THE COMMUNICATION AND INFORMATION THEORY ASPECTS OF THE NERVOUS SYSTEM BY EUGENE AGALIDES RE STIMULI TRANSMISSION

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• Document Creation Date: January 21, 2025
• Document Release Date: January 15, 1983
• Publication Date: November 18, 1964

THE COMMUNICATION AND INFORMATION THEORY ASPECTS
OF THE NERVOUS SYSTEM
By
Eugene Agalides
Head of the
Biophysical Communications Laboratory
Paper presented at the
17th Annual Conference in Engineering in Medicine and Biology,
November 18, 1964, Cleveland, Ohio
Approved for Release
Data
General Dynamics! Electronics
Biophysical Communications Laboratory
Research Department
Rochester, New York
THE COMMUNICATION AND INFORMATION THEORY ASPECTS
OF THE NERVOUS SYSTEM*
by
Eugene Agalides
Paper presented at the 17th Annual Conference in Engineering
in Medicine and Biology, November 18, 1964, Cleveland, Ohio.
The quest for a quantitative expression of natural phenomena has
lead, in communication theory, to the definition of a quantity of infor-
mation. The fact that information theory is today applied to several
fields other than electrical communications underlines its importance.
Information theory fulfills the needs of these various fields for quanti-
tative organization because they present characteristics very similar
to those of telecommunication. In the case of the nervous system,
for instance, communication is present in the form of impulses
(stimuli) conveyed to the central nervous system (CNS) for integration,
detection, and computation, or from the CNS to the effectors (muscles,
internal glands, etc.).
Having established the link between information theory and the
biophysical sciences, we are led to regard the central nervous system
as a gigantic information processing device.
There are two ways to consider the phenomenon of nervous communi-
cation. First, it may be thought of as a problem in communication itself
*This research is sponsored jointly by the Air Force Office of Scientific
Research, Information System Directorate under Contract AF 49(638)-1185;
by the Office of Naval Research, Biology Branch under Contract Nonr 3993(00);
and by General Dynamics/Electronics, Research Department.
2
in which noise is to be eliminated from the message content through the
application of coding and redundancy. Second, nervous communication
may be thought of as a problem in data processing where the messages
must be stripped of their redundant parts in order to be accommodated
in the CNS. These two problems are not contradictory. The first one
concerns the retrieval of information from noise; i.e. , the coding of
information to be transmitted, with a consequent increase in reliability.
The second problem concerns the processing of data or the coding of
the source information so that redundancy is eliminated. As an analogy,
the transmission of English language over a noisy channel can be
considered. Before messages are transmitted on the line, all re-
dundancies pertaining to the language have to be removed; when
this is done, the messages could be coded to combat noise.
The duality of this problem might raise the question: Why does an
organism need an elaborate coding scheme if only the pertinent infor-
mation is used by its CNS? The answer could lie in the possibility
that the data processing is not done only at the CNS but also in the
ganglions present along the transmission path. Thus, there would be
a great need for efficient coding close to the periphery of the sensorial
mechanism. As the information travels up to the CNS, this need might
diminish as far as the processing is concerned. But, processing is
still needed as far as the noise is concerned since it is reasonable to
3
assume that the noise increases as the information approaches the
CNS. (Noise, as used here, means all unwanted information con-
verging on the CNS at the same time as the wanted information.)
To illustrate this attributed quality of the ganglion, it is only
necessary to recall that a constant stimulus, after a certain period of
time, does not elicit a response in the neuron. We may postulate that
this saving in transmission is accomplished by an accommodation
phenomenon in the nervous system.
In order to understand the processes involved in neuron firing,
various mathematical models have been evolved such as those by
Goldstein,' Rosenblith,2 and Agalides.3 Goldstein and Rosenblith
have represented neuron activity as a resultant of the summation of
responses from a whole population of nervous fibers exhibiting the
same characteristics. This approach leads to a microscopic view of
neural mechanism.4 Thus, a modified shot noise effect is brought in
the picture.
To organize the amount of data available and to extricate from
the apparently random nature of the data the statistical parameters
necessary for the understanding of the processes at hand, constitute
another scientific challenge. We might mention along these lines the
contribution already given by spectral analysis to the interpretation of
data, as expounded by Wiener5 and Brazier,6 where autocorrelation
4
techniques have helped to detect low frequency phenomena in Electro-
Encephalography and to assign different locking frequencies for the
various rhythmic activities of the brain (a -rhythm = 10 cps, f3 -rhythm
= 20-25 cps, y -rhythm = 40-60 cps, (5-rhythm = 1,-2 cps, e-rhythm =
4-7 cps, k (kappa) -rhythm 10 cps).
