اختلال شخصیت مرزی: اختلال ادراک بصری و حافظه کاری

Abstract The neurobiology of borderline personality disorder (BPD) is still elusive. There are a few studies on neuropsychological performance in BPD, which report a broad spectrum of abnormalities. The present study evaluates perception and working memory as instances of basic cognitive functions. Female subjects diagnosed with DSM-IV borderline personality disorder (n=22) were compared with age- and education-matched controls (n=25). Perception speed was assessed by a backward masking paradigm. Working memory was tested by a series of delayed matching-to-sample paradigms involving varying subsidiary functions like mental rotation, retrieval from memory, ignoring distracters, and cross-modal performance. In backward masking, BPD subjects required significantly longer stimulus onset asynchrony (SOA) than controls to identify the visual target, and there was an additional slowing of the motor response. Working memory accuracy was impaired in BPD subjects, but did not worsen when the cognitive load was increased. With increasing task difficulty, they traded off speed for accuracy similarly as the controls. Impulsivity and dissociation ratings were not correlated with performance. It is concluded that perceptional speed and working memory are impaired in BPD, but that the deficits are not augmented by increasing cognitive load.

Introduction Borderline personality disorder (BPD) is characterized by an enduring pattern of abnormal behavior, cognition, and affect, with onset in early adolescence. The etiology of BPD is unknown. Andrulonis et al., 1980, Andrulonis et al., 1982 and Van Reekum et al., 1996 reported that more BPD subjects than controls had suffered traumatic brain injury, and that the neuropsychologic profile of BPD subjects resembled that of persons with brain trauma. EEGs of BPD were reported to contain abnormal slow wave activity (Ogiso et al., 1993 and De La Fuente et al., 1998). Neurological soft signs (subtle abnormalities on neurological examination) were significantly more frequent in BPD patients than in controls (Quitkin et al., 1976, Gardner et al., 1987 and Stein et al., 1993). Only a few studies pertain to the neuropsychological performance of BPD patients. Burgess, 1991a and Burgess, 1991b), in persons with dramatic personality disorder, found impairments of memory, of sequence planning and performance. Van Reekum et al., 1993 and Van Reekum et al., 1996 suggested a dysfunction of prefrontal circuits because of deficits on impulse control and on the Wisconsin Card Sorting Test (WCST Heaton et al., 1993). O'Leary et al. (1991) reported impairments of visual perception, of memory for complex material, of visual discrimination, and of flexibility in the digit symbol test. In a broader sense, inappropriate behavior in BPD might be based on improper decisions about what to do. Decision-making has been found to correlate with working memory performance (Hinson et al., 2002 and Hinson et al., 2003), but decision-making certainly involves other processes as well. Baddeley (2001) recently proposed a four-component model of working memory, adding as a new component the episodic buffer to the ‘classic’ elements, which comprise the phonological loop, the visuospatial sketchpad and the central executive. The episodic buffer is thought to act as a limited storage system capable of integrating information from a variety of sources. Nuechterlein et al. (1994) and, more recently, Lencz et al. (2003) pointed out that many cognitive tasks, and visual working memory in particular, require a representation of the stimulus to be formed as a first step of information processing. They also demonstrate that backward masking paradigms can differentiate perceptual impairments from deficits in maintaining and manipulating the stimuli. For these reasons, a visual backward masking paradigm was included in the present experiment. Schubert et al. (1985) investigated backward masking in depressed patients with BPD, but they found no differences compared with controls. The present study attempts to evaluate perception speed (by means of a backward masking paradigm) and working memory (through a series of delayed matching-to-sample tasks in BPD subjects. To explore the impact of the stimulus modality, auditory and visual delayed matching-to-sample (DMS) tasks are employed. In order to differentiate the effects of load from interference, the tasks were performed with and without interfering stimuli, an additional (within-modality) task-mental rotation was added, and finally a cross-modal version (auditory and visual stimuli) was administered. The following hypotheses were formulated: Compared with controls, (1) BPD patients are impaired in stimulus perception (measured as speed deficit, while accuracy is controlled); (2) BPD patients show impaired working memory (measured as accuracy or speed deficit); (3) more specifically, BPD patients perform worse when the load on the working memory is increased by growing task complexity. Hypothesis (4) assumes that within BPD subjects, dissociation scores correlate with working memory performance.

