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Direct afferents to interpositus nucleus responsible for triggering movement
Brain Research, 177 (1979) 367-372 © Elsevier/North-Holland Biomedical Press
367
Direct afferents to interpositus nucleus responsible for triggering movement
VINCENZO PERCIAVALLE, FRANCESCA SANTANGELO, SALVATORE SAPIENZA, MARIA FRANCESCA SERAPIDE* and ANTONIO URBANO Institute of Human Physiology, University of Catania, l,'iale Andrea Doria 6, 95125 Catania (Italy)
(Accepted August 2nd, 1979)
In the cat, activation of cerebellar afferents within the brachium pontis (BP) and the restiform body (RB) can produce contractions of single muscles of limbs which are mediated by the interposito-rubrospinal pathway 11-13. Both anatomical and electrophysiological findings have shown that the cerebellar afferents impinge cortical and/or nuclear cells ~. Two opposite hypotheses have been pointed out concerning the cerebellar afferent action on cortical and nuclear elements. According to one hypothesis, the major action of the cerebellar input could be exerted on the cerebellar cortex while any direct influence on nuclear cells could be subsidiaryl,4,1L The other hypothesis considers a subsidiary influence of afferents on the cerebellar cortex and a paramount action on the nucleiL We thought that BP- and RB-induced movements could be produced directly via the interpositus nucleus (IN) without any effective participation of overlying cortex. This possibility was tested in the present experiments which were carried out on acute and chronic cerebello-decorticated cats. Three animals were used for acute cerebellar decortication. Cerebellar cortex was suctioned under general anesthesia (40 ~ 02/60 ~ N20 supplemented with 0.5-1 Halothane). As shown in the microphotography of Fig. 1, decortication extended to the cortical areas projecting on both sides to IN 9, as well as to the vermal cortex situated between these areas. The exposed surface was covered with vaseline and the posterior fossa was closed with a thin perforable film (PVC acetate). Before discontinuing anesthesia, the head was definitively fixed to the stereotaxic frame using two Plexiglas cylinders cemented to the skull. Care was taken to infiltrate the wounds with 1 ~ Xylocaine (Astra) and tranquilizing doses of sodium pentobarbital (Nembutal, 5 mg i.m.) were administered when hyperactive motor behavior appeared. BP and RB microstimulation and electromyographic recordings (EMGs)were made as already described 11-13. First, a site was identified within the BP as well as the RB from which a single limb muscle contraction could be produced by very low threshold current (below 50/~A), and then the rubrospinal tract (RST) ipsilateral to the stimulating electrode was interrupted by diatermy 12,~3. After completion of the * Fellow of the Ministero della Pubblica Istruzione, 1978-1979.
368
Fig. 1. Microphotography showing extension of cerebellar decortication in a cat. observations, the stimulating sites were marked by a small electrolytic lesion (15 #A negative current delivered for 15 sec). Chronic cerebellar decortication was carried out on two cats two and three weeks before the experimental session. The BP and the RB were stimulated as in acute animals while unitary activity was recorded from the ipsilateral IN with tungsten microelectrodes (bare tips 10/zm in length and 20 # m in diameter; 3-5 Mr2 resistance). IN cells were identified for antidromic firing from the contralateral red nucleus. After recording unitary discharges, recording sites were stimulated (0.01-2 sec trains of negative 0.2-0.5 msec pulses at 10-700 Hz) in order to investigate the motor effect elicited by their activation (cf. refs. 2 and 14). At the end, the ipsilateral brachium conjunctivum was sectioned and the motor effect from the BP and the RB was tested again12,13. Histological examinations were made on frozen sagittal and/or frontal sections of the encephalon, stained by the K1/.iver-Barrera method 10. Muscles examined were controlled by autopsy. For quantitative analysis, unitary discharges (60 responses) were converted through a computer CYBER in post-stimulus time histograms (PSTHs) and cumulative frequency distributions (CFDs); averaged PSTHs were also constructed. Example experiments are shown in Figs. 2 and 3. Fig. 2 illustrates a part of the experiment performed on the cat submitted to the acute cerebellar decortication shown in Fig. 1. In Fig. 2A a depth-threshold curve is reported that was constructed during an electrode penetration which interested the left BP at lateral plane 7.2 (see ref.
