by Guedry, Cramer, and Koella (28) led them
to conclude that the secondary subjective re-
action {ie., a sensed tuming, without adequate
stimulation, in a direction opposite ‘to an initial
rotatory sensation appropriate to a given stimi-
lus) is best described as a process which de-
velogs to counteract the primary subjotive
reaction.

4) Central and peripheral factors, Recently,
Fluur and Mendel (8, 9} obtained secondary
and spontaneous nystagmus’ from normal
humans subjected to repeated unilateral caloric
stimulation. They regard both kinds of re-
sponse as a part of the habituation process and
emphasize a relation to efferent activity. Re-
peated caloric stimulation of a given ear is
regarded as either inhibiting or enhancin,, et-
ferent activity (depending upon stimulus tem-
perature), and results in a disturbance of the
dynamic state of balance between the two
labyrinths (8, 9). “Habituation could thus de-

- velop in any one of three ways: via the cere-

bellum from the contralateral labyrinth, via the
recticular formation or, possibly, via direct
communications between the two vestibular
nuclei by secondary fibers” (9).

Data currently available appear too incom-
plete to allow a clear choice of the explana-
tions for nystagmus reversals. It is possible that
several causes may be operative, depending
upon the stimulus situation, with only the end
result (inversion of nystagmus )i‘common to all
conditions. The explanations presented point
to a number of approaches for determining the
cause and meaning of nystagmus reversals, and
the cat appears to be an adequate subject for
the exartination of these problems,

’ /

* A clarification of sume terms is prybably in order.
Haufy and Wendt (2) define 4 sponkineous nystagmus
ax “a sustained nystagmus with ‘the slow phase in a pare
ticular direction and of a very Jow level of intensity or
amplitude. ft cannot be attributed to physical stim
tion.” Most authors. would agree on such a definit
A. secund type of sustained nystagnus which persists
the absence of a physical stimulas is “nystagmus altern:
Tere, Miivever, the direction af the “nystagmus ch;
pesiodically. If a similar response should occur as a result
bf vestibular stimulation (eg. reversals af nystagmus: ev
weeding a tertiary gesponse), it is smggested that
reaction be differentiated by the term “induced alte
any stugmus.”

REFERENCFS

A. Collins, W. Fo and RL HL Poe. J. Pharmarol. Exper.
Therap C38 120, 1962

2 Meuty, G0 aid GR. Wendt, SAM Repert 60-29.
Bronks AFE ‘Texas, 1960,

3. Cramepten, ©, and W. J. Schwam, Amer. J. Physive
209.29, 138

J. Sehwam. Be comp. phys

5. Aschan, G. and M. Bergstedt. Acta Soc. Med. Upul.
60:123, 1955.

6. Jonghees, 1. 8. W > Arch. Otoluryngol. 48:645, 184%.
7. Fluur, E. and L. Mendel, Acta Otolaryngol. 55 35.

1562.

#8. Fluur, E. and L. Mendel. Acta Otolaryngol. 55.136,
1962.

9. Riskaer, N. and &. Pernin. Acta Otolaryngol. 44 €1
1934.

10. Kobrak, F. Beitr. Anat. dex Ohr.  10:214, 1918.

LL. Grahe, K. Beitr. 2. Anat., Physiol, Path. u. Therap.
d. Ohres, 17-251, 1921.

12, ‘Thomval, A. Acta Otolaryngol. 17:163, 1892.

13, Fischer, M.-H. =. f. Hals-Nasen-u. Ohrenheitk. 29:216,
1931.

14. Kristensen, H. K. Acta Otolaryngol. 44:126,1954.
15. Collins, W. E. Nature, 195:803, 1962

16. Crampton, G. H., W. J. Schwam, and S, Warburton.
USAMRL Report No. 416, Ft. Knox, Ky., 1960.

17. Henrikson, N. G., C. Fernandez, and R. L. Kohut.
Acta Otolaryngol. 53:21, 1961.

18, Wendt, G. R. Vestibular functions, In S. S. Stevens
Ed.) Handbook of experimental psychology.

