INTRODUCTION
The impairment of executive functions1 2 3 4 4 5 6 7 3 8 9
The close interlinking of similar type of brain substrates and neural circuits in both executive dysfunction as well as in the OCD suggests a possible role of neuropsychological deficit condition in the pathogenesis of OCD. As the executive function is the basic mechanism to regulate the cognitive functions, an executive dysfunction is expected to interfere with the overall information processing system. It is surmised, therefore, that the cognitive style, which determines a mode of processing and organizing cognitive information by disembedding the figure from the ground, may, also be a function of one's neuro-psychological disposition. Since figure-ground visual perception depends on top–down processing of visual stimuli as well,10 9 11
With the objective to better understand the (i) status of executive function and cognitive style in patients with OCD as compared to normal controls, (ii) the neuropsychological disposition and its relationship with executive function and cognitive style in patients with OCD, and, (iii) the relationship of executive functions and cognitive style, a thorough neuropsychological investigation was carried out by employing the Adult Neuropsychological Questionnaire (ANQ), the Wisconsin Card Sorting Test (WCST) and the Embedded Figure Test (EFT).
METHODS
Sample
Twenty patients (14 males, 6 females) with OCD diagnosed using the DSM-IV criteria by psychiatrists of the Department of Psychiatry, R.G. Kar Medical College and Hospital, Kolkata, were included in the study. All the selected patients were right-handed, urban individuals, with at least Standard X educational level without having a history of head injury, neurological disease, past psychiatric disorder, alcoholism or any drug abuse. Their age ranged from 18 to 63 years with a mean and standard deviation of 35.65 years and 12.89 years, respectively. The severity of their symptoms was assessed on the Yale-Brown Obsessive Compulsive Scale14 n =7), ‘moderate’ (n =8) and ‘severe’ (n =5) subgroups.
Twenty subjects who matched in all respect with the OCD patients were selected to serve as normal controls. Their age ranged from 18 to 62 years with a mean and standard deviation of 35.55 years and 12.79 years, respectively. These individuals consumed no drugs that are known to affect the functions of the central nervous system. Detailed case history eliciting absence of neurological/neurosurgical problems obtained along with the below cut-off score on Mini Mental Status Examination (MMSE)12 13
Measures
The following measures were used:
Yale-Brown Obsessive Compulsive Scale (Y-BOCS)14
Wisconsin Card Sorting Test (WCST)15
General Health Questionnaire (GHQ)13
Mini Mental Status Examination (MMSE)12
Adult Neuropsychological Questionnaire (ANQ)16
Embedded Figure Test (EFT)17
Procedure
Following the inclusion and exclusion criteria as mentioned in the ‘sample’, 20 patients with OCD diagnosed by psychiatrists were taken up for the study. First, the Y-BOCS was applied on them and categorized under mild, moderate and severe subgroups. Twenty normal healthy individuals were selected following the inclusion and exclusion criteria and screening through the GHQ and MMSE. All the 40 individuals were administered the WCST to investigate their executive ability. The variables of the WCST considered were: perseverative responses (PR), perseverative errors (PE), non-perseverative errors (NPE), conceptual level response (CLR), number of categories completed (NOCC).
This was followed by administering the ANQ, which provided scores on the neuropsychological status of the following domains: general health (GH), substance abuse (SA), psychiatric problem (PP), general neurological (GN), right hemisphere (RH), left hemisphere (LH), subcortical–cerebeller–spinal (SCS) and sensory or perceptual (S/P).
The EFT was then administered and information was collected on cognitive style of field dependence or independence.
Statistical treatment
Means (X) and standard deviation (SD) were computed for each of the chosen variables from the WCST, ANQ, EFT. The Mann-Whitney U Test for independent sample was computed for each variable to evaluate the intergroup comparison on all the variables. The difference between the two groups on particular variables was considered as significant only when the probability of occurrence was beyond 0.05 level. The Spearman correlation was computed to find out the relationship between the domains of ANQ and the variables of WCST and EFT.
