The electrophysiology of the nervous system is studied using cats and human subjects. Data cover effects of chlorolose on evoked potential, the evoked resistance shift that accompanies evoked potentials, and the relationship of eye movements to potentials aroused by visual stimulation

Galambos, R.

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FINAL REPORT NGR-05-009-083
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Electrophysiological Studies of the Nervous System
Robert Galambos, Principal Investigator
University of California, San Diego
June 1972
This is the final report on the above project originally funded
for the period January 1970 - June 1971 and finally completed in May 1972.
As initially conceived the electrophysiological studies to be per-
.formed fell und.er 3 headings, all pertinent to the mechanisms by which
potentials are evoked in a brain by sensory stimulation:
1. The effects of chloralose on the evoked potential;
2. Studies on the evoked resistance shift that accom-
panies evoked potentials;
3. The relationship of eye movements to potentials,
aroused by visual stimulation.
As the following report will make clear, two of the above sets of
experiments were completed (numbers 1 and 3), while the experiments on
the evoked resistance shift were actually done on the cochlea, not upon
j
the brain, as originally intended. In addition, several new types of
studies not envisaged in the original project description were undertaken,
and in some cases completed and published.
1. Effects of. Chloralose on the Nervous System
We have studied some.10 cats under chloralose anesthesia in various
tests of this general hypothesis: chloralose may impair the ability of
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glial' cells to .clear K+ ion extruded during.normal neuronal activity,
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thus prolonging the recovery of neurons that have already fired and
lowering the threshold of those that have not. Using-cats with electrodes
implanted throughout the classical auditory pathway we simultaneously
established the so-called click recovery curve at the cochlear nucleus,
inferior colliculus and auditory cortex. As compared to the situation
in the same cat when unanesthetired, the electrical response to the
second of a pair of clicks was profoundly depressed at the cortex, but
not at the cochlear nucleus or inferior colliculus; furthermore, we
could collect no evidence that, under the drug, two subthreshold or'
subminimal stimuli would summate differently than they did in the normal
animal. . Both aspects of the hypothesis were thus disconfirmed and the
project was abandoned. This negative result was not considered of suf-
ficient general interest to warrant publication (Millyard, Galambos).
^' Resistance Shifts and Other Electrophysiological Measurements
on the Cochlea
These experiments are designed to measure the resistances and
capacitances between the 3 fluid-filled compartments of the cochlea
(scala media, tympani and vestibuli) Under 2 conditions: when the
basilar membrane is at rest and when it is active.
According to the most popular modern theory, the cochlear micro-
phonic response is the result of a resistance change in the hair cell
membrane that follows bending of the hair cells; this resistance change
alters the flow of current moving across the basilar membrane from
the electropositive Scala Media ( +30 mv) to the scala tympani, and
is recorded externally by an electrode on, say, the round window.
\ . • ' •
As yet, however, no direct measurements exist to validate what
is at the crux of this theory - the assertion that hair cells behave
as variable resistance elements. Recent developments in methodology
make such measurements feasible now, and we are in the midst of making
them. We are attempting to approximate accurately the actual.impedance
•of the cochlea fluids and partitions; such measurements are an essen-
tial first step for establishing how much current flows through the hair
cells at rest, before it is modulated by acoustic stimulation.
This attempt to determine the distributive electrical properties
of the cochlea is presently under way in the laboratory of Dr. Vincente
Honrubia at the University of California at Los Angeles. The collabora-
tive effort has already yielded some highly reproducible values1 for im-
pedance and capacitance at the basal turn in the resting guinea pig
cochlea, and should shortly be extended to analysis of the' dynamic state,
with various tones being impressed upon the ear to drive the basilar
membrane.(Steven Sitko).
3. Lambda Waves Evoked by Retinal Stimulation
Lambda waves appear in the human occipital F.F.G about 80 msec, after
the onset of eye movement across a structured visual field. Since their
discovery in the early 1950s, they have been discussed and studied as
possible useful central correlates of visual perception, eye movement
control, and similar events related to visual processing. Our studies
under this heading were initiated in order to clarify in cats the con-
ditions under which lambda waves appear.
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Unanesthetized and flaxedil-immobilized cats with chronically
x
implanted electrodes were used. Retinal stimulation comparable to
that produced by%eye movements was accomplished by moving vertical black
and white stripes past their immobilized eyes during 200 msec periods.
Potentials identical to.human and feline lambda waves were elicited
hot only at the cortex, but at lateral geniculate and optic tract as
well. This means that lambda waves originate at the retinal level, not
at the cortex, as has hitherto been thought. Cellular mechanisms re-
sponsible for these phenomena can be hypothesized, and the lambda waves
can be differentiated from other eye-movement related potentials such
as the PGO wave, calcarine cortex potential, corollary discharge and
efference copy.
The following report on this work has been submitted to the editor
of Electrophysiol. clin. Neurophysiol. for consideration for publication:
F:bersole, J. and R. Galambos. Lambda waves
evoked by retinal stimulation in the absence
of eye movements.
4. Human Electrophysiological Studies
A. Studies completed.
. A list of 8 papers published during the past two years in
this area is appended.
