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Regional cerebral blood flow for singers and nonsingers while speaking, singing, and humming a rote passage
BRAIN AND LANGUAGE
36,
690-698 (1989)
NOTE AND DISCUSSION Regional Cerebral Blood Flow for Singers and Nonsingers while Speaking, Singing, and Humming a Rote Passage C. FORMBY’ Departments of Communicative Disorders and Neurology, University of Florida
R. G. THOMAS Department of Biometry, Emory University AND
J. H. HALSEY, JR. Department of Neurology, University of Alabama-Birmingham
(UAB)
Two groups of singers (n = 12,13) and a group of nonsingers (n = 12) each produced the national anthem by (1) speaking and (2) singing the words and by (3) humming the melody. Regional cerebral blood flow (rCBF) was measured at rest and during each phonation task from seven areas in each hemisphere by the “‘Xe-inhalation method. Intrahemisphere, interhemisphere, and global rCBF were generally similar across phonation tasks and did not yield appreciable differences among the nonsingers and the singers. o 1989 Academic Press, hc.
Audie White and Tina Davis collected these data. We thank Professor Andrew Gainey and Dr. Gene Black and their students for assistance in this study. We also thank our colleagues, Janet Falgout, Dano Leli, Ed Wills, and Judy Blumsack, for their comments, and Laura Ellsworth and Cindy Lynn for their help in preparing this manuscript. The National Institute of Neurological and Communicative Disorders and Stroke provided partial support of this research through Grant NS-08802 to UAB. All correspondence and requests for reprints should be addressed to C. Formby at Departments of Communicative Disorders and Neurology, Box J-174/JHMHC, University of Florida, Gainesville, FL 32610. ’ Data were collected while C. Formby was a postdoctoral fellow in the Department of Neurology, UAB. 690 0093-934X/89 $3.00 Copyright 0 1989 by Academic Press, Inc. AU rights of reproduction in any form reserved
NOTE AND DISCUSSION
691
INTRODUCTION In a previous report (Formby, Thomas, Brown, & Halsey, 1987) we considered whether continuous phonation confounded ‘33Xe respired air curves of the type used in mathematical models to estimate regional cerebral blood flow (rCBF). We concluded that although the inhalation and exhalation patterns for singers and nonsingers may differ, the average ‘33Xeair curve derived from end-tidal breathing did not differ appreciably across subjects nor across conditions of speaking, singing, and humming the national anthem. This was an important methodological issue because during passive breathing the respired air curve is known to mirror the concentration of radioactivity in the arterial blood. This information is used as an input function in the rCBF model. If the air curve were distorted by continuous phonation, then estimates of rCBF measured during these phonation tasks, or during any task of continuous phonation, would have questionable validity. After establishing that continuous talking, singing, and humming had not seriously confounded the respired air curves, we proceeded to analyze the companion rCBF data for these tasks. These are the data presented in this report. Our purpose was to compare rCBF from both hemispheres for rest and for speaking, singing, and humming of a rote passage among trained and untrained vocalists. METHOD A description of the subjects, along with the inhalation system and method, were described in an earlier report (Formby et al., 1987). To review briefly, healthy college-age men participated as members in one of three groups: 12 subjects were voice students, 13 subjects were college choir members, and 12 subjects had no formal musical training (i.e., “nonsingers”). All subjects were nonsmokers and were right-handed. Half of the subjects in each group performed a controlled resting condition initially, while the other half received the resting condition as the last measurement. We counterbalanced the order of the three phonation tasks across the subjects within each group. For the contolled rest condition, which provided a baseline measurement of rCBF, each subject passively inhaled “‘Xe mixed with room air for 1 min. Then he was switched to room air and he continued passive breathing for the final 10 min of the measurement period. The experimental conditions called for each subject to recite, sing, and hum the national anthem. Subjects began each phonation task about 2 min before ‘33Xewas presented and continued phonation throughout the 1I-min measurement period. Immediately after each measurement, blood pressure was measured by auscultation. Subjects waited 20 min between conditions and usually completed an entire session within 2 hr. We monitored regional “‘Xe clearance with two collimated, scintillation-detector arrays. [Detailed information on the monitoring arrays can be found in Wilson, Wills, Risberg, Halsey, Gerard, & May (1977).] The arrays were positioned on opposite sides of the subject’s head in the manner shown in Fig. 1. We sampled simultaneously over time the concentrations of I’Xe in the respired air and from the separate regions for each cerebral
692
NOTE AND DISCUSSION NONSINGFRS
90 80 70 60 50 40 -
30
g
20
\ cn 0
‘0 0
’
80
z
70
--
60
-
50
A
s
c
D
E
G
H
A
n
c
D
E
c
H
40 30 20 IO c-l ”
FIG. 1. Left-hemisphere and right-hemisphere distributions of J at rest and for each phonation task as a function of detector for the nonsingers. Differences between f, values for the left hemisphere and the right hemisphere are shown at bottom for each task as a function of detector. hemisphere. The counts of radioactivity were digitized and used in a two-compartment model (Obrist, Thompson, King, & Wang, 1967) to estimate a rCBF. We consider only the blood flow parameter fi in this study. Parameter f, is a relative measure of gray matter flow which is expressed in milliliters/100 g/min. We used measures of analysis of variance to compare the mean f, data for global (whole-head) changes and for changes both within and across hemispheres, across subject groups and phonation tasks.
