ning cerebral SGsa J, Silfvenius H, Christianson S-A. Visual half-field testing for defining cerebral hemisphere speech laterality. Acta Neurol Scand 1990: 82: 346-349.
The purpose of this study was to investigate to what extent the noninvasive visual half-field (VHF)test can reliably determine cerebral speech dominance for the individual patient with partial epilepsy considered for surgical treatment. The present VHF test consisted of a list of 36 words presented correctly and mirrored in the lateral visual fields to 13 right-handed and 14 left-handed control subjects and to 14 right-handed and 2 left-handed patients with partial epilepsy. In the controls, it was found that all righthanded and 10 out of 14 left-handed control subjects showed a right VHF (i.e., left hemisphere) advantage. Three of the left-handed control subjects showed the opposite pattern, and one showed no visual field advantage. All of the right-handed patients showed a right VHF advantage, except one who showed no VHF advantage. The two left-handed patients had both a left VHF advantage. Intracarotid amytal speech testing documented left hemisphere speech dominance in all right-handed patients. Of the two left-handed patients, one had right-sided, the other bilateral speech representation.The results suggest that the present VHF test reliably predicts cerebral hemisphere speech in patients with epilepsy.
The aim of the present study was to improve the sensitivity of the non-invasive visual half-field (VHF) test in evaluating cerebral hemisphere dominance for speech in normal controls and in patients considered for surgical treatment of drug resistant partial epilepsy. It is a well known fact that one of the cerebral hemispheres, in most persons the left hemisphere, harbours the speech functions. Currently, the intracarotid sodium amytal technique introduced by Wada (1) is the most conclusive method for determining hemisphere dominance for speech and also to predict postoperative language and memory outcome. With this technique, one hemisphere is anesthetized for 4-5 min by an injection of sodium amytal into the internal carotid artery and the speech and language capabilities of the non-injected hemisphere are evaluated, normally hemispheric memory functions are tested as well (2-6). Recently, intracranial, selective arterial injection of sodium amytal has been described to study regonal cortical sedation effects on speech and memory (7). Although the intracarotid sodium amytal test has proven itself a safe and valid method, it involves some difficulties. There is some distress for the patient during the catheterization, and the method also carries potential risks of neurological complications. Current non-invasive lateralization tests for determining hemisphere speech dominance are the VHF 346
’,
J. Sziisl H. Silfvenius*, S.-A. Christianson
’
’
Departments of Psychology, Neurosurgery, University of Umeh and University Hospital, Umeh, Sweden
Key words: epilepsy; hemisphere speech; visual half-field test; amytal test Jouko Stiisti, Department of Psychology, University of Umeh, Rhdhusesplanaden2, S-902 47 Urneh, Sweden Accepted for publication June 14, 1990
technique and the dichotic listening techniques. The logc behind these techniques is essentially that the input (visual/auditory) from the left visual field or the left ear is projected to the right hemisphere, and vice versa. Although a considerable amount of research has been done (8, 9), there is, as yet, no generally available and reliable, non-invasive method for assessing hemispheric speech capabilities for a specific individual. For example most of the previous studies in this area of research have used the same presentation and response conditions for all subjec t s, without adjusting for individual differences. The VHF technique has been used to study the functional asymmetry of the hemispheres in different fields of research, including studies on patients with neurological diseases, e.g., epilepsy and the effect of surgical treatment (10, ll), and on normal subjects (12). Essentially, research utilizing this technique has reported a right visual-field (RVF) advantage for both unilaterally and bilaterally presented words (8). Commonly, the RVF advantage is stronger with bilateral word presentation (13). It is possible that bilateral presentation constitutes a competing situation for the brain and that this extra ‘load’ on the cognitive system creates a situation which makes individual assessment of hemisphere dominance for language more differentiating. To test whether a modified VHF word presentation test could improve the sensitivity of the VHF
VHF & CH speech laterality technique, we performed a study carried out on 27 control subjects and on 16 patients with severe partial epilepsy. In this study the results of the VHF tests on the patients were validated against the findings of the intracarotid sodium amytal test regarding cerebral hemisphere speech dominance. Material and methods
