Errors Copying a Simple Pattern on the BNI Screen for Higher Cerebral Functions
Sarah Hahn, PhD
George P. Prigatano, PhD
Division of Neurology, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona
We retrospectively compared the presence or absence of errors made by acute brain dysfunctional patients and normal controls when copying a simple pattern of pluses and zeros as a part of the BNI Screen for Higher Cerebral Functions. Of 93 brain dysfunctional patients, 32 (34.4%) performed this task incorrectly. Of 92 control subjects, only 5 (5.4%) made similar errors. Half of the brain dysfunctional patients who made simple errors in copying also showed errors of perseveration. These patients also tended to show left-handed constructional dyspraxia when drawing a Greek cross. Simple pattern copying may provide information useful for brief assessments of higher cerebral functions.
Key Words: constructional dyspraxia, hemi-inattention, neuropsychology, perseveration, psychological testing
The BNI Screen for Higher Cerebral Functions (BNIS) is a valid and reliable measure of cognitive functioning. The BNIS is clinically useful for making certain differential diagnoses and for predicting acute and postacute rehabilitation outcomes.[10,11,16] Performances on selected BNIS subtests are sensitive to lateralized cerebral dysfunction and also provide qualitative information useful in making differential diagnoses.
We retrospectively analyzed performance on one BNIS item designed to assess difficulties with copying a series of repetitive stimuli. The pattern-copying item on the BNIS correlates with problem-solving measures on functional outcomes scales. Theoretically, this item, which consists of copying a pattern of pluses and zeros, should also elicit potential perseverative errors in brain dysfunctional patients.<sup>6</sup> We explored whether this was, in fact, the case or if errors on this task were related to behavioral signs of hemi-inattention or constructional dyspraxia. These latter problems are common after acute brain dysfunction, particularly when right hemisphere lesions are present.[2,4]
Ninety-three acute brain dysfunctional patients (52 males and 41 females) undergoing clinical examination at the Barrow Neurological Institute served as subjects. Their mean age was 57.5 years (standard deviation [SD]=17.9), and their mean number of years of education was 13.28 years (SD=2.8).
Two patients were ambidextrous, four were left-handed, and 87 were right-handed. Forty-eight patients had sustained a cerebrovascular accident, 27 patients had a traumatic brain injury, and 6 patients had a neoplasm. The remaining 12 patients had a variety of miscellaneous diagnoses.
Ninety-two individuals (33 males and 59 females) without brain dysfunction serving as part of the BNIS standardization sample were used as controls. Their mean age was 45.28 years (SD=21.52), and their mean number of years of education was 13.69 years (SD=2.14). One patient was ambidextrous, four patients were left-handed, and 87 were right-handed.
As part of the BNIS, an individual is asked to copy the following pattern:
This simple task of copying pluses and zeros occurs approximately halfway through the BNIS, which normally takes 15 to 20 minutes to administer. The individual is given a pencil and an 8.5¥11 inch piece of paper. The paper is not completely blank (because other drawings and writings are made on it as part of the screening test), but the individual is given ample space to copy the row of these symbols on a single, relatively straight line. A priori we had considered that an individual who failed to budget enough space for the pattern as reflected above would make what we tentatively describe as a planning error.
Planning errors. A planning error was considered to have occurred if the subject (1) required two lines to copy the row, (2) touched an unrelated item on the page with the copy, (3) turned a corner to avoid an unrelated item while copying, or (4) reached/touched the absolute right edge of the paper with the copy (no margin of error). No planning error was considered to have occurred if the subject copied the pattern in one relatively straight line without encountering any space constraints. For patients judged to have made a planning error according to these criteria, the frequencies of hemi-inattention, perseveration, and constructional dyspraxia were then calculated as follows.
Hemi-Inattention. Subjects who started their copy to the right of the exact midline of the page were considered to have made an error of hemi-inattention. The judgment was determined by imposing a vertical line that bisected the patient’s sheet of paper after the task was completed (Fig. 1).
Perseveration. Patients who wrote more pluses or zeros than were required by the relevant section of the model stimuli and/or who mistakenly inserted another mark or symbol (besides a plus or a zero) into the copy were considered to have made a perseverative error (Fig. 2).
Constructional dyspraxia. As part of the BNIS, subjects are required to copy a Greek cross using both their dominant and their nondominant hands. An error of constructional dyspraxia was considered to have occurred if a subject failed to make a reasonable facsimile of the Greek cross. The copies made with the dominant hand and the nondominant hand are scored separately (Fig. 3).
