Acta Otolaryngol80: 197-205, 1975
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
THE ORIENTATION OF THE SEMICIRCULAR CANALS IN THE GUINEA PIG
I. S. Curthoys,' E. J. Curthoys,2R. H. I. Blanks3 and C. H. Markham4 From the Department of Psychology, University of Sydney, Sydney, N . S . W., Australia'* and the Department of Neurology, Medical School, University of California, Los Angeles, Calif., USA3*
(Received December 14, 1974)
Abstract. In 10 adult guinea pigs the stereotaxic coordinates of a series of points along each osseous semicircular canal were analysed to yield an equation of that canal plane in stereotaxic space. Angular relationships among the canal planes and between the canal planes and the major stereotaxic planes are presented together with the optimal positions of the head for physiological stimulation of each canal or pair of synergistic canals. The planes of the semicircular canals in each labyrinth are not perpendicular to one another and the planes of contralateral synergistic canals depart from parallelism by about 30".
In order to specify the mechanical forces involved in semicircular canal stimulation it is necessary to have information about, among other things, the fine structure of the canal and the orientation of the canal relative to the plane of the stimulating acceleration. Optimal physiological stimulation occurs when the canal plane is parallel to the plane of rotation. As a canal is tilted from parallelism the magnitude of the angular acceleration stimulation decreases as a cosine function (Blanks, 1973; van Egmond et al., 1952) and other canals are increasingly stimulated. We have developed a technique which determines the This research was supported by grants from the National Health and Medical Research Council of Australia, Sydney University Research grants, and US Public Health Service grant NS 06658. Computing assistance was obtained from the Health Sciences Computing Facility, UCLA, sponsored by NIH Special Resources Grant RR-3.
orientation of the semicircular canal planes with reference to external skull landmarks (Blanks et al., 1972, 1975) enabling the head to be positioned to optimally stimulate any canal. This technique has yielded data for the cat and human: the present paper reports comparable information for the guinea pig. The guinea pig has been used extensively in anatomical and physiological studies of the vestibular system. Its semicircular canals are about the same size as those of the cat and much more easily accessible (Curthoys et al., 1971). Nevertheless there is surprisingly little data concerning the orientation of these canals in the skull. Kristensen (1954) reported that the planes of the horizontal canals are parallel with a plane passing through the external auditory meati and the supraorbital margins. Wersdl(l956) reported that the two horizontal canals are in the same plane and the vertical canals are perpendicular to this plane. He estimated the angle between the ipsilateral anterior and posterior canal planes to be 100"; Bodechtel(l930) has estimated this angle to be 115". Wersall also reported that the two posterior canals formed an angle of 110" with each other. These results lead to the deduction that both pairs of vertical synergistic canals (the left anterior-right posterior and right anteriorActa Otolaryngol80
198
I . S . Curthoys et al. +z
DORSAL
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
POS
-z
VENTRAL
Fig. 1. The stereotaxic planes of the guinea pig and the mathematical conventions used.
left posterior) are misaligned from parallelism means of the heights of the skull surface 6 mm and 14 mm anterior to the interaural axis by about 25". Because of the need for a more complete (Luparello, 1967). Instead of using one of and accurate specification of semicircular these systems we chose to use the Kopf guinea canal planes in the guinea pig, particularly for pig head holder with the incisor vertical adskull positioning during angular acceleration justment set at zero. In this way the horizonstimulation we applied a technique, described tal plane becomes the plane through the in detail elsewhere (Blanks et al., 1972) to de- centres of the two external auditory canals and termine these planes in the stereotaxic axes the inferior-most portion of the bone just posterior to the incisors (i.e. the rostra1 edge of the system. incisor bar). Measurements of a number of skull dimensions enabled simple translation of METHODS the semicircular canal planes to the systems Guinea pig stereotaxic planes outlined above. The sagittal plane is perIn stereotaxic systems the horizontal plane is pendicular to the horizontal plane passing the most difficult to define: for the cat, mon- through the midsagittal suture. The frontal key and human, something akin to the Reid plane is perpendicular to the two other planes plane is used (the plane joining the centres of passing through the centres of the external the external auditory canals and the inferior auditory meati. The Hixson, Niven and Cormargins of the orbits). Definitions of the reia mathematical conventions were used stereotaxic horizontal plane for rodents are far (1966): in this system the x axis is the nasoocless uniform (de Groot, 1959; Hurt et al., 1971; cipital axis (anterior positive), the y axis is the Konig & Klippel, 1963; Luparello, 1967; interaural axis (left ear positive), and the z axis Luparello et al., 1964; Pellegrino & Cushman, is the vertical axis (dorsal positive) (see Fig. 1 1967, 1971 ; Tindal, 1965). Tindal did define the for these conventions). horizontal plane for the guinea pig by the external auditory canals and the inferior margin Dissection and measurement of medial canthi. However, his animals were Eleven adult guinea pigs with weights ranging so unusually large (700-830 g) that he was able from 3 1 1 to 487 g (mean 381 g) were killed by to use a Kopf cat/monkey head-holder. The barbiturate overdose and the tissue removed other widely used stereotaxic system for the from their skulls. Dental cement was applied guinea pig defines the horizontal plane by to the skull sutures to prevent dislocation. Acta Otolatyngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
Guinea p i g semicircular canal planes
199
Fig. 2. An overview of a guinea pig skull from a right viewpoint posterior to the interaural axis to show the perspective of Fig. 3 and Fig. 4 A, B , C.