RESULTS
The mean regional distributions of fi at rest and for each task are shown as a function of detector in Figs. 1, 2, and 3 for the nonsingers, the choir members, and the vocalists, respectively. The bar data in the upper panel reflect left-hemisphere activity while the data in the middle panel represent activity for the right hemisphere. The mean regional distributions offi also are presented at the bottom of each figure in terms of left-hemisphere minus right-hemisphere differences for the tasks as a function of detector. The values in the three figures are similar across the three groups of subjects. Absolute values in the upper and middle panels decline systematically from anterior to posterior detectors. We
693
NOTE AND DISCUSSION CHOIR MEMBERS
EYlsRERE
A m
C
0 REST
a
D DETECTOR
TALK
E
Em SING
H
G m
HUM
FIG. 2. Regional hemispheric distributions and differences in f, for the choir members (as described in Fig. 1.).
measured the highest regional f, values from frontal detector, A. These values ranged from 87.7 to 74.3 across groups and tasks. The regional values measured with detector H, over the temporo-occipital area, were reduced the most; those values ranged from 67.0 to 56.8. These regional distributions off, are consistent with normal resting regional distributions reported previously in our laboratory (e.g., Risberg, Halsey, Wills, & Wilson, 1975; Halsey, Blauenstein, Wilson, & Wills, 1979; Leli, et al., 1984). The left-minus-right differences in the bottom panels of each figure were within 5 units for any detector and revealed no obvious hemisphere advantage. Percentage values are shown by bar data in Fig. 4 for each subject group as a function of phonation task. The values in the upper panel represent within-hemisphere changes. Left-hemisphere and right-hemisphere values are shown separately. We calculated these values by dividing each hemisphere mean f, for each phonation task by the corresponding hemisphere meanf, at rest. The values in the middle panel reflect betweenhemisphere changes infr. We obtained these results for each phonation task by subtracting the right-hemisphere value in the upper panel from
694
NOTE AND DISCUSSION VOCALISTS 90, LEFT l+XKISREKE
FIG. 3. Regional hemispheric distributions and differences in fi for the vocalists (as described in Fig. 1.).
the corresponding left-hemisphere value. Values in the bottom panel represent global changes in f, . We derived these values by dividing the global meanfi for each phonation task by the corresponding resting global meanf,. Across all three groups of subjects, the global changes as well as the within- and between-hemisphere variations in blood flow for the phonation tasks typically were within 5% of resting blood flow values. None of these changes were significant statistically. DISCUSSION
Popularly cited clinical studies, most notably the experiments at Montreal Neurological Institute (see Rasmussen & Milner, 1975) with electrical stimulation, cortical ablation techniques, and intracarotid injection of amytal, have provided compelling clinical evidence that speech is a function under the control of the left hemisphere. In contrast, production of song is suggested to be a function which is either lateralized to the right hemisphere or, at least more than for speech and language, depends on bilateral interaction between the two hemispheres (Gordon & Bogen, 1974).
