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Attention in focal and centrencephalic epilepsy
EXPERIMENTAL
NEUROLOGY
Attention
9,
in Focal HERBERT
Surgical
463-469
Neurology Blindness,
(1964)
and
LANSDELL
Centrencephalic AND
ALLAN
F.
Epilepsy MIRSKY~
Branch, National Institute of Neurological Diseases and Division of Psychiatry, Boston University Medical Center, Boston, Massachusetts Recsivcd
January
and
24, 1964
Nineteen epileptic patients with centrencephalic type of electrographic abnormalities were compared on a test of attention with sixty-five patients with focal abnormalities. The latter group performed better on the Continuous Performance Test, although the two groups were similar in their scores on the Wechsler-Bellevue Intelligence Scale and in the duration of their illness. Thirtythree patients were tested before and after unilateral temporal lobe resections; after surgery the average scores on the test showed a slight rise, probably attributable to practice. These results are interpreted as showing that maintenance of attention is partly dependent on the integrity of central subcortical structures. Introduction
The Continuous Performance Test (CPT) has been used to show an impairment associated with the centrencephalic and unlocalized types of epileptic disorder and which is not found with the focal type (4). The the data imply there is a disturbance of attention in centrencephalic epilepsy, and the mechanism of attention is considered to be more a function of midline subcortical structures than parts of the neopallium. The present research on another group endeavored to confirm the previous findings and in addition, investigated the effect on the test scores of surgical removal of epileptogenic foci. Methods Subjects. Eighty-four patients were used in comparing the effects of focal and centrencephalic epilepsy. They were selected from a group of 1 We are indebted to Dr. Maitland Baldwin, Clinical Director of NINDB, who performed the temporal resections, for his encouragement of this research on his patients, and to Dr. Cosimo Ajmone Marsan for reviewing his EEG records on more than two dozen cases which we were not able to classify with confidence. Part of the costs of preparing this paper for publication were borne by a grant from the Foundations Fund for Research in Psychiatry. 463
464
LANSDELL
AND
MIRSKY
more than 150 patients who had taken the CPT. The patients who were excluded from the study had no seizures while hospitalized and without medication, neither a focal nor a centrencephalic disorder according to EBG records (e.g., “borderline normal,” ‘(diffuse” or “multiple foci”), a history of syphilis, pneumographic evidence of large cysts, an operative diagnosis of tumor, or no appropriate IQ scores available.” Of the eighty-four patients included in the study, sixty-five were classified as having focal epilepsy, and it usually involved the temporal area. In a majority of them the disorder was localized within one hemisphere, but the group also included patients with bifrontal or independent bitemporal abnormalities. They were being considered for neurosurgical therapy because of poor control of their seizures by medication. Twentythree were female. The other nineteen had centrencephalic epilepsy and eleven of them were female. Twelve of these cases with centrencephalic epilepsy were not admitted as part of the neurosurgical research program, but as patients for other medical investigations (6, 9). The criteria for classifying the cases and the terminology are that of Ajmone Marsan and Ralston (1) . The duration of illness was based on the date of the beginning of recurrent seizures. Thirty-three patients had the CPT before and after unilateral temporal lobe neurosurgery for relief of epilepsy. Eleven of them were among the eighty-four described above; the other twenty-two were part of the previous study of focal and nonfocal epilepsy. The operated group also included three patients who had tumors removed and two with a history of syphilis. Apparatus and Tests. The CPT presents letters, about 5 mm high, on a loop of film strip which moves past an aperture at the rate of about one letter per second. When a letter is at the center of the aperture it is transilluminated for about 0.2 sec. There are two parts to the test. The task during the first 11 min is to press a button held in the hand whenever an X appears. After a brief rest, the test is resumed for 11 min with the instruction to respond to an X only if it is immediately preceded by an A. The performance during the first minute of each task is disregarded in the scoring as practice for the subject. A response is recorded as correct i’f it occurs within about 0.7 set of the appearance of the X. ” The number of patients who had taken the CPT in each of these six excluded categories were, respectively, 13, 22, 4, 2, 7, 10; a few others were excluded for miscellaneous similar types of reasons.