The skulls were dried and for each animal the osseous canal of every semicircular canal was opened along as much of its length as possible by drilling. An attempt was made to standardize this dissection, so that for all animals the lateral-most bone in each canal was removed (see Figs. 2 and 3). The bony external auditory meati and most of the bullae were left intact, permitting the skull to be mounted in a Kopf guinea pig stereotaxic head holder (Model 1216) in fairly normal fashion. Standard guinea pig ear-bars were used and the height of the incisor bar was set at 0. Thus the positioning of the skull in the stereotaxic apparatus was the same as that which would be used with a living guinea pig. A Kopf electrode carriage with micromanipulator controls (model 1260) was placed on the stereotaxic frame and its planes of excursion were aligned with the stereotaxic planes. About 50 mm of fine (80 p m diameter) stainless steel wire insulated except at the tip was affixed to the electrode holder and connected to a voltage follower, audio amplifier and loudspeaker. Touching the tip of this wire 14 -752953
to an osseous canal or reference point resulted in a loud “pop” which considerably assisted identifying the “touch point”. The reference point consisted of a short piece of 80 pm wire cemented to the top of a bolt. The cement was fiied so the tip of the wire was flush with the surface. This reference point was bolted to the stereotaxic frame and it remained untouched during all measurements. Each skull was placed in the stereotaxic device and its position was not changed during measurement. The x, y and z coordinates of a series of approximately equally spaced points along each canal were obtained by advancing the wire probe until it just touched the medial-most wall of the osseous canal and reading the scales to the nearest 0.05 mm. Points in the ampullary and common crus regions were avoided. An average of 28 points per canal were recorded (range 17 to 50). After measuring the canals in one labyrinth a check was made to ensure the probe had not been displaced and if this check was satisfactory the probe was repositioned to enable readings of the contralateral labyrinth. The coordinates of Acta Otolaryngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
200 I . S . Curthoys et al.
Fig. 3. An enlargement of portion of Fig. 2. This figure shows the osseous semicircular canals which are shown schematically in Fig. 4 A, B, C.
points along a semicircular canal were always referred to the reference point which was in turn referred to the stereotaxic zero (the point of intersection of the three planes defined above), thus relating all canal measurements to stereotaxic zero. RESULTS Statistical treatment For each skull the raw data consisted of the x, y and z coordinates of points along each canal. This data was punched onto cards and the coordinates translated into stereotaxic space AC~U Orolaryngul80
by subtraction. This data was plotted by line printer to ensure there were no punching errors, outlying data points or substantial gaps between data points along any canal. The latter occurred for the anterior canals of three animals because of breakage during dissection of the extremely thin part of the anterior canal near the common crus (see Fig. 2). These canals were excluded from all further analysis. One animal was excluded entirely because detailed analysis showed it had not been positioned properly in the sterotaxic device. A plane was fitted to the data for each canal by a least squares technique and by principal com-
Guinea pig semicircular canal planes Table I. Equations of the planes parallel to the semicircular canals passing through the stereotaxic zero The figure in brackets below each coefficient is the standard deviation Left horizontal
+.71&u (5.008) Left anterior - .57& l~.~ f.013) Left posterior - .771x (k.011) Right horizontal +.716x ( f.008) Right anterior +.57&( (5.013) Right posterior - .77 Ix (f.011)
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
I
-, 2 6 3 ~ (2.020) .793y (2.008) -.38Oy (k.014) + .263y (k.020) + .793y (f.008) + .38Oy (k.014)
+
-.637~ (k.011) -.167~ (k.018) -.SO32 (k.010) -.637~ (k.011) +.167z ( k.O 18) -.SO32 (f.O1O)
=O =O =O =O =O =O
ponent analysis. As in earlier studies both techniques gave virtually identical results but only the results of the principal component analysis are reported here. This technique yields the direction cosines of a plane passing through the origin parallel to the plane of best fit of the data points of a given canal (Thurstone, 1957). In other words the D term of the generalized equation of a plane in three dimen-
201
sions Ax+By+Cz+D=O has been set to zero (Bers, 1969). The equations of the plane parallel to each canal are presented in Table I. The coefficients in these equations are the mean direction cosines. Since magnitude differences between direction cosines from left and right labyrinths were small, they were combined to improve estimation. This average value was then given the correct sign for the appropriate labyrinth. For each animal the direction cosines of its canal planes served as input for another program which computed the angles among the canal planes and between each canal plane and the stereotaxic planes. Magnitude differences for angles from left and right labyrinths were small and hence these angles were combined wherever possible to improve estimation. These meanangles are presented in Table I1 together with the numbers upon which each mean is based, the standard deviations and two-tailed 95% confidence intervals (Guenther, 1965). Figs. 2 and 3 show the orientation of the canals in a guinea pig skull and provide the perspective for Fig. 4 A, B, and C
Table 11. Means, number of measurements (n), standard deviations and 95% confidence limits for angles, in degrees, among ipsilateral canal planes, between contralateral synergistic canal planes and between each canal plane and the stereotaxic planes. The locations of these last set of angles are shown in Fig. 4 (see Column 1) 95% confidence limits Location and identification
Fig. 4 A , O1 Fig. 4 A, O2 Fig. 4 A, 0, Fig. 4 B, el Fig. 4 B , O2 Fig. 4 B, 19, Fig. 4 C, 0, Fig. 4 C, O2 Fig. 4 C , O3
Angle between the plane of the Horizontal canal Anterior canal Horizontal canal Left horizontal canal Left anterior canal Left posterior canal Horizontal canal Horizontal canal Horizontal canal Anterior canal Anterior canal Anterior canal .Posterior canal Posterior canal Posterior canal
S.D.
Mean
n
Anterior canal Posterior canal Posterior canal
122.15 76.71 82.36
17 17 20
6.13 5.49 4.74
Right horizontal canal Right posterior canal Right anterior canal Stereotaxic frontal Stereotaxic horizontal Stereotaxic sagittal Stereotaxic frontal Stereotaxic horizontal Stereotaxic sagittal Stereotaxic frontal Stereotaxic horizontal Stereotaxic sagittal
30.82 32.17 36.16 44.17 50.31 105.34
10 8 9 20 20 20
54.71 99.78 37.36 39.34 59.77 67.60
17 17 17 20 20 20
Lower
Upper 125.30 79.53 84.58
10.05 4.42 4.86 2.98 3.80 5.43
118.99 73.89 80.14 23.63 28.47 30.81 42.78 48.53 102.80
38.01 35.87 41.51 45.57 52.09 107.88
3.82 4.36 3.24 4.39 2.84 3.99
52.75 97.54 35.69 37.29 58.44 65.74
56.67 102.02 39.03 41.40 61.10 69.47
Acta Otolaryngol80
I . S. Curthoys et al.