RESULTS
The data obtained on 8 domains of ANQ have been given in Table 1 and graphically represented in Fig. 1 . Table 1 shows that the patients with OCD obtained significantly higher scores, denoting a deficit with respect to their neuro-psychological status on all the variables of ANQ except in the domains of SA and S/P. The failure of the domain of SA to distinguish the two groups may be owing to the criteria of exclusion of substance abusers from the study. As expected, the OCD being an anxiety disorder with intact judgement and insight, showed no difference on the domains of S/P function from their normal counterparts.
Fig. 1: Comparative status of the patients with OCD and normal controls on Adult Neuropsychological Questionnaire
Table 1: Comparative status of the patients with OCD and normal controls on Adult Neuropsychological Questionnaire
The significantly higher mean score on EFT in patients with the OCD in comparison to the normal controls reveals a significantly greater field dependence in them (Table 2 , Fig. 2 ). Low scores on the dimensions of PR, PE, NPE, CLR, and NOCC of WCST in the OCD group reflect executive dysfunction.
Fig. 2: Comparative status of the patients with OCD and normal controls on Embedded Figure Test and Wisconsin Card Sorting Test
Table 2: Comparative status of the patients with OCD and normal controls on Embedded Figure Test and Wisconsin Card Sorting Test
Table 3 shows that there exists an inter-correlation between GH and all other variables of ANQ whereas GN and PP were found to be highly correlated with RH, LH, SCS and S/P. An interesting observation is that SCS, SP and PR were closely related to LH deficits and although S/P did not show any significant group difference, its positive correlation to SCS and CLR could have a clinical significance. Considering the general neurological disposition and executive function, it is noted that PP as well as left hemispheric dysfunction is positively related to perseveration (PR and PE) and RH dysfunction is correlated with NPE. Regarding the EFT a positive correlation is obtained with GH and SCS (Table 3 ).
Table 3: Correlation between variables of ANQ and WCST and EFT
DISCUSSION
That the OCD group has impairment in neuropsychological disposition, cognitive style and executive functions is evident from the comparative evaluation of the data obtained from the 2 groups. As a neuropsychological deficit condition is observed in the OCD group, their performance on each of its variables warrants an explanation.
The poor general health condition as reported by the OCD on the ANQ seems to arise from their persistent and uncontrollable thoughts that cause feelings of distress in them, giving rise to anxiety and irritability, which interferes with their everyday functioning. The catabolic conditions initiated by their chronic anxiety state have the possibility to prime their attention bias towards their health status in 50% of the patients in the present study.
The domain of psychiatric problem as assessed on the ANQ reflects the symptoms of OCD, characterized by the presence of recurrent thought and worries. The correlation of PP with RH, LH, SCS and S/P suggests that psychiatric symptoms are associated with the thought which the patients are neither able to suppress nor mould, resulting in the interference with their test performance.
The deficit observed in the general neurological status as felt by the patients in comparison with the normal controls, is in good agreement with the results of other studies, which suggests that OCD symptoms are mediated by multiple brain regions, including anterior cingulate gyrus,18 6 19 11 7
The greater random error observed through the higher score on the variable of NPE of the WCST in the OCD group in comparison with the normal controls indicates it to be the function of an individual's arousal and attentional system. Accordingly, the significant correlation between neuro-psychological dysfunction of RH and NPE may be attributed to its mediation through RH, owing to the greater reti-culocortical and corticoreticular innervation to the RH than the LH.20 2
The deficit function of the SCS domain observed from the response of the OCD group corroborates with the findings of the previous researchers who showed impairment in the limbic and subcortical circuitry, specifically in the putamen and caudate nucleus of the basal ganglia,11 21 22 23 24 25
Regarding cognitive style, an inverse correlation between the score of NOCC and that of EFT suggests an association between field dependence and poor number of category completion, an index of poor cognitive flexibility, indicating less cognitive differentiation with set shifting difficulty confirms that dysexecution6
CONCLUSION
The performance of the OCD group on the WCST and EFT revealed that they have less cognitive differentiation and impairment in executive function compared to the normal control group. The SCS function as evident on the ANQ is found to be associated with these functions. Moreover, the impaired executive function is also linked with field-dependent cognitive style.
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