B. Manuscripts covering the following experiments are currently
in press:
- 4 -
Picton, T. W. and S. A. Ilillyard, Cephalic skin
potentials in electroencepholography. Electrq-
enceph. din. Neurophysiol.
This study undertook to map the skin potentials record-
able from the scalp and to differentiate them from po-
tentials originating in the underlying brain. Large skin
potentials timelocked to auditory stimuli were recorded
under conditions where they could seriously contaminate
EEC recordings made during perceptual tasks. Simple
methods are described for completely eliminating these
unwanted skin potential artifacts which several experi-
menters seem to have been confusing with responses from
the brain.
'Picton, Terence W., Steven A. Hillyard £ Robert
Galambos. Cortical evoked responses to omit-
ted stimuli. Major Problems of Brain Electro-
physiology. Ed. M. N. Livanov. USSR Academy
of Sciences, 1972.
The click evoked response in man shows a large positive
wave (the P3) at 300-400 msec, which appears during de-
cision-making, attentiveness, and similar states where
the signal has special significance for the listener.
In this study the listener is required to report correct-
ly on how many clicks are absent in a long train of them
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being presented at I/sec; a positive wave is also
shown to be time-locked to the moment a click is
expected but does not occur. This electrical event ': .
shares so many latency, amplitude, scalp-distribu-
tion and wave-shape features with the P3 as to make
it probable that the two waves represent the same
underlying cortical processes. If this is so, the
omitted-stimulus paradigm should prove of great use
in perceptual studies, since the "decision-complex",
as we have come to call these waves, is entirely un-
contaiTiinated by any stimulus-evoked electrical acti-
vity.
This paper also advances and develops the idea that the
P3 waves represent, or reflect, the comparison of 2
separate neuronal "models" of a stimulus that is being
detected, evaluated or attended. One model consists of
the actual processing achieved in the classical audi-
tory pathway and its nuclei; the other model, represent-
ing the expectations of the listener, and therefore
related to memory and attention, is taken to be the out-
put of the reticular formation, medial thalamus and as-
sociation cortex, at least. The primary auditory cortex
appears to analyze and display incoming d^ta, whereas the
secondary system seems to anticipate and recognize the
specific acoustic signals which are being attended. This
- 6 -
view, which is not unlike that of Sokolov, E. Roy
John and others, has the human brain make a comparison
between the sensory input processed by the primary audi-
tory system and the possibilities proposed by the second-
ary auditory system. "Between the reality and the pro-
phecy rests the judgement of perception," to quote the
final sentence of the paper in press.
^• Psychophysical Studies on Loudness Enhancement in Man .
The following abstract of a paper presented at the October
1971 meeting of the Acoustical Society of America summarizes some new
experiment to which we have given increasing -attention over the past
6 months.
Galambos, R., J. Bauer, T. Picton, K. Squires and
N. Squires. Loudness enhancement following con-
tralateral stimulation. • • • • • •
The apparent loudness of a tone pip can be increased
by 15 dB or more if it is preceded by a tone burst to
the contralateral ear. The experiment is don,e by de-
laying the pip, Sj, by a variable time,AT, after the
offset of a contralateral tone; the listener assesses
the loudness of S, by adjusting the intensity of a
second tone pip, 82- that follows S, by 1500 msec.
Some parametric explorations of the phenomenon are re-
ported here.
A paper covering this material has been accepted for publication
by J. Acoust. Soc. Amer.
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In subsequent studies by Robert Elmasian the parametric explora-
tion of this interesting phenomenon was continued, and it has been, es-
tablished that the monaural and binaural conditions yield at least as
large a loudness enhancement as does the dichotic case first explored.
Our purpose in undertaking these experiments was to look into
the possibility that the human olivp-cochlear bundle, or. efferent auditory
tract, might be activated by a sound, and thus alter the perceptability
of a second sound following closely thereafter. While the hypothesis
seeros to have been confirmed, we have not yet been able to establish
by electrophysiological recordings at the ear canal that the auditory
nerve response to the enhanced signal covari.es with it in amplitude,
as it should do if the cochlear efferents are involved.
These experiments are to be continued under a grant from NIH
%
(NS 10482-01).
- 8 -
Publications
Hillyard, S.A. and R. Galambos. Eye movement artifact in the CNV.
Electroenceph. clin. NeuYophysiol. 28: 173-182, 1970.
Galambos, R. and S.A. Hillyard. Determinants of neural and behavioral
plasticity: an overview. In: P.O. Schmitt (Ed.)> Tne'Neurosciences:
Second Study Program, The Rockefeller University Press, New York
289-297, 1970. . .
R. Galambos, 1970. Determinants of neural and behavioral plasticity.
In: P.O. Schmitt (Ed.), The Neurosciences: Second Study Program,
The Rockefeller University Press, New York, 161-163.
Hillyard, S.A,., K.C. Squires, J.W. Bauer and P.H. Lindsay. Evoked
potential correlates of auditory.signal detection. Science, 172:
1357-1560, 1971.
Gazzaniga, M.S. and S.A. Hillyard. Language and speech capacity of
the right hemisphere. Neuropsychologia 9: 273-280, 1971.
Hillyard, S.A. The psychological specificity of the contingent nega-
tive variation and late evoked potential (P300). Electroenceph.
cjj.n. Neurophysiol. 31: 302-303, 1971.
Picton, T.W., S.A. Hillyard, R. Galambos, M. Schiff. Human auditory
attention: a central or peripheral process? Science, 173: 351-353,
1971.
Nottebohm, F., M. Konishi, S. Hillyard, and P. Marler. Auditory
templates and the ontogeny of birdsong. In: F. Worden and
R. Galambos (Eds.)- Auditory processing of biologically significant
Sounds. Neurosciences Res. Prog. Bull. 10: 34-59, 1972.


Electrophysiological studies of the nervous system

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