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
202
Fig. 4 A , B , C. The intersection of the semicircular canal planes on the right side of the head with the guinea pig stereotaxic planes. 8,, 8,, O3 identify the angles between the canal plane and each stereotaxic plane, the magnitudes of which are given in Table 11. Ar to Orolaryngol80
which locate and identify the angles between the semicircular canal planes and the stereotaxic planes. The planes of the semicircular canals in a labyrinth are not perpendicular to one another: none of the 95% confidence intervals for the angles between these planes includes 90". Our estimate of the angle between the anterior and posterior canal planes is 76.71",approximately the complement of the value estimated by Wersdl(l956) and Bodechtel(l930). The planes of the three pairs of contralateral synergistic canals are all about 30" divergent from parallelism. One implication of this result is that, as Wersiill noted, the vertical canals form unequal angles with the sagittal plane. Our measures confirm this: the anterior canal forms an angle of 37" and the posterior canal forms an angle of 67" with the sagittal plane. Each horizontal canal forms an angle of 50.3 1" (open anteriorly) with the horizontal stereotaxic plane and is inclined (lower laterally) from the stereotaxic sagittal plane by 105.34". The vertical canals are not per-
Guinea pig semicircular canal planes
Table 111. Magnitude of pitch and roll manoeuvres, in degrees, and direction of rotation required to bring any semicircular canal into an earth horizontal plane of rotation
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
PND=pitch nose down; PTD=pitch tail down; PRED =roll right ear down; RLED=roll left ear down Canal
Pitch
Direction
Roll
Direction
Left horizontal Left anterior Left posterior Right horizontal Right anterior Right posterior
48.37 73.48 56.83 48.37 73.48 56.83
PND PTD PTD PND PTD PTD
15.34 52.64 22.40 15.34 52.64 22.40
RRED RLED RRED RLED RRED RLED
pendicular to the stereotaxic horizontal plane: the anterior canal forms an angle of 99.78' and the posterior canal an angle of 59.77' with the horizontal plane. This nonperpendicularity would have resulted in errors if canal plane angles had been estimated by Fernhdez & Valentinuzzi's (1968) projection method. For the purpose of positioning a guinea pig €or angular acceleration stimulation the pitch and roll angles of each canal are needed. The pitch angle is that angle formed between the line of intersection of the canal plane and the sagittal plane measured along the nasooccipital axis. After pitching the animal by the required amount the roll angle is the angle formed between the interaural axis and the line of intersection between an earth vertical plane perpendicular to the sagittal plane and the canal plane. The pitch and roll angles for each canal and the direction of rotation for physiological stimulation by an earth horizontal plane of rotation are given in Table 111. In actually positioning the animal the rotations are not independent (Goldstein, 1965) and the order of the manoeuvres must be pitch then roll. The manoeuvres start from the skull being in the standard stereotaxic position shown in Fig. 1. So for example to bring the right anterior canal into an (earth horizontal) plane of rotation requires pitching the head 73.48' tail down and then rolling the animal 52.64' right ear down.
203
Translation to other stereotaxic systems Luparello (1967) specified that when the heights of the two points on the skull surface 6 mm and 14 mm anterior to the interaural axis were identical the guinea pig skull was horizontal. In our stereotaxic system these points were an average of 1.10 mm discrepant (k0.50 standard deviation). These points would be at the same height if the skull were pitched nose down by 7.38'. Thus to translate the positioning angles presented above into Luparello' s system requires a pitch nose down of 7.38': the pitch angle of the horizontal canals becomes 40.54' open anterior. The inferior margins of the medial canthi were on average 21.79" above (k1.35) the stereotaxic horizontal plane. Translation to Tindal's stereotaxic system requires a pitch nose down by this amount: the pitch angle of the horizontal canals becomes 26.58' open anterior. In some definitions of stereotaxic horizontal for rodents the incisor bar is set 2.5 mm below the external auditory meatus (Hurt et al., 1971). In our skulls this corresponds to a pitch of 3.34' (k0.12) nose down. The junction of the coronal suture and the superior orbital ridge was 40.13' above (k1.51) the stereotaxic horizontal plane. This point was measured as being the most probable to lie on Kristensen's line between the external meatus and the superior margin of the orbit. As an estimator of the pitch of the horizontal canal Kristensen's line probably underestimates the true pitch by about 8' (48.37'40.13' =8.24').
DISCUSSION It is important to emphasize that the planes of the semicircular canals given in this paper are planes derived from measurement of the osseous semicircular canals. The extent to which these planes correspond to the planes of the membranous ducts depends on the width of the perilymphatic space. A. A. Gray (1907) and 0. Gray (1951) have noted that the Acta Otolaryngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
204
I . S.Curthoys et al.
perilymphatic space of rodents is usually very small or absent. This fact can be verified by a photograph of a decalcified guinea pig labyrinth in 0. Gray (1955) and we have also confirmed it by measurements of guinea pig membranous labyrinths fixed in 10% formalin. Since the radius of curvature of the guinea pig canals is of the order of 1.90 mm (Jones & Spells, 1963; Curthoys et al., 1975 a ) and the perilymphatic space is of the order of 0.02 mm, it follows that any deviation between the plane of the osseous canal and that of the membranous duct would be about 1" (arctan (0.02/ 1.90)). It should also be stressed that the statistical techniques we used provide a best fitting plane to the series of data points for a canal. It was apparent from insepction of the dissected osseous semicircular canals that there are systematic departures from a plane, particularly for the anterior and posterior canals. Nevertheless these departures are not large and for the purposes of this investigation it was deemed adequate to use a linear approximation. This issue of the planarity of semicircular canals will be considered in more detail in a forthcoming paper (Curthoys et al., 1975a ) . One of the major aims of this study was to establish the optimal positioning of the guinea-pig skull for physiological stimulation of a given set of semicircular canals and to determine the extent to which other canals would be stimulated when the head was in this optimal position. It is clear from Tables I1 and I11 that it is impossible to position any two canals to be parallel to a single plane of stimulation. The optimal position for bilateral stimulation of the horizontal canals is with the skull tipped 48" nose down relative to an earth horizontal plane of stimulation. In this position each horizontal canal is approximately 15" out of the plane of stimulation, the anterior canals both form an angle of 71.19" and the posterior canals both form an angle of 75.91" with the plane of stimulation. Thus when the guinea pig head is optimally positioned for stimulation of Acta Otolaryngol80
both horizontal canals the vertical canals will receive an appreciable proportion of the stimulating angular acceleration. For instance if a guinea pig were positioned for optimal stimulation of both horizontal canals and given an angular acceleration of 4"/sec2 then the anterior canals would both receive an angular acceleration of 1.29"/sec2 (cos 71.91°x4) and the posterior canals an angular acceleration of 0.97"/sec2 (cos 75.91 x4). These stimulus levels of the vertical canals would be sufficient to influence the firing of sensitive primary and secondary vertical canal neurons (Blanks, 1973) and could lead to misidentification and misinterpretation in studies of neural convergence (Curthoys et al., 1971; Blanks, 1973; Markham & Curthoys, 1972).