369
A
f
i
EDC
1'o 2'0 3'0 ,'~ io
Threshold{)~A) 2mm B
15.0 ,
I
~ I
I
'
-10 '
0mm
Fig. 2. Acute decorticated cat of Fig. 1. A: depth-threshold curve obtained from stimulating the brachium pontis (BP) in the course of a penetration performed at sagittal plane L" 7.2 (cf. Berman's atlasa). Filled circles along the electrode trajectory indicate the extent of the area tested for motor effect (200/~m steps). Filled triangles in the curve represent sites effective in promoting contraction of the ipsilateral m. extensor digitorum communis (EDC). B: EMGs (10 trials at 2 sec intervals) recorded from EDC upon activation of the same site within BP before (pre) and after (post) acute interruption of rubrospinal tract (RST; cf. Verhaart's atlas18). Current intensity was 14/~A and 140 #A, respectively. Inset diagram on the right shows the greatest extent of lesions involving RST ipsilateral to BP stimulated (etched area). Abbreviations: CBL, lateral cerebellar nucleus; CDV, pars caudalis of the descending trigeminal nucleus; CN, cochlear nuclei; DRV, descending root of the trigeminal nerve; FL, nucleus funiculi lateralis; IO, inferior olive; PT, pyramidal tract. Further explanations are in the text.
3). As can be seen, after the electrode h a d penetrated the BP, c o n t r a c t i o n of the ipsilateral m. extensor d i g i t o r u m c o m m u n i s ( E D C ) was elicited at threshold strength of 50 # A . A t successive points, threshold progressively decreased until a site was f o u n d from
370
\
~
e a
\ \
EDC
\
.
.
.
.
.
.
.
.
.1
. . m m/dlv.
.
.
.
.
10
z'o
3'0
Threshold
~0
'
50
(FA)
EDC ~•
15 1
2 msec/div.
40 rnsec/div.
Fig. 3. Chronic cerebello-decorticated cat. A: electrode trajectory and unitary recording sites (filled circles) from which successive stimulation produced at different threshold intensity excitation of m. biceps brachii (BIB) and m. extensor digitorum communis (EDC). B: averaged PSTHs constructed from extracellular unitary potentials recorded in correspondence with the interpositus nucleus (IN) sites for the BIB and the EDC illustrated in A; responses were obtained upon single pulse stimulation of a site within the brachium pontis from which contraction of the BIB was elicited at very low threshold (28/~A). Further explanations are in the text.
which activation o f the same muscle was obtained with threshold current o f 14 ~A. Latency, calculated at 3-4 times the threshold from starting o f stimulation to beginning o f E M G response (cf. ref. 7), was about 19 msec (cf. ref. 11). Fig. 2B shows E M G s recorded before (pre) and after (post) RST interruption (left), and the maximal extent o f the lesions in this tract (right). As can be seen, no m o t o r effect was observed after the interruption, although a stimulating current was used which was 10 times higher (140/~A) than before lesions. The same findings were obtained by stimulating the RB. In the chronic cat o f Fig. 3 minimal threshold stimulation o f the left BP (28/~A) and RB (21 /~A) produced contraction o f m. biceps brachii (BIB) and m. triceps brachii (TRB), respectively. Latency o f muscle response was 18 msec from the BP and 19 msec from the RB. Ipsilateral I N was then penetrated. Fig. 3A shows an electrode trajectory and the corresponding depth-threshold curve. Filled circles in this curve were sites from which unitary activity was recorded and which were successively stimulated. As can be seen, the stimulation produced contraction o f BIB and E D C in
371 succession. Averaged PSTHs in Fig. 3B were constructed from unitary activities recorded from all ( n = 7 ) I N cells encountered. The cells (n----3) located in the nuclear area for BIB were monosynaptically fired (1.1-1.5 msec latency) upon single pulse (0.2 msec) stimulation of the BP area for the same muscle (left), whereas those ( n = 4 ) included within the area for E D C were not (right). On the other hand, microstimulation of the RB area for TRB was uneffective on all neurons examined. The successive section of BC abolished the muscle response from both the BP and the RB. As was expected, in the second experiment these observations were confirmed. The RB provoked contraction of BIB and the BP excited the m. biceps femoris (BIF). Five IN cells were