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Important requirements for JAR: Absolute value of the difference in frequency less than 20 Hz 2. Mixing of signals 3. Variation in mixing ratio 4. Modulation of phase and amplitude of the mixed signal.
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The regularity of the electric organ discharge is determined by an endogenous oscillator in medulla oblongata called the pacemaker nucleus (PN).
PN(f) = EOD (f)
May or may not be
equal to PN(f)
EOD replaced by electric sine wave of similar amplitude and frequency
EOD mimic (Sine) of neighbor’s electric field
Result: Correct jamming avoidance behavior
Lowers its pacemaker frequency if DF=(+)ve
Raises its pacemaker frequency if DF=(-)ve
Do not tell much about the behavioral mechanism involved in
determining the sign of DF.
NO INTERNAL REFERENCEUses the electrical field frequency rather than internal frequency of the pacemaker nucleus
Frequency of the EOD mimic (Sine) was decreased to a frequency 50 Hz below the frequency of the pacemaker nucleus
PN (f) = 300 hz, EOD mimic of self (Sine) = 250hz,
EOD mimic of neighbor (Sine) = 254hz
When confronted with neighbor’s EOD mimic it responded as if this 50 Hz lower frequency was its own frequency.
Fish needs a mixture of its own signal and neighbor’s signal to execute JAR
Fish placed in two compartment chamber
Pectoral region sealed
No EOD could be detected by head region
Jamming stimulus presented to the head
JAR elicited when
EOD leaked into head chamber
Jamming signal entered the tail chamber
Mimics of two EODs (Sine) were
added and presented.
Electrical fields had different
Frequency, but identical geometry
NO VARIATION IN MIXINGRATIO OVER BODY SURFACE----NO JAR
Under natural situation
electrical fields vary both in
frequency and geometry
VARIATION IN MIXING RATIO-----JAR
How are the behavioral rules for execution of a correct JAR implemented at the neural level?
ELL: electrosensory lateral line lobe
TS: torus semicircularis
nE: nucleus electrosensorius
PPn: prepacemaker nucleus
Pn: pacemaker nucleus
Extraction of the sine of DF by electrosensory processing of phase and
Translation of the determination of the sign of the DF into change of the motor output,
that is of the pacemaker frequency
Ampullary receptors:Tuned to DC and low frequency AC signals of both
biological and non biological sources.
Used for ---- Prey detection
Detection of earths magnetic field
Tuberous receptors: Tuned to AC signals with
frequencies in the range of fish’s own EOD
P type: Fire intermittently and increase their rate of firing with rise in stimulus amplitude.
T type: Fire one spike on each cycle of the stimulus.
Firing of T unit
Firing of P unit
Electrosensory lateral line lobe
(preserves spatial order)
Parallel processing (Ptype and Ttype information processed seperately)
Inputs from several Ttype receptors are received by one sperical cell via electronic synapse
Ptype receptors form excitatory synapse onto basilar pyramidal cells and inhibitory synapse
onto nonbasilar pyramidal cells (via exciting the granule cells)
Excitation of basilar pyramidal cells reflect rise in stimulus amplitude
Inhibition of non basilar pyramidal cells reflectrise in stimulus amplitude
Excitationof non basilar pyramidalcells reflect fall of stimulus amplitude
Divided into laminae
Sperical cells project onto laminae 6
Encodes phase differences
Basilar and non basilar pyramidal cellsproject ontovarious laminae
Encodes phase and amplitude information
Convergence of amplitude and phase information is achieved by vertical connections between different layers
Receives input from torus semicircularis
Somatotopic arrangement of the toral layers is lost in this area
Cells encode sign of DF
Cells of dorsal part of nE raises the EOD frequency--- nE
Cells of ventral part of nE lowers the
Lglutamate – stimulate dorsal cluster -- raises EOD frequency
Lglutamate – stimulate ventral cluster -- lowers EOD frequency
Bilateral lesion of these two areas eliminate the frequency shift in the JAR.
nE innervates via excitatory synapses the CP/PPn-G in dorsal thalamus
PPn- prepacemaker nucleus is the dorsolateral portion of central posterior nucleus
CP/PPn-G innervates Pacemaker cells via AMPA type glutamate receptors
Lesion or CNQX application abolishes frequency rise due to –ve DF
CNQX- 6 cyano 7 nitroquinoxaline –2,3- dione
nE innervates via inhibitory synapses (GABA) the SPPn in mesencephalon
SPPn- sublemniscal prepacemaker nucleus
SPPn innervates Relay cells via NMDA type glutamate receptors
Lesion or APV application abolishes lowering of frequency due to +ve DF
APV- 2 amino 5 phosphonovaleric acid
Final motor control achieved in the Pacemaker nucleus