ACKNOWLEDGEMENT We are grateful to Miss Gwynne Gloege for the illustrations, Mr N . Simpson for photography, Dr Max Mickey and Dr Peter Wenderoth for statistical advice and Miss Lorraine Nash for typing.
ZUSAMMENFASSUNG Bei 10 ausgewachsenen Meerschweinchen wurden stereotaktische Koordinaten von einer Reihe von Punkten an jedem knochernen Bodenganges entlang analysiert, urn eine mathematische Gleichung fur den jeweiligen Bodengang im stereotaktischen Raum zu erhalten. Winkelbeziehungen innerhalb der Gehorgange und zwischen den Gehorgangen werden angegeben sowie optimale Stellungen des Kopfes fur den physiologischen Reiz jedes Gangs oder jedes Paars von synergistischen Gangen. Die Ebenen der Bodengange in jedem Labyrinth stehen nicht senkrecht zueinander, und die Ebenen der kontralateralen synergistischen Gange weichen von der Parallelitat urn 30 Grad ab.
REFERENCES Bers, L . 1969. Calculus. Holt, Rinehart and Winston, New York. Blanks, R. H . I. 1973. Dynamic aspects of the cat semicircular canal receptive field: I. Anatomy 11. Physiology. Unpublished doctoral dissertation, University of California, Los Angeles. Blanks, R. H. I . , Curthoys, I. S. L Markham, C. H. 1972. Planar relationships of semicircular canals in the cat. Am J Physiol223, 55.
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
Guinea pig semicircular canal planes - 1975. Planar relationships of the semicircular canals in man. In preparation. Bodechtel, G. 1930. Vergleichende entwicklungsgeschichtliche Untersuchungen am Labyrinthorgan der Wirbeltier. Z Anat Entwicklungsgesch 92, 492. Curthoys, I. S., Blanks, R. H. I. & Markham, C. H. 1975 a . The radii of curvature (R) of the semicircular canals in cat, guinea pig and man. In preparation. - 1975 b. Biophysical characteristics of the semicircular canals in cat, guinea pig and man. In preparation. Curthoys, I. S., Markham, C. H. &Blanks, R. H. I. 1971. The orientation of middle and inner ear structures in cat and man. UCLA Brain Information Service, Brain Research Institute Publications Office, Los Angeles. van Egmond, A. A. H., Groen, J. J. & Jongkees, L. B. W. 1952. The function of the vestibular organ. Pract Otorhinolaryngol (Basel) 14, Suppl. 2 , 1. Fernandez, C. & Valentinuzzi, M. 1968. A study on the biophysical characteristics of the cat labyrinth. Acta Otolaryngol (Stockh) 65, 293. Goldstein, H. 1965. Classical mechanics. AddisonWesley, Massachusetts. Gray, A. A. 1907. The labyrinth of animals. Volumes I and 11. J & A Churchill, London. Gray, 0 . 1951. An introduction to the study of the comparative anatomy of the labyrinth. J Laryngol Otol65, 681. - 1955. A brief survey of the phylogenesis of the labyrinth. J Laryngol Otol69, 151. de Groot, J. 1959. The rat forebrain in stereotaxic coordinates. N. V. North Holland, Amsterdam. Guenther, W. C. 1965. Concepts of statistical inference. McGraw-Hill, New York. Hixson, W. C., Niven, J. I. & Correia, M. J. 1966. Kinematics nomenclature for physiological accelerations: with special reference to vestibular applications. Naval Aerospace Medicine Centre, Pensacola, Florida. NAMI Monograph 14. Hurt, G. A., Hanaway, J. & Netsky, M. G. 1971. Stereotaxic atlas of the mesencephalon in the albino rat. Confin Neurol33, 93.
205
Jones, G. M. & Spells, K. E. 1963. A theoretical and comparative study of the functional dependence of the semicircular canal upon its physical dimensions. Proc R Soc Lond 157 B , 403. Konig, J. F. R. & Klippel, R. A. 1963. The rat brain. A stereotanic atlas of the forebrain and lower parts of the brain stem. Williams & Wilkins, Baltimore. Kristensen, H. K. 1954. Caloric reactions in guinea pig and rabbit. Acta Otolaryngol (Stockh) 44, 126. Luparello, T. J. 1967. Stereotaxic atlas of the forebrain of the guinea pig. Karger, Basel. Luparello, T. J., Stein, M. & Park, C. D. 1964. A stereotaxic atlas of the hypothalamus of the guinea pig. J Comp Neuroll22, 201. Markham, C. H. & Curthoys, I. S . 1972. Labyrinthine convergence on vestibular nuclear neurons using natural and electrical stimulation. In Basic aspects of central vestibular mechanisms, progress in brain research37 (ed. A. Brodal & 0 . Pompeiano), p. 121. Pellegrino, L. J. & Cushman, A. J. 1967. A stereotaxic atlas of the rat brain. Appleton-Century-Crofts, New York. - 1971. Use of the stereotaxic technique. In Methods in phychobiology, Vol. I. Laboratory techniques in neuropsychology and neurobiology (ed. R. D. Myers). Academic Press, London. Thurstone, L. L . 1957. Multiple factor analysis. University of Chicago Press, Chicago. Tindal, J. S. 1965. The forebrain of the guinea pig in stereotaxic coordinates. J Comp Neuroll24, 259. Wersiill, J. 1956. Studies on the structure and innervation of the sensory epithelium of the crista ampullaris in the guinea pig. Acta Otolaryngol (Stockh), Suppl. 126, 1. I . S . Curthoys, Ph.D. Dept. of Psychology University of Sydney Sydney, N.S. W . Australia
Actu Otolupngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
THE ORIENTATION OF THE SEMICIRCULAR CANALS IN THE GUINEA PIG
I. S. Curthoys,' E. J. Curthoys,2R. H. I. Blanks3 and C. H. Markham4 From the Department of Psychology, University of Sydney, Sydney, N . S . W., Australia'* and the Department of Neurology, Medical School, University of California, Los Angeles, Calif., USA3*
(Received December 14, 1974)
Abstract. In 10 adult guinea pigs the stereotaxic coordinates of a series of points along each osseous semicircular canal were analysed to yield an equation of that canal plane in stereotaxic space. Angular relationships among the canal planes and between the canal planes and the major stereotaxic planes are presented together with the optimal positions of the head for physiological stimulation of each canal or pair of synergistic canals. The planes of the semicircular canals in each labyrinth are not perpendicular to one another and the planes of contralateral synergistic canals depart from parallelism by about 30".
