$ pt 2: sensory input $ ch 2: echolocation in bats $ bat behavior $ decoding the acoustic environment $ hunting bats $ neural mechanisms $ moth responses to predation $ summary PART 2: SENSORY WORLDS #06: ECHOLOCATION IN BATS II

$ pt 2: sensory input $ ch 2: echolocation in bats $ bat behavior $ decoding the acoustic environment $ hunting bats $ neural mechanisms $ moth responses to predation $ summary PART 2: SENSORY WORLDS #06: ECHOLOCATION IN BATS II

$ 2 polar views of brain structure-function relationships... $ ball of wool... $ anatomical homogeneity $ cell function diversity $ network & structure... $ anatomical diversity $ cell function homogeneity $ both... BRAIN STRUCTURE – FUNCTION

$ brain functions determined by... $ experimentation $ proximity & connectivity  known inputs & outputs ( eg, olfaction) BRAIN STRUCTURE – FUNCTION

$ Drosophila brain BRAIN STRUCTURE – FUNCTION

 antenna   antennal lobe   antennal gl. tract  mushroom  body   lateral horn  $ Drosophila olfactory BRAIN STRUCTURE – FUNCTION

$ human brain BRAIN STRUCTURE – FUNCTION

$ human auditory NEURAL MECHANISMS

$ human auditory NEURAL MECHANISMS

$ bat auditory $ ear drum vibration $  hair displacement $ amplitude $ frequency $ 1° auditory neurons in spiral ganglion $  CNS  ) ) ) ) ) ) ) NEURAL MECHANISMS

$ human auditory ( b ) $ hair cells on basilar membrane = basilar fibers $ base,  frequency $ apex,  frequency $ excitation...    $ inhibition...  NEURAL MECHANISMS

$ ranges of auditory perception K10K100K FREQUENCY (Hz) HUMAN BAT NEURAL MECHANISMS

$ bat auditory specializations  echolocation  ) ) ) ) ) ) ) $ frequency range $ CF bats... acoustic fovea on membrane $ thicker $ longer $ 1° auditory neurons $ more of them NEURAL MECHANISMS

$ bat auditory specializations  echolocation $ frequency range $ CF bats... acoustic fovea on membrane $ thicker $ longer $ 1° auditory neurons $ more of them $ tuned to acoustic fovea NEURAL MECHANISMS

$ bat auditory specializations  echolocation $ frequency range $ CF bats... acoustic fovea on membrane $ thicker $ longer $ 1° auditory neurons $ more of them $ tuned to acoustic fovea ? NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ bat auditory specializations  echolocation $ FM bats... sensitivity to emitted call  during call $ contract middle ear muscles $ attenuation in nucleus of lateral lemniscus* $ CF bats... remain sensitive to signal during call $ ~ deaf to narrow band of call,  membrane sensitivity NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ inferior colliculus  encoding FM signal-echo delay $ inferior colliculus neurons  fixed spike rate ~ $ call $ echo delay $ not ~ intensity $ frequency tuned $ low threshold NEURAL MECHANISMS

$ inferior colliculus  encoding CF Doppler effect $  # of frequency tuned neurons at acoustic fovea $ target information $ encode insect wing beats NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex auditory cortex sensory interneuron sensory interneuron auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus CF-CFFM-FMDSCF auditory cortex auditory cortex sensory interneuron NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus CF-CFFM-FMDSCF auditory cortex auditory cortex auditory cortex lower centers NEURAL MECHANISMS

$ auditory cortex  lower centers $ individual parameters $ parallel centers NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus auditory cortex NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus CF-CFFM-FMDSCF NEURAL MECHANISMS

$ mustached bat $ CF & FM components $ pulse & echo $ 4 harmonic frequencies $ H 1 = fundamental $ 4 amplitudes (volumes) $ H 2 > H 3 > H 4 > H 1 $ map onto different cortical areas NEURAL MECHANISMS

$ mustached bat $ FM-FM area  distance & size coding NEURAL MECHANISMS

$ FM-FM area  distance coding $ respond best to FM call + delayed FM echo $ FM-FM neurons delay tuned, in columns $ FM 1 -FM 2, FM 1 -FM 3 & FM 1 -FM 4 zones NEURAL MECHANISMS

$ FM-FM area  size coding $ FM-FM neurons delay & amplitude tuned $ disruption  no influence on freq. discrimination NEURAL MECHANISMS

