No Evidence of a Homogeneous Frontal Neuropsychological Profile in a Sample of Schizophrenic Subjects

Eighty-one schizophrenic outpatients participated in the study. Patients were recruited from the outpatient facility of the Psychiatric Branch of the Department of Medicine, Surgery, and Dentistry of the University of Milan Medical School.

Diagnosis was made independently by two of the authors (S.S., O.G.) according to DSM-IV criteria.¹¹ Each patient was included in the study sample only if both the psychiatrists agreed on the diagnosis of schizophrenia. Exclusion criteria were a history of perinatal traumas, organic illnesses involving the central nervous system, substance and/or alcohol abuse, clinical evidence of mental retardation, and marked extrapyramidal symptomatology. All of the patients were already being treated with antipsychotic medications at the time of the recruitment.

Mental state was evaluated with a clinical interview administered by two of the authors (O.G., A.C.) just before the neuropsychological session and was scored by the same two authors using the Brief Psychiatric Rating Scale (BPRS),¹² the Scale for the Assessment of Positive Symptoms (SAPS),¹³ and the Scale for the Assessment of Negative Symptoms (SANS).¹³ IQ was assessed with the Wechsler Adult Intelligence Scale–Revised (WAIS-R).¹⁴

Information about the purpose of the study was provided to each subject, and informed consent was obtained before starting the testing procedure.

A trained neuropsychologist administered the tests in a quiet laboratory. WAIS-R verbal and nonverbal IQ were assessed before the neuropsychological session. All patients completed all the tests, which were submitted in a fixed order. The details of the complete procedure for each test are reported elsewhere.^6–10 The tests are described briefly below. In the A-not-B test,⁶ the patient sits facing two identical hiding wells, one on the left and one on the right. The examiner shows an object to the patient and puts it into one of the two hiding wells and the subject has to look for the correct answer immediately, without delay. The subject scores successfully if he or she makes no more than one error.

The Delayed Response Task⁶ is performed like the A-not-B test, but with a 10-second delay between the moment the object is positioned in one of the wells and the subject's answer. The object is hidden according to a predetermined schedule with a pseudo-random Gellerman sequence.⁶ The DRT is scored in the same way as the A-not-B test.

In the Object Alternation Test,⁷ the subject and the examiner are separated by a wooden platform 60 cm wide and 60 cm high. A black curtain is anchored to the platform and can be moved to reveal the stimulus board, where there are two plaques. When the curtain is lowered, the patient can see neither the plaques nor the investigator. When the curtain is raised, the subject can see the two objects and only the hands of the investigator. An object, such a penny, is placed under one of the two black plaques. The subject is asked to choose one of the two. After each response the curtain is lowered, and if the subject has given a correct response the investigator changes the position of the penny. On the first trial both plaques are baited with a penny. For the other trials, the penny is put under the side that was not previously chosen. The penny remains on the same side until the subject finds the coin. After a correct response, the penny is put under the opposite plaque. Each task is composed of 25 complete trials; the learning criterion is 15 consecutive correct responses. OAT performance was scored as the total number of perseverative errors. An error is scored positively if the subject chooses the incorrect object two or more times consecutively before shifting strategy.

The Weigl Sorting Test⁹ consists of 20 wooden blocks varying in shape, color, thickness, symbol printed on the surface, and size. The subject is requested to form homogeneous groups, according to a common feature, in 3 minutes. The score is based on the number of categories that the subject recognizes, and it ranges from 0 to 5.

The Wisconsin Card Sorting Test is performed according to standardized criteria.¹⁰ Four stimulus cards with different symbols (one single red square, two green stars, three yellow crosses, four blue circles) are placed in front of the subject, who is given a pack of 128 response cards, eight of which are identical to the stimulus cards. The subject is instructed to place each response card under one of the four stimulus cards and is told that the examiner will say whether the coupling criterion is right or wrong. According to the examiner's response the subject has to place as many cards as possible with the correct strategy. After coupling 10 cards with the first criterion (color), the subject has to shift to the second criterion (shape) and then to the third (number). This procedure is repeated twice or until all 128 cards have been placed.

Out of the three indices of WCST performances (i.e., number of total errors, number of stages, and number of perseverative errors), only the perseverative errors score (PE) is considered in this paper. A perseverative error is scored when the subject continues to sort the cards in the same way (e.g., i.e., according to color criterion) even when the examiner says the card is wrong or changes the criterion.

The Word Fluency Test⁸ consists of three word-naming trials. The letters F, A, S are employed, and for each letter there is a one-minute time limit to produce as many words as possible. The score consists of the total number of words recalled and is corrected for age, sex, and education, according to Benton's procedures.

Because all subjects performed correctly on the A-not-B and the DRT tests, those results were not included in the statistical analyses.

We first computed z scores for neuropsychological and clinical variables to normalize the distributions. Then we looked for particular patterns of frontal function profiles by evaluating the data with cluster analysis, where OAT, WFT, WST, and WCST z scores were the clustering variables. Clustering techniques were the squared Euclidean distance and the Ward's method. Analysis of variance (ANOVA) with Scheffé's multiple comparison test, chi-square, and correlation analysis were also used when appropriate.¹⁵

External validity of the descriptive cluster statistics was obtained by performing ANOVA with clusters as independent variables and OAT, WFT, WST, WCST as dependent variables.

Correlation analysis was performed to evaluate the relationships between neuropsychological performances and verbal IQ, nonverbal IQ, age, and education.