Our symmetric blood flow findings do not confirm the clinical evidence
695
NOTE AND DISCUSSION WITHIN HEMISPHERE CHANGE r-e REST 6 TALK SING
HUN
3 ; a be
o
1
NS C ~’ NS C Y BETWEEN HEMISPHERE CHANGE re REST
NS
C
”
NS
C
”
Y
NS
C
”
GLOBAL CHANGE re REST SING
TALK
c
v
NS C V SUBJECT GROUP
HUM
NS
C
V
FIG. 4. Intrahemisphere, interhemisphere, and global changes in f, for each phonation task relative tof, at rest as a function of subject group (NS = nonsingers, C = choir, V = vocalists).
of left-hemisphere and right-hemisphere control for speech and song, respectively. Our data also do not reveal a difference in rCBF in terms of muscial training, which has been reported in at least one EEG study (Davidson & Schwartz, 1977). [In a related study, Schwartz, Davidson, Maer, & Bromfield (1974) also reported evidence of right-hemisphere dominance for whistling, left-hemisphere dominance for recitation, and bilateral representation for singing.] To our knowledge, no study of normal rCBF has corroborated leftto-right hemisphere control for production of speech and song. Ryding, Br%dvik, and Ingvar (1987) apparently provide the only other investigation of rCBF during production of speech and song in (arguably) normal individuals (i.e., patients who had suffered transient ischemic attacks but who exhibited no neurologic deficits and who had normal CT-scans). Ryding et al. measured rCBF with carotid injection of ‘33Xe during rest, simple recitation, and humming. The patients produced greater bilateral mean hemisphere blood flow during recitation than during humming. Notably, they measured increased rCBF in the right hemisphere relative to rCBF for the left hemisphere during recitation. Their finding is consistent
6%
NOTE AND DISCUSSION
with that of Larsen, Skinhoj, and Lassen (1978) who also documented greater relative right-hemisphere rCBF during automatic speech. Ryding et al. found that humming did not yield significant differences in rCBF between the two hemispheres. Although we also found symmetric rCBF during humming, we did not find, as Ryding et al. (1987) reported, slight but statistically significant increases in rCBF for the right hemisphere during simple recitation. [Our results, however, are consistent with a report of equivalent bilateral activity during automatic speech (Halsey, Blaustein, Wilson, & Wills, 1980).] We also did not measure increased global blood flow during recitation. The differences between the two studies presumably reflect the better resolution and sensitivity available to Ryding et al. with direct injection of 13’Xe and their monitoring by 30 detectors over each hemisphere. Also, we used the same passagefor speaking, singing, and humming, whereas Ryding et al. asked their subjects to hum a nursery rhyme and to recite the days of the week. We do not know the reason for our negative findings. One may argue that the sensitivity and resolution of our system, and to a lesser extent that used by Ryding et al. (1987), were too crude to reveal the cerebral asymmetries underlying production of speech and song. It is also arguable that our tasks and methodology hindered us from obtaining positive results. For such a familiar and overlearned song as the national anthem, the strategies and mechanics of the tasks required to produce the passage, with or without words, may not be sufficiently different (nor taxing) to evoke pronounced differences in rCBF within or between hemispheres. This notion follows in part from the finding (Formby et al., 1987)that our singers produced different breathing patterns from those of our nonsingers for all three phonation tasks, including talking. In contrast, other investigators (Allen & Wilder, 1977) have reported that trained singers and nonsingers may use different respiratory patterns during singing, but not during speaking. One interpretation of the singers’ breathing patterns is that they were unable to break completely from the song mode during the talking task (Formby et al., 1987). If this conclusion is correct, then our talking task may be viewed more accurately as an extreme condition along the musical continuum, and thus may be too far removed from conventional spontaneous speech to be considered a natural speaking condition. Variation in pC0, also may have been a confounding factor in this study. Although average pCOz values for our groups were typically within one unit of the commonly accepted standard value of 40 mm Hg, we did not evaluate individual changes in pCOz across tasks. We therefore cannot rule out the possibility that phonation, which may reduce endtidal pCOz, could, in some cases, have obscured rCBF differences among subjects and conditions.