$ auditory pathway: mustached bat (FM & CF) cochlea auditory nerve cochlear nucleus inferior colliculus nucleus of lateral lemniscus medial geniculate nucleus superior olivary nucleus CF-CFFM-FMDSCF auditory cortex auditory cortex NEURAL MECHANISMS

$ FM-FM area  distance & size coding $ medial geniculate nuc. delays call signal  FM-FM $  call + delay coincidence  FM-FM auditory cortex auditory cortex NEURAL MECHANISMS

$ mustached bat $ FM-FM area  distance & size coding $ CF-CF area  velocity coding NEURAL MECHANISMS

$ CF-CF area  velocity coding (Doppler shift) $ CF-CF neurons Doppler shift tuned, in columns $ CF 1 - CF 2  compares 30 vs 61 kHz tones $ CF 1 - CF 3  compares 30 vs 92 kHz tones NEURAL MECHANISMS

$ CF-CF area  velocity coding (Doppler shift) $ columns map relative velocity coordinates $ -2  +9 m/s $ most 0  +4 m/s (biologically relevant) NEURAL MECHANISMS

$ mustached bat $ FM-FM area  distance & size coding $ CF-CF area  velocity coding $ DSCF area  Doppler shifted CF 2 NEURAL MECHANISMS

$ DSCF area  Doppler shifted CF 2 signals $ 60.6  62.2 kHz $ 61 kHz $ neurons tuned for freq. & amplitude of echo $ cortical acoustic fovea $ disruption  no influence on delay discrimination NEURAL MECHANISMS

$ why harmonics ? $ many bats & signals $ H 2 > H 3 > H 4 > H 1 $ fundamental H 1 weak $ only heard by sender $ vs other harmonics $ ~ dual password NEURAL MECHANISMS

$ why are there any moths left ? $ moths hear  rate signals $ early stages (...6) $ moth hears pulse before bat hears echo $ fly in opposite direction MOTH RESPONSES TO PREDATION

$ why are there any moths left ? $ moths hear  rate signals $ late stages (9...) $ moth hears pulse after detection $ moths dive  ground & shelter $ erratic flight  confusing echo MOTH RESPONSES TO PREDATION

$ bats echolocate to $ navigate $ locate, identify, track & capture prey (flying insects) $ 2 kinds of signals $ FM, broad band, short duration (< 5 ms) $ CF, narrow band, long duration (5 – 100 ms) $ complex analyses of emitted calls & returning echos SUMMARY

$ complex analyses of emitted calls & returning echos $ FM call-echo delay  distance $ echo amplitude (volume)  angular size $ distance + amplitude  absolute size $ spatial location... $ binaural comparisons  azimuth $ different ear positions  horizontal $ CF Doppler shift  relative velocity of target SUMMARY

$ acoustic fovea $ narrow CF range  Doppler shift analyses $ overrepresented throughout auditory system $ Doppler shift compensation of call  echo in acoustic fovea $ 3 stages of hunting ~ # pulses / s (resolution of target) $ ~ 10 Hz $ ~ 50 Hz $ ~ Hz SUMMARY

$ auditory specializations  echolocation $ acoustic fovea  Doppler shifted CF echoes $ basilar membrane (cochlea)  expanded AF range $ nuc. of lateral lemniscus  attenuate FM calls $ inferior colliculus  responds to FM echo delays $ medial geniculate nuc.  call-echo coincidence detection & relay to auditory cortex $ auditory cortex  tonotopic maps SUMMARY

$ flow diagram $ basilar membrane  expanded AF $ inferior colliculus  FM echo delays $ med. geniculate nuc.  FM coincidence $ auditory cortex  tonotopic maps SUMMARY

$ auditory specializations  echolocation $ auditory cortex  tonotopic maps $ FM-FM area  distance information map onto freq. & delay-sensitive columns of neurons $ CF-CF area  velocity information maps onto Doppler shift-sensitive columns of neurons $ DCSF area  velocity information maps onto AF range of Doppler shift-sensitive neurons SUMMARY

$ bat-moth co-evolution... maintains balance $ moths respond to bat signals $ signal rate  (approach), moths fly away from signal $ signal rate  (terminal), moths either dive or fly irratically $ some emit pulses to jam bat radar SUMMARY