Twenty-seven normal subjects, (14 women, 13 men, age 21-57; mean 29 years) and 16 patients (10 women, 6 men, age 17-60; mean 28 years) with severe partial epilepsy participated in the study, 11 had left temporal lesion (LT), 5 had right temporal lesion (RT). The age at epilepsy onset varied between 0.5-45 years, mean 10 years. Thirteen of the control subjects were right-handed, and 14 were left-handed. In the patient group, 14 were right-handed and 2 were left-handed. A list of 36 pairs of three-letter common, concrete Swedish words were shown to the patients and control subjects, one word in each lateral VHF. The word pairs were either shown mirror imaged or correctly lined depending on the appropriate degree of difficulty for each subject (see below). The stimulus quality (correctly shown or mirrored) was always the same in both VHFs. The presentation was effected by means of a projection unit and an eye-movement detector. The presentation device has been described in detail elsewhere and only a condensed description is presented here (14). The projection unit was composed of a wide-angle slide projector with an electronic shutter. The screen was vertically divided into two equal half fields. A permanently illuminated red light emitting diode (i.e. the fixation point) was located at the center of the screen (5 mm in size). The words were projected on the screen 3 ' 4 " to the right, and to the left of the fixation point. Eye movements were detected using an ocular limbus tracking technique. The right eye of the subject was illuminated with infra-red (IR) light, and IR-sensitive detectors in an adjustable stand 12 mm in front of and just below the eye were used to measure the reflected IR light from the limbus area. A control board containing electronic circuitry for stimulus presentation, received an eye movement logical signal, and a stimulus onset signal. Each VHF presentation was initiated by the experimenter by forwarding a stimulus slide. However, the stimulus could not be presented unless the eyes of the subject were centered on the fixation point, and therefore exclude false presentations. The subject was seated 1 m in front of the projection screen. A chin and a forehead rest were used to prevent head movements. To calibrate the eye movement detector, the subject was asked to look at the fixation point and then at four other, temporarily illuminated diodes 3 and 8
degrees horizontal to the right and left of the fixation point. Before the presentation of the word pair the subject was instructed to immediately name the flashed words he/she had seen. Each trial began when the experimenter pressed a button to start the presentation of the stimuli. When the subject looked steadily on the fixation point, the shutter opened and exposed the slide. After the subject had responded to the stimuli, the experimenter advanced the slide tray and presented the next word pair. In the adaptional VHF testing procedure used in this study the presentation time (20, 50, 100, or 150 msec) and the rotation of the words (correctly shown or mirrored) was varied for each subject. For example, one person might have been unable to read any of the words when they were mirrored and presented during 20ms and would therefore not produce a VHF advantage, because the task is too difficult. If the words are presented correctly for 50 ms, the same subject may respond correctly for all words and therefore not produce a VHF advantage, because the task is too easy. But when shown mirrored words for 150 ms the subject may produce a VHF advantage. Before the actual 36 pairs of test items were presented, between 8-15 pretrial items were shown in the adaptional procedure to find out for each individual the appropriate degree of difficulty. We began with the most difficult condition and then successively made the task easier by lengthening the presentation time and if necessary, showing the words correctly lined. After the level of difficulty was determined the actual test started. The experimenter recorded the words the subject recognized and named, and in which visual field they had been presented. Results
Thirteen of the 16 patients with intractable partial epilepsy were right-handed, all showing a right VHF advantage. One (SA) showed no VHF advantage. This was due to his low performance in the task. Two patients were left-handed and both showed a left VHF advantage. The differences between the visual fields are presented in Table 1. The VHF advantage was assumed to reflect the superiority of the speech dominant hemisphere (15), i.e. right VHF advantage indicates left hemisphere speech dominance and left VHF advantage indicates right hemisphere speech dominance. Predictions were made about hemispheric speech representation based on the differences of the VHFs for 15 of the 16 patients. For the 16th patient (SA) no prediction was possible because of his low performance in the task. The predictions based on the VHF-test were compared with the results of the intracarotid sodium 341