NOTE AND DISCUSSION
697
We (Formby et al., 1987) did attempt to rule out possible confounding effects of phonation on the ‘33Xeair curves. Although continuous phonation probably did not appreciably affect the shapes of the ‘33Xe air curves used in estimating rCBF, we did not measure arterial concentrations of 133Xedirectly. Without this evidence, we cannot know unequivocally whether the arterial concentrations of 133Xeremained in equilibrium with the respired-air concentrations of ‘33Xe. However, whatever air-curve artifacts might have entered into the rCBF calculations should have been distributed symmetrically throughout the brain since the same error would have appeared in every calculation. Thus, the relative differences measured between homologous regions of the cerebral hemispheres still should have validity. CONCLUSIONS
Our symmetric rCBF data for normal subjects, like those of Ryding et al. (1987), do not support the left-to-right pattern of cerebral dominance for production of speech and song which is often described in clinical studies. It remains to be determined whether these negative findings for phonation reflect the limitations of our instrumentation and methodologies or the normal pattern of interaction between the cerebral hemispheres in the intact brain. REFERENCES Allen, E., & Wilder, C. 1977. Respiratory patterns in singers: A proposed research design. In V. Lawrence (Ed.), Transcripts of the sixth symposium on care of the professional voice. New York: The Voice Foundation. Pp. 18-20. Davidson, R. J., & Schwartz, G. 1977. The influence of muscial training on patterns of EEG asymmetry during muscial and nonmusical self-generation tasks. Psychophysio/ogy, 14, 58-63.
Formby, C., Thomas, R. G., Brown, W. S., Jr., & Halsey, J. H., Jr. 1987. The effects of continuous phonation on “‘Xenon-inhalation air curves (of the kind used in deriving regional cerebral blood flow). Brain and Language, 31, 346-363. Gordon, H. W., & Bogen, J. E. 1974.Hemispheric lateralization of singing after intracarotid and Psychiatry, 31, sodium amylobarbitone. Journal of Neurology, Neurosurgery, 727-738. Halsey, J. H., Jr., Blauenstein, U. W., Wilson, E. M., & Wills, E. W. 1979. Regional cerebral blood flow comparison of right and left hand movement. Neurology, 29, 2128. Halsey, J. H., Jr., Blauenstein, U. W., Wilson, E. M., & Wills, E. W. 1980.Brain activation in the presence of brain damage. Brain and Language, 9, 47-60. Larsen, B., Skinhoj, E., &. Lassen, N. A. 1978. Variations in regional cortical blood flow in the right and left hemispheres during automatic speech. Brain, 101, 193-209. Leli, D. A., Hannay, H. J., Falgout, J. C., Katholi, C. R., Wilson, E. M., Wills, E. L., & Halsey, J. H., Jr. 1984.Relevance of sensorimotor task components to the interpretation of task related blood flow changes. Neuropsychologia, 22, 79-84. Obrist, W. D., Thompson, H. K., Jr., King, C. H., & Wang, H. S. 1%7. Determination of regional cerebral blood flow by inhalation of 133-Xenon. Circu/ation Research, 20, 124-135.
698
NOTE AND DISCUSSION
Rasmussen, T., & Milner, B. 1975. Clinical and surgical studies of the cerebral speech areas in man. In K. J. Zulch, 0. Creutzfeldt, & G. C. Gailbraith (Eds.), Cerebral localization. New York: Springer-Verlag. Pp. 238-255. Risberg, J., Halsey, J. H., Jr., Wills, E. L., & Wilson, E. M. 1975.Hemispheric specialization in normal man studied by bilateral measurements of the regional cerebral blood flow. Brain, 98, 511-524. Ryding, E., Br&dvik, B., & Ingvar, D. H. 1987. Changes of regional cerebral blood flow measured simultaneously in the right and left hemisphere during automatic speech and humming. Brain, 110, 1345-1358. Schwartz, G. E., Davidson, R. J., Maer, F., & Bromfield, E. 1974. Patterns of hemispheric dominance in musical, emotional, verbal and spatial tasks. Psychophysiology, 4, 227. Wilson, E. M., Wills, E. L., Risberg, J., Halsey, J. H., Jr., Gerard, J. D., & May, C. P. 1977. Measurement of regional cerebral blood flow by the “‘Xenon-inhalation method with an on-line computer. Computers in Biology and Medicine, 7, 143-157.
36,
690-698 (1989)
NOTE AND DISCUSSION Regional Cerebral Blood Flow for Singers and Nonsingers while Speaking, Singing, and Humming a Rote Passage C. FORMBY’ Departments of Communicative Disorders and Neurology, University of Florida
R. G. THOMAS Department of Biometry, Emory University AND
J. H. HALSEY, JR. Department of Neurology, University of Alabama-Birmingham
(UAB)
Two groups of singers (n = 12,13) and a group of nonsingers (n = 12) each produced the national anthem by (1) speaking and (2) singing the words and by (3) humming the melody. Regional cerebral blood flow (rCBF) was measured at rest and during each phonation task from seven areas in each hemisphere by the “‘Xe-inhalation method. Intrahemisphere, interhemisphere, and global rCBF were generally similar across phonation tasks and did not yield appreciable differences among the nonsingers and the singers. o 1989 Academic Press, hc.