studied. Of these, 2 were located at sites from which contraction of BIB was elicited and the remaining ones belonged to an area for the m. palmaris longus. It was found that the cells situated in correspondence of sites, the stimulation of which elicited contraction of BIB, were all monosynaptically activated by the RB. N o effect was seen in the same cells from the BP, and the RB stimulation was ineffective on cells included within an area for the m. palmaris longus (PAL). The idea that stimulation of cerebellar afferents causes cerebeUofugal discharges via cerebellar nuclei is not new4,S, 15. This report clearly demonstrates that cerebellar afterents are capable of triggering single muscle contractions of limbs independently of cerebellar cortex. As a matter of fact, disappearance after BC interruption of motor effects induced from the BP and RB directly shows that they were mediated by a transcerebellar pathway. Moreover, persistence in chronic cerebello-decorticated cats of motor responses to the BP and RB excludes the possibility that an antidromic activation of cerebellar efferents giving collaterals to I N could in any manner participate in modifying I N activity. Since the RST section abolished BP- and RB-induced movements, no doubt remains about the existence of a direct motor input from the BP and RB to interpositorubral cells. Conclusively, these experiments give proof, although indirect, that cerebellar afferents involved in triggering movement can exert a direct paramount action on nuclear cells and, if existent, only a subsidiary influence through the overlying cortex. Such an organization appears to be coherent with the specificity (single muscle mechanism) of the motor cerebellar input 11-1~ and interpositorubral output (Giuffrida, Li Volsi, Pantb, Perciavalle, Sapienza and Urbano, submitted for publication). This is clearly confirmed in the present study by the observation that I N cells monosynaptically fired from the BP and RB belonged to the nuclear area controlling the same muscle activated upon peduncular stimulation.
1 Allen, G. I. and Tsukahara, N., Cerebrocerebellar communication system, Physiol. Rev., 54 (1974) 957-1006. 2 Asanuma, H. and Hunsperger, W., Functional significance of projection from the cerebellar nuclei to the motor cortex in the cat, Brain Research, 98 (1975) 73-92. 3 Berman, A. L., The Brain Stem of the Cat, University of Wisconsin Press, Madison, Wisc., 1968, 175 pp. 4 Blomfield, S. and Marr, D., How the cerebellum may be used, Nature (Lond.), 227 (1970) 1224-1228.
5 Eccles, J. C., The cerebellum as a computer: patterns in space and time, J. PhysioL (Lond.), 229 (1973) 1-32.
372 6 Eccles, J'. C., Ito, M. and Szentagothai, J., The Cerebellum as a Neuronal Machine, SpringerVerlag, Berlin, Heidelberg, New York, 1967, pp. 227-261. 7 Ghez, C., Input-output relations of the red nucleus in the cat, Brain Research, 98 (1975) 93-108. 8 Ito, M., Neuropbysiological aspects of the cerebellar motor control system, Int. J. Nearol. (Montevideo), 7 (1970) 162-176. 9 Jansen, J. and Brodal, A., Aspects of Cerebellar Anatomy, Tanum, Oslo, 1954, 423 pp. 10 Klfiver, H. and Barrera, E., A method for the combined staining of cells and fibers in the nervous system, J. Neuropath. exp. NeuroL, 12 (1953) 400-403. 11 Perciavalle, V., Santangelo, F., Sapienza, S., Savoca, F. and Urbano, A., Motor effects produced by microstimulation of brachium pontis in the cat, Brain Research, 126 (1977) 557-562. 12 Perciavalle, V., Santangelo, F., Sapienza, S., Savoca, F. and Urbano, A., A ponto-interpositorubrospinal pathway for single muscle contractions in limbs of the cat, Brain Research, 155 (1978) 124-129.
13 Perciavalle, V., Santangelo, F., Sapienza, S., Serapide, M. F. and Urbano, A., Motor responses evoked by microstimulation of restiform body in the cat, Exp. Brain Res., 33 (1978) 241-255. 14 Perciavalle, V., Santangelo, F., Sapienza, S., Serapide, M. F. and Urbano, A., Dentate nucleus incapability to trigger movement in the cat, Neurosci. Lett., Suppl. 1 (1978) S152. 15 Thach, W. T., Cerebellar output: properties synthesis and uses, Brain Research, 40 (1972) 89-97. 16 Verhaart, W. J. C., A Stereotactie Atlas of the Brain Stem of the Cat, Van Gorcum, Assen, 1964.