In order to specify the mechanical forces involved in semicircular canal stimulation it is necessary to have information about, among other things, the fine structure of the canal and the orientation of the canal relative to the plane of the stimulating acceleration. Optimal physiological stimulation occurs when the canal plane is parallel to the plane of rotation. As a canal is tilted from parallelism the magnitude of the angular acceleration stimulation decreases as a cosine function (Blanks, 1973; van Egmond et al., 1952) and other canals are increasingly stimulated. We have developed a technique which determines the This research was supported by grants from the National Health and Medical Research Council of Australia, Sydney University Research grants, and US Public Health Service grant NS 06658. Computing assistance was obtained from the Health Sciences Computing Facility, UCLA, sponsored by NIH Special Resources Grant RR-3.
orientation of the semicircular canal planes with reference to external skull landmarks (Blanks et al., 1972, 1975) enabling the head to be positioned to optimally stimulate any canal. This technique has yielded data for the cat and human: the present paper reports comparable information for the guinea pig. The guinea pig has been used extensively in anatomical and physiological studies of the vestibular system. Its semicircular canals are about the same size as those of the cat and much more easily accessible (Curthoys et al., 1971). Nevertheless there is surprisingly little data concerning the orientation of these canals in the skull. Kristensen (1954) reported that the planes of the horizontal canals are parallel with a plane passing through the external auditory meati and the supraorbital margins. Wersdl(l956) reported that the two horizontal canals are in the same plane and the vertical canals are perpendicular to this plane. He estimated the angle between the ipsilateral anterior and posterior canal planes to be 100"; Bodechtel(l930) has estimated this angle to be 115". Wersall also reported that the two posterior canals formed an angle of 110" with each other. These results lead to the deduction that both pairs of vertical synergistic canals (the left anterior-right posterior and right anteriorActa Otolaryngol80
198
I . S . Curthoys et al. +z
DORSAL
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
POS
-z
VENTRAL
Fig. 1. The stereotaxic planes of the guinea pig and the mathematical conventions used.
left posterior) are misaligned from parallelism means of the heights of the skull surface 6 mm and 14 mm anterior to the interaural axis by about 25". Because of the need for a more complete (Luparello, 1967). Instead of using one of and accurate specification of semicircular these systems we chose to use the Kopf guinea canal planes in the guinea pig, particularly for pig head holder with the incisor vertical adskull positioning during angular acceleration justment set at zero. In this way the horizonstimulation we applied a technique, described tal plane becomes the plane through the in detail elsewhere (Blanks et al., 1972) to de- centres of the two external auditory canals and termine these planes in the stereotaxic axes the inferior-most portion of the bone just posterior to the incisors (i.e. the rostra1 edge of the system. incisor bar). Measurements of a number of skull dimensions enabled simple translation of METHODS the semicircular canal planes to the systems Guinea pig stereotaxic planes outlined above. The sagittal plane is perIn stereotaxic systems the horizontal plane is pendicular to the horizontal plane passing the most difficult to define: for the cat, mon- through the midsagittal suture. The frontal key and human, something akin to the Reid plane is perpendicular to the two other planes plane is used (the plane joining the centres of passing through the centres of the external the external auditory canals and the inferior auditory meati. The Hixson, Niven and Cormargins of the orbits). Definitions of the reia mathematical conventions were used stereotaxic horizontal plane for rodents are far (1966): in this system the x axis is the nasoocless uniform (de Groot, 1959; Hurt et al., 1971; cipital axis (anterior positive), the y axis is the Konig & Klippel, 1963; Luparello, 1967; interaural axis (left ear positive), and the z axis Luparello et al., 1964; Pellegrino & Cushman, is the vertical axis (dorsal positive) (see Fig. 1 1967, 1971 ; Tindal, 1965). Tindal did define the for these conventions). horizontal plane for the guinea pig by the external auditory canals and the inferior margin Dissection and measurement of medial canthi. However, his animals were Eleven adult guinea pigs with weights ranging so unusually large (700-830 g) that he was able from 3 1 1 to 487 g (mean 381 g) were killed by to use a Kopf cat/monkey head-holder. The barbiturate overdose and the tissue removed other widely used stereotaxic system for the from their skulls. Dental cement was applied guinea pig defines the horizontal plane by to the skull sutures to prevent dislocation. Acta Otolatyngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
Guinea p i g semicircular canal planes
199
Fig. 2. An overview of a guinea pig skull from a right viewpoint posterior to the interaural axis to show the perspective of Fig. 3 and Fig. 4 A, B , C.