Audie White and Tina Davis collected these data. We thank Professor Andrew Gainey and Dr. Gene Black and their students for assistance in this study. We also thank our colleagues, Janet Falgout, Dano Leli, Ed Wills, and Judy Blumsack, for their comments, and Laura Ellsworth and Cindy Lynn for their help in preparing this manuscript. The National Institute of Neurological and Communicative Disorders and Stroke provided partial support of this research through Grant NS-08802 to UAB. All correspondence and requests for reprints should be addressed to C. Formby at Departments of Communicative Disorders and Neurology, Box J-174/JHMHC, University of Florida, Gainesville, FL 32610. ’ Data were collected while C. Formby was a postdoctoral fellow in the Department of Neurology, UAB. 690 0093-934X/89 $3.00 Copyright 0 1989 by Academic Press, Inc. AU rights of reproduction in any form reserved
NOTE AND DISCUSSION
691
INTRODUCTION In a previous report (Formby, Thomas, Brown, & Halsey, 1987) we considered whether continuous phonation confounded ‘33Xe respired air curves of the type used in mathematical models to estimate regional cerebral blood flow (rCBF). We concluded that although the inhalation and exhalation patterns for singers and nonsingers may differ, the average ‘33Xeair curve derived from end-tidal breathing did not differ appreciably across subjects nor across conditions of speaking, singing, and humming the national anthem. This was an important methodological issue because during passive breathing the respired air curve is known to mirror the concentration of radioactivity in the arterial blood. This information is used as an input function in the rCBF model. If the air curve were distorted by continuous phonation, then estimates of rCBF measured during these phonation tasks, or during any task of continuous phonation, would have questionable validity. After establishing that continuous talking, singing, and humming had not seriously confounded the respired air curves, we proceeded to analyze the companion rCBF data for these tasks. These are the data presented in this report. Our purpose was to compare rCBF from both hemispheres for rest and for speaking, singing, and humming of a rote passage among trained and untrained vocalists. METHOD A description of the subjects, along with the inhalation system and method, were described in an earlier report (Formby et al., 1987). To review briefly, healthy college-age men participated as members in one of three groups: 12 subjects were voice students, 13 subjects were college choir members, and 12 subjects had no formal musical training (i.e., “nonsingers”). All subjects were nonsmokers and were right-handed. Half of the subjects in each group performed a controlled resting condition initially, while the other half received the resting condition as the last measurement. We counterbalanced the order of the three phonation tasks across the subjects within each group. For the contolled rest condition, which provided a baseline measurement of rCBF, each subject passively inhaled “‘Xe mixed with room air for 1 min. Then he was switched to room air and he continued passive breathing for the final 10 min of the measurement period. The experimental conditions called for each subject to recite, sing, and hum the national anthem. Subjects began each phonation task about 2 min before ‘33Xewas presented and continued phonation throughout the 1I-min measurement period. Immediately after each measurement, blood pressure was measured by auscultation. Subjects waited 20 min between conditions and usually completed an entire session within 2 hr. We monitored regional “‘Xe clearance with two collimated, scintillation-detector arrays. [Detailed information on the monitoring arrays can be found in Wilson, Wills, Risberg, Halsey, Gerard, & May (1977).] The arrays were positioned on opposite sides of the subject’s head in the manner shown in Fig. 1. We sampled simultaneously over time the concentrations of I’Xe in the respired air and from the separate regions for each cerebral
692
NOTE AND DISCUSSION NONSINGFRS
90 80 70 60 50 40 -
30
g
20
\ cn 0
‘0 0
’
80
z
70
--
60
-
50
A
s
c
D
E
G
H
A
n
c
D
E
c
H
40 30 20 IO c-l ”
FIG. 1. Left-hemisphere and right-hemisphere distributions of J at rest and for each phonation task as a function of detector for the nonsingers. Differences between f, values for the left hemisphere and the right hemisphere are shown at bottom for each task as a function of detector. hemisphere. The counts of radioactivity were digitized and used in a two-compartment model (Obrist, Thompson, King, & Wang, 1967) to estimate a rCBF. We consider only the blood flow parameter fi in this study. Parameter f, is a relative measure of gray matter flow which is expressed in milliliters/100 g/min. We used measures of analysis of variance to compare the mean f, data for global (whole-head) changes and for changes both within and across hemispheres, across subject groups and phonation tasks.
