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Final
The neural network: Making simple neurons part of complex machines
Primary olfactory processing networks
Eyeblink conditioning circuits
Take home points about networks:
1. Evolved to perform specific functions (broadly defined).
2. Circuit diagrams typically described at one or more levels of complexity.
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.
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.
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:
Number of neurons (adult):
Est: 1012
Number of neurons in cerebral
cortex (adult):
Est: 20,000,000,000
Number of synapses (adult):
1014 (2,000-5,000 per neuron)
Power consumption (adult):
20-40 Watts (0.5-4 nW/neuron)
Percentage of body:
2% weight, 0.04-0.07% cells, 20-44%
power consumption
Atrophy/death of neurons:
50,000 per day (between ages 20 and 75)
–Probably more on Fridays
Maximum firing frequency of a
neuron (across species):
250-2,000 Hz (0.5-4 ms intervals)
Signal propagation speed inside
axon:
90 m/s sheathed, <0.1 m/s unsheathed
Sensory systems: our connection to the world
1. Taste
2. Smell
3. Touch
4. Vision
5. Audition
6. Vestibular (balance)
7. Nocioception (pain)
8. Proprioception (joint position)
This weeks reading assignment is posted: Moss and Sinha 2003
Frog Eating Bat
Gothic Bat
Wahlberg's Epauleted Bat
(megabat)
Echo location in bats
Pallid bat
Chapin's Free-Tailed Bat
For more interesting bat images and links go to:
http://www.debbiesthemes.com/forbes/bats/bats.html
Vampire bats
hairy-legged vampire bat
Bat man
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
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
Bat ears are built the same as ours; bats are just far more specialized
Typical bat ear
Human 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!
FM and CF sound production in bats
Echo locating bats use one or both (predominantly):
1. 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
2. Constant Frequency (CF) pulses
• Narrow frequency band
• Fewer harmonics
• Typically greater than 5 ms
• Provides Doppler shift information
(object movement relative to the bat)
Different bats have different calls with different spectral profiles
Source: http://www.sfsu.edu/~sierra/cavabats.htm
Different bats have different calls with different spectral profiles
Spotted bat
Source: http://www.sfsu.edu/~sierra/cavabats.htm
Different bats have different calls with different spectral profiles
Pallid Bat
Source: http://www.sfsu.edu/~sierra/cavabats.htm
Different bats have different calls with different spectral profiles
Big Brown Bat
Source: http://www.sfsu.edu/~sierra/cavabats.htm
Townsend's Big Eared Bat
Different bats have different calls with different spectral profiles
Source: http://www.sfsu.edu/~sierra/cavabats.htm
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
Doppler shift and acoustic fovea
The speed of sound at sea level:
m/s km/h mph knots
340 1225 761
661
Movement relative to a sound
source will compress or stretch
sound waves
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
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 Frequencyamplitude profiles.
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
Final
Echolocation and foraging behavior in bats
Four stages:
1. Active searching (seeking a target)
2. Approach/stalk (target acquired moving to
intercept or waiting to pounce).
3. Active tracking (chasing)
4. Terminal stage (capture)
• As the behavior progress to stage 4 FM
pulse rate increases, FM range decreases
Bats in action: Interpreting the bat flight video
http://www.bsos.umd.edu/psyc/batlab/jasa03/