Saisa et al. Table 1. Proportion correct responses from recognizing and naming words in the left and right VHF for each patient. Location of lesion is given, LT= Left Temporal, RT = Right Temporal Patient
Locationof lesion
RVF
LVF
Difference
LT LT RT LT RT LT LT LT LT LT RT LT RT LT LT RT
0.72 0.67 0.44 0.69 0.53 0.28 0.3 1 0.31 0.75 0.78 0.25 0.61 0.53 0.39 0.03 0.03
0.17 0.03 0.22 0.03 0.11 0.17 0.06 0.00 0.00 0.14 0.08 0.06 0.03 0.78 0.25 0.03
0.55 0.64 0.22 0.66 0.42 0.1 1 0.25 0.3 1 0.75 0.64 0.17 0.55 0.50 0.39 0.22 0.00
LK HJ MK UM KA A0
8
SF UJ FO MN MJ At AW SA
amytal speech test (Table2) (see 3 for the amytal testing procedure). For the first 14 patients the sodium amytal test confirmed the predictions based on the VHF results. The 15th patient (AW) was predicted to have a right hemisphere speech representation. The sodium amytal test result showed a bilateral speech representation. However, a later inspection of the amytal test protocol indicated that the right hemisphere harboured more speech capacity than the left one, because more language errors occurred after the right sided sodium amytal injection. The results of the 13 right-handed control subjects showed that they all had a right VHF advantage, Table 2. Cerebral hemispherespeech laterality based on VHF and sodium amytal tests. Speech-dominant hemisphere is indicated. Location of lesion is given, LT = Left Temporal, RT = Right Temporal Patient LK HJ MK UM KA A0 AE KA SF UJ
FO MN MJ AL AW SA
348
Locationof lesion
Handedness
VHF results
Amytal results
LT LT RT LT RT LT LT IT LT LT RT LT RT LT LT RT
Risht Riiht Right Right Right Right Right Right Right Right Right Right Right Left Left Right
Left Left Left Left Left Left Left Left Left Left Left Left Left Right Right No prediction was made
Left Left Left Left Left Left Left Left Left Left Left Left Left Right Bilateral. Rt > Lt Left
mean right VHF was 0.57, mean left VHF was 0.08. Ten of the 14 left-handed subjects also showed a right VHF advantage, mean right VHF was 0.51, mean left VHF was 0.16. Three of the left-handed subjects had a left VHF advantage, mean right VHF was 0.05, mean left VHF was 0.46, and one showed no VHF advantage, 0.33 in both VHFs. Discussion
The results of the present VHF test are encouraging. They show that the predictions were correct, as checked with the intracarotid sodium amytal test, for 14patients of 15. In the case of the invalid prediction, a plausible explanation was found. It was interpreted that his right hemisphere harboured more speech functions than his left hemisphere. The results of the right- and left-handed control subjects are approximately in accordance with the literature of handedness and cerebral speech dominance (16). However, more testing with this technique on lefthanders and ambidextrous are needed. No left VHF advantage was found in the right-handed control group; in the left-handed group, three such cases were found. Also a case of equally many detections from both VHFs was found in the left-handed group. One problem with the present VHF test is that it does not identify persons with bilateral speech representation. For example, in cases without VHF advantage, like the left-handed control subject, one cannot be sure if the appropriate level of difficulty has been applied to produce a laterality effect or if the person in fact has bilateral speech representation. For the patient (SA) who showed no VHF advantage it is clear that the appropriate level of difficulty was not found. The task was too difficult for him even in the easiest condition. This problem, however, might be possible to solve if we use easier or more difficult stimuli, for example, two- or five-letter words. To decide whether a patient has left or right or cerebral hemisphere speech representation on the basis of these data, is evident in most patients. Only two patients showed a difference, less than 0.20, between the dominant- and non-dominant hemisphere (the greatest differencewas 0.75). It is tempting to speculate on the variance in difference in VHF scoring. It could be argued that a high difference indicates a well lateralized speech capacity while those with a minor difference could harbour some speech capacity in either hemisphere. One also has to take into consideration what criteria should be applied (i.e. what is the smallest difference between VHFs to predict speech representation) when deciding if the results reflects a bilateral speech representation or a unilateral speech representation. This has to be worked out in relation to the results of the sodium amytal test.
