Dr. Moira van Staaden
office: LSC 304
phone: 2-0341
Email: mvs@caspar.bgsu.edu
Generation of the song pattern
wing elevator muscles = wing closers i.e. drive file/scraper
mechanism
wing depressor muscles = wing openers
myogram - measure of muscle activity
[FIG 4]
o Evidence for central pattern generation of song (CPG)
- Various ablation experiments
=> Song pattern generated by interneurons in thoracic ganglia
without sensory feedback
But feedback from sense organs monitoring wings can
influence song pattern
e.g. mechanoreceptors (stretch receptors, campaniform organs)
sensory hairs on cerci reset the chirp rhythm
- Motor output elicited by electrical stimulation/localized lesions
in brain
=> interneurons descending from brain to thoracic ganglia trigger
song CPG
- active for the duration of singing
- electrical stimulus continuous but motor response rhythmical
Thoracic CPG requires excitation from triggering (command) interneurons to maintain activity above threshold
Genetic basis of song-producing systems
Teleogryllus commodus X T. oceanicus
- morphologically similar but distinctly different songs
- interspecific hybrids fertile; can backcross with parental species
- song pattern shifts systematically according to proportion of
genes from the 'parental' species
- F1 song intermediate between parental species
- each backcross song intermediate between F1 and parental species
=> information specifying song pattern is genetically coded
- precisely determines form of species-specific neuronal networks
Responding to sound signals
Kramer locomotion compensator
[FIGS 5 & 6]
The Anatomy of Hearing
Cricket ears
o tympana (ears) - located on tibia of the foreleg
o tracheal system - insect respiratory system; a system of tubes which arborize throughout the body and move gases to and from cells
o central nervous system
[FIG 7]
- Sound reaches receptors via direct and indirect paths
- Tympanal vibration reflects net interaction of these
- Tracheal system turns tympana into pressure difference receivers
- Transduction pathway not yet understood
Ear provides information on:
o Intensity
o Frequency
o Direction
[FIG 8a]
o Neural threshold - the just-detectable increase in firing
over resting level
- firing rate increases with intensity to max. of 200-300 impulses/sec
o Tuning curves
- generally v-shaped
- usually corresponds to CF of calling song, but exceptions exist
- tuning of individual neurons similarly v-shaped but smaller
frequency range; (dynamic ranges ca. 30-40 db SPL)
o Sensory neurons tonotopically organized
- spatial arrangement in order of frequency sensitivity (low -
proximal; high - distal)
- spread of sensitivities => frequency analysis by comparing
output of differently tuned neurons
o Directional information
Test: auditory threshold with constant frequency sound
from different directions
[FIG 8b]
Result: threshold varies with direction giving cardioid plot of directional sensitivity
- time or intensity differences unavailable to small animals
- differences too small for nervous system to resolve, e.g. cricket ears ca. 1 cm apart => time 30 µs, intensity 1-2 dB, (wavelength 10 cm at 4 kHz)
- tympanal motion determined by net sound pressure across it
- waves are out of phase
- pressure-difference receiver = pressure-gradient receiver, an inherently directional mechanism of sound reception
- used by majority of insects because are directional irrespective of animal size
o Sensory filtering is not just a CNS function.
The cricket ear:
- preferentially detects & localizes sound frequency used
by own species
- has good directional sensitivity only for frequencies close
to CF
What is the underlying neural (or receptor) mechanism for song recognition?
Recognition mechanisms: 3 working hypotheses
[FIG 9]
o The Common Neural Elements Hypothesis (primarily Hoy
et. al.)
- posits that homologous neurons in a neural system shared by
sender and receiver are involved in both signal pattern generation
and recognition
oo The Delay Line Hypothesis (primarily Reiss et. al.)
- describes a possible neuron/set of neurons that act to delay
the first syllable by a set time (e.g. 35 ms for Gryllids)
ooo The Anded High and Low Pass Filters (primarily Schildberger
et. al)
- two sets of neurons act as high- and low-pass frequency filters
in series with a logical AND gate => band-pass filter
Last modified: 00/04/28