The skulls were dried and for each animal the osseous canal of every semicircular canal was opened along as much of its length as possible by drilling. An attempt was made to standardize this dissection, so that for all animals the lateral-most bone in each canal was removed (see Figs. 2 and 3). The bony external auditory meati and most of the bullae were left intact, permitting the skull to be mounted in a Kopf guinea pig stereotaxic head holder (Model 1216) in fairly normal fashion. Standard guinea pig ear-bars were used and the height of the incisor bar was set at 0. Thus the positioning of the skull in the stereotaxic apparatus was the same as that which would be used with a living guinea pig. A Kopf electrode carriage with micromanipulator controls (model 1260) was placed on the stereotaxic frame and its planes of excursion were aligned with the stereotaxic planes. About 50 mm of fine (80 p m diameter) stainless steel wire insulated except at the tip was affixed to the electrode holder and connected to a voltage follower, audio amplifier and loudspeaker. Touching the tip of this wire 14 -752953
to an osseous canal or reference point resulted in a loud “pop” which considerably assisted identifying the “touch point”. The reference point consisted of a short piece of 80 pm wire cemented to the top of a bolt. The cement was fiied so the tip of the wire was flush with the surface. This reference point was bolted to the stereotaxic frame and it remained untouched during all measurements. Each skull was placed in the stereotaxic device and its position was not changed during measurement. The x, y and z coordinates of a series of approximately equally spaced points along each canal were obtained by advancing the wire probe until it just touched the medial-most wall of the osseous canal and reading the scales to the nearest 0.05 mm. Points in the ampullary and common crus regions were avoided. An average of 28 points per canal were recorded (range 17 to 50). After measuring the canals in one labyrinth a check was made to ensure the probe had not been displaced and if this check was satisfactory the probe was repositioned to enable readings of the contralateral labyrinth. The coordinates of Acta Otolaryngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
200 I . S . Curthoys et al.
Fig. 3. An enlargement of portion of Fig. 2. This figure shows the osseous semicircular canals which are shown schematically in Fig. 4 A, B, C.
points along a semicircular canal were always referred to the reference point which was in turn referred to the stereotaxic zero (the point of intersection of the three planes defined above), thus relating all canal measurements to stereotaxic zero. RESULTS Statistical treatment For each skull the raw data consisted of the x, y and z coordinates of points along each canal. This data was punched onto cards and the coordinates translated into stereotaxic space AC~U Orolaryngul80
by subtraction. This data was plotted by line printer to ensure there were no punching errors, outlying data points or substantial gaps between data points along any canal. The latter occurred for the anterior canals of three animals because of breakage during dissection of the extremely thin part of the anterior canal near the common crus (see Fig. 2). These canals were excluded from all further analysis. One animal was excluded entirely because detailed analysis showed it had not been positioned properly in the sterotaxic device. A plane was fitted to the data for each canal by a least squares technique and by principal com-
Guinea pig semicircular canal planes Table I. Equations of the planes parallel to the semicircular canals passing through the stereotaxic zero The figure in brackets below each coefficient is the standard deviation Left horizontal
+.71&u (5.008) Left anterior - .57& l~.~ f.013) Left posterior - .771x (k.011) Right horizontal +.716x ( f.008) Right anterior +.57&( (5.013) Right posterior - .77 Ix (f.011)
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
I
-, 2 6 3 ~ (2.020) .793y (2.008) -.38Oy (k.014) + .263y (k.020) + .793y (f.008) + .38Oy (k.014)
+
-.637~ (k.011) -.167~ (k.018) -.SO32 (k.010) -.637~ (k.011) +.167z ( k.O 18) -.SO32 (f.O1O)
=O =O =O =O =O =O
ponent analysis. As in earlier studies both techniques gave virtually identical results but only the results of the principal component analysis are reported here. This technique yields the direction cosines of a plane passing through the origin parallel to the plane of best fit of the data points of a given canal (Thurstone, 1957). In other words the D term of the generalized equation of a plane in three dimen-
201
sions Ax+By+Cz+D=O has been set to zero (Bers, 1969). The equations of the plane parallel to each canal are presented in Table I. The coefficients in these equations are the mean direction cosines. Since magnitude differences between direction cosines from left and right labyrinths were small, they were combined to improve estimation. This average value was then given the correct sign for the appropriate labyrinth. For each animal the direction cosines of its canal planes served as input for another program which computed the angles among the canal planes and between each canal plane and the stereotaxic planes. Magnitude differences for angles from left and right labyrinths were small and hence these angles were combined wherever possible to improve estimation. These meanangles are presented in Table I1 together with the numbers upon which each mean is based, the standard deviations and two-tailed 95% confidence intervals (Guenther, 1965). Figs. 2 and 3 show the orientation of the canals in a guinea pig skull and provide the perspective for Fig. 4 A, B, and C
Table 11. Means, number of measurements (n), standard deviations and 95% confidence limits for angles, in degrees, among ipsilateral canal planes, between contralateral synergistic canal planes and between each canal plane and the stereotaxic planes. The locations of these last set of angles are shown in Fig. 4 (see Column 1) 95% confidence limits Location and identification
Fig. 4 A , O1 Fig. 4 A, O2 Fig. 4 A, 0, Fig. 4 B, el Fig. 4 B , O2 Fig. 4 B, 19, Fig. 4 C, 0, Fig. 4 C, O2 Fig. 4 C , O3
Angle between the plane of the Horizontal canal Anterior canal Horizontal canal Left horizontal canal Left anterior canal Left posterior canal Horizontal canal Horizontal canal Horizontal canal Anterior canal Anterior canal Anterior canal .Posterior canal Posterior canal Posterior canal
S.D.
Mean
n
Anterior canal Posterior canal Posterior canal
122.15 76.71 82.36
17 17 20
6.13 5.49 4.74
Right horizontal canal Right posterior canal Right anterior canal Stereotaxic frontal Stereotaxic horizontal Stereotaxic sagittal Stereotaxic frontal Stereotaxic horizontal Stereotaxic sagittal Stereotaxic frontal Stereotaxic horizontal Stereotaxic sagittal
30.82 32.17 36.16 44.17 50.31 105.34
10 8 9 20 20 20
54.71 99.78 37.36 39.34 59.77 67.60
17 17 17 20 20 20
Lower
Upper 125.30 79.53 84.58
10.05 4.42 4.86 2.98 3.80 5.43
118.99 73.89 80.14 23.63 28.47 30.81 42.78 48.53 102.80
38.01 35.87 41.51 45.57 52.09 107.88
3.82 4.36 3.24 4.39 2.84 3.99
52.75 97.54 35.69 37.29 58.44 65.74
56.67 102.02 39.03 41.40 61.10 69.47
Acta Otolaryngol80
I . S. Curthoys et al.
