The neural network: Making simple neurons part of complex machines

1. Final The neural network: Making simple neurons part of complex machines Primary olfactory processing networks Eyeblink conditioning circuits • Take home points about networks: • Evolved to perform specific functions (broadly defined). • Circuit diagrams typically described at one or more levels of complexity.

2. Establishing a causal relationship between neurons and behavior • Correlation does not mean causation!!! • Establishing a causal relationship means: • Establishing the neuron or neuropil (a discrete region of neural interaction) is necessary for the behavior to occur. • Ablation • Pharmacology • Gene silencing • Establishing that the neuron or neuropil is sufficient for the behavior to occur.

3. Establishing a causal relationship between neurons and behavior • Test example: The Crayfish escape response is mediated by the lateral giant interneuron (LGI). • Correlation: Every time animal is tactilely stimulated, LGI fires and the escape response (tail flip) occurs. • Sufficiency: Every time the LGI is stimulated the escaper response occurs. • Necessity: If LGI is action potentials are blocked even tactile stimulation will fail to elicit behavior.

4. For reference the length of a football field is 91.44 meters • Conduction velocity of a squid giant axon is ~25m/s • Conduction velocity of a myelinated motor unit ~120m/s Interesting facts about the human brain:

5. Sensory systems: our connection to the world • Taste • Smell • Touch • Vision • Audition • Vestibular (balance) • Nocioception (pain) • Proprioception (joint position) This weeks reading assignment is posted: Moss and Sinha 2003

6. Wahlberg's Epauleted Bat (megabat) Frog Eating Bat Gothic Bat Pallid bat Chapin's Free-Tailed Bat Echo location in bats For more interesting bat images and links go to: http://www.debbiesthemes.com/forbes/bats/bats.html

7. hairy-legged vampire bat Bat man Vampire bats For taxonomic information and detailed descriptions of various bat families got to: http://www.abdn.ac.uk/~nhi708/classify/animalia/chordata/mammalia/chiroptera/chiroptera.html

8. Sonar (sound navigation and ranging) is a technique that uses sound propagation under water to navigate or to detect other watercraft. There are two kinds of sonar, active and passive. Bats use echolocation which is the same as Active Sonar Ghost Faced Bat

9. Human ear Bat ears are built the same as ours; bats are just far more specialized Typical bat ear • Echo locating bats can: • Have a ~60 degree field of aural view (per pulse) • Detect sounds as high as 200Khz (optimal freq is species specific) • Detect objects less than a mm in diameter • Discriminate: • Object size • Object trajectory • Objects made of foam vs hard plastic vs live food • Insects based on wing flapping of the insect • Differences in echo delays as small as 10ns!

10. FM and CF sound production in bats • Echo locating bats use one or both (predominantly): • Frequency Modulated (FM) pulses 20-200 kHz • Broadband signals • < 5 ms in duration • Pulse starts high frequency, sweeps down • used to calculate target distance/detail • Constant Frequency (CF) pulses • Narrow frequency band • Fewer harmonics • Typically greater than 5 ms • Provides Doppler shift information • (object movement relative to the bat)

11. Different bats have different calls with different spectral profiles Source: http://www.sfsu.edu/~sierra/cavabats.htm

12. Different bats have different calls with different spectral profiles Spotted bat Source: http://www.sfsu.edu/~sierra/cavabats.htm

13. Different bats have different calls with different spectral profiles Pallid Bat Source: http://www.sfsu.edu/~sierra/cavabats.htm

14. Different bats have different calls with different spectral profiles Big Brown Bat Source: http://www.sfsu.edu/~sierra/cavabats.htm

15. Townsend's Big Eared Bat Different bats have different calls with different spectral profiles Source: http://www.sfsu.edu/~sierra/cavabats.htm

16. Specific parameters that bats extract from echoes about objects • Distance: (FM). Based on echo delay • Subtended angle or angular size. Based on echo loudness; (CF-FM) • Absolute object size, based on Delay + loudness (CF-FM) • Azimuth: the horizontal position (angle) of an object relative to the face. Based on aural delay (CF-FM) • Elevation of object (vertical angle relative to face) differential loudness based on changing ear position • Texture of object based on FM • Velocity/relative velocity of object • (change in distance relative to bat) Doppler shift

17. Movement relative to a sound source will compress or stretch sound waves Doppler shift and acoustic fovea

18. Doppler shift and acoustic fovea • Doppler shift compensation • Bats have a very narrow frequency band that they are particularly sensitive to. • Thus if they emit sounds at the most sensitive frequency and the object is moving Doppler shift will produce an echo that falls to one side of the optimal frequency • Bats therefore actively adjust their pulse emission frequency to compensate for this

19. What kinds of information can bats glean about targets from echoes? • Each moth species has a characteristic wing beat frequency and amplitude. • Bats are able to discriminate insects based on the different Frequency-amplitude profiles.

20. What kinds of information can bats glean about targets from echoes? • Bats are able to discern echo delay differences of 10ns • Equates to a distance of 2mm

21. Final Echolocation and foraging behavior in bats • Four stages: • Active searching (seeking a target) • Approach/stalk (target acquired moving to intercept or waiting to pounce). • Active tracking (chasing) • Terminal stage (capture) • As the behavior progress to stage 4 FM pulse rate increases, FM range decreases

22. Bats in action: Interpreting the bat flight video http://www.bsos.umd.edu/psyc/batlab/jasa03/