Throughout the experimental work on the nervous system, both
macroscopic and microscopic considerations tend to influence the
development of theoretical explanations in nervous transmission in
separate, although well-defined, directions. In both cases, we are
led to consider the problem of coding and redundancy. These concepts
arise when we study the ability of a receiver to detect accurately the
nature of the message being sent in the presence of interferring noise.
In applying information theory to the nervous system, this problem
becomes complicated by two factors not usually encountered in usual
telecommunication practice. One, already mentioned above, reflects
the difference between macroscopic and microscopic phenomena.
The other, which is perhaps more complex involves the presence of
both spatial and temporal effects in coding.
It may be said that the presence of both macroscopic and micro-
scopic points of view should not necessarily lead to a conflict. This
is true in thermodynamics where the former leads to analysis on the
basis of ensemble averages, whereas the latter illustrates the dynamics
5
of individual particles. The study of the nervous system is virtually
carried out on this dual basis. However, if we want to analyze com-
munication in the nervous system from the point of view of coding, a
conceptual difficulty arises because coding and redundancy do not by
necessity belong to either a macroscopic or a microscopic mode.
Dr. Brazier,6 in affect, has suggested that the existence of a multi-
coding scheme in the nervous system might explain the conveyance of
both temporal and spatial information.
The existence of multicoding in the transmission of stimuli to the
central nervous system and the macroscopic and microscopic aspects
of stimuli transmission are studied. The approaches to the study of
these aspects of stimuli transmission are:
1. Microscopic Approach. The transmission of equal stimuli
along different individual fibers of the same nervous bundle
are studied, and'a signal is observed as it travels along the
path of the nervous bundle and as it is interpreted by the
central nervous system or an integrating organ.
2. Macroscopic Approach. The transmission of equal stimuli
along different nervous bundles is studied again with
observation of a signal as it travels along an integrating
path, and an analysis is made of the signal as it is interpreted
by the central nervous system or an integrating organ.
6
Two types of coding are investigated. In the microscopic approach
we attempt to verify that the signal traveling along similar fibers is
not necessarily transmitted by similar coding or modulating schemes,
but that a multitype of coding is used to provide better noise recording
properties. In the macroscopic approach we are concerned with the
integration of possible different codes along a complex nervous path,
again with a possible gain in information capacity through improved
noise contributing properties.
The two approaches have been defined above in broad terms.
Note that we have not mentioned the problem of distinguishing between
temporal and spatial types of coding. This is because we are only
concerned here with the problem of "how" the stimuli are being coded,
not with "what" is being coded. This latter problem could only be
studied after some definite forms of coding have been established.
To find these coding forms we neglect, as a first approximation,
another aspect of nervous communication; i. e., the orientation of
neural structures.
It is evident that the outlined approaches are of a general
� nature. As we consider the vast array of neural structures, we find
differences in functions.
In the nervous system we are faced with two problems derived
from the specific needs of information transmission. One is to find how
7
to obtain maximum efficiency. The other is how to obtain minimum
equivocation. The first problem calls for making maximum use of
the capacity of the transmission channels. The second is to find the
way to -minimize the noise effect, environment, and threshold vari-
ation in order to overcome equivocation or misunderstanding.
In the first case, a multiple coding system would be beneficial.
Here the term "multiple" means not only the coding in itself but also
the system as such. For example, the use of pulse position modulation,
pulse duration modulation, and pulse amplitude modulation could be
one way to solve the problem of transmitting three different messages
over one and the same channel. The effect of noise and the resulting
equivocation could be determined by using three or more types of
coding systems for one and the same message. Each coded message
could then be transmitted over separate channels or over a single
channel, depending on the reliability required. See Fig. 1.
A particular noise at a time "t" will not affect all three different
modulation systems in the same way and to the same degree. Three
types of modulation and two types of noise are shown in Fig. 2. Any
one of the noise types will not affect in the same way a pulse duration
modulation system, a pulse position modulation system, and a pulse
amplitude modulation system.
Figure 3 shows a modulation system with three degrees of freedom.