VHF & CH speech laterality The results of the present study are interesting and could stimulate surgical epilepsy centers to create an empirical basis for substitution of the sodium amytal test by a non-invasive technique concerning language functions. However, even if a non-invasive technique in which both hemispheres are active would assess language dominance as well as the sodium amytal test, it would not be sufficient to replace it because of reasons of memory testing. It should be noted however, that such non-invasive techniques are under development (17, 18). Hopefully future research will provide valid non-invasive methods that will predict both postoperative language and postoperative memory functions. Acknowledgements This research was supported by Grant, 84/253 : 2 from the Bank of Sweden Tercentenary Foundation, and by a Grant from the Medical Faculty at University of Umel.
References I . WADA,J. A new method for the determination of the side of speech dominance. A preliminary report on the intracarotid injection of sodium amytal in man. Med Biol 1949: 14: 221-222 (in Japanese). 2. MILNERB, BRANCHC, RASMUSSEN T. Study of short-term memory after hemisphere intracarotid injection of sodium amytal. Trans Am Neurol Assoc 1962: 87: 224-226. 3. CHRISTIANSON S-A, SAISAJ, SILFVENIUS H. Hemispheres memory differences in sodium amytal testing of epileptic patients. Clin Exp Neuropsychol (in press). 4. CHRISTIANSON S-A, SILFVENIUS H, NILSSONL-G. Hemisphere memory of concrete and abstract information determined with the intracarotid sodium amytal test. Epilepsy Res 1987: 1: 185-193. 5. RAUSCHR. The neuropsychological evaluation. In: ENGEL Jr J, ed. Surgical treatment of the epilepsies. New York: Raven Press, 1987: 181-195. 6. RAUSCHR, RISINGER M. Intracarotid sodium amobarbital
technique. In: BOULTON et al., eds. Neuromethods. Humana Press (in press). 7. JACKCR, NICHOLSDA, SHARBROUGH FW, et al. Selective posterior cerebral artery amytal test for evaluating memory function before surgery for temporal lobe seizure. Radiology 1988: 168: 787-793. 8. BEAMOUNT JG. Divided visual field studies of cerebral organization. London: Academic Press, 1982. 9. GEFFENG, QUINNK. Hemispheric specialization and ear advantages in processing speech. Psychol Bull 1984: 96: 273-291. 10. SPERRYRW. Lateral specialization in the surgically separated hemisphere. In: SCHMITTFO, WORDENFG, eds. The neurosciences: third study program. Cambridge, MA: MIT Press, 1974. 11. NEBESRD. Direct examination of cognitive function in the right and left hemispheres. In: KINSBOURNE M, ed. Assymetrical function of the brain. New York: Cambridge University Press, 1978. 12. SPRINGERSP. Tachitoscopic and dichotic listening investigation of laterality in normal human subjects. In: HARNARD S et al., eds. Lateralization in the nervous system. New York: Academic Press, 1977. 13. MCKEEVERWF. Lateral word recognition: effects of unilateral and bilateral presentation, asynchrony of bilateral presentation and forced order of report. Q J Exp Psychol 1971: 23: 410-416. 14. LINDAHL0, BACKLUND T, CHRISTIANSON S-A, NILSSON L-G, SILFVENIUS H. An optical eye movement detector for visual half-filed studies of hemisphere memory. J Med Eng Techno1 1988: 12: 106-111. 15. STRAWSE, WADAJ, KOSAKAB. Visual laterality effects and cerebral speech dominance determined by the carotid amytal test. Neuropsychologia 1985: 23: 567-570. 16. MILNERB. Hemispheric specialization: scope and limits. In: SCHMITTFO, WORDENFG, eds. The neurosciences: third study program. Cambridge, MA: MIT Press, 1974. 17. CHRISTIANSON S-A, NILSSON L-G, SILFVENIUS H. Pre- and postoperative memory of dichotically presented words in patients with complex partial seizures. Neuropsychologia 1989: 27: 427-436. 18. NILSSONL-G. Methodological and theoretical considerations as a basis for an integration of research on memory functions in epileptic patients. Acta Neurol Scand 1980: 62 (SUPPI80): 62-74.