ATTENTION
AND
EPILEPSY
465
The film strip contains two thirty-letter series. The left side is used for the X task and it includes eight X’s. The right side, used for the second task, includes six AX sequences. During the test periods the subject is exposed to 160 X’s in the first part and to 120 X’s following A’s in the second part. The number of errors and correct responses are both recorded on counters on a separate piece of apparatus. The test is probably not entirely a visual task since there is a barely audible closing of a relay in the recording apparatus when a response to an X is required. Form I of the Wechsler-Bellevue Intelligence Scale was usually administered along with a few other tests. Form II was usually used postoperatively on those cases which went to surgery, but three cases had the reverse order of the two forms. Procedure. The patients were tested on the CPT in ward rooms; during the test the room illumination was reduced so that the letters on the film strip could not be seen except when transilluminated. The patients were allowed to sit with their eyes anywhere from about 60-120 cm from the aperture, and the preferred hand was used for pressing the button. If glasses were normally worn a patient was strongly encouraged to use them during the test. A pause of 0.5 min or more was allowed between the two parts of the CPT. Results
The two groups with centrencephalic and focal types of epilepsy were comparable in intelligence and in the length of time they had suffered from seizures (Table 1). However, the centrencephalic group was younger. This age difference did not present a problem in comparing the two groups because efficiency on the CPT showed a tendency to decline with age in the younger centrencephalic group, and this group did not do as well on the average as the group with focal epilepsy on the X task (p < 0.01). Although the negative correlations with age were not statistically significant, it was possible by taking the age of the patients into account by an analysis of covariance to show a difference beween the means of these two groups on the AX task (p < 0.05). The medians for the percentage correct on the CPT tasks are somewhat higher than the means (Table 1) _ This negative skewness of the score distribution indicates that the tasks were usually too easy. The medians indicate also that the difference between the means is largely the result of a different proportion of very poor scores; the better half of the
466
LANSDELL
AND
MIRSKY
centrencephalic cases do nearly as well as the better half of the selected cases with focal epilepsy. The difference in scores on the X task between the two types of patient was almost entirely the result of a difference between female cases (t = 2.8, d.f. = 33, p < 0.01); the difference between the scores for males was not significant (t = 1.3, d.f. = 47. p > 0.10). This difference beTABLE MEAN
AGE,
DURATION
FOR THE
Measure (70 correct resp.)” X task Mean Median AX task Mean Median .4ge (years) Duration illness (years) Wechsler-Bellevue scores Verbal IQ Performance IQ Full scale IQ
1 INTELLIGENCE
OF ILLNESS,
Two
TYPES
Focal (n = 65)
AND
MEDIAN
CPT
SCORES
OF EPILEPSY
Centrencephalic (n = 19)
P
CPT
96.0 97.8 80.0 88.3 31.4 13.8
85.5 95.2 78.1 22.8 12.6
0.01
100.1 100.1 100.1
100.2 96.4 98.5
ns. ns. ns.
71.5
0.01
n.s.h
ns.
a Twenty-five nonepileptic subjects of normal verbal intelligence whose average age was 31.5 years had a mean of 88.0% on the X task and 78.8% on AX (8). On the X task, the cases with focal epilepsy obtained scores better than those control subjects; however, the present cases were selected on the basis of criteria likely to have excluded some of the controls. b Adjusting these scores for age differences between the groups by means of analysis of covariance yielded a significant difference (p < 0.05).
tween the two types of epilepsy was not due to age or intelligence differences in these females. The AX task showed the same tendency for scores of the females to differ more than those of the males, although neither of the differences was significant.3 The thirty-three patients undergoing temporal lobe resections were retested 3 weeks (mean of 20.7 days) after the surgery. Their postoperaa This difference between male and female patients may represent only a peculiarity of this sample. Examination of the data of the previous study (4) (pooling all focal patients) indicated that the differences between mule centrencephalic and focal patients on the CPT were more significant than the differences in the female patients. However, a number of the patients in that study would likely have been excluded from the present one because of the more stringent selection criteria employed.