Wie, 1951.

19. Collins, W. E. CARI Report, Oklahoma City, Okla-
oma, 1963 {in press).

20. Collins, W. E. J. exp. Paychol, 63:191, 1962.

21. Collins, W. E., FE. Guedry, ard J.B. Posner. Ann.
Oto-, Rhino-, Laryngol. 71:187, 1962.

22, Seentagngluai, J. J. Neurophysiol, 19:395, 1950
23. ‘Thornval, A. Acta Otolaryngol. 10:575, 1927.

24, Guedry, F. E. and A. Graybiel. NAS-NRC Public.
‘0, 908, Washington D, C., 1961.

23. Hood, J... and C. B. Pfaltz, 2 Physiol, 12421580,

1954.

26 Guedky, Fe umd AL Gravbiel, 2. appl Physiol.
72308, L6.,

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CAT W-STMULUS: WATER 235 C TO RIGHT EAR FOR 30 SEC

Me. Provas 5. Recordings obtained from Cat Wo The bat 15 seconds of the 30-ce stimulus (applied in total darkness)
7 ate depicted. The secondary is brisk on all tridk. Note the clew inverted primary nystagmus ena Triad TH

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ments to the right; deflections, to the left. Each record begins with the onset of the stimulus Vertic
wee cts tiation of stimulstion In all cases, the response is in the appropriate direction (fast-pha:
eft). Note changes in lowphate slope with repeated teting brisk secondary nystagmus on Trial 17, and di
ferences in the time of appearance of the secondary on later trials.
mas
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CAT Pe STmULUS WATER 9. TO ROHT EAR FON IS MC

Ficeys 2 Nystagmus tracings from Cat P. Test procedure and figure markings are the same ay for Cat A.
appropriate response wax obtained during the first four trial, Note the early appearance of a vigorous seconds
in Trial 3, the clear inverted: primary response in thefast 4 depicted trial, and on Trial 20, the brisk secondary
the direction expected for the primary

~4d—


a

ing the secundary, under the term “homo-
lateral.” More recently (15), this term was
restricted, for <escriptive purposes, to an
anomalous initial nystagms (reversed fast and
slow phases} obtained under conditions of cold
caloric irrigation. “Inverted primary nystag-
mus” is probably an equally descriptive term
for this latter phenomenon, and one with more
general applications,

The observations presented here were ob-
tained from 5 cats selected from a larger group
which had been used in a series of pilot studies.
The stimulus situation and the number of trials
differed in each of the preliminary studies
and only these 5 animals demonstrated prom-
inent inverse responses.

METHops
Recording Apparatus

An Offner Type-T Electroencephalograph,
located in an adjoining room, was used to re-
cord horizontal eye movements. Leads from
needle electrodes inserted into the skin at the
outer canthus of each eye and on the crown at
the mid-line of the skull were plugged into a
patch-panel. Changes in potential were trans-
mitted through slip-rings to the recorder. A
1.4 sec RC time constant was employed in am-
plification.

Restraint

y
With one animal (Cat P), a casting tech-
nique was used (16). Briefly, a plaster cast
was fitted for the cat and was bisected length-
wise to provide 2 shells into which the aninial
could be placed; The method used with Cats
A, Z, W, and S'w.s similar to that reported by
Henrikson, Fernandez, and Kohut (17). Sev-
eral days prior to testing, cat were anesthetized +
and a tiny hole was drilled transversely through
each of their canine teeth. For testing, the cat
was wrapped snugly in a towel, placed jin a re-
straint box, and a strand of piano wire was in-
segted through the holes in the teeth, The wire
was tightened by means of a device attached to
the front of the box, fixing the animal's head in
2 position elevated slightly from that of normal
carriage,

Procedure

Data obtained from 5 animals are presented
here. Three of these, cats A, P, and Z had re-
ceived previous rotatory tests (12-15 rotations,
2.3 weeks earlier). For cats P, A, W. and S
stimulation was applied in total
Cat Z, the room was illuminated during inriga-
tion. For all animals, the room was in total
darkness for the several minutes of recording
immediately after cessation of stimulation and
rest periods were in full-room illumination. A
procedural outline appears in Table 1.