367
Direct afferents to interpositus nucleus responsible for triggering movement
VINCENZO PERCIAVALLE, FRANCESCA SANTANGELO, SALVATORE SAPIENZA, MARIA FRANCESCA SERAPIDE* and ANTONIO URBANO Institute of Human Physiology, University of Catania, l,'iale Andrea Doria 6, 95125 Catania (Italy)
(Accepted August 2nd, 1979)
In the cat, activation of cerebellar afferents within the brachium pontis (BP) and the restiform body (RB) can produce contractions of single muscles of limbs which are mediated by the interposito-rubrospinal pathway 11-13. Both anatomical and electrophysiological findings have shown that the cerebellar afferents impinge cortical and/or nuclear cells ~. Two opposite hypotheses have been pointed out concerning the cerebellar afferent action on cortical and nuclear elements. According to one hypothesis, the major action of the cerebellar input could be exerted on the cerebellar cortex while any direct influence on nuclear cells could be subsidiaryl,4,1L The other hypothesis considers a subsidiary influence of afferents on the cerebellar cortex and a paramount action on the nucleiL We thought that BP- and RB-induced movements could be produced directly via the interpositus nucleus (IN) without any effective participation of overlying cortex. This possibility was tested in the present experiments which were carried out on acute and chronic cerebello-decorticated cats. Three animals were used for acute cerebellar decortication. Cerebellar cortex was suctioned under general anesthesia (40 ~ 02/60 ~ N20 supplemented with 0.5-1 Halothane). As shown in the microphotography of Fig. 1, decortication extended to the cortical areas projecting on both sides to IN 9, as well as to the vermal cortex situated between these areas. The exposed surface was covered with vaseline and the posterior fossa was closed with a thin perforable film (PVC acetate). Before discontinuing anesthesia, the head was definitively fixed to the stereotaxic frame using two Plexiglas cylinders cemented to the skull. Care was taken to infiltrate the wounds with 1 ~ Xylocaine (Astra) and tranquilizing doses of sodium pentobarbital (Nembutal, 5 mg i.m.) were administered when hyperactive motor behavior appeared. BP and RB microstimulation and electromyographic recordings (EMGs)were made as already described 11-13. First, a site was identified within the BP as well as the RB from which a single limb muscle contraction could be produced by very low threshold current (below 50/~A), and then the rubrospinal tract (RST) ipsilateral to the stimulating electrode was interrupted by diatermy 12,~3. After completion of the * Fellow of the Ministero della Pubblica Istruzione, 1978-1979.
368
Fig. 1. Microphotography showing extension of cerebellar decortication in a cat. observations, the stimulating sites were marked by a small electrolytic lesion (15 #A negative current delivered for 15 sec). Chronic cerebellar decortication was carried out on two cats two and three weeks before the experimental session. The BP and the RB were stimulated as in acute animals while unitary activity was recorded from the ipsilateral IN with tungsten microelectrodes (bare tips 10/zm in length and 20 # m in diameter; 3-5 Mr2 resistance). IN cells were identified for antidromic firing from the contralateral red nucleus. After recording unitary discharges, recording sites were stimulated (0.01-2 sec trains of negative 0.2-0.5 msec pulses at 10-700 Hz) in order to investigate the motor effect elicited by their activation (cf. refs. 2 and 14). At the end, the ipsilateral brachium conjunctivum was sectioned and the motor effect from the BP and the RB was tested again12,13. Histological examinations were made on frozen sagittal and/or frontal sections of the encephalon, stained by the K1/.iver-Barrera method 10. Muscles examined were controlled by autopsy. For quantitative analysis, unitary discharges (60 responses) were converted through a computer CYBER in post-stimulus time histograms (PSTHs) and cumulative frequency distributions (CFDs); averaged PSTHs were also constructed. Example experiments are shown in Figs. 2 and 3. Fig. 2 illustrates a part of the experiment performed on the cat submitted to the acute cerebellar decortication shown in Fig. 1. In Fig. 2A a depth-threshold curve is reported that was constructed during an electrode penetration which interested the left BP at lateral plane 7.2 (see ref.