ATTENTION
AND
EPILEPSY
467
tive average scores (X = 93.9, AX = 82.1% ) showed a nonsignificant improvement over the preoperative scores (90.5, 77.9%).4 There were no CPT differences related to sex or to side of removal, but the left temporal resection cases for whom Wechsler scores were available (n = 13) demonstrated a not unexpected drop in Verbal IQ (t = 2.18, p < 0.05) (3); neither left nor right resection cases showed a drop in Performance IQ. Of subsidiary interest are the relation between ability on the CPT and the factors of intelligence and duration of illness in the group of eighty-four patients. The correlations between the scores on both parts of the CPT and the Wechsler-Bellevue Full Scale IQ were significant (p < 0.01) in both the centrencephalic and focal groups. The correlations between the CPT and both the Verbal and the Performance weighted scores of the intelligence test were similar; these r’s ranged from 0.45 to 0.70. Duration of illness correlated significantly with the CPT scores in the group with focal epilepsy (rs = -0.40; IAx = -0.47). Discussion
As in the previous study (4), a group of patients with centrencephalic epilepsy has not performed as well on the CPT as a group with focal epilepsy. The previous finding is confirmed, and the results of both investigations can be used to argue that the maintenance of attention depends on normal functioning of central subcortical structures. Additional, indirect support for the hypothesis is provided by the surgical cases in this study: ablation of cerebral tissue (primarily cortex) that spared central structures led to no drop in scores on the test of attention. And yet these lesions were not without significant effect on verbal intelligence in certain cases. There were some differences between the present results and those of the previous study. There were no differences in IQ between the focal and centrencephalic patients, eliminating the necessity for the extensive statistical manipulations employed previously to correct for the unequal intellectual levels. However, the differences between groups on the AX 4 The improvement in scores for thirty-one bright two placebo conditions during drug studies (n = from Reference 5) was from 96.8 to 98.1% for the for AX; the retest correlations were 0.79 and 0.46. with feebleminded subjects in Reference 8 were 0.89
practiced normal subjects under 19 from Reference 2; n = 12 X task and from 94.2 to 95.1% The average retest correlations and 0.76.
468
LANSDELL
AND
MIRSKY
task were not as marked as in the earlier study. This may be related to the somewhat different selection criteria employed in the present work; in general these were more stringent than those employed previously. Thus, in contrast with the other study, patients with nonfocal but not clearly centrencephalic disorders were eliminated from the sample. The selection of patients was intended to purify the sample under investigation. However, the group as a whole is not clinically typical because of the severity of their epilepsy. More than half of those with centrencephalic epilepsy were admitted for study because their consistently high seizure rate offered an opportunity for medical therapeutic studies (9) or for behavior research with simultaneous EEG recording (6). Similarly, the focal cases were admitted as possible surgical candidates who were generally poorly controlled on medication. The results obtained from such specially selected patients may not be generally applicable; clearly caution would be necessary in interpreting CPT scores if they were to be used diagnostically in distinguishing between these two types of epilepsy. The need for caution is underlined by the considerable overlap of the range of scores of the patients in the two groups; the more alert members of the centrencephalic group performed nearly as efficiently as the better cases of the focal group. The marked variability in CPT scores within the centrencephalic group raises the issue of the relation between performance on the test and the frequency of attacks at the time of testing. The cases with low scores might be assumed to be suffering from frequent seizures resembling petit mal. Conversely, those with high scores might be assumed to be relatively seizure-free at the time of their examination. Other studies with the CPT (6), however, have indicated that this may be too simple an explanation. Poor performance has been observed in the absence of simultaneous electrographic abnormality, suggesting that the CPT may also be measuring some more or less persistent deficit or deterioration that is associated with centrencephalic epilepsy specifically, and to some extent with epilepsy in general. This is borne out by the correlations of the CPT with both verbal and performance intelligence, and with duration of illness (in the focal group). The primary disorder in patients classified as having centrencephalic epilepsy according to their EEG is believed to involve the central reticular network in the upper brain stem (7). The results of the present study have indicated that the effect of a subcortical epileptic focus on attention
ATTENTION
AND
EPILEPSY
469
may be quite varied, ranging from severe impairment through normal ability. Although the variability may indeed relate to the electrographic state of the patients at the time of testing, it may also reflect differences in the locus, extent or other characteristics of the pathological process within the central core of the brain. References 1. 2.