The hypothesis that patients with acute brain damage would demonstrate a higher incidence of planning errors than normal control subjects was supported. Of the 93 brain-injured patients, 32 (34.4%) made a planning error. In contrast, only five (5.4%) of the 92 normal control subjects made a planning error. This difference was highly significant (c2 (1, 93)=24.26, p<.000).
Hemi-inattention did not appear to relate to planning errors. Of the 32 patients who made planning errors, only 4 (12.5%) showed clear signs of hemi-inattention. In contrast, perseverative errors were common when planning errors occurred. Half of the 32 brain-injured patients who made planning errors also made errors of perseveration.
Patients who made planning errors exhibited minimal difficulties with constructional dyspraxia when drawing a Greek cross with their right hand (3/32, 9%). In contrast, about a third of patients who made constructional dyspraxic errors with their left hand (10/32, 31%) also showed planning errors.
Post hoc analyses revealed that patients who performed at a low level on the BNIS also tended to make more planning errors. More than 60% of the patients who had a total BNIS T-score of less than 30 made an error in planning (Fig. 4).
This retrospective study demonstrated that approximately a third of patients with acute brain injuries made errors in copying a simple pattern of pluses and zeros. In contrast, few normal controls made such an error. Many other brief screening tests of higher cerebral functions (e.g., Mini-Mental Status Examination) fail to sample these errors adequately.
Initially, the pattern copying task was included in the BNIS for the purpose of measuring several clinically relevant neuropsychological sequelae of brain injury, including perseveration. The current findings indicate that 50% of patients who made a planning error also made at least one error of perseveration. Perseveration occurs when aspects of a prior event interfere with a current function or when the expected termination of a completed task (or subtask) fails to occur.
Perseveration may reflect errors of self-monitoring, which relate to planning. Such errors have been associated with frontal lobe damage in various studies; however, diffuse traumatic brain damage may produce planning errors even when the frontal lobes are not specifically identified as impaired. Our findings revealed no significant correlations between lesion location and the presence or absence of planning errors.
Global neuropsychological difficulties often follow an acute brain injury, even when the focus of the lesion appears to be discrete on imaging studies. Likewise, neuropsychological profiles often suggest bilateral cerebral dysfunction, even in acute patients whose lesions are visualized as unilateral on radiological studies.[5,9] The diffuseness of brain dysfunction after acute insults potentially reflects several factors, including disrupted neurotransmitter systems secondarily affecting remote parenchyma and subtle areas of damage not fully captured by current neuroimaging techniques (e.g., volumetrically minute but clinically important disruptions in brain microvasculature).
Approximately a third of the patients who made planning errors could not draw the Greek cross with their left hand, suggesting the presence of significant right hemispheric dysfunction. This finding is interesting given that hemi-inattentive errors only occurred in 9% of patients who made planning errors on this simple copying task. This low incidence may reflect our stringent criterion for hemi-inattention, which was scored as positive only if the patient’s entire production was right of midline. The relative paucity of hemi-inattentive errors may also imply that the visuospatial disturbance underlying a patient’s poor visual planning, constructional dyspraxia, and perseveration might reflect factors other than left neglect. Recent studies of inattention suggest that patients with right brain damage may be inattentive to objects on both the right and left side of space. Rather than showing purely lateralized attention, our subjects may have had a visuospatial disorder that caused intermittent problems with scanning, sequencing, anticipating, and monitoring visuospatial information in both their left and right visual fields.
Level of performance, as measured by the BNIS, related to the presence or absence of planning errors. More than 60% of patients with a T score of less than 30 (i.e., 2 SDs below average) made planning errors, suggesting that such errors may indicate the presence of significant neuropsychological impairment. Being able to assess and document severe neuropsychological impairment rapidly is extremely important to the management of brain-injured patients in the acute setting. Superficially, our results may appear to be incompatible with previous reports of planning errors that correlated poorly with global level of performance measures. In such studies, however, a patient’s performance on complicated planning tasks was often studied postacutely rather than acutely. Thus, timing of assessment and level of performance may be important determinants of when planning errors occur.
Besides reflecting a potential visuospatial disturbance, errors in copying a simple series of pluses and zeros may also reflect significant cognitive compromise, which may not be evident when speaking with a patient. Such errors may be especially important for discharge planning. For example, a patient could have no subjective cognitive complaints and no overt disturbances in language or verbal memory but be unable to copy this simple pattern of pluses and zeros accurately. In such cases, a clinician should further explore the patient’s level of higher cognitive functioning before recommending levels of independence for the patient after discharge.
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