Resutts
Cat A

Cat A, tested in total darkness, received 50
trials and in no case exhibited inverted primary
nystagmus, However, she demonstrated an
occasional clear secondary reaction (see Fig. 1,
trials 17 and 19).

Cat P

Cat P received stimuli of the same temper-
ature and duration as Cat A and demonstrated
an appropriate response with a strong second-
ary during the first 4 trials. On the fifth trial,
a particularly vigorous secondary appeared. In
trials 10-15, 17, 19, and 20, inverted primary
responses were obtained. In addition, during
these two latter trials, a secondary (which was
in the appropriate direction for the primary)
began to evidence itself (see Fig. 2).

Four days later, Cat P was re-tested under
the same schedule and demonstrated the same
type of reversals. During the first 6 trials, a
appropriate and brisk response was eli .
Trials and 8 yielded an appropriate reection
with a vigorous secondary, Trials 9, 10, 11, 16,
and 18 showed an inverted primary response of
long duration and high magnitude. A series of
trials was then conducted with inter-trial rest
intervals reduced to 4 min. Inverse primary
reactions did not reappear.

Catz

Cat Z was the only animal tested in the left
ear and stimulated in full-room illumination.

~3~


*

TRIAL

10
5
RIGHT EAR
e
mle
‘ CAT Z- STIMULUS: WATER 5 C FOR 35 SEC
Fieve 4. Re-test of Cat Z one day later. ‘Test conditions and record are the same as in Figure 3.
Inverted primary nystagmus during each of the first 15 left-ear triaks Tight car was then stimulated

and’ an abpropriate’ response ‘as elicited. (last phase left).

Total darkness was achieved at the moment of
stimulus cessation, An appropriate response
was elicited during the first 10 trials, Inverted
primary nystagmus appeared’ in trials 11, 12,
92, 23, 24, and 30, Intervening trials yielded
an appropriate reaction, (See Fig. 3).

Cat Z was re-tested on the following day and
continued to give inverted primary nystagmus.
After 25 trials, she was stimulated with water
of the same temperature and for the same dura-
tion but in the opposite ear (seé Fig. 4). The
response was in the proper diréction, but also in
the same direction as the 15 previous tests for
the other ear (inverted primary nystagmus).

Cat W ,

Cyt W received a stimulus milder than that
administered to the aforementioned cats (23.5
C for 30 sec) and was tested in total darkness.
In all cases, the nystagmic response took sev-
eral seconds to build up after termination of
stimulation. In early trials, a response appro-

priate in direction was evidenced, and was fol-
lowed by a strong secondary reaction. In sev-
eral trials, this was in tum, followed by a third
(tertiary) response in the same direction as the
primary (see Trial 8, Fig. 5). In trial 13, the
build-up period for this animal yielded several
reverse beats (inverted primary nystagmus)
and, later, a vigorous secondary. The follow-
ing trial yielded an inverted primary nystag-
mus of hrief duration which gave way to brisk
secondary ‘find tertiary responses.

One mdnth later, with no intervening tests,
the same animal underwent 20 trials in total
darkness with a more potent stimulus (5 C for
15 sec). . No suggestion of an inverted primary
nystagmus ever appeared. However, a clear
secondary reaction was evidenced. (Fig. 6).

Cat S

Cat S was given 20 right-ear calorizations
using water of 23.5 C temperature for irrigation

~6—


OBSERVATIONS ON THE ELICITATION
OF SECONDARY AND
INVERTED PRIMARY NYSTAGMUS
FROM THE CAT BY
UNILATERAL CALORIC IRRIGATION

| AUG LO tgca si
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FEDERAL AVIATION AGENCY
AVIATION MEDICAL SERVICE
AEROMEDICAL RESEARCH DIVISION
CIVIL AEROMEDICAL RESEARCH INSTITUTE
OKLAHOMA CITY, OKLAHOMA