3. 4.
5.
6.
7. 8.
9.
AJMONE MARSAN, C., and B. L. RALSTON. 1957. “The Epileptic Seizure.” Thomas, Springfield, Illinois. KORNETSXY, C., A. F. MIRSKY, E. K. KESSLER, and J. E. DORFF. 1959. The effects of dextro-amphetamine on behavioral deficits produced by sleep loss in humans. J. Pharmacol. Exjtl. Therap. l2i’: 46-50. MEYER, V. 1961. Psychological effects of brain damage, pp. 529-563. In “Handbook of Abnormal Psychology,” H. J. Eysenck red.]. Basic Books, New York. MIRSXY, A. F., D. W. PRIMAC, C. AJMONE MARSAN, H. E. ROSVOLD, and J. R. STEVENS. 1960. A comparison of the psychological test performance of patients with focal and nonfocal epilepsy. Exptl. Neurol. 2: 75-89. MIRSKY, A. F., D. W. PF.IMAC, and R. BATES. 1959. The effects of chlorpromazine and secobarbital on the continuous performance test. J. Nervous Mental Disease 128: 12-17. MIRSKY, A. F., and H. E. ROSVOLD. 1963. Behavioral and physiological studies in impaired attention, pp. 302-315. In “Psychopharmacological methods,” 2. Votava et al. [eds.]. Pergamon Press, Oxford. PENFIELD, W., and H. H. JASPER. 1954. “Epilepsy and the Functional Neuroanatomy of the Human Brain.” Little, Brown, Boston, Massachusetts. ROSVOLD, H. E., A. F. MIRSKY, I. SARASON, E. B. BRANSOME, JR., and L. H. BECK. 1956. A continuous performance test of brain damage. J. Consult. Psychol. 20: 343-350. The administration of gamma-aminohutyric acid to man: TOWER, D. B. 1960. systemic effects and anticonvulsant action, pp. 562-578. In “Inhibition in the Nervous System and y-aminobutyric Acid,” E. Roberts red.]. Pergamon Press, New York.
NEUROLOGY
Attention
9,
in Focal HERBERT
Surgical
463-469
Neurology Blindness,
(1964)
and
LANSDELL
Centrencephalic AND
ALLAN
F.
Epilepsy MIRSKY~
Branch, National Institute of Neurological Diseases and Division of Psychiatry, Boston University Medical Center, Boston, Massachusetts Recsivcd
January
and
24, 1964
Nineteen epileptic patients with centrencephalic type of electrographic abnormalities were compared on a test of attention with sixty-five patients with focal abnormalities. The latter group performed better on the Continuous Performance Test, although the two groups were similar in their scores on the Wechsler-Bellevue Intelligence Scale and in the duration of their illness. Thirtythree patients were tested before and after unilateral temporal lobe resections; after surgery the average scores on the test showed a slight rise, probably attributable to practice. These results are interpreted as showing that maintenance of attention is partly dependent on the integrity of central subcortical structures. Introduction
The Continuous Performance Test (CPT) has been used to show an impairment associated with the centrencephalic and unlocalized types of epileptic disorder and which is not found with the focal type (4). The the data imply there is a disturbance of attention in centrencephalic epilepsy, and the mechanism of attention is considered to be more a function of midline subcortical structures than parts of the neopallium. The present research on another group endeavored to confirm the previous findings and in addition, investigated the effect on the test scores of surgical removal of epileptogenic foci. Methods Subjects. Eighty-four patients were used in comparing the effects of focal and centrencephalic epilepsy. They were selected from a group of 1 We are indebted to Dr. Maitland Baldwin, Clinical Director of NINDB, who performed the temporal resections, for his encouragement of this research on his patients, and to Dr. Cosimo Ajmone Marsan for reviewing his EEG records on more than two dozen cases which we were not able to classify with confidence. Part of the costs of preparing this paper for publication were borne by a grant from the Foundations Fund for Research in Psychiatry. 463
464
LANSDELL
AND
MIRSKY
more than 150 patients who had taken the CPT. The patients who were excluded from the study had no seizures while hospitalized and without medication, neither a focal nor a centrencephalic disorder according to EBG records (e.g., “borderline normal,” ‘(diffuse” or “multiple foci”), a history of syphilis, pneumographic evidence of large cysts, an operative diagnosis of tumor, or no appropriate IQ scores available.” Of the eighty-four patients included in the study, sixty-five were classified as having focal epilepsy, and it usually involved the temporal area. In a majority of them the disorder was localized within one hemisphere, but the group also included patients with bifrontal or independent bitemporal abnormalities. They were being considered for neurosurgical therapy because of poor control of their seizures by medication. Twentythree were female. The other nineteen had centrencephalic epilepsy and eleven of them were female. Twelve of these cases with centrencephalic epilepsy were not admitted as part of the