The nucleus preeminentialis of mormyrid fish, a center for recurrent
electrosensory feedback: I. Electrosensory and corollary discharge responses.
Von der Emde, Gerhard & Curtis C. Bell.
Good Samaritan Hospital and Medical Center, R. S. Dow Neurological Sciences
Institute, 1120 N.W. 20th Ave., Portland, OR 97209-1595, USA.
APStracts 3:0074N, 1996.
SUMMARY AND CONCLUSIONS
1. The nucleus preeminentialis (PE) is a large central structure that projects
both directly and indirectly to the electrosensory lobe (ELL) where the
primary afferents from electroreceptors terminate. PE receives electrosensory
input directly from ELL and also from higher stages of the electrosensory
pathway. PE is thus an important part of a central feedback loop that returns
electrosensory information from higher stages of the system to the initial
stage in ELL. 2. This study describes the field potentials and single unit
activity that are evoked in PE by electrosensory stimuli and by corollary
discharge signals associated with the motor command that drives the electric
organ to discharge. All recordings were extracellular in this study. 3. Two
types of negative-going corollary discharge-evoked field potentials were found
in PE. : (1) a shallow, long-lasting negative wave with a latency at the peak
of about 11 ms; and (2) a more sharply falling and larger negative wave with a
shorter latency at the peak of about 9 ms. The long latency wave was
predominant in the dorso-lateral and posterior parts of PE whereas the short
latency wave was predominant in the medial and rostral regions. Both waves
were only found in PE and thus can serve for its identification. 4.
Electrosensory stimuli given either locally to a restricted skin region or
symmetrically to the entire body evoked characteristic field potentials in
both regions of PE. The mean latency between the stimulus and the peak of the
response was 6.9 msec in the early negativity region and 12.2 msec in the late
negativity region. The responses to such stimuli were strongly facilitated by
the electric organ corollary discharge. 5. Field potential responses to the
electric organ corollary discharge were markedly plastic. Responses to the
corollary discharge plus a paired electrosensory stimulus decreased over time
and the response to the corollary discharge alone was markedly enhanced
following a period of such pairing. 6. Local electrosensory stimulation of the
skin showed that the caudal-rostral body axis is mapped from dorsal-medial to
ventral-lateral in PE. The same somatotopy was found in the regions of the
early and late negativities. The ventral and dorsal body appeared not to be
separately mapped in PE. The areas representing the head and chin appendage
("Schnauzenorgan") are especially large in PE, due presumably to the high
density of electroreceptors in these areas. 7. Two main types of units were
recorded in PE: 1) I (inhibitory)- cells with a corollary discharge response
that was inhibited by an electrosensory stimulus to the center of their
receptive fields; and (2) E (excitatory)-cells with an excitatory response to
electrosensory stimuli that was facilitated by the corollary discharge. Some
of the E cells responded to the corollary discharge alone and some did not.
Most cells appeared to be responding to input from mormyromast
electroreceptors but a few cells were driven by ampullary electroreceptors and
a few by Knollenorgan electroreceptors. 8. The corollary discharge effects on
I-cells and E-cells were plastic and depended upon previous pairing with a
sensory stimulus. The corollary discharge facilitation of E-cells and
inhibition of I-cells decreased during pairing with a sensory stimulus, and
the corollary discharge-driven excitation of I-cells was much larger after
pairing than before. 9. The results provide an initial overview of a major
component in the control of electrosensory information processing by recurrent
feedback from higher stages of the system.
Received 26 December 1995; accepted in final form 4 April 1996.
APS Manuscript Number J8606-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 May 96