FEBRUARY 1963 ome


TRIAL

* platy fy —

———

2s ffladarvewripiitny>

800 pv |
sec

CAT S - STIMULUS: WATER 53.5 C TO LEFT EAR
FOR 30 SEC

Ficune 7. Nj us recordings obtained from Cat 5. In previous
(285 ©. for 20 tal a (535 C. for 1 tial) irrigations. Note the inverted primary beats in the upper record.

trials) and warm

periods of 30 sec. In the twenty-first trial, the
stimulus temperature was raised to 53.5 C. In
the following trial, the 53.5 C stimulus was ap-
plied to the opposite (left) ear, yielding an
inverted primary, a secondary, and a tertiary re-
sponse. An appropriate primary and a second-
ary appeared during the next trial under identi-
cal sticmulos condition (Fig. 7).
Discussion

The data presented here indicate that both
secondary and inverted primary nystagmus may
be elicited from cats by meany’ of unilateral
caloric stimulation applied undér a variety of
test conditions. The reaction has appeared after
irrigation in light and in darkness, with stimulus
temperatures of 23.5 and 53.5 C applied for 30
sec, and 5.0 C applied for 15, 30, arid 35 sec.
Howeger, not all cats demonstrate an inverse
Tes} .
In agreement with studies of rabbits (9),
the inverse caloric reaction most frequently
noted is the secondary. It is, however, a labile
response and differs in this regard from one

trials, the right ear was stimulated with cool

produced by rotation. Under usual rotatory con-
ditions with normal cats and humans, the sec-
ondary is a fairly common occurrence and is
most often, if not invariably, present during the
first trial (1, 2, 3, 4, 18). There appears to be a
tendency for the reaction to remain relatively
stable over several trials (2),.or to Jecline in
inl «with repeated testing (19) under con-
trolled conditions of alertness, a factor ex-
tremely important for the maintenance of nys-
tagmus in total darkness (20, 21). The caloric
secondary does not seem to be regulated as
systematicdlty.

« In summarizing their findings with rabbits,
Riskaer and Permin (9) noted that, (a) with
repeated irrigations, inverted nystagmus was
more likely. to occur, and (b) stimulus repeti-
tion did not yield a constant type of nystagmus,
ie. the inverse reaction did not always recur.
Data obtained in the present study are in agree-
ment with these two observations.

Several explanations for the occurrence of the
inverse responses, obtained here and in the
other cited reports, may be examined:

~9-


.¥

TRIAL 1

we
~~ ~~
a eee
y r ~~ sr f— S—
TRAL S
WWW
ni _~
‘ é — I~
s

) Tra

wel
CAT W- sTIMULUS: WATER 5 C TO RIGHT EAR FoR (5 SEC

Ficuns 6, ’ Re-test of Cat W one month later with a more potent stimulus, The eutire stimulus period (total darkness)
is presented, Sevoutlary reactions: are clearly evident but no inverted primary responses appeared.


*

+

Ficeas 3. Nystagmic responses obta

stimulis (applied “in illumination) are depicted.
total darkness, Appropriate responses were obtained during
vigorous inverted: primary responses on Trials 24 and 30,

THD

oe vioen cen aces “amen a ane enn eta
pe

Tria 13

oe RE ee

~— SM 1 5
‘TRIAL 14

“eee — a
TRIAL 21

RN ee

——_ ——

TMAL 24
nyse ru tle

‘ Teal, 23 s
Ret
ae 4

: . ' TRIAL 30

RON NW ay satan cnets nara: wena a om aren
NL NYA 7 v

worn Rn

*

WA ¢

aaron —— el
GAT Z- STMMAUS: WATER 3. TO LEFT EAR FoR 39 stC

Vertical bars indicate moment of stimuh

termi

the first 10 triak (fast-phace right),

~5-

from left-ear stimulation of Cat Z. The last 15 seconds of the 35-sec

vn and onset of

ote the particularly


OBSERVATIONS ON THE
ELICITATION OF SECONDARY AND INVERTED PRIMARY NYSTAGMUS
FROM THE CAT BY UNILATERAL CALORIC IRRIGATION’
William E. Collins, Ph.D.

