians has steady ITD peak with their function. This is Characteristic Delay and it closely stays within physiological range. Mammal’s neuron, however, has different ITD peaks according to the frequencies. [Each Neurons have Characteristic Frequencies] Mammals utilize steepest slope of ITD functions.

  8. 3. Different Patterns of Inhibitory Input • Mammal uses glycinergic pathways to inhibit Medial Superior Olive(MSO). • Avian utilize GABAergic pathways to inhibit Nuclei Laminaris(NL) . • ➤ Within this difference, mammal utilize hyper-polarizing mechanism in • inhibiting whereas avian applies depolarizing mechanism. • Mammal’s MNTB implies feed-forward inhibition. • Avian’s SON implies feed-backward inhibition. • Mammal’s inhibition is related with time-window shift. • Avian’s inhibition is characterized as de-correlation. • (No temporal shift, but gain control)

  9. New Model Suggestion • [New Model Suggestion] • Jeffress-like model with the avians. • New model for mammals are so • called “two-hemispheric channel” model. • ➤ Azimuthal change of position in • one channel accompanied by • channel in other side by opposite sign.

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