For a modulation system with three degrees of freedom, the
modulated wave can be represented by:
8
Filtering
Detection
and
Coincidence and
Channel x
Decision
Element
Transmission
Di
.1�101�IMINIP
Point
Noise
Information
V
Channel z
Dz
Information
IN
OUT
Channel k
System I
Transmission
Point
Information
IN
Combined Channel
x +z +k
System II
Filtering
and
Detection
Coincidence and
Decision Element
Information
110
OUT
Fig. 1. Multichannel multicoding and unichannel-multicoding
transmission and reception systems.
(,Dm).1111111111111-1.1-10 111111
[I 1 11 A 11
(PPM) z
(PAM) k
Noise
(Type A)
Noise
(Type B)
r, 11 11 it n II 1111 11), n
KzVz
K V 14 �I K V
IF 1 r I z
Fig. 2. PDM, PPM, PAM, and two Fig. 3. Pulse modulation with
types of noise transmitted three degrees of freedom
simultaneously. (applying PDM, PPM, and
PAM at the same time).
9
t
M(t) t K3 V (Tn) 2An
= + 3
4. 2AnK3V3 (Tn) co 2
+ � [1 + K3V3 (Tr)]
m=1 M
to
sin mw � + An] cos (mwct - mweBn),
c 2
where
An -
KJ:VI (Tn) - K2V2 (re)
(T
Bn -
2
K2V2 (Tn)
2
An + Bn = K (Tn)
Bn - An = K2V2 (Tn)
a(n) =
d
[1 + K3V3 (Tn)] dt
I + K3V3 (T)
to +2A
2 [1 + K3 V3 (Tn)]
am(11) -
bm(n) -
M Tr
t
sin mo, [� + Al cos mac Bn
c 2 ri
2 [1 + K3V3 (Tn)]
Mr.
sinwc Bn sin rn4, [-Q- + An]
c 2 �
10
The unmodulated pulses are ideal rectangular pulses with time dur-
ation to, amplitude unity, and repetition period T. The leading edge
is modulated with modulation factor K1 and the trailing edge with a
modulation factor K2. V.1 (t) and V2 (t) are independent modulating
waves; n = 0, � 1, � 2; and Tni and ;2 denote the respective times
in the nth period that Vi(t) and V2(t) are sampled. We may assume
that Tni = Tn .-: T. With uniform sampling, Tn , Tnz , � � Tnn
2 1
can be replaced by T. The terms am(n) and bm(n) are constants
over any one period T1 but may vary from period to period. Also
we = 2 Tr/T. Finally, K3is a modulation factor applied to the amplitude
of the pulse.
A modulation form prevalent in living organisms is Pulse Repetition
Rate Modulation (PRRM). This type of modulation is a digital equivalent
of the frequency modulation of an analog signal. A form of pulse
repetition rate modulation is found in the spinal cord. In the skin
receptors, transmission of stimuli seems to occur in the form of a
pulse position modulation system. Graded signals in the nervous
system seem to belong to an amplitude modulation system.
We can now state that in complex living organism like vertebrates
there are many modulation systems used for transmitting information.
In addition there are different types of coding. The name of multi-
dimensional coding could be applied to the form in which different
coded signals are transmitted over one and the same channel at the same
time.
11
Brazier mentioned the multitude of codes existing in the nervous sys-
tem at the 1960 Moscow Conference on Higher Nervous Activity. It can be
shown that the multiple coding system represents an economy in the trans-
mission channels in the case of different timuli. On the other hand, .if the
same stimulus is transmitted by a multi-channel multi-coding system, there
is a definite advantage as compared with the transmission of the stimulus
by a single coding system. This is true regardless of how good a single
coding system can be because it can be one of the multiple coding systems.
To ascertain the existence of different types of codes, we investigated
the response of different stimuli on the skin sensory receptors. The first
receptor to be studied was the Pacinian Corpuscle (Fig. 4). Agalides com-
pared the elicited responses to mechanical and acoustic stimuli.7 The
Fig. 4. Photomicrograph of a Pacinian Corpuscle, 40X.
(Nikon Interference Phase Microscope, Nikon
Microflex Camera, Tri-Pan-X Kodak Film;
exposure time, 0.5 sec.)
12
difference between the form,amplitude and latency involved for each response
was shown (Figs. 5, 6, 7). The power and frequency curves of the trans-
ducers were plotted. There is a definite difference between the response
of the same receptor to mechanical and to acoustical stimuli. This was an
investigation in vitro. If the coding in the nervous system in vivo should be
studied, then either gross recording electrodes or microelectrodes can be used.
Fig. 5. Impulses from a Pacinian Corpuscle; stimulus, mechanical
pressure; vertical scale, 20 iv/division (large scale); horizontal
scale, 10 ms/division (large scale).