ABSTRACT

Vestibular stimulation by repeated unilateral caloric isrigation of cats occasioned the
appearance of secondary, tertiary, and inverted primary nystagmus in some animals, These
inverse responses were recorded with stimulus temperatures of 5, 23.5, and 53.5 C, applied
for durations ranging from 15-35 seconds. The inverse reaction most frequently obtained

was the secondary nystagmus. Several possi
aa. e the finds

nomena were e:

explanations for the occurrence of the phe-

related to “habituation” of the vestibular sys-

findings
tem, and thus have implications for vestibular adaptation in clinical situations and during

air-vehicle maneuvers.

Secondary nystagmus occurs after, and is in
an opposed direction to, a primary response to
a vestibular stimulus. It appears in the ab-
sence of a change in vestibular stimulation,
when the primary has begun to decline. The
secondary is a commonly observed response to
rotatory stimuli both in humans (1,2) and
animals (3,4). Under conditions of caloric
irrigation, Aschan and Bergstedt (5) have
stated that a secondary appears in man only
when both ears are simultaneously stimulated
with warm water to one, agd cold to the other.
although unusually prolonged unilateral calori-
zations (20 min pr more) have sometimes pro-
duced a weak, sljort-duration secondary nystag-
mus (6), More recently, Fluur and Mendel

7:8) have reported the occurrence of a second-
ary“as a result 6f repeated unilateral stimulation
under ordinary clinical conditions. Little in-
formation is available, conceshing such findings
in animals (9).* ‘ .

* Data collected at U.S, Army Medical Research
Laboratory, Fort Knox, Kentucky. The technical assistance
of Stanton Warburton, IIL, and Kenneth yin is grate
fully acknowledged.

® Dr. Joseph Meck (U.S. N. School of Aviation Medi
cine, Pensacola, Florida) has observed a_secondary wystags
mus in squire monkeys as a result of ice-water caloric
stimulation (penonal communicating, In addition, revent
experiments i this Laboratory with a) Westem Ewe have
indicated that a secondary ‘reaction may be elicit by
beth cool (30 Cr and wana (45 C) ctimulation.

Kobrak (10) and Grahe (11) noted the ap-
pearance of an unusual response in normal
humans — a reversed initial nystagmus (i.e. a
primary response in which the direction of the
fast and slow phases was reversed )—which was
elicited with very minimal cold caloric stimula-
tion. Thornval (12) reported a single similar
occurrence under different stimulus conditions.
Fischer (13), using “pulsion reflexes” as a me.s-
ure and employing “double irrigations”, related
reversals of primary nystagmus in humans to
repeated stimulation. Such inverted primary
responses are almost never seen during rotation.”

In caloric studies of rabbits, Riskaer and
Permin (9) observed various combinations of
primary. reversed primary, and secondary nys-
tagmus, although a marked inverse reaction
could be demonstrated only with water of 15
C or ess. Kristensen (14), however, using 10
rabbits ‘and mild stimulation, reported that
“within various categories of head positions the
reactions are uniform from one animal to an-
other”, and “nystagmus was always reversed
when the nose of the animal was lowered by
15-20° in relation to the normal position.”

Riskaer and Permin (9) subsumed all forms
of inverse response to cold calorizations, includ-

"Dr. FOE Guedry (U.S. N. School of Aviation Medi-
wine, Penta, Florida) has observed this unusual reaction
iwi one haman subject after repeated exposure to prolonged,
constant, angular acceleration (personal communication),

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OBSERVATIONS ON THE ELICITATION OF SECONDARY AND
INVERTED PRIMARY NYSTAGMUS FROM THE CAT BY
UNILATERAL CALORIC IRRIGATION

WILLIAM E. COLLINS, Ph.D

Sensory Psychology Section
Psychology Branch
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FEDERAL AY TION AGENCY
AVIATION MbuiCAL SERVICE
AEROMEDICAL RESEARCH DIVISION
CIVIL AEROMEDICAL RESEARCH INSTITUTE
OKLAHOMA CITY, OKLAHOMA

