اختلال عملکرد موتور در اختلال شخصیتی

Abstract Past research has revealed that schizophrenia is associated with voluntary movement abnormalities, as well as higher rates of involuntary movements. On instrumental motor tasks, patients manifest reduced motor stability, excessive force and more contralateral motor overflow (movement in the non-responding hand). In the present study, an instrumental motor task (manual response forced-choice task) was administered to a group of adults with schizotypal personality disorder (SPD) in order to determine whether they show motor deficits similar to those observed in schizophrenia. As predicted, the schizotypal subjects were excessive and more variable in motor force, compared to healthy controls and other personality-disordered subjects. Additionally, the force and variability of the motor responses were positively correlated with ratings of both positive and negative SPD symptoms. Finally, motor overflow and negative symptoms were associated with higher salivary cortisol levels. The pattern of findings is consistent with previous reports linking motor abnormalities and heightened cortisol with schizotypal personality disorder.

Introduction Some relatives of schizophrenia patients manifest a personality syndrome (e.g. schizotypal personality disorder; SPD) that resembles the symptoms of schizophrenia (e.g. Kendler and Walsh, 1995, Maier, 1994 and Torgersen, 1994). Moreover, factor analytic studies indicate that these personality features parallel the positive, negative and disorganized symptom dimensions of schizophrenia (Bergman et al., 1996, Raine et al., 1994 and Vollema and van den Bosch, 1995). It has also been shown that there are biological, cognitive and phenonmonological similarities between schizophrenia and SPD (e.g. Siever, 1994 and Siever et al., 1993). For instance, Lees-Roitman et al. (1997) recently reported that schizotypal subjects display attentional impairments that are similar in pattern to those seen in schizophrenia. Also, similar to schizophrenia patients, individuals with symptoms of SPD display reaction time cross-over deficits (Drewer and Shean, 1993 and Sarkin et al., 1998), reductions in prepulse inhibition (Cadenhead et al. 1993), facial recognition deficits (Mikhailova et al., 1996), reduced P300 amplitudes over the left temporal lobe (Sailsbury et al., 1996), retarded habituation in skin conductance orienting (Raine et al., 1997) and more perseverative errors on the Wisconsin Card Sort Test (Raine et al., 1992). Spontaneous movement abnormalities have been documented in numerous studies of schizophrenia patients, both medicated and neuroleptic-naïve [for a review, see Walker (1994)]. A recent investigation found that individuals with schizotypal personality manifested more spontaneous dyskinetic-like movements than subjects with schizoid personality or healthy controls (Cassidy et al., 1998). Similarly, Walker et al. (in press) found that adolescents with SPD showed an elevated rate of spontaneous involuntary movements when compared with normal adolescents and those with other personality disorders. Walker et al. (in press) also found that salivary cortisol levels were positively correlated with the rate of involuntary movements. It is noteworthy that schizophrenic patients show abnormalities in daily cortisol levels and a reduction in the normative later-day decline (Kaneko et al., 1992 and Van-Cauter et al., 1991). That is, cortisol levels naturally decline during the afternoon, but schizophrenic patients have been found to show less of the expected decline over the course of the day. Therefore, one would expect group differences in cortisol to be maximized during the later afternoon. In order to measure motor dysfunctions more precisely, some investigators have developed instrumental procedures that index motor pressure and stability. Using an instrumental motor task, Caligiuri and Lohr (1994) examined voluntary control of a steady-state force and found that neuroleptic-naïve schizophrenia patients showed more manual force instability than comparison subjects. These authors also found that force instability was correlated with positive, but not negative, symptom ratings. Similarly, Vrtunski et al. (1989) administered a bimanual, choice reaction-time task and found that schizophrenia patients, compared to normals and psychiatric controls, displayed a greater force instability, increased peak force, and more contralateral