RESULTS
The mean regional distributions of fi at rest and for each task are shown as a function of detector in Figs. 1, 2, and 3 for the nonsingers, the choir members, and the vocalists, respectively. The bar data in the upper panel reflect left-hemisphere activity while the data in the middle panel represent activity for the right hemisphere. The mean regional distributions offi also are presented at the bottom of each figure in terms of left-hemisphere minus right-hemisphere differences for the tasks as a function of detector. The values in the three figures are similar across the three groups of subjects. Absolute values in the upper and middle panels decline systematically from anterior to posterior detectors. We
693
NOTE AND DISCUSSION CHOIR MEMBERS
EYlsRERE
A m
C
0 REST
a
D DETECTOR
TALK
E
Em SING
H
G m
HUM
FIG. 2. Regional hemispheric distributions and differences in f, for the choir members (as described in Fig. 1.).
measured the highest regional f, values from frontal detector, A. These values ranged from 87.7 to 74.3 across groups and tasks. The regional values measured with detector H, over the temporo-occipital area, were reduced the most; those values ranged from 67.0 to 56.8. These regional distributions off, are consistent with normal resting regional distributions reported previously in our laboratory (e.g., Risberg, Halsey, Wills, & Wilson, 1975; Halsey, Blauenstein, Wilson, & Wills, 1979; Leli, et al., 1984). The left-minus-right differences in the bottom panels of each figure were within 5 units for any detector and revealed no obvious hemisphere advantage. Percentage values are shown by bar data in Fig. 4 for each subject group as a function of phonation task. The values in the upper panel represent within-hemisphere changes. Left-hemisphere and right-hemisphere values are shown separately. We calculated these values by dividing each hemisphere mean f, for each phonation task by the corresponding hemisphere meanf, at rest. The values in the middle panel reflect betweenhemisphere changes infr. We obtained these results for each phonation task by subtracting the right-hemisphere value in the upper panel from
694
NOTE AND DISCUSSION VOCALISTS 90, LEFT l+XKISREKE
FIG. 3. Regional hemispheric distributions and differences in fi for the vocalists (as described in Fig. 1.).
the corresponding left-hemisphere value. Values in the bottom panel represent global changes in f, . We derived these values by dividing the global meanfi for each phonation task by the corresponding resting global meanf,. Across all three groups of subjects, the global changes as well as the within- and between-hemisphere variations in blood flow for the phonation tasks typically were within 5% of resting blood flow values. None of these changes were significant statistically. DISCUSSION
Popularly cited clinical studies, most notably the experiments at Montreal Neurological Institute (see Rasmussen & Milner, 1975) with electrical stimulation, cortical ablation techniques, and intracarotid injection of amytal, have provided compelling clinical evidence that speech is a function under the control of the left hemisphere. In contrast, production of song is suggested to be a function which is either lateralized to the right hemisphere or, at least more than for speech and language, depends on bilateral interaction between the two hemispheres (Gordon & Bogen, 1974).
Our symmetric blood flow findings do not confirm the clinical evidence
695
NOTE AND DISCUSSION WITHIN HEMISPHERE CHANGE r-e REST 6 TALK SING
HUN
3 ; a be
o
1
NS C ~’ NS C Y BETWEEN HEMISPHERE CHANGE re REST
NS
C
”
NS
C
”
Y
NS
C
”
GLOBAL CHANGE re REST SING
TALK
c
v
NS C V SUBJECT GROUP
HUM
NS
C
V
FIG. 4. Intrahemisphere, interhemisphere, and global changes in f, for each phonation task relative tof, at rest as a function of subject group (NS = nonsingers, C = choir, V = vocalists).