349
The purpose of this study was to investigate to what extent the noninvasive visual half-field (VHF)test can reliably determine cerebral speech dominance for the individual patient with partial epilepsy considered for surgical treatment. The present VHF test consisted of a list of 36 words presented correctly and mirrored in the lateral visual fields to 13 right-handed and 14 left-handed control subjects and to 14 right-handed and 2 left-handed patients with partial epilepsy. In the controls, it was found that all righthanded and 10 out of 14 left-handed control subjects showed a right VHF (i.e., left hemisphere) advantage. Three of the left-handed control subjects showed the opposite pattern, and one showed no visual field advantage. All of the right-handed patients showed a right VHF advantage, except one who showed no VHF advantage. The two left-handed patients had both a left VHF advantage. Intracarotid amytal speech testing documented left hemisphere speech dominance in all right-handed patients. Of the two left-handed patients, one had right-sided, the other bilateral speech representation.The results suggest that the present VHF test reliably predicts cerebral hemisphere speech in patients with epilepsy.
The aim of the present study was to improve the sensitivity of the non-invasive visual half-field (VHF) test in evaluating cerebral hemisphere dominance for speech in normal controls and in patients considered for surgical treatment of drug resistant partial epilepsy. It is a well known fact that one of the cerebral hemispheres, in most persons the left hemisphere, harbours the speech functions. Currently, the intracarotid sodium amytal technique introduced by Wada (1) is the most conclusive method for determining hemisphere dominance for speech and also to predict postoperative language and memory outcome. With this technique, one hemisphere is anesthetized for 4-5 min by an injection of sodium amytal into the internal carotid artery and the speech and language capabilities of the non-injected hemisphere are evaluated, normally hemispheric memory functions are tested as well (2-6). Recently, intracranial, selective arterial injection of sodium amytal has been described to study regonal cortical sedation effects on speech and memory (7). Although the intracarotid sodium amytal test has proven itself a safe and valid method, it involves some difficulties. There is some distress for the patient during the catheterization, and the method also carries potential risks of neurological complications. Current non-invasive lateralization tests for determining hemisphere speech dominance are the VHF 346
’,
J. Sziisl H. Silfvenius*, S.-A. Christianson
’
’
Departments of Psychology, Neurosurgery, University of Umeh and University Hospital, Umeh, Sweden
Key words: epilepsy; hemisphere speech; visual half-field test; amytal test Jouko Stiisti, Department of Psychology, University of Umeh, Rhdhusesplanaden2, S-902 47 Urneh, Sweden Accepted for publication June 14, 1990
technique and the dichotic listening techniques. The logc behind these techniques is essentially that the input (visual/auditory) from the left visual field or the left ear is projected to the right hemisphere, and vice versa. Although a considerable amount of research has been done (8, 9), there is, as yet, no generally available and reliable, non-invasive method for assessing hemispheric speech capabilities for a specific individual. For example most of the previous studies in this area of research have used the same presentation and response conditions for all subjec t s, without adjusting for individual differences. The VHF technique has been used to study the functional asymmetry of the hemispheres in different fields of research, including studies on patients with neurological diseases, e.g., epilepsy and the effect of surgical treatment (10, ll), and on normal subjects (12). Essentially, research utilizing this technique has reported a right visual-field (RVF) advantage for both unilaterally and bilaterally presented words (8). Commonly, the RVF advantage is stronger with bilateral word presentation (13). It is possible that bilateral presentation constitutes a competing situation for the brain and that this extra ‘load’ on the cognitive system creates a situation which makes individual assessment of hemisphere dominance for language more differentiating. To test whether a modified VHF word presentation test could improve the sensitivity of the VHF
VHF & CH speech laterality technique, we performed a study carried out on 27 control subjects and on 16 patients with severe partial epilepsy. In this study the results of the VHF tests on the patients were validated against the findings of the intracarotid sodium amytal test regarding cerebral hemisphere speech dominance. Material and methods