FEBRUARY 1963


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1: Cooling effects. Some .xptinations of
3 caloric zesponses invol.e

£ cooling effects, either»
stincture or ihe ce ebellum
}. tn favor sf this view are the facts that the
respiaise has been elicited mast ccadily after
vepeated stimulation, with extreine teinpera-
‘ares, or with prolonged irrigation, The view
appears weakened, however, by the following
corsiderations: (a) ‘the inverse responses ap-
near unpredictable with respect to occurrence
on srecessive trials, time of onset of the reac-
dion, and vigor of the beats; (h) inverse re-
sponses have been obtained hy. pressure-induced
endolymph currents and appear ielated to a
changed state of contraction of the involved
occular muscle (22); (c) follow-up data from
one animal indicate retention of the inverted
primary nystagmus for the “practiced” ear a
day later {see Fig. 3); (d) another animal
(Cat W) gave inverted primary nystagmus
to the milder of two stimuli (23.5 C vs, 5 C).
It should be noted, however, that the duration
of stimulation was longer for the less extreme
temperature.

2) Peripheral events. Thornval (23) pro-
duced inverted nystagmus experimentally by
caloric stimulation of the exposed canals of pi-
geons. Depending upon the orientation of the
canal and the point at which the stimulus was
applied, responses in one direction or another,
or a lack of response could be Pbserved. Thorn-
val (12) felt that certain endolymph move-
ments (which he des¢ribed in the pigeon study)
caused the inverted primary response he ob-
served: in one normal Luman. In addition, he
stated that the response probably, occurred in
every caloric test, but was usually too weak to
be observed.* ' i

Thornval (12) also differentiated between
secondary (which he obtained with hot as well

* Within a series of repeated  irtigations, invertéd re
sponses were occasionally observed during the stimulus
period although an appropriate primary nystagmus was
evidenced upon stimulus termination. Attempts to inter-
rupt the stimulus at such times’ were unsuccessful in
eliciting the inverse response, but, rather, a directionally
nystagmus woukl appear, usually ofter brief

a» wold irtigations) and inverted primary nys-
tagiaus. The secondary, he felt, had a central
origin, the inverted primary response was pe-
ripherally caused. It would seem somewhat
questionable, however, to attribute to the pe-
ripheral events detailed by Thornval (23) the
inverted primary nystagmus observed in the
Present study. Initial, weak endolymph cur-
tents would appear to be an inadequate cause
for the production of some of the mare vigorous
inverse reactions obtained. Neither do such
currents seem sufficient to explain tke findings
of Fischer (13) nor the pressure-induced re-
sponses obtained by Szentagothai (22). The
posssibility of peripheral causation, however,
must be given careful evaluation.

3) Central factors. Several authors have ex-
pressed the view that secondary nystagmus
responses are due to central rather than periph-
eral events (2, 5, 12, 18). Hauty and Wendt
(2), for example, indicate that the secondary
phase of nystagmus “may be attributed to the
reciprocal after-effects of primary nystagmus
which cause the discharge of opposable central
components to become imbalanced.” Fischer
(13) has also ascribed a central process to the
production of inverted primary responses.

There is the possibility that the inverse reac-
tion is an active process which is built up mainly
to inhibit the primary response. It may rep-
resent one of the means by which the organ-
ism responds to repeated vestibular stimulation
(24, 25) and nystagmus becomes “habituated”.
However, the only clear direct evidence pres-
ently Available to support this hypothesis is
from recent studies of adaptation to Coriolis
accelerations (26). As a result of living in a
rotating room, human subjects developed an
inverse nfstigmus when tipping their heads in
@ static cqndition. That is, a compensatory
nystagmus, in a direction opposite to that which
the same: head-tilt would produce during rota-
tion, was present in a non-rotating environment
after many hours of rotatory experience. More-
over, a‘similar reaction was evident for the
aculogyral illusion (27).

Additional, though less direct, supportive evi-
dence may be adduced from studies of subjec-
tive rotatory responses, Human data obtained

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