Figs. 6 and
Stimulus
Stimulus
7. Effect of acoustical wave pressure on Pacinian Corpuscle.
B and K heterodyne oscillator and amplifier; 70 cps,
keyed; 100 v rms on the piezo-electric acoustic transducer,
one electrode grounded. Recorded between the Pacinian
Corpuscle and first node of Ranvier and the axon of the
sensory receptor at a distance of 7 mm from the corpuscle.
Vertical scale, 10 p.v/division (large scale); horizontal
scale, 1 ms /division (large scale).
13
The damage done to the surrounding cells by inserting electrodes into
the nervous system cannot be overlooked. Another approach for
studying in vivo coding processes in living organisms is via an in-
vestigation of the electrical activity of electric fishes.
Figure 8 shows some representatives of gymnotid fishes from
tropical and equatorial South America and mormyrid fishes from
tropical and equatorial Africa. Some of the fishes having electric
organs use them for offensive and defensive purposes. These are
strong electric fishes whose discharge can paralize prey or at least
scare away enemies. Torpedo Nobiliana, a marine electric fish,
can discharge electric pulses of some 220 volts. The short-circuit
current of an adult Torpedo can reach 50 amperes. The output
capabilities of Electrophorus Electricus, the Electric Eel, (Fig. 9),
a fresh-water electric fish, were studied. Voltage discharges of
over 600 volts were measured. The maximum current at 10 ohms
load resistance was close to one ampere. The pulse peak power was
around 100 watts.
There are other electric fishes, called weak electric fishes,
which use electric coded impulses for navigation and communication
purposes. Pulse shape and pulse duration are very different de-
pending on species.
The electric eel has three electric organs, each of which per-
forms different functions. One is called the main electric organ and
14
MormyrIdae
Mormyrus
kannume
Gnathonemus
curvirostris
Mormyrops bouiengeri
Gymnarchus
niloticus
Gymnoticlan
.10,,\NA0 \\\,\Nx
Sternarchus
hasemani
Porotergus
imams
Sternarchorhynchus
oxyrhynchus
4tser
Gymnorhamphichthys
hypostomus
4C261166651.."---
� sW, \\\A\VZ\S\ \\\\\NO 4., �
Eigenmannia
macros
Figure 8. Representative types of the Mormyridae and Gymnotidae.
The convergent evolution between these unrelated families
is expressed in terms of their electric discharges, reduction
of the tail fin, propulsion through an elongated unpaired fin,
development of long snouts, and several other features.
15
Fig. 9. Electrophorus Electricus (electric eel).
produces high voltage pulses used for stunning purposes. Another electric
organ, called the organ of Hunter, is used for communication and navi-
gation purposes. A third electric organ, called the organ of Sachs, is
thought to have an auxiliary function and its electric discharge is much
weaker than that of the main electric organ.
By studying the form and shape of the coded impulses, we can dis-
tinguish a large variety of coding systems (Figs. 10, 11). Gymnarchus
Niloticus, an electric fish from equatorial and tropical Africa, studied
in detail by Lissman and Machina, is one of the most sensitive electric
fishes. It can sense any disturbance of the surrounding water produced
by objects. It can distinguish between electric conductors and micro-
conductors. Charges of the electric field of 0.03 iv/cm produced by
direct currents can be detected by Gymnarchus Niloticus. Its receptor
system operates in the second derivative mode. The change in current
in the electroreceptors was calculated to about 0.003 pia for 1 ms pulses
at a frequency of 300 cps.
16
I.� 5 -41
IT1S
800
ms
Torpedo and Astroscopus Raia
�A_ 1
0
14-2 resp.
ms
[4--- 3
ms
0
Electrophorus Eigenmannia and Sternopygus
0
0
14� 3 P1
M S /T1S
Gymnotus (other than Electrophorus) Gnathonemus
1
0
0
14� 2
Ins
NIormyrus Malapterurus
Fig, 10. Pulse shape arid pulse duration of the discharges of some species
of electric and magnetic sensitive fish. (After H. Grundfest, 1952)
17
%mmtmi
�4 100 m s
II I I II I
(7.171-711
Fig. 11. Cross communication between two electric eels in two separate
aquaria; optical galvanometer recorder, dc to 10 kc frequency
range, speed 76 mm per second.
Gnathonemus Petersii (Figs. 12, 13), an African electric Mormyrid,
utilizes a pulse position plus pulse amplitude modulation. The slope of the
pulse is less than 50 �sec, and the entire pulse duration is 250 �sec.