369
A
f
i
EDC
1'o 2'0 3'0 ,'~ io
Threshold{)~A) 2mm B
15.0 ,
I
~ I
I
'
-10 '
0mm
Fig. 2. Acute decorticated cat of Fig. 1. A: depth-threshold curve obtained from stimulating the brachium pontis (BP) in the course of a penetration performed at sagittal plane L" 7.2 (cf. Berman's atlasa). Filled circles along the electrode trajectory indicate the extent of the area tested for motor effect (200/~m steps). Filled triangles in the curve represent sites effective in promoting contraction of the ipsilateral m. extensor digitorum communis (EDC). B: EMGs (10 trials at 2 sec intervals) recorded from EDC upon activation of the same site within BP before (pre) and after (post) acute interruption of rubrospinal tract (RST; cf. Verhaart's atlas18). Current intensity was 14/~A and 140 #A, respectively. Inset diagram on the right shows the greatest extent of lesions involving RST ipsilateral to BP stimulated (etched area). Abbreviations: CBL, lateral cerebellar nucleus; CDV, pars caudalis of the descending trigeminal nucleus; CN, cochlear nuclei; DRV, descending root of the trigeminal nerve; FL, nucleus funiculi lateralis; IO, inferior olive; PT, pyramidal tract. Further explanations are in the text.
3). As can be seen, after the electrode h a d penetrated the BP, c o n t r a c t i o n of the ipsilateral m. extensor d i g i t o r u m c o m m u n i s ( E D C ) was elicited at threshold strength of 50 # A . A t successive points, threshold progressively decreased until a site was f o u n d from
370
\
~
e a
\ \
EDC
\
.
.
.
.
.
.
.
.
.1
. . m m/dlv.
.
.
.
.
10
z'o
3'0
Threshold
~0
'
50
(FA)
EDC ~•
15 1
2 msec/div.
40 rnsec/div.
Fig. 3. Chronic cerebello-decorticated cat. A: electrode trajectory and unitary recording sites (filled circles) from which successive stimulation produced at different threshold intensity excitation of m. biceps brachii (BIB) and m. extensor digitorum communis (EDC). B: averaged PSTHs constructed from extracellular unitary potentials recorded in correspondence with the interpositus nucleus (IN) sites for the BIB and the EDC illustrated in A; responses were obtained upon single pulse stimulation of a site within the brachium pontis from which contraction of the BIB was elicited at very low threshold (28/~A). Further explanations are in the text.
which activation o f the same muscle was obtained with threshold current o f 14 ~A. Latency, calculated at 3-4 times the threshold from starting o f stimulation to beginning o f E M G response (cf. ref. 7), was about 19 msec (cf. ref. 11). Fig. 2B shows E M G s recorded before (pre) and after (post) RST interruption (left), and the maximal extent o f the lesions in this tract (right). As can be seen, no m o t o r effect was observed after the interruption, although a stimulating current was used which was 10 times higher (140/~A) than before lesions. The same findings were obtained by stimulating the RB. In the chronic cat o f Fig. 3 minimal threshold stimulation o f the left BP (28/~A) and RB (21 /~A) produced contraction o f m. biceps brachii (BIB) and m. triceps brachii (TRB), respectively. Latency o f muscle response was 18 msec from the BP and 19 msec from the RB. Ipsilateral I N was then penetrated. Fig. 3A shows an electrode trajectory and the corresponding depth-threshold curve. Filled circles in this curve were sites from which unitary activity was recorded and which were successively stimulated. As can be seen, the stimulation produced contraction o f BIB and E D C in
371 succession. Averaged PSTHs in Fig. 3B were constructed from unitary activities recorded from all ( n = 7 ) I N cells encountered. The cells (n----3) located in the nuclear area for BIB were monosynaptically fired (1.1-1.5 msec latency) upon single pulse (0.2 msec) stimulation of the BP area for the same muscle (left), whereas those ( n = 4 ) included within the area for E D C were not (right). On the other hand, microstimulation of the RB area for TRB was uneffective on all neurons examined. The successive section of BC abolished the muscle response from both the BP and the RB. As was expected, in the second experiment these observations were confirmed. The RB provoked contraction of BIB and the BP excited the m. biceps femoris (BIF). Five IN cells were