Auditory Communication

  • Auditory communication models demonstrate convergent evolution

    • crickets, toadfish, midshipman fish boat whistles, anuran (Xenopus humming frogs and frog calling), owls (barn owls), mice, and primates

  • Fundamental concepts from crickets (applies to vertebrates as well; convergent evolution)

    • command neurons - an interneuron whose excitation is both necessary (required for behavior) and sufficient (can evoke behavior alone) to evoke a behavior

    • central motor pattern generation (CPG) - two neurons that feed back on each other, without other input (walking)

    • corollary discharge processing - brain sending copies of movement commands to other parts of the brain, distinguishes between internal and external sensory info

    • pattern recognition by sensory feature detection - identifying patterns within sensory input by focusing on specific distinctive features of the stimuli (ILD, ITD)

  • Midshipman fish (and toadfish) humming

    • hormones (melatonin) release humming at night (during mating season)

    • CPG is in the hindbrain; neural firing matches with call changes

    • 11-ketotestosterone increases boat whistle calls, cortisol decreases calls (predators and/or stress)

    • females tune male calls and hearing by season

    • saccule, in females and males contains sensory hair cells, are more sensitive to calls; saccule afferents are phase-locked to specific parts of an action potential

    • whole genome duplication events results in subtypes of ERs and ARs (difference responses of different genes alpha and beta)

  • Anuran (frog and toad) calling

    • two distinct auditory organs: amphibian papilla and basilar papilla conduct sounds for calls

    • sexual differences in the auditory system of the tree frog

      • females have a basis for certain features of sounds males cannot make

    • temporal selectivity in the central auditory system of the leopard frog

  • Barn Owl

    • ILD (interaural level differences) - intensity

    • ITD (interaural time differences) - timing

    • Parallel pathways combine and form a map (MASP) of auditory space in the owl midbrain

    • mammals and birds have differing maps

      • they independently evolved auditory computations (before tympanic hearing)

    • Hebbian learning - neurons fire together wire together (increases strength, and fires easier)

      • can lead to long-term potentiation - increases excitation from one neuron to another

    • Jeffress Model - coincidence detections (neuron only fires when receiving signals from two places at the same time) and delay lines (different times for signals to get to coincidence detector neurons)

    • Hears sounds better head-on, sound shadows occur when sound comes from the side of the head opposite of the ear that detects it

    • Low frequencies travel farther and scatter/bounce of objects less than high frequency sounds