Twenty-seven normal subjects, (14 women, 13 men, age 21-57; mean 29 years) and 16 patients (10 women, 6 men, age 17-60; mean 28 years) with severe partial epilepsy participated in the study, 11 had left temporal lesion (LT), 5 had right temporal lesion (RT). The age at epilepsy onset varied between 0.5-45 years, mean 10 years. Thirteen of the control subjects were right-handed, and 14 were left-handed. In the patient group, 14 were right-handed and 2 were left-handed. A list of 36 pairs of three-letter common, concrete Swedish words were shown to the patients and control subjects, one word in each lateral VHF. The word pairs were either shown mirror imaged or correctly lined depending on the appropriate degree of difficulty for each subject (see below). The stimulus quality (correctly shown or mirrored) was always the same in both VHFs. The presentation was effected by means of a projection unit and an eye-movement detector. The presentation device has been described in detail elsewhere and only a condensed description is presented here (14). The projection unit was composed of a wide-angle slide projector with an electronic shutter. The screen was vertically divided into two equal half fields. A permanently illuminated red light emitting diode (i.e. the fixation point) was located at the center of the screen (5 mm in size). The words were projected on the screen 3 ' 4 " to the right, and to the left of the fixation point. Eye movements were detected using an ocular limbus tracking technique. The right eye of the subject was illuminated with infra-red (IR) light, and IR-sensitive detectors in an adjustable stand 12 mm in front of and just below the eye were used to measure the reflected IR light from the limbus area. A control board containing electronic circuitry for stimulus presentation, received an eye movement logical signal, and a stimulus onset signal. Each VHF presentation was initiated by the experimenter by forwarding a stimulus slide. However, the stimulus could not be presented unless the eyes of the subject were centered on the fixation point, and therefore exclude false presentations. The subject was seated 1 m in front of the projection screen. A chin and a forehead rest were used to prevent head movements. To calibrate the eye movement detector, the subject was asked to look at the fixation point and then at four other, temporarily illuminated diodes 3 and 8
degrees horizontal to the right and left of the fixation point. Before the presentation of the word pair the subject was instructed to immediately name the flashed words he/she had seen. Each trial began when the experimenter pressed a button to start the presentation of the stimuli. When the subject looked steadily on the fixation point, the shutter opened and exposed the slide. After the subject had responded to the stimuli, the experimenter advanced the slide tray and presented the next word pair. In the adaptional VHF testing procedure used in this study the presentation time (20, 50, 100, or 150 msec) and the rotation of the words (correctly shown or mirrored) was varied for each subject. For example, one person might have been unable to read any of the words when they were mirrored and presented during 20ms and would therefore not produce a VHF advantage, because the task is too difficult. If the words are presented correctly for 50 ms, the same subject may respond correctly for all words and therefore not produce a VHF advantage, because the task is too easy. But when shown mirrored words for 150 ms the subject may produce a VHF advantage. Before the actual 36 pairs of test items were presented, between 8-15 pretrial items were shown in the adaptional procedure to find out for each individual the appropriate degree of difficulty. We began with the most difficult condition and then successively made the task easier by lengthening the presentation time and if necessary, showing the words correctly lined. After the level of difficulty was determined the actual test started. The experimenter recorded the words the subject recognized and named, and in which visual field they had been presented. Results
Thirteen of the 16 patients with intractable partial epilepsy were right-handed, all showing a right VHF advantage. One (SA) showed no VHF advantage. This was due to his low performance in the task. Two patients were left-handed and both showed a left VHF advantage. The differences between the visual fields are presented in Table 1. The VHF advantage was assumed to reflect the superiority of the speech dominant hemisphere (15), i.e. right VHF advantage indicates left hemisphere speech dominance and left VHF advantage indicates right hemisphere speech dominance. Predictions were made about hemispheric speech representation based on the differences of the VHFs for 15 of the 16 patients. For the 16th patient (SA) no prediction was possible because of his low performance in the task. The predictions based on the VHF-test were compared with the results of the intracarotid sodium 341