of left-hemisphere and right-hemisphere control for speech and song, respectively. Our data also do not reveal a difference in rCBF in terms of muscial training, which has been reported in at least one EEG study (Davidson & Schwartz, 1977). [In a related study, Schwartz, Davidson, Maer, & Bromfield (1974) also reported evidence of right-hemisphere dominance for whistling, left-hemisphere dominance for recitation, and bilateral representation for singing.] To our knowledge, no study of normal rCBF has corroborated leftto-right hemisphere control for production of speech and song. Ryding, Br%dvik, and Ingvar (1987) apparently provide the only other investigation of rCBF during production of speech and song in (arguably) normal individuals (i.e., patients who had suffered transient ischemic attacks but who exhibited no neurologic deficits and who had normal CT-scans). Ryding et al. measured rCBF with carotid injection of ‘33Xe during rest, simple recitation, and humming. The patients produced greater bilateral mean hemisphere blood flow during recitation than during humming. Notably, they measured increased rCBF in the right hemisphere relative to rCBF for the left hemisphere during recitation. Their finding is consistent
6%
NOTE AND DISCUSSION
with that of Larsen, Skinhoj, and Lassen (1978) who also documented greater relative right-hemisphere rCBF during automatic speech. Ryding et al. found that humming did not yield significant differences in rCBF between the two hemispheres. Although we also found symmetric rCBF during humming, we did not find, as Ryding et al. (1987) reported, slight but statistically significant increases in rCBF for the right hemisphere during simple recitation. [Our results, however, are consistent with a report of equivalent bilateral activity during automatic speech (Halsey, Blaustein, Wilson, & Wills, 1980).] We also did not measure increased global blood flow during recitation. The differences between the two studies presumably reflect the better resolution and sensitivity available to Ryding et al. with direct injection of 13’Xe and their monitoring by 30 detectors over each hemisphere. Also, we used the same passagefor speaking, singing, and humming, whereas Ryding et al. asked their subjects to hum a nursery rhyme and to recite the days of the week. We do not know the reason for our negative findings. One may argue that the sensitivity and resolution of our system, and to a lesser extent that used by Ryding et al. (1987), were too crude to reveal the cerebral asymmetries underlying production of speech and song. It is also arguable that our tasks and methodology hindered us from obtaining positive results. For such a familiar and overlearned song as the national anthem, the strategies and mechanics of the tasks required to produce the passage, with or without words, may not be sufficiently different (nor taxing) to evoke pronounced differences in rCBF within or between hemispheres. This notion follows in part from the finding (Formby et al., 1987)that our singers produced different breathing patterns from those of our nonsingers for all three phonation tasks, including talking. In contrast, other investigators (Allen & Wilder, 1977) have reported that trained singers and nonsingers may use different respiratory patterns during singing, but not during speaking. One interpretation of the singers’ breathing patterns is that they were unable to break completely from the song mode during the talking task (Formby et al., 1987). If this conclusion is correct, then our talking task may be viewed more accurately as an extreme condition along the musical continuum, and thus may be too far removed from conventional spontaneous speech to be considered a natural speaking condition. Variation in pC0, also may have been a confounding factor in this study. Although average pCOz values for our groups were typically within one unit of the commonly accepted standard value of 40 mm Hg, we did not evaluate individual changes in pCOz across tasks. We therefore cannot rule out the possibility that phonation, which may reduce endtidal pCOz, could, in some cases, have obscured rCBF differences among subjects and conditions.
NOTE AND DISCUSSION
697
We (Formby et al., 1987) did attempt to rule out possible confounding effects of phonation on the ‘33Xeair curves. Although continuous phonation probably did not appreciably affect the shapes of the ‘33Xe air curves used in estimating rCBF, we did not measure arterial concentrations of 133Xedirectly. Without this evidence, we cannot know unequivocally whether the arterial concentrations of 133Xeremained in equilibrium with the respired-air concentrations of ‘33Xe. However, whatever air-curve artifacts might have entered into the rCBF calculations should have been distributed symmetrically throughout the brain since the same error would have appeared in every calculation. Thus, the relative differences measured between homologous regions of the cerebral hemispheres still should have validity. CONCLUSIONS
Our symmetric rCBF data for normal subjects, like those of Ryding et al. (1987), do not support the left-to-right pattern of cerebral dominance for production of speech and song which is often described in clinical studies. It remains to be determined whether these negative findings for phonation reflect the limitations of our instrumentation and methodologies or the normal pattern of interaction between the cerebral hemispheres in the intact brain. REFERENCES Allen, E., & Wilder, C. 1977. Respiratory patterns in singers: A proposed research design. In V. Lawrence (Ed.), Transcripts of the sixth symposium on care of the professional voice. New York: The Voice Foundation. Pp. 18-20. Davidson, R. J., & Schwartz, G. 1977. The influence of muscial training on patterns of EEG asymmetry during muscial and nonmusical self-generation tasks. Psychophysio/ogy, 14, 58-63.
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