neurosurgical research program, but as patients for other medical investigations (6, 9). The criteria for classifying the cases and the terminology are that of Ajmone Marsan and Ralston (1) . The duration of illness was based on the date of the beginning of recurrent seizures. Thirty-three patients had the CPT before and after unilateral temporal lobe neurosurgery for relief of epilepsy. Eleven of them were among the eighty-four described above; the other twenty-two were part of the previous study of focal and nonfocal epilepsy. The operated group also included three patients who had tumors removed and two with a history of syphilis. Apparatus and Tests. The CPT presents letters, about 5 mm high, on a loop of film strip which moves past an aperture at the rate of about one letter per second. When a letter is at the center of the aperture it is transilluminated for about 0.2 sec. There are two parts to the test. The task during the first 11 min is to press a button held in the hand whenever an X appears. After a brief rest, the test is resumed for 11 min with the instruction to respond to an X only if it is immediately preceded by an A. The performance during the first minute of each task is disregarded in the scoring as practice for the subject. A response is recorded as correct i’f it occurs within about 0.7 set of the appearance of the X. ” The number of patients who had taken the CPT in each of these six excluded categories were, respectively, 13, 22, 4, 2, 7, 10; a few others were excluded for miscellaneous similar types of reasons.
ATTENTION
AND
EPILEPSY
465
The film strip contains two thirty-letter series. The left side is used for the X task and it includes eight X’s. The right side, used for the second task, includes six AX sequences. During the test periods the subject is exposed to 160 X’s in the first part and to 120 X’s following A’s in the second part. The number of errors and correct responses are both recorded on counters on a separate piece of apparatus. The test is probably not entirely a visual task since there is a barely audible closing of a relay in the recording apparatus when a response to an X is required. Form I of the Wechsler-Bellevue Intelligence Scale was usually administered along with a few other tests. Form II was usually used postoperatively on those cases which went to surgery, but three cases had the reverse order of the two forms. Procedure. The patients were tested on the CPT in ward rooms; during the test the room illumination was reduced so that the letters on the film strip could not be seen except when transilluminated. The patients were allowed to sit with their eyes anywhere from about 60-120 cm from the aperture, and the preferred hand was used for pressing the button. If glasses were normally worn a patient was strongly encouraged to use them during the test. A pause of 0.5 min or more was allowed between the two parts of the CPT. Results
The two groups with centrencephalic and focal types of epilepsy were comparable in intelligence and in the length of time they had suffered from seizures (Table 1). However, the centrencephalic group was younger. This age difference did not present a problem in comparing the two groups because efficiency on the CPT showed a tendency to decline with age in the younger centrencephalic group, and this group did not do as well on the average as the group with focal epilepsy on the X task (p < 0.01). Although the negative correlations with age were not statistically significant, it was possible by taking the age of the patients into account by an analysis of covariance to show a difference beween the means of these two groups on the AX task (p < 0.05). The medians for the percentage correct on the CPT tasks are somewhat higher than the means (Table 1) _ This negative skewness of the score distribution indicates that the tasks were usually too easy. The medians indicate also that the difference between the means is largely the result of a different proportion of very poor scores; the better half of the
466
LANSDELL
AND
MIRSKY
centrencephalic cases do nearly as well as the better half of the selected cases with focal epilepsy. The difference in scores on the X task between the two types of patient was almost entirely the result of a difference between female cases (t = 2.8, d.f. = 33, p < 0.01); the difference between the scores for males was not significant (t = 1.3, d.f. = 47. p > 0.10). This difference beTABLE MEAN
AGE,
DURATION
FOR THE
Measure (70 correct resp.)” X task Mean Median AX task Mean Median .4ge (years) Duration illness (years) Wechsler-Bellevue scores Verbal IQ Performance IQ Full scale IQ
1 INTELLIGENCE
OF ILLNESS,
Two
TYPES
Focal (n = 65)
AND
MEDIAN
CPT
SCORES
OF EPILEPSY
Centrencephalic (n = 19)
P
CPT
96.0 97.8 80.0 88.3 31.4 13.8
85.5 95.2 78.1 22.8 12.6
0.01
100.1 100.1 100.1
100.2 96.4 98.5
ns. ns. ns.
