Mormyrid electric fish communicate using pulse-type electric organ discharges (EODs). The fine temporal structure of the waveforms of EODs varies widely throughout the 200 or more species of mormyrids. These signals carry information about the species, the sex and even the individual identity of the signaller. Behavioral experiments have shown that some species of fish are capable of using this information. Of the four known types of electroreceptors in mormyrid fish, the knollenorgan electroreceptor is the one most likely to be involved in the detection of conspecific EOD signals. Here, we review some recent advances in understanding how the central knollenorgan pathway might be analyzing the temporal structure of the EOD waveform. Fine temporal analysis appears to take place in the nucleus exterolateralis pars anterior (ELa), where tightly phase-locked inputs from the hindbrain drive a direct, excitatory input through a long axonal delay line and also drive an indirect, inhibitory input with negligible delay through the ELa large cell. These two inputs converge on ELa small cells, where they are hypothesized to interact in a ‘delay-line/blanking’ model. This initial temporal analysis is further refined in the nucleus exterolateralis pars posterior, where units tuned to ranges of pulse durations have been identified physiologically.

REFERENCES

Bass
A. H.
,
Hopkins
C. D.
(
1982
).
Comparative aspects of brain organization of an African ‘wave’ electric fish, Gymnarchus niloticus
.
J. Morph
174
,
313
–.
Bell
C. C.
(
1981
).
Central distribution of octavolateral afferents and efferents in a teleost (Mormyridae)
.
J. Comp. Neurol
195
,
391
–.
Bell
C. C.
,
Grant
K.
(
1989
).
Corollary discharge inhibition and preservation of temporal information in a sensory nucleus of mormyrid electric fish
.
J. Neurosci
9
,
1029
–.
Bell
C. C.
,
Russell
C. J.
(
1978
).
Termination of electroreceptor and mechanical lateral line afferents in the mormyrid acousticolateral area
.
J. Comp. Neurol
182
,
367
–.
Carr
C. E.
(
1986
).
Time coding in electric fish and barn owls
.
Brain Behav. Evol
28
,
122
–.
Carr
C. E.
,
Konishi
M.
(
1990
).
A circuit for detection of interaural time differences in the brain stem of the barn owl
.
J. Neurosci
10
,
3227
–.
Carr
C. E.
,
Maler
L.
,
Taylor
B.
(
1986
).
A time-comparison circuit in the electric fish midbrain. II. Functional morphology
.
J. Neurosci
6
,
1372
–.
Crawford
J. D.
(
1992
).
Individual and sex specificity in the electric organ discharges of breeding mormyrid fish (Pollimyrus isidori)
.
J. Exp. Biol
164
,
79
–.
Enger
P. S.
,
Libouban
S.
,
Szabo
T.
(
1976
).
Fast conducting electrosensory pathway in the mormyrid fish, Gnathonemus petersii
.
Neurosci. Lett
2
,
133
–.
Finger
T. E.
,
Bell
C. C.
,
Russell
C. J.
(
1981
).
Electrosensory pathways to the valvula cerebelli in mormyrid fish
.
Exp. Brain Res
42
,
23
–.
Friedman
M. A.
,
Hopkins
C. D.
(
1996
).
Tracking mormyrid electric fish in the field using individual differences in electric organ discharges
.
Anim. Behav
51
,
391
–.
Friedman
M. A.
,
Hopkins
C. D.
(
1998
).
Neural substrates for species recognition in the time-coding electrosensory pathway of mormyrid electric fish
.
J. Neurosci
18
,
1171
–.
Friedman
M. A.
,
Kawasaki
M.
(
1997
).
Calretinin-like immunoreactivity in mormyrid and gymnarchid electrosensory and electromotor systems
.
J. Comp. Neurol
387
,
341
–.
Haugede-Carre
F.
(
1979
).
The mesencephalic exterolateral posterior nucleus of the mormyrid fish Brienomyrus niger: Efferent connections studied by the HRP method
.
Brain Res
178
,
179
–.
Hopkins
C. D.
(
1981
).
On the diversity of electric signals in a community of mormyrid electric fish in West Africa
.
Am. Zool
21
,
211
–.
Hopkins
C. D.
(
1986
).
Temporal structure of non-propagated electric communication signals
.
Brain Behav. Evol
28
,
43
–.
Hopkins
C. D.
(
1999
).
Design features for electric communication
.
J. Exp. Biol
202
,
1217
–.
Hopkins
C. D.
,
Bass
A. H.
(
1981
).
Temporal coding of species recognition signals in an electric fish
.
Science
212
,
85
–.
Kawasaki
M.
(
1997
).
Sensory hyperacuity in the jamming avoidance response of weakly electric fish
.
Curr. Opin. Neurobiol
7
,
473
–.
Knudsen
E. I.
(
1982
).
Auditory and visual maps of space in the optic tectum of the owl
.
J. Neurosci
2
,
1177
–.
Konishi
M.
(
1991
).
Deciphering the brain's codes
.
Neural Computat
3
,
1
–.
Kramer
B.
(
1997
).
Electric organ discharges and their relation to sex in mormyrid fishes
.
Naturwissenschaften
84
,
119
–.
Mugnaini
E.
,
Maler
L.
(
1987
).
Cytology and immunocytochemistry of the nucleus exterolateralis anterior of the mormyrid brain: Possible role of GABAergic synapses in temporal analysis
.
Anat. Embryol
176
,
313
–.
Mugnaini
E.
,
Maler
L.
(
1987
).
Cytology and immunocytochemistry of the nucleus of the lateral line lobe in the electric fish Gnathonemus petersii (Mormyridae): Evidence suggesting that GABAergic synapses mediate an inhibitory corollary discharge
.
Synapse
1
,
32
–.
Szabo
T.
,
Ravaille
M.
(
1976
).
Synaptic structure of the lateralline lobe nucleus in mormyrid fish
.
Neurosci. Lett
2
,
127
–.
Szabo
T.
,
Ravaille
M.
,
Libouban
S.
,
Enger
P. S.
(
1983
).
The mormyrid rhombencephalon. I. Light and EM investigations on the structure and connections of the lateral line lobe nucleus with HRP labelling
.
Brain Res
266
,
1
–.
Wulliman
M. F.
,
Northcutt
R. G.
(
1990
).
Visual and electrosensory circuits of the diencephalon in mormyrids: An evolutionary perspective
.
J. Comp. Neurol
297
,
537
–.
Young
S. R.
,
Rubel
E. W.
(
1983
).
Frequency-specific projections of individual neurons in chick brainstem auditory nuclei
.
J. Neurosci
3
,
1373
–.
Zipser
B.
,
Bennett
M. V. L.
(
1976
).
Interaction of electrosensory and electromotor signals in lateral line lobe of a mormyrid fish
.
J. Neurophysiol
39
,
713
–.
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