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Editor's note. Articles based on APA award addresses that appear in the American Psychologist are scholarly articles by distinguished contributors to the field. As such, they are given special consideration in the American Psychologist's editorial selection process.

INTRODUCTIONAlthough evidence for the presence of lateralized cognitive deficits in man is not unequivocal(8), acute destructive lesions of the dominant cerebral hemisphere have been shown to produce selective verbal impairment while nondominant hemisphere lesions have been associated with visuospatial dysfunction", l a ) . Such differential patterns of psychological test performance have appeared more consistently in cases with lateralized posterior lesions @). Furthermore, the verbal deficits arising out of left hemisphere involvement have been more clearly measurable in the presence of aphasic disturbances ( I ) , although more incisive assessment procedures have revealed subtle verbal deficits without gross impairment of verbal functioning(5, 9, li, l6).Since many of these investigations have operationally defined the independent lateralization variable by sampling representative neurological groups, factors such as nature of the neuropathological process, interruption of function through cerebral edema or intracranial pressure, lesion-induced changes in vascular supply to other areas, and pre-existing diffuse cerebral deterioration have not been amenable to direct surveillance and control. As a consequence, these factors have probably been confounded with the lateralization variable to obscure higher order interactions among such dimensions and, in so doing, have served to produce seemingly contradictory findings("). On the other hand, systematic investigation of lateral hemispheric differences in intellectual function has been actualized through cognitive assessment before and after unilateral temporal lobectomy in the neurosurgical treatment of temporal lobe epilepsy. Since the epileptogenic lesions in such patients are typically rather static in nature and, thus, less complicated by such irrelevant variables, resection of the anterior temporal lobe has provided a basis for more precise determination of lateral differences in cerebral dysfunction. 9 , a general tendency toward higher subtest scores in patients with epileptogenic foci of predominantly right temporal lobe origin was observed preoperatively, especially on the verbal tests. One month postoperatively, their nondominant group showed an increased superiority on all subtests largely as a function of a verbal subtest decline in the dominant group. This finding led to the postulation of a dysphasic basis for the obtained result. By contrast, Milner(lO) reported a deficit on the Picture Arrangement subtest of the Wechsler-Bellevue Form I before and after unilateral temporal lobectomy, but she did not mention any differential deficit between the left and right temporal lobectomy groups. A similar defect in the sequential ordering of complex pictorial stimuli was found in a small group of cases with acutely destructive right as compared with the left anterior temporal lobe lesions(la). However, none of the previous pre-to postoperative comparisons were made over a significant time interval longitudinally so that transient operative effects might have b...

PROBLEMThe functional role of the temporal lobe and related limbic system structures in the organization and expression of inotivational-emotional behaviors has been a subject of intense neuropsychological research since the classic 3* * ) in monkeys of massive behavior changes following extensive bilateral temporal neocortical and paleocortical ablations. .\lthough numerous contradictory findings have emerged in the eiisuing literature, the paleocortical structures of the limbic system have been accepted as central and critical in the mediation of emotional patterns of behavior in the monkey, cat, dog, and rat. ( 4 )Systematic studies W ) of limbic system involvement in man have been relatively infrequent and focused upon the iiitellectual functions of the temporal lobe in psychomotor epileptics. (LI) More recently, with increased interest in the neurosurgical treatment of teinporal lobe epilepsy via unilateral temporal lobectomy, clinical observations and systeiiiatic docuinentatioii of a significant incidence of personality disturbance ainong psychomotor epileptics have been reported. (I4) In addition, a few studies(6-l o ) have attempted to relate tcmporal lobe EEG classifications to some external criterion of personality functioning such 89 ratings of aggressiveness, neurotic nianifestations from case history examinations, and Rorschach patterns. In her review of the literature, Tizard ( 1 4 ) pointed out numerous inconsistencies between sets of data resulting from utilization of non-representative institutionalized samples, incomplete assessment of criterion reliability, failure to control for I&, loose clinical and EEG criteria for selection of patients, and absence of histological studies.This study attempts to interrelate some objective response-restricted personality variables as measured by the Minnesota Multiphasic Personality Inventory (MMPI) to bilateral and unilateral EEG temporal lobe abnormalities among clinically established psychomotor epileptics. Since the neurophysiologically and neuroanatomically more precise animal studies had shown that emotion and motivation derived behavioral manifestations arose when limbic system lesions were placed bilaterally rather than unilaterally, it seemed reasonable to predict greater MMPI indications of personality disturbance among psychomotor epileptics with (1) bilateral as compared with unilateral EEG abnormalities, and (2) bitemporal independent spike foci as compared with bitemporal EEG abnormalities but only a unilateral spike focus. METHOD Subjects. The Ss were 53 patients on whom temporal lobectomies were performed for psychomotor seizures. These Ss were originally referred through the Neurosurgery and Neurology out-patient clinics at the University of Minnesota Hospitals as candidates for unilateral temporal lobectomy . The criteria for'excision of the temporal lobe included: psychomotor seizures that were poorly controlled in spite of anticonvulsant medication, determination of a temporal lobe spike focus with scalp and /or nasopharynged recordin...

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