71.5
0.01
n.s.h
ns.
a Twenty-five nonepileptic subjects of normal verbal intelligence whose average age was 31.5 years had a mean of 88.0% on the X task and 78.8% on AX (8). On the X task, the cases with focal epilepsy obtained scores better than those control subjects; however, the present cases were selected on the basis of criteria likely to have excluded some of the controls. b Adjusting these scores for age differences between the groups by means of analysis of covariance yielded a significant difference (p < 0.05).
tween the two types of epilepsy was not due to age or intelligence differences in these females. The AX task showed the same tendency for scores of the females to differ more than those of the males, although neither of the differences was significant.3 The thirty-three patients undergoing temporal lobe resections were retested 3 weeks (mean of 20.7 days) after the surgery. Their postoperaa This difference between male and female patients may represent only a peculiarity of this sample. Examination of the data of the previous study (4) (pooling all focal patients) indicated that the differences between mule centrencephalic and focal patients on the CPT were more significant than the differences in the female patients. However, a number of the patients in that study would likely have been excluded from the present one because of the more stringent selection criteria employed.
ATTENTION
AND
EPILEPSY
467
tive average scores (X = 93.9, AX = 82.1% ) showed a nonsignificant improvement over the preoperative scores (90.5, 77.9%).4 There were no CPT differences related to sex or to side of removal, but the left temporal resection cases for whom Wechsler scores were available (n = 13) demonstrated a not unexpected drop in Verbal IQ (t = 2.18, p < 0.05) (3); neither left nor right resection cases showed a drop in Performance IQ. Of subsidiary interest are the relation between ability on the CPT and the factors of intelligence and duration of illness in the group of eighty-four patients. The correlations between the scores on both parts of the CPT and the Wechsler-Bellevue Full Scale IQ were significant (p < 0.01) in both the centrencephalic and focal groups. The correlations between the CPT and both the Verbal and the Performance weighted scores of the intelligence test were similar; these r’s ranged from 0.45 to 0.70. Duration of illness correlated significantly with the CPT scores in the group with focal epilepsy (rs = -0.40; IAx = -0.47). Discussion
As in the previous study (4), a group of patients with centrencephalic epilepsy has not performed as well on the CPT as a group with focal epilepsy. The previous finding is confirmed, and the results of both investigations can be used to argue that the maintenance of attention depends on normal functioning of central subcortical structures. Additional, indirect support for the hypothesis is provided by the surgical cases in this study: ablation of cerebral tissue (primarily cortex) that spared central structures led to no drop in scores on the test of attention. And yet these lesions were not without significant effect on verbal intelligence in certain cases. There were some differences between the present results and those of the previous study. There were no differences in IQ between the focal and centrencephalic patients, eliminating the necessity for the extensive statistical manipulations employed previously to correct for the unequal intellectual levels. However, the differences between groups on the AX 4 The improvement in scores for thirty-one bright two placebo conditions during drug studies (n = from Reference 5) was from 96.8 to 98.1% for the for AX; the retest correlations were 0.79 and 0.46. with feebleminded subjects in Reference 8 were 0.89
practiced normal subjects under 19 from Reference 2; n = 12 X task and from 94.2 to 95.1% The average retest correlations and 0.76.