studied. Of these, 2 were located at sites from which contraction of BIB was elicited and the remaining ones belonged to an area for the m. palmaris longus. It was found that the cells situated in correspondence of sites, the stimulation of which elicited contraction of BIB, were all monosynaptically activated by the RB. N o effect was seen in the same cells from the BP, and the RB stimulation was ineffective on cells included within an area for the m. palmaris longus (PAL). The idea that stimulation of cerebellar afferents causes cerebeUofugal discharges via cerebellar nuclei is not new4,S, 15. This report clearly demonstrates that cerebellar afterents are capable of triggering single muscle contractions of limbs independently of cerebellar cortex. As a matter of fact, disappearance after BC interruption of motor effects induced from the BP and RB directly shows that they were mediated by a transcerebellar pathway. Moreover, persistence in chronic cerebello-decorticated cats of motor responses to the BP and RB excludes the possibility that an antidromic activation of cerebellar efferents giving collaterals to I N could in any manner participate in modifying I N activity. Since the RST section abolished BP- and RB-induced movements, no doubt remains about the existence of a direct motor input from the BP and RB to interpositorubral cells. Conclusively, these experiments give proof, although indirect, that cerebellar afferents involved in triggering movement can exert a direct paramount action on nuclear cells and, if existent, only a subsidiary influence through the overlying cortex. Such an organization appears to be coherent with the specificity (single muscle mechanism) of the motor cerebellar input 11-1~ and interpositorubral output (Giuffrida, Li Volsi, Pantb, Perciavalle, Sapienza and Urbano, submitted for publication). This is clearly confirmed in the present study by the observation that I N cells monosynaptically fired from the BP and RB belonged to the nuclear area controlling the same muscle activated upon peduncular stimulation.
1 Allen, G. I. and Tsukahara, N., Cerebrocerebellar communication system, Physiol. Rev., 54 (1974) 957-1006. 2 Asanuma, H. and Hunsperger, W., Functional significance of projection from the cerebellar nuclei to the motor cortex in the cat, Brain Research, 98 (1975) 73-92. 3 Berman, A. L., The Brain Stem of the Cat, University of Wisconsin Press, Madison, Wisc., 1968, 175 pp. 4 Blomfield, S. and Marr, D., How the cerebellum may be used, Nature (Lond.), 227 (1970) 1224-1228.
5 Eccles, J. C., The cerebellum as a computer: patterns in space and time, J. PhysioL (Lond.), 229 (1973) 1-32.
372 6 Eccles, J'. C., Ito, M. and Szentagothai, J., The Cerebellum as a Neuronal Machine, SpringerVerlag, Berlin, Heidelberg, New York, 1967, pp. 227-261. 7 Ghez, C., Input-output relations of the red nucleus in the cat, Brain Research, 98 (1975) 93-108. 8 Ito, M., Neuropbysiological aspects of the cerebellar motor control system, Int. J. Nearol. (Montevideo), 7 (1970) 162-176. 9 Jansen, J. and Brodal, A., Aspects of Cerebellar Anatomy, Tanum, Oslo, 1954, 423 pp. 10 Klfiver, H. and Barrera, E., A method for the combined staining of cells and fibers in the nervous system, J. Neuropath. exp. NeuroL, 12 (1953) 400-403. 11 Perciavalle, V., Santangelo, F., Sapienza, S., Savoca, F. and Urbano, A., Motor effects produced by microstimulation of brachium pontis in the cat, Brain Research, 126 (1977) 557-562. 12 Perciavalle, V., Santangelo, F., Sapienza, S., Savoca, F. and Urbano, A., A ponto-interpositorubrospinal pathway for single muscle contractions in limbs of the cat, Brain Research, 155 (1978) 124-129.
13 Perciavalle, V., Santangelo, F., Sapienza, S., Serapide, M. F. and Urbano, A., Motor responses evoked by microstimulation of restiform body in the cat, Exp. Brain Res., 33 (1978) 241-255. 14 Perciavalle, V., Santangelo, F., Sapienza, S., Serapide, M. F. and Urbano, A., Dentate nucleus incapability to trigger movement in the cat, Neurosci. Lett., Suppl. 1 (1978) S152. 15 Thach, W. T., Cerebellar output: properties synthesis and uses, Brain Research, 40 (1972) 89-97. 16 Verhaart, W. J. C., A Stereotactie Atlas of the Brain Stem of the Cat, Van Gorcum, Assen, 1964.