motor overflow (increased force in the non-responding hand). The latter measure, motor overflow, is suggestive of involuntary movement. Schizophrenia patients on and off medication did not differ on any of the motor indices. These and related findings suggest that the brain regions that give rise to schizophrenia and spectrum disorders may also play a role in motor regulation. Further, because motor dysfunction is known to precede the clinical onset of schizophrenia by many years (Walker et al., 1994), motor assessments may be promising, along with other indicators (Neumann and Walker, 1996), for identifying individuals at risk. Compared to clinical ratings based on observations, instrumental motor assessment procedures appear to offer a more precise and objective approach to the delineation of motor abnormalities. To date, instrumental procedures have not been used in studies of subjects at genetic or behavioral risk for schizophrenia. In the study described here, a motor task similar to that employed by Vrtunski et al. (1989) was administered to SPD subjects to determine whether they showed a performance profile similar to that observed in schizophrenia. The computerized task used in this study assesses multiple aspects of motor function, including reaction time (RT), movement time (MT), force, force instability and contralateral motor overflow (involuntary movement—IM). A key feature is its capacity to differentiate reaction time (RT) from movement time (MT), with the former being determined by both cognitive and motor factors, and the latter being predominantly determined by motor factors (bradykinesia). It yields indices that have been shown to differentiate various syndromes of motor dysfunction. For example, patients with Parkinson's disease, a DA depletion disorder, show a pronounced increase in MT, but not RT or IM (Ebmeier et al., 1992), whereas schizophrenia patients manifest increased RT and IM, but not MT (Caligiuri et al., 1993). We tested the hypotheses that SPD subjects, when compared to normals and subjects with other personality disorders, will manifest a greater variability in motor force, higher response force and more contralateral motor overflow. The asociations of motor indices with symptom ratings and cortisol release were also examined.

. Results Demographic data for the subjects are presented in Table 1. The three groups did not differ significantly in mean age or education in years (all p values >0.05), nor did the groups differ in the proportions of females, although there was a trend toward more females in the OPD group [Chi(2)=2.05, p>0.05]. Table 1. Subject characteristics for schizotypal personality disorder (SPD), other personality disorder (OPD), and no personality disorder (NPD) groups Subjects Age Education M/F M (s.d.) M (s.d.) SPD 41 (10.84) 16 (2.36) 7/10 OPD 45 (14.39) 16 (0.99) 1/7 NPD 35 (17.83) 16 (2.41) 10/19 Table options To address the study hypotheses, initial analyses of group effects were carried out via a multivariate analysis of variance (MANOVA) using the motor data for mean force, mean force variability and motor overflow for both hands. The results of the MANOVA indicated a significant effect for group, Wilks lambda=0.589, F(12, 88)=2.23, p<0.05. The means and standard deviations for the motor data are listed in Table 2. Table 2. Means and standard deviations for motor response indices (mV and ms) and cortisol level (μg dl−1)a Variables NPD SPD OPD Group differences Mean s.d. Mean s.d. Mean s.d. Mean force—LH (mv) 0.4902 0.190 0.5502 0.253 0.4236 0.177 Mean force—RH (mv) 0.5970 0.267 0.7694 0.359 0.5518 0.226 SPD>NPD, OPD Mean force variability—LH (mv) 0.1680 0.072 0.1894 0.101 0.1379 0.076 Mean force variability—RH (mv) 0.2061 0.090 0.2958 0.162 0.1562 0.064 SPD>NPD, OPD Right motor overflow—LHb 0.026 0.347 0.197 0.271 −0.127 0.265 SPD>NPD, OPD Left motor overflow—RHb 0.131 0.241 0.232 0.319 −0.004 0.264 SPD>OPD Movement time—LH (ms) 550 160 442 131 514 128 NPD>SPD Movement time—RH (ms) 532 148 428 95 533 118 NPD, OPD>SPD Reaction time—LH (ms) 657 179 614 146 603 81 Reaction time—RH (ms) 630 154 599 153 570 84 Cortisol 1 p.m. 0.5 0.4 0.46 0.24 0.35 0.14 Cortisol 2 p.m. 0.36 0.16 0.4 0.34 0.39 0.18 Cortisol 3 p.m. 0.25 0.13 0.33 0.14 0.3 0.13 SPD>NPD Cortisol 4 p.m. 0.2 0.12 0.3 0.17 0.21 0.12 SPD>NPD Mean cortisol 0.31 0.15 0.35 0.16 0.3 0.12 a LH: left-hand response; RH: right-hand response; SPD: schizotypal personality disorder; OPD: other