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
202
Fig. 4 A , B , C. The intersection of the semicircular canal planes on the right side of the head with the guinea pig stereotaxic planes. 8,, 8,, O3 identify the angles between the canal plane and each stereotaxic plane, the magnitudes of which are given in Table 11. Ar to Orolaryngol80
which locate and identify the angles between the semicircular canal planes and the stereotaxic planes. The planes of the semicircular canals in a labyrinth are not perpendicular to one another: none of the 95% confidence intervals for the angles between these planes includes 90". Our estimate of the angle between the anterior and posterior canal planes is 76.71",approximately the complement of the value estimated by Wersdl(l956) and Bodechtel(l930). The planes of the three pairs of contralateral synergistic canals are all about 30" divergent from parallelism. One implication of this result is that, as Wersiill noted, the vertical canals form unequal angles with the sagittal plane. Our measures confirm this: the anterior canal forms an angle of 37" and the posterior canal forms an angle of 67" with the sagittal plane. Each horizontal canal forms an angle of 50.3 1" (open anteriorly) with the horizontal stereotaxic plane and is inclined (lower laterally) from the stereotaxic sagittal plane by 105.34". The vertical canals are not per-
Guinea pig semicircular canal planes
Table 111. Magnitude of pitch and roll manoeuvres, in degrees, and direction of rotation required to bring any semicircular canal into an earth horizontal plane of rotation
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
PND=pitch nose down; PTD=pitch tail down; PRED =roll right ear down; RLED=roll left ear down Canal
Pitch
Direction
Roll
Direction
Left horizontal Left anterior Left posterior Right horizontal Right anterior Right posterior
48.37 73.48 56.83 48.37 73.48 56.83
PND PTD PTD PND PTD PTD
15.34 52.64 22.40 15.34 52.64 22.40
RRED RLED RRED RLED RRED RLED
pendicular to the stereotaxic horizontal plane: the anterior canal forms an angle of 99.78' and the posterior canal an angle of 59.77' with the horizontal plane. This nonperpendicularity would have resulted in errors if canal plane angles had been estimated by Fernhdez & Valentinuzzi's (1968) projection method. For the purpose of positioning a guinea pig €or angular acceleration stimulation the pitch and roll angles of each canal are needed. The pitch angle is that angle formed between the line of intersection of the canal plane and the sagittal plane measured along the nasooccipital axis. After pitching the animal by the required amount the roll angle is the angle formed between the interaural axis and the line of intersection between an earth vertical plane perpendicular to the sagittal plane and the canal plane. The pitch and roll angles for each canal and the direction of rotation for physiological stimulation by an earth horizontal plane of rotation are given in Table 111. In actually positioning the animal the rotations are not independent (Goldstein, 1965) and the order of the manoeuvres must be pitch then roll. The manoeuvres start from the skull being in the standard stereotaxic position shown in Fig. 1. So for example to bring the right anterior canal into an (earth horizontal) plane of rotation requires pitching the head 73.48' tail down and then rolling the animal 52.64' right ear down.
203
Translation to other stereotaxic systems Luparello (1967) specified that when the heights of the two points on the skull surface 6 mm and 14 mm anterior to the interaural axis were identical the guinea pig skull was horizontal. In our stereotaxic system these points were an average of 1.10 mm discrepant (k0.50 standard deviation). These points would be at the same height if the skull were pitched nose down by 7.38'. Thus to translate the positioning angles presented above into Luparello' s system requires a pitch nose down of 7.38': the pitch angle of the horizontal canals becomes 40.54' open anterior. The inferior margins of the medial canthi were on average 21.79" above (k1.35) the stereotaxic horizontal plane. Translation to Tindal's stereotaxic system requires a pitch nose down by this amount: the pitch angle of the horizontal canals becomes 26.58' open anterior. In some definitions of stereotaxic horizontal for rodents the incisor bar is set 2.5 mm below the external auditory meatus (Hurt et al., 1971). In our skulls this corresponds to a pitch of 3.34' (k0.12) nose down. The junction of the coronal suture and the superior orbital ridge was 40.13' above (k1.51) the stereotaxic horizontal plane. This point was measured as being the most probable to lie on Kristensen's line between the external meatus and the superior margin of the orbit. As an estimator of the pitch of the horizontal canal Kristensen's line probably underestimates the true pitch by about 8' (48.37'40.13' =8.24').
DISCUSSION It is important to emphasize that the planes of the semicircular canals given in this paper are planes derived from measurement of the osseous semicircular canals. The extent to which these planes correspond to the planes of the membranous ducts depends on the width of the perilymphatic space. A. A. Gray (1907) and 0. Gray (1951) have noted that the Acta Otolaryngol80
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
204
I . S.Curthoys et al.
perilymphatic space of rodents is usually very small or absent. This fact can be verified by a photograph of a decalcified guinea pig labyrinth in 0. Gray (1955) and we have also confirmed it by measurements of guinea pig membranous labyrinths fixed in 10% formalin. Since the radius of curvature of the guinea pig canals is of the order of 1.90 mm (Jones & Spells, 1963; Curthoys et al., 1975 a ) and the perilymphatic space is of the order of 0.02 mm, it follows that any deviation between the plane of the osseous canal and that of the membranous duct would be about 1" (arctan (0.02/ 1.90)). It should also be stressed that the statistical techniques we used provide a best fitting plane to the series of data points for a canal. It was apparent from insepction of the dissected osseous semicircular canals that there are systematic departures from a plane, particularly for the anterior and posterior canals. Nevertheless these departures are not large and for the purposes of this investigation it was deemed adequate to use a linear approximation. This issue of the planarity of semicircular canals will be considered in more detail in a forthcoming paper (Curthoys et al., 1975a ) . One of the major aims of this study was to establish the optimal positioning of the guinea-pig skull for physiological stimulation of a given set of semicircular canals and to determine the extent to which other canals would be stimulated when the head was in this optimal position. It is clear from Tables I1 and I11 that it is impossible to position any two canals to be parallel to a single plane of stimulation. The optimal position for bilateral stimulation of the horizontal canals is with the skull tipped 48" nose down relative to an earth horizontal plane of stimulation. In this position each horizontal canal is approximately 15" out of the plane of stimulation, the anterior canals both form an angle of 71.19" and the posterior canals both form an angle of 75.91" with the plane of stimulation. Thus when the guinea pig head is optimally positioned for stimulation of Acta Otolaryngol80
both horizontal canals the vertical canals will receive an appreciable proportion of the stimulating angular acceleration. For instance if a guinea pig were positioned for optimal stimulation of both horizontal canals and given an angular acceleration of 4"/sec2 then the anterior canals would both receive an angular acceleration of 1.29"/sec2 (cos 71.91°x4) and the posterior canals an angular acceleration of 0.97"/sec2 (cos 75.91 x4). These stimulus levels of the vertical canals would be sufficient to influence the firing of sensitive primary and secondary vertical canal neurons (Blanks, 1973) and could lead to misidentification and misinterpretation in studies of neural convergence (Curthoys et al., 1971; Blanks, 1973; Markham & Curthoys, 1972).