Saisa et al. Table 1. Proportion correct responses from recognizing and naming words in the left and right VHF for each patient. Location of lesion is given, LT= Left Temporal, RT = Right Temporal Patient
Locationof lesion
RVF
LVF
Difference
LT LT RT LT RT LT LT LT LT LT RT LT RT LT LT RT
0.72 0.67 0.44 0.69 0.53 0.28 0.3 1 0.31 0.75 0.78 0.25 0.61 0.53 0.39 0.03 0.03
0.17 0.03 0.22 0.03 0.11 0.17 0.06 0.00 0.00 0.14 0.08 0.06 0.03 0.78 0.25 0.03
0.55 0.64 0.22 0.66 0.42 0.1 1 0.25 0.3 1 0.75 0.64 0.17 0.55 0.50 0.39 0.22 0.00
LK HJ MK UM KA A0
8
SF UJ FO MN MJ At AW SA
amytal speech test (Table2) (see 3 for the amytal testing procedure). For the first 14 patients the sodium amytal test confirmed the predictions based on the VHF results. The 15th patient (AW) was predicted to have a right hemisphere speech representation. The sodium amytal test result showed a bilateral speech representation. However, a later inspection of the amytal test protocol indicated that the right hemisphere harboured more speech capacity than the left one, because more language errors occurred after the right sided sodium amytal injection. The results of the 13 right-handed control subjects showed that they all had a right VHF advantage, Table 2. Cerebral hemispherespeech laterality based on VHF and sodium amytal tests. Speech-dominant hemisphere is indicated. Location of lesion is given, LT = Left Temporal, RT = Right Temporal Patient LK HJ MK UM KA A0 AE KA SF UJ
FO MN MJ AL AW SA
348
Locationof lesion
Handedness
VHF results
Amytal results
LT LT RT LT RT LT LT IT LT LT RT LT RT LT LT RT
Risht Riiht Right Right Right Right Right Right Right Right Right Right Right Left Left Right
Left Left Left Left Left Left Left Left Left Left Left Left Left Right Right No prediction was made
Left Left Left Left Left Left Left Left Left Left Left Left Left Right Bilateral. Rt > Lt Left
mean right VHF was 0.57, mean left VHF was 0.08. Ten of the 14 left-handed subjects also showed a right VHF advantage, mean right VHF was 0.51, mean left VHF was 0.16. Three of the left-handed subjects had a left VHF advantage, mean right VHF was 0.05, mean left VHF was 0.46, and one showed no VHF advantage, 0.33 in both VHFs. Discussion
The results of the present VHF test are encouraging. They show that the predictions were correct, as checked with the intracarotid sodium amytal test, for 14patients of 15. In the case of the invalid prediction, a plausible explanation was found. It was interpreted that his right hemisphere harboured more speech functions than his left hemisphere. The results of the right- and left-handed control subjects are approximately in accordance with the literature of handedness and cerebral speech dominance (16). However, more testing with this technique on lefthanders and ambidextrous are needed. No left VHF advantage was found in the right-handed control group; in the left-handed group, three such cases were found. Also a case of equally many detections from both VHFs was found in the left-handed group. One problem with the present VHF test is that it does not identify persons with bilateral speech representation. For example, in cases without VHF advantage, like the left-handed control subject, one cannot be sure if the appropriate level of difficulty has been applied to produce a laterality effect or if the person in fact has bilateral speech representation. For the patient (SA) who showed no VHF advantage it is clear that the appropriate level of difficulty was not found. The task was too difficult for him even in the easiest condition. This problem, however, might be possible to solve if we use easier or more difficult stimuli, for example, two- or five-letter words. To decide whether a patient has left or right or cerebral hemisphere speech representation on the basis of these data, is evident in most patients. Only two patients showed a difference, less than 0.20, between the dominant- and non-dominant hemisphere (the greatest differencewas 0.75). It is tempting to speculate on the variance in difference in VHF scoring. It could be argued that a high difference indicates a well lateralized speech capacity while those with a minor difference could harbour some speech capacity in either hemisphere. One also has to take into consideration what criteria should be applied (i.e. what is the smallest difference between VHFs to predict speech representation) when deciding if the results reflects a bilateral speech representation or a unilateral speech representation. This has to be worked out in relation to the results of the sodium amytal test.
