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

Echolocation and foraging behavior in batsFinal

Bats in action: Interpreting the bat flight video

http://www.bsos.umd.edu/psyc/batlab/jasa03/

Auditory cortex

Medial Geniculate Body(of the thalamus)

Inferior Colliculus

Lateral Lemniscus

Cochlear Nucleus

CochleaSuperior Olivary Complex

Trapezoidal body

Commissures(crossways)

Corpus callosum

Auditory processing (Bat, rat, cat or any verte-brat)

Themes:•Transduction•Encoding•Decoding

Models/figures swiped from caltech

Auditory transduction

Amplified mechano-signal drives a wave that will crest in the cochlea

Cresting sound waves:•displace the basilar membrane•drives stereocilia-depolarizes cell

Models/figures swiped from caltech

Auditory transduction

Where the sound wave crests depends on its frequency

Human cochlea

Bat cochlea is specialized:•Frequency range higher than other vertebrates•Acoustic fovea

The lower the frequency of the wave the further it travels before cresting

5KHz 15KHz

Models/figures swiped from caltech

Auditory transduction: examples of basilar membrane displacement

The Inferior Colliculus: A pulse-echo delay Filter (encoder)

Neurons in the inferior colliculus are sensitive to the time interval between a call and its echo. •Individual cells are sharply tuned to one particular frequency in an FM sweep•Low action potential thresholds•Invariant response latencies to calls and echoes. As the pulse-echo intensity shifts, the response latency and size remain constant. •Invariant response magnitude to calls and echoes. 1 to 2 spikes per call or echo.•FM sweeps are encoded by an ensemble of responding neurons. Each cell is tuned to narrow frequency range and responds to both the call and echo at that frequency.

•A subset of cells also project back to the ear to control tensor tympani (a muscle that attenuates amplitude on middle ear bones.

•Disproportionate representation of CF as well (acoustic fovea)

Portfors & Wenstrup: J Neurophysiol 82: 1326-1338, 1999

The Mustached Bat (Pteronotus) and its call

Note that FM1 is the lowest frequency and smallest amplitude; this is the part of the pulse that the bat monitors. For the echo, these bats monitor the other harmonics

Cortical organization

The cortex is made up of a matrix of cells (called columns) like a honeycomb Each column contains numerous neurons and can be considered a discrete functional unit. The columns are all layered (typically 6) in a common pattern

• layers based on differential concentrations of cell bodies of a particular type (subpopulation) or the dendrites from a specific subpopulation of cells.

Typically sensory representations are topographically very organized in a manner reflective of the salient perceptual dimensions of that sensory mode.

Recording from the cortex

•Neurons in this area respond specifically to time separated pairs of FM1 pulses and an FM(2,3) harmonic echo. (FM1call & FM2 echo)•Neurons are tuned to

•best delay: indicates distance •amplitude: indicate subtend angle of target

•Collectively these cells could encode absolute size.

•Neurons are frequency tolerant - enables cells to respond to broadband components of pulses and echoes.

•Because they are frequency tolerant neurons of the FM-FM region are blind to Doppler shift.

•Selective disruption of this area results in loss of delay discrimination in behavioral tests

FM-FM region:

FM1/FM2

FM1/FM3

FM2 Delaylow (close) High (far)

FM

1 am

pl.

FM

1 am

pl.

FM3 Delaylow (close) high (far)

•Regions contain neurons that are sensitive to varying combinations of the CF1 of the pulse and a harmonic of the CF echo (i.e. CF1 & CF2). •Respond only to pulse-echo combinations with differing fundamental frequencies (i.e. different amounts of Doppler shift). •Thus each P-E pair of frequencies encodes a different relative velocity and is coded in a physical place in the cortex.•Velocity range represented is typically -2 to 9 m/s, most sensitive to 0-4 m/s

CF

CF-CF region

CF1/CF2

CF1/CF3

CF2 freqlow (loosing) High (gaining)

====C

F1 fr

eqC

F1 fr

eq

CF3 freqlow (loosing) High (gaining)

•Largest single cortical region in bat auditory system •Neurons responds only to echo CF2 regardless of call frequency. •Develops specifically to the individual bats call.•Sensitive to faint echoes from distant targets. •Very selective frequency and amplitude discrimination •Represents the acoustic fovea:

•High resolution Doppler shift•High resolution angular size

•Selective disruption of this area results in loss of frequency discrimination in behavioral tests

CF

DSCF region

60.5KHz61.6KHz

63.0KHz

Echo frequency

Reading assignment: Shiva and Moss (2003)•Elaborates on circuit complexities (cortical and subcortical)•Ties in motor control/coordination