ACKNOWLEDGEMENT We are grateful to Miss Gwynne Gloege for the illustrations, Mr N . Simpson for photography, Dr Max Mickey and Dr Peter Wenderoth for statistical advice and Miss Lorraine Nash for typing.
ZUSAMMENFASSUNG Bei 10 ausgewachsenen Meerschweinchen wurden stereotaktische Koordinaten von einer Reihe von Punkten an jedem knochernen Bodenganges entlang analysiert, urn eine mathematische Gleichung fur den jeweiligen Bodengang im stereotaktischen Raum zu erhalten. Winkelbeziehungen innerhalb der Gehorgange und zwischen den Gehorgangen werden angegeben sowie optimale Stellungen des Kopfes fur den physiologischen Reiz jedes Gangs oder jedes Paars von synergistischen Gangen. Die Ebenen der Bodengange in jedem Labyrinth stehen nicht senkrecht zueinander, und die Ebenen der kontralateralen synergistischen Gange weichen von der Parallelitat urn 30 Grad ab.
REFERENCES Bers, L . 1969. Calculus. Holt, Rinehart and Winston, New York. Blanks, R. H . I. 1973. Dynamic aspects of the cat semicircular canal receptive field: I. Anatomy 11. Physiology. Unpublished doctoral dissertation, University of California, Los Angeles. Blanks, R. H. I . , Curthoys, I. S. L Markham, C. H. 1972. Planar relationships of semicircular canals in the cat. Am J Physiol223, 55.
Acta Otolaryngol Downloaded from informahealthcare.com by Karolinska Institutet University Library on 01/27/15 For personal use only.
Guinea pig semicircular canal planes - 1975. Planar relationships of the semicircular canals in man. In preparation. Bodechtel, G. 1930. Vergleichende entwicklungsgeschichtliche Untersuchungen am Labyrinthorgan der Wirbeltier. Z Anat Entwicklungsgesch 92, 492. Curthoys, I. S., Blanks, R. H. I. & Markham, C. H. 1975 a . The radii of curvature (R) of the semicircular canals in cat, guinea pig and man. In preparation. - 1975 b. Biophysical characteristics of the semicircular canals in cat, guinea pig and man. In preparation. Curthoys, I. S., Markham, C. H. &Blanks, R. H. I. 1971. The orientation of middle and inner ear structures in cat and man. UCLA Brain Information Service, Brain Research Institute Publications Office, Los Angeles. van Egmond, A. A. H., Groen, J. J. & Jongkees, L. B. W. 1952. The function of the vestibular organ. Pract Otorhinolaryngol (Basel) 14, Suppl. 2 , 1. Fernandez, C. & Valentinuzzi, M. 1968. A study on the biophysical characteristics of the cat labyrinth. Acta Otolaryngol (Stockh) 65, 293. Goldstein, H. 1965. Classical mechanics. AddisonWesley, Massachusetts. Gray, A. A. 1907. The labyrinth of animals. Volumes I and 11. J & A Churchill, London. Gray, 0 . 1951. An introduction to the study of the comparative anatomy of the labyrinth. J Laryngol Otol65, 681. - 1955. A brief survey of the phylogenesis of the labyrinth. J Laryngol Otol69, 151. de Groot, J. 1959. The rat forebrain in stereotaxic coordinates. N. V. North Holland, Amsterdam. Guenther, W. C. 1965. Concepts of statistical inference. McGraw-Hill, New York. Hixson, W. C., Niven, J. I. & Correia, M. J. 1966. Kinematics nomenclature for physiological accelerations: with special reference to vestibular applications. Naval Aerospace Medicine Centre, Pensacola, Florida. NAMI Monograph 14. Hurt, G. A., Hanaway, J. & Netsky, M. G. 1971. Stereotaxic atlas of the mesencephalon in the albino rat. Confin Neurol33, 93.
205
Jones, G. M. & Spells, K. E. 1963. A theoretical and comparative study of the functional dependence of the semicircular canal upon its physical dimensions. Proc R Soc Lond 157 B , 403. Konig, J. F. R. & Klippel, R. A. 1963. The rat brain. A stereotanic atlas of the forebrain and lower parts of the brain stem. Williams & Wilkins, Baltimore. Kristensen, H. K. 1954. Caloric reactions in guinea pig and rabbit. Acta Otolaryngol (Stockh) 44, 126. Luparello, T. J. 1967. Stereotaxic atlas of the forebrain of the guinea pig. Karger, Basel. Luparello, T. J., Stein, M. & Park, C. D. 1964. A stereotaxic atlas of the hypothalamus of the guinea pig. J Comp Neuroll22, 201. Markham, C. H. & Curthoys, I. S . 1972. Labyrinthine convergence on vestibular nuclear neurons using natural and electrical stimulation. In Basic aspects of central vestibular mechanisms, progress in brain research37 (ed. A. Brodal & 0 . Pompeiano), p. 121. Pellegrino, L. J. & Cushman, A. J. 1967. A stereotaxic atlas of the rat brain. Appleton-Century-Crofts, New York. - 1971. Use of the stereotaxic technique. In Methods in phychobiology, Vol. I. Laboratory techniques in neuropsychology and neurobiology (ed. R. D. Myers). Academic Press, London. Thurstone, L. L . 1957. Multiple factor analysis. University of Chicago Press, Chicago. Tindal, J. S. 1965. The forebrain of the guinea pig in stereotaxic coordinates. J Comp Neuroll24, 259. Wersiill, J. 1956. Studies on the structure and innervation of the sensory epithelium of the crista ampullaris in the guinea pig. Acta Otolaryngol (Stockh), Suppl. 126, 1. I . S . Curthoys, Ph.D. Dept. of Psychology University of Sydney Sydney, N.S. W . Australia
Actu Otolupngol80