Results 3.1. Backward masking In the control group 21/25 subjects reached criterion, as compared with 19/22 subjects in the BDP group. The RT and SOA data approximately following a normal distribution, so a repeated measures MANOVA was calculated, with SOA from the block at which criterion was reached and RT as dependent variables, group as between-subject factor, and measurement type (SOA, RT) as within-subject factor. A MANOVA was used because SOA and RT are supposed to correlate. There was a significant main effect for group (F1, 38=3.66, Greenhouse–Geisser ε=1.00, P<0.03), as both SOA and RT were longer in BPD patients ( Table 2, Fig. 2). The interaction group×measurement type was also significant (F1, 38=3.64, P<0.03). Table 2. Backward masking BPD Controls Mean±S.D. Mean±S.D. SOA at criterion (ms) 120±7 83±3* RT at criterion (ms) 870±118 807±88* The table lists the SOA required by the subjects to achieve correct identification of 18 test stimuli in one block of 20 trials (=criterion). Beneath, the reaction time in that block is indicated. *group difference P<0.05. Table options Backward masking SOA. The graph shows SOA vs. group. BPD subjects need longer ... Fig. 2. Backward masking SOA. The graph shows SOA vs. group. BPD subjects need longer SOA (**P<0.001) for secure stimulus identification than controls. Figure options 3.2. DMS accuracy The accuracy of responses was evaluated in two repeated-measure ANOVAs. The first comprised VIS1, VIS2, AUD1, and AUD2 and assessed main effects for group, sensory modality, and task complexity. The second ANOVA compared cross-modal performance with each uni-modal task. In both ANOVAs, the number of correct responses (=hits+correct rejections) was the dependent variable, sensory modality and difficulty the within-subject factor, and group the between-subject factor. Premature responses (RT<200 ms) were excluded. ANOVA 1 indicated a main effect for group (F1, 45=6.71, Greenhouse–Geisser ε=1.00, P<0.01), as BPD patients scored fewer correct responses than controls. There was a main effect for modality (F1, 45=19.2, P<0.001), as greater accuracy was achieved in the visual tasks. Increasing the difficulty also yielded a significant effect (F1, 45=91.9, P<0.001), with fewer correct answers in the auditory task with distracters, while only a marginal reduction of response accuracy was seen in the visual task requiring mental reduction. The interactions were not significant. ANOVA 2 reproduced the main effect for group (F1, 45=6.72, Greenhouse–Geisser ε=1.00, P<0.001) and indicated a main effect for condition (F4, 180=42.6, P<0.001). In both groups accuracy in the cross-modal task (CROSS) was similar as in the visual tasks (n.s.), less than in the simple auditory task (CROSS-AUD1: F1, 45=5.31, P<0.02) and more than in the auditory task with distracters (CROSS-AUD2: F1, 45=102.5, P<0.001). The interaction group condition was not significant. (F4, 180=0.42, n.s.) ( Table 3 and Fig. 3a). The sum of premature reactions (there were few) across all tasks showed a trend for more premature responses in the patient group [t(2)=1.47, P<0.08]. Table 3. Delayed matching-to-sample: number of correct responses (n) Task BPD Controls Mean±S.D. Mean±S.D. VIS1 74.0±18.3 87.0±11.5 VIS2 73.1±17.7 81.3±13.3 AUD1 78.3±27.3 90.4±6.6 AUD2 52.5±21.2 60.5±16.8 CROSS 74.2±21.2 85.0±10.2 Premature responses (n) 8.9±12.2 3.3±6.1 The table lists the number of correct responses in the DMS paradigm. Table options (a) Working memory accuracy. The number of correct responses is shown for each ... Fig. 3. (a) Working memory accuracy. The number of correct responses is shown for each group across the trials. Accuracy of BPD subjects constantly trails that of controls (P<0.01). (b) Working memory reaction times. Average reaction time per group (for hits only) is represented. There is no main effect for group, but for condition, with slower reaction time in the more complex task (P<0.001). (c) Working memory: ratio accuracy/reaction time. A measure of processing speed (sum of correct responses/reaction time) was calculated. In both groups, ‘speed’ varies with task complexity (P<0.001). As the curves for both groups run parallel, a preserved speed/accuracy trade-off in BPD is assumed. Figure options 3.3. DMS reaction time Reaction times were evaluated for hits and correct rejections, using two repeated measures ANOVAs (similar as for accuracy). ANOVA 1 indicated significant effects for response type (F1, 45=51.7, Greenhouse-Geisser ε=1.00, P<0.001) as the RTs were longer for hits than for correct rejections; for complexity (F1, 45=68.8, P<0.001) with longer RT in the more complex tasks, but not for group, nor for sensory modality ( Table 4, Fig. 3b). Only the interaction of group×complexity was significant (F1, 45=4.1, P<0.05) as BPD subjects performed faster in the more complex tasks. ANOVA 2 reproduced the effect for response type (F1, 45=14.6, Greenhouse–Geisser ε=1.00, P<0.001) and gave a significant effect for condition (F4, 180=34.6, P<0.001). RTs were longer in CROSS than in all other tasks (CROSS-VIS1: F1, 45=80.1, P<0.001, CROSS-VIS2: F1, 45=34.8, P<0.001, CROSS-AUD1: F1, 45=66.3, P<0.001, CROSS-AUD2: F1, 45=21.7, P<0.001). Only one interaction, group×condition, was significant (F4, 180=3.01, P<0.05). As both RT and accuracy varied, a speed measure was calculated [speed(hits)=number of hits/average RT for hits and speed(correct rejections)=number of correct rejections/average RT for correct reactions]. A repeated measures ANOVA gave a significant effect for group (F1, 45=5.21, Greenhouse–Geisser ε=1.00, P<0.03), for response type (F4, 180=89.3, P<0.001), and condition (F4, 180=62.6, P<0.001), but none of the interactions reached significance ( Fig. 3c). Table 4. Working memory: reaction times Task BPD Controls Mean±S.D. Mean±S.D. VIS1 hit 663±94 620±71 VIS1 correct rejection 604±71 584±55 VIS2 hit 775±112 747±98 VIS2 correct rejection 693±93 681±70 AUD1 hit 594±88 579±88 AUD1 correct rejection 601±70 563±76 AUD2 hit 678±95 674±86 AUD2 correct rejection 678±108 701±64 CROSS hit 755±133 821±98 CROSS correct rejection 800±165 840±91 This table indicates the mean RTs per group, condition and response type. Table options 3.4. Impact of psychopathology scores and medication on SOA and RT Pearson's r was calculated within the BPD group for DIB impulsivity and dissociation scores vs. SOA at criterion (BWM), RT for hits and number of correct responses (CROSS). None reached significance. When the three BPD patients taking tricyclic antidepressants were omitted from the analyses (BWM and DMS), essentially the same results were obtained and all effects preserved. Then, Pearson's r was calculated for correlations between both the dissociation score (FDS) and the BfS with SOA as criterion, mean RT for hits in each DMS task and the number of correct responses. No correlation reached significance