personality disorder; NPD: no personality disorder. b Motor overflow represents the mean correlation of applied pressure between two hands during all left- or right-hand responses; the greater the positive correlation, the more the overflow in the non-responding hand. Table options Because of a trend for more females in the OPD group, the MANOVA was re-run with sex as a covariate using all three groups; whereas the group effect remained significant, the covariate was not significant, Wilks lambda=0.868, F(6,43)=1.08, p>0.05. Univariate analyses involved specific planned tests for group differences using t-tests. When compared to the NPD group, the SPD subjects displayed a greater mean force with their right hand [t(42)=−1.82, p<0.05], more variability in mean force for their right hand [t(42)=−2.37, p<0.05], and more right-handed motor overflow during a left-handed response [t(42)=−1.69, p<0.05]. Finally, the SPD subjects showed significantly shorter movement times for both their right hand [t(42)=2.50, p<0.01] and their left hand [t(42)=2.28, p<0.05], compared to the NPD subjects. There were no differences between the SPD and NPD groups in reaction time. In comparing the motor responses of the OPD and SPD groups, the SPD subjects showed a greater variability in mean force for their right hand [t(22)=2.34, p<0.05], more left-handed overflow during right-handed responses [t(22)=1.80, p<0.05] and more right-handed overflow during left-handed responses [t22)=2.78, p<0.01]. The SPD subjects were also faster in movement time compared to the OPD subjects for their right hand [t(22)=2.36, p<0.05]. There was also a trend for the SPD subjects to manifest a greater right-handed mean force [t(22)=1.56, p=0.06] than the OPD group. (Note that the OPD group contained a small number of subjects, thus reducing the statistical power for detecting group differences.) The NPD and OPD subjects were not significantly different on any of the motor variables. There were no significant group differences in cortisol for the 1–2 p.m. assessments. (See Table 2 for means and standard deviations.) However, the SPD subjects had a higher cortisol level at the 3 p.m. [t(41)=−2.04, p<0.05] and 4 p.m. [t(39)=−2.18, p<0.05] assessments, compared to the NPD subjects. The results above should be interpreted with caution because no correction for multiple comparisons has been made. Pearson correlation coefficients were computed to examine the relation of the SPD symptom composites (SPD-Pos, SPD-Neg) with the motor and cortisol data; these correlations are presented in Table 3 and are based on the total sample. Both schizotypal symptom composites show significant correlations with the motor indices. Specifically, for both left- and right-handed responses, increases in mean force are correlated with increases in both positive (SPD-Pos) and negative (SPD-Neg) schizotypal symptoms. However, for right-handed responses only, increases in mean force variability were correlated with increases in both positive and negative SPD symptoms. Table 3. Intercorrelations between symptom scores, cortisol level and motor functioning (total sample, n=54) a Cortisol level SPD-POS SPD-NEG 1 p.m. 2 p.m. 3 p.m. 4 p.m. Cortisol level 1 p.m. −0.06 0.11 Cortisol level 2 p.m. 0.03 0.17 0.47b Cortisol level 3 p.m. 0.06 0.14 0.30c 0.55b Cortisol level 4 p.m. 0.20d 0.25c 0.22d 0.70b 0.53b Mean force—LH 0.28c 0.26c −0.16 −0.21d −0.22d 0.03 Mean force—RH 0.30c 0.34b −0.09 −0.12 −0.09 0.04 Mean force variability—LH 0.18 0.12 0.06 −0.07 −0.16 0.09 Mean force variability—RH 0.29c 0.36b 0.08 −0.10 −0.07 0.01 Left motor overflow—RHe −0.07 0.10 0.18 0.15 0.22d 0.29c Right motor overflow—LHe −0.06 0.17 −0.03 0.10 0.18 0.27c a SPD-POS: positive schizotypal symptoms; SPD-NEG: negative schizotypal symptoms; LH: left-hand response; RH: right-hand response. b p<0.01. c p<0.05 d Trend, p<0.08. e Motor overflow represents the mean correlation of applied pressure between two hands during all left- or right-hand responses; the greater the positive correlation, the more the overflow in the non-responding hand. Table options Only the SPD-Neg composite was significantly correlated with the 4 p.m. cortisol level (note that the SPD-Pos composite does approach significance with this variable, p=0.078). Lastly, the left-hand and right-hand motor overflow measures were significantly, but moderately, correlated with 4 p.m. cortisol (r=0.29 and r=0.27, respectively, p<0.05; see Table 3).