Sternarchus Albifrons (Figs. 14, 15, 16), a South American Ster-
narchid, utilizes a permuted phase plus 'an amplitude modulation coding
system.
Electrophorus Electricus utilizes a very complicated coding method
in conjunction with a modulation system with three degrees of freedom.
It was verified that the fish can decode the electric signals emitted by
other fish of the same species. The experiment proving this fact was
reported at the 1964 Rochester Conference on Data Acquisition and Processing
in Biology and Medicine. 9
18
� By studying the types of coding used by fishes for perhaps twenty or
thirty million years, we can once more observe that evolution has solved
biochemical, electrical, and mechanical problems of energy transformation
by always finding the way to utilize minimum energy combined with excel-
lent efficiency. In the case reported on here, evolution found the way to
extract signals from noise with little power utilization. The study of the
natural phenomena and of living organisms still can provide the scientist
with new clues and means to further the general progress of science.
Acknowledgement
I wish to express my appreciation for the support offered by the Air
Force Office of Scientific Research, Information System Directorate; the
Office of Naval Research, Biology Branch; and General Dynamics/Electronics.
In particular I wish to thank Dr. H. C. Nedderman, Director of Research
for GD/E, for his managerial assistance. Mr. Bernardini was responsible
for the excellent microsurgery required to dissect the Pacinian Corpuscle,
the electric organs of electric fishes, and their brains. Mr. R. Zinsmeister
set up the electric equipment and skillfully recorded the electrical activity
of electric fishes and that of the skin sensory receptors. Finally I would
like to thank Mr. R. Doughty for his help in editing this article.
19
Fig. 12. Gnathonemus Petersii
(African electric fish).
Fig. 13. Electrical signals emitted by Gnathonemus Petersii.
T-n-cr Irli,+� 7,0
20
Fig. 14. Sternarchus Albifrons
(South American electric fish).
Fig. 15. Electrical signals emitted by Sternarchus Albifrons.
Scales: vertical, 2 mv/div; horizontal, 1 ms/div.
111111 11 I'll
" " " \kk \\LIII
�
Recording made with two stainless steel electrodes, 7 inches long, placed in the water tank.
Recorder: Midwestern Optical Recorder.
Amplifiers: (1) Tektronix and (2) specially constructed units.
Date of recording: 2 February 1963 Time: 2:00 PM Recorder speed: 60 ips
Voltage at electrode: 1 my (equals 1.6-inch deflection on recording paper).
Voltage at output of second amplifier: 1.1 v (equals 1-inch deflection on recording paper).
Fig. 16. Recording of the electrical activity of Sternarchus Albifrons.
22
BIBLIOGRAPHY
1. Goldstein, M. H. , Jr., "A Statistical Model for Interpreting
Neuroelectric Responses," Information and Control, 3,
pp. 1-17 (1960).
2. Rosenblith, W. A., editor,. "Sensory Communication," MIT
Press and John Wiley and Sons, Inc., p. 196 (1961).
3. Agalides, E., "The Mathematical Model of the Neuron,"
Rochester Conference on Data Acquisition and Data Processing
in Medicine and Biology, Pergamon Press 1962.
4. Adolph, A. R., "Sensory Neurology and Analog" Technical
Document LMSD 49752, Lockheed Aircraft Corp. (June 1959).
5. Wiener, N., "Cybernetics," or "Control and Communication
in the Animal and the Machine, MIT Press and John Wiley
and Sons, Inc., Chapt. 10 (1961).
6. Brazier, M. A. B., "Long-persisting Electrical Traces in the
Brain of Man and Their Possible Relationship to Higher
Nervous Activity," Moscow Symposium on Higher Nervous
Sensitivity, 1960.
7. Agalides, E., "The Effect of Acoustical Waves on the Pacinian
Corpuscle," Transaction of the New York Academy of Sciences,
Vol. , No. , April 1964.
8. Lissman, H. W. and K. E. Machin, "The Mechanism of Object
Location in Gymnarchus Niloticus and similar Fishes,"
J. Exper. Biology, 35, 451 (1958).
23
3. Agalides, E., J. Bernardini, and R. Zinsmeister, "Infor-
mation Processing by Electric Fishes," Proceedings of the
1964 Rochester Conference on Data Acquisition and Procesing
in Medicine and Biology, ed., by K. Enslein, in press:
Pergamon Press, London and New York.