VHF & CH speech laterality The results of the present study are interesting and could stimulate surgical epilepsy centers to create an empirical basis for substitution of the sodium amytal test by a non-invasive technique concerning language functions. However, even if a non-invasive technique in which both hemispheres are active would assess language dominance as well as the sodium amytal test, it would not be sufficient to replace it because of reasons of memory testing. It should be noted however, that such non-invasive techniques are under development (17, 18). Hopefully future research will provide valid non-invasive methods that will predict both postoperative language and postoperative memory functions. Acknowledgements This research was supported by Grant, 84/253 : 2 from the Bank of Sweden Tercentenary Foundation, and by a Grant from the Medical Faculty at University of Umel.
References I . WADA,J. A new method for the determination of the side of speech dominance. A preliminary report on the intracarotid injection of sodium amytal in man. Med Biol 1949: 14: 221-222 (in Japanese). 2. MILNERB, BRANCHC, RASMUSSEN T. Study of short-term memory after hemisphere intracarotid injection of sodium amytal. Trans Am Neurol Assoc 1962: 87: 224-226. 3. CHRISTIANSON S-A, SAISAJ, SILFVENIUS H. Hemispheres memory differences in sodium amytal testing of epileptic patients. Clin Exp Neuropsychol (in press). 4. CHRISTIANSON S-A, SILFVENIUS H, NILSSONL-G. Hemisphere memory of concrete and abstract information determined with the intracarotid sodium amytal test. Epilepsy Res 1987: 1: 185-193. 5. RAUSCHR. The neuropsychological evaluation. In: ENGEL Jr J, ed. Surgical treatment of the epilepsies. New York: Raven Press, 1987: 181-195. 6. RAUSCHR, RISINGER M. Intracarotid sodium amobarbital
technique. In: BOULTON et al., eds. Neuromethods. Humana Press (in press). 7. JACKCR, NICHOLSDA, SHARBROUGH FW, et al. Selective posterior cerebral artery amytal test for evaluating memory function before surgery for temporal lobe seizure. Radiology 1988: 168: 787-793. 8. BEAMOUNT JG. Divided visual field studies of cerebral organization. London: Academic Press, 1982. 9. GEFFENG, QUINNK. Hemispheric specialization and ear advantages in processing speech. Psychol Bull 1984: 96: 273-291. 10. SPERRYRW. Lateral specialization in the surgically separated hemisphere. In: SCHMITTFO, WORDENFG, eds. The neurosciences: third study program. Cambridge, MA: MIT Press, 1974. 11. NEBESRD. Direct examination of cognitive function in the right and left hemispheres. In: KINSBOURNE M, ed. Assymetrical function of the brain. New York: Cambridge University Press, 1978. 12. SPRINGERSP. Tachitoscopic and dichotic listening investigation of laterality in normal human subjects. In: HARNARD S et al., eds. Lateralization in the nervous system. New York: Academic Press, 1977. 13. MCKEEVERWF. Lateral word recognition: effects of unilateral and bilateral presentation, asynchrony of bilateral presentation and forced order of report. Q J Exp Psychol 1971: 23: 410-416. 14. LINDAHL0, BACKLUND T, CHRISTIANSON S-A, NILSSON L-G, SILFVENIUS H. An optical eye movement detector for visual half-filed studies of hemisphere memory. J Med Eng Techno1 1988: 12: 106-111. 15. STRAWSE, WADAJ, KOSAKAB. Visual laterality effects and cerebral speech dominance determined by the carotid amytal test. Neuropsychologia 1985: 23: 567-570. 16. MILNERB. Hemispheric specialization: scope and limits. In: SCHMITTFO, WORDENFG, eds. The neurosciences: third study program. Cambridge, MA: MIT Press, 1974. 17. CHRISTIANSON S-A, NILSSON L-G, SILFVENIUS H. Pre- and postoperative memory of dichotically presented words in patients with complex partial seizures. Neuropsychologia 1989: 27: 427-436. 18. NILSSONL-G. Methodological and theoretical considerations as a basis for an integration of research on memory functions in epileptic patients. Acta Neurol Scand 1980: 62 (SUPPI80): 62-74.
349