468
LANSDELL
AND
MIRSKY
task were not as marked as in the earlier study. This may be related to the somewhat different selection criteria employed in the present work; in general these were more stringent than those employed previously. Thus, in contrast with the other study, patients with nonfocal but not clearly centrencephalic disorders were eliminated from the sample. The selection of patients was intended to purify the sample under investigation. However, the group as a whole is not clinically typical because of the severity of their epilepsy. More than half of those with centrencephalic epilepsy were admitted for study because their consistently high seizure rate offered an opportunity for medical therapeutic studies (9) or for behavior research with simultaneous EEG recording (6). Similarly, the focal cases were admitted as possible surgical candidates who were generally poorly controlled on medication. The results obtained from such specially selected patients may not be generally applicable; clearly caution would be necessary in interpreting CPT scores if they were to be used diagnostically in distinguishing between these two types of epilepsy. The need for caution is underlined by the considerable overlap of the range of scores of the patients in the two groups; the more alert members of the centrencephalic group performed nearly as efficiently as the better cases of the focal group. The marked variability in CPT scores within the centrencephalic group raises the issue of the relation between performance on the test and the frequency of attacks at the time of testing. The cases with low scores might be assumed to be suffering from frequent seizures resembling petit mal. Conversely, those with high scores might be assumed to be relatively seizure-free at the time of their examination. Other studies with the CPT (6), however, have indicated that this may be too simple an explanation. Poor performance has been observed in the absence of simultaneous electrographic abnormality, suggesting that the CPT may also be measuring some more or less persistent deficit or deterioration that is associated with centrencephalic epilepsy specifically, and to some extent with epilepsy in general. This is borne out by the correlations of the CPT with both verbal and performance intelligence, and with duration of illness (in the focal group). The primary disorder in patients classified as having centrencephalic epilepsy according to their EEG is believed to involve the central reticular network in the upper brain stem (7). The results of the present study have indicated that the effect of a subcortical epileptic focus on attention
ATTENTION
AND
EPILEPSY
469
may be quite varied, ranging from severe impairment through normal ability. Although the variability may indeed relate to the electrographic state of the patients at the time of testing, it may also reflect differences in the locus, extent or other characteristics of the pathological process within the central core of the brain. References 1. 2.
3. 4.
5.
6.
7. 8.
9.
AJMONE MARSAN, C., and B. L. RALSTON. 1957. “The Epileptic Seizure.” Thomas, Springfield, Illinois. KORNETSXY, C., A. F. MIRSKY, E. K. KESSLER, and J. E. DORFF. 1959. The effects of dextro-amphetamine on behavioral deficits produced by sleep loss in humans. J. Pharmacol. Exjtl. Therap. l2i’: 46-50. MEYER, V. 1961. Psychological effects of brain damage, pp. 529-563. In “Handbook of Abnormal Psychology,” H. J. Eysenck red.]. Basic Books, New York. MIRSXY, A. F., D. W. PRIMAC, C. AJMONE MARSAN, H. E. ROSVOLD, and J. R. STEVENS. 1960. A comparison of the psychological test performance of patients with focal and nonfocal epilepsy. Exptl. Neurol. 2: 75-89. MIRSKY, A. F., D. W. PF.IMAC, and R. BATES. 1959. The effects of chlorpromazine and secobarbital on the continuous performance test. J. Nervous Mental Disease 128: 12-17. MIRSKY, A. F., and H. E. ROSVOLD. 1963. Behavioral and physiological studies in impaired attention, pp. 302-315. In “Psychopharmacological methods,” 2. Votava et al. [eds.]. Pergamon Press, Oxford. PENFIELD, W., and H. H. JASPER. 1954. “Epilepsy and the Functional Neuroanatomy of the Human Brain.” Little, Brown, Boston, Massachusetts. ROSVOLD, H. E., A. F. MIRSKY, I. SARASON, E. B. BRANSOME, JR., and L. H. BECK. 1956. A continuous performance test of brain damage. J. Consult. Psychol. 20: 343-350. The administration of gamma-aminohutyric acid to man: TOWER, D. B. 1960. systemic effects and anticonvulsant action, pp. 562-578. In “Inhibition in the Nervous System and y-aminobutyric Acid,” E. Roberts red.]. Pergamon Press, New York.