Introduction
It is well known that mood, psychotic and substance use disorders are the most prevalent mental illnesses in the southern region of Peru 1, where, in addition, mental health services are limited or inadequate for both, assessment and follow-up interventions and, particularly, those related to the neuropsychological examination of cognitive profiles. The literature related to this topic reports on the difficulties at familiar, social and professional levels, as well as compliance with treatment programs 2. In this context, the results of neuropsychological evaluations have been associated to the level of commitment to treatment, its results and relapse risks, with a greater cognitive impairment seemingly related to better levels of recovery among patients with schizophrenia and alcohol abuse or dependence 3,4,5,6.
Moreover, Chambers et al., report that, in many cases, there is a close relationship between vulnerability to addiction and schizophrenia, the former preceding the latter 7, which also seems to be related to abnormal brain development 8. In addition, neural abnormalities in schizophrenia appear to match the neural substrates that regulate addictive behaviors, e.g., mesolimbic and mesocortical circuits 7. Many studies claim that patients with schizophrenia and alcohol dependence or abuse disorder show an active neurophysiological involvement of these circuits eventually leading to cognitive impairment 9. Against this background, the most affected cognitive skills in both types of patients would be attentional control, abstract reasoning, cognitive flexibility, strategic global planning, sequential response, and working memory 3,6,10,11,12. All these processes are linked to the executive function 13; but, not to be forgotten, verbal memory, verbal fluency and motor speed also seem to be affected 14.
In schizophrenia, marked cognitive deficits have been described mainly in the areas of attention and visual working memory 6,4,9; within the impaired attentional system, deterioration predominates in the areas of executive attentional network (in charge of inhibitory control) 15 and sustained attention 16. These shortcomings are more noticeable when the disease has evolved for longer periods. Within the memory problems, episodic memory shows most damage 16; the memory system is, in fact, the most demanding of all processes because it requires a temporal-space context 17.
Thus, cognitive impairment in executive function is a permanent and central feature of schizophrenia, in cases of both, remission or relapse 5. Executive function has to do with an integrated set of cognitive skills involved in the generation, monitoring and control of goal-directed behaviors 18. The alterations in executive functions have historically been considered prototypical pathology of the frontal lobe, mainly through lesions affecting prefrontal dorsolateral 19, orbitofrontal 20 and cingulate 21 regions. As a whole, this would cause a “dysexecutive syndrome” affecting the regulation of cognition and behavior. Laurenson et al., 5 found that cognitive processes related to attentional and semantic components, not only cognitive inhibition, are impaired.
In the alcoholism camp, Corral-Varela & Cadaveira 2 report that not all alcoholics manifest cognitive impairments. That is, changes observed in executive functions and memory are interpreted as increased impulsivity and specific vulnerability of the frontal lobes to the toxic effects of alcohol 12,22,23. Besides, in substance abuse patients, there would be a further deterioration at both attentional level and in the processing of emotions, in addition to impairment in executive functions. However, Bates et al., 22 and Cabe et al., 3, indicate that the strength of the different cognitive impairments present in alcoholic patients is varied and very heterogeneous.
In a review of brain and cognitive impairment in alcohol-dependent subjects, Bernardin et al., showed a “striking” level of brain atrophy in the frontal lobes, the limbic system and the cerebellum 24. These were related to alterations in executive function, memory systems and motor coordination. The authors concluded that it is important to analyze the cognitive processes in these patients in order to better tailor the treatment and alleviate the difficulties of daily life.
In short, there are patterns of deterioration in memory and executive function, seemingly associated to deficiencies in prefrontal and temporal-medial structures in both disorders. However, the level of deterioration brought about by these pathologies vis- à-vis the brain circuits, remains uncertain, considering especially the close linking between addiction and schizophrenia during the CNS developmental process 7.
Given this reality it is necessary to have a better understanding of the cognitive profile of the two disorders, as it could help to improve the treatment, achieve its goals more effectively, and strengthen the patients’ cognitive processes. This could even be an important predictor of remission and patient’s functionality (3, 5). Such is the objective of our study: to compare the cognitive performance of both patients with schizophrenia and alcohol-dependent patients by means of a short test battery of neuropsychological evaluation (NEUROPSI). This analysis will allow us to identify the levels of cognitive involvement and use it as a foundation to a better sequence of treatment and follow-up of these patients.
Material and methods
This is an observational/comparative study on patients with pre-existing clinical diagnoses. Fifty patients were tested, 18 with the clinical diagnosis of mental disorders due to alcohol (F10), and 32 diagnosed with schizophrenia (F20), at the NationalHospital ES SALUD “Carlos Seguin Escobedo” in the city of Arequipa, Perú. The probands’ ages ranged between 17 and 70 years, with an average of 50. 70% of the sample was male(n = 35), and 30%, female (n = 15). From a clinical view, there was a high variability in duration of illness and number of hospitalizations (table 1).
Table 1.MinimumMaximumMeanSDFrecuencyPercentageWe used the Mexican version of the brief neuropsychological test battery (in Spanish) NEUROPSI, developed by Ostrosky, Ardila and Rosselli in 1994. This battery has not been used in previous psychometric studies in Peru. It assesses cognitive functions such as orientation, attention and concentration, language, memory, executive functions, reading, writing and arithmetic. It takes approximately 25 to 30 minutes to be individually performed, by probands aged 16 or more, and can be applied to illiterate and poorly educated people.
Assessment sessions, approximately 50 minutes long, were conducted in hospital settings. After the assessment and rating of the test battery, raw scores were converted to z scores to better appreciate the eventual contrasts between the two groups. Nonparametric contrast statistic tests were used.
Results
The results show significant differences in executive function (U = 154, p <.05), memory (U= 162.5, p <0.05), and the overall score (U = 164, p<0.05) between the two groups (table 2).
Alchoholic patients | Ezquizophrenia patients | |||||||
---|---|---|---|---|---|---|---|---|
Mean | SD | Mean | SD | Mann Whitney U | p value | |||
Orientation | 5.78 | .548 | 5.41 | .946 | 232.5 | .155 | ||
Attention | 16.56 | 5.008 | 13.84 | 3.819 | 214.0 | .132 | ||
Concentration | 21.72 | 30.835 | 24.31 | 34.880 | 256.5 | .521 | ||
Language | 21.78 | 1.734 | 20.56 | 2.435 | 211.0 | .115 | ||
Reading | 2.28 | .826 | 2.19 | 1.030 | 285.0 | .947 | ||
Writing | 1.94 | .236 | 1.94 | .354 | 281.5 | .699 | ||
Executive F. | 14.44 | 2.307 | 11.78 | 3.471 | 154.0 | .006** | ||
Memory | 20.00 | 5.678 | 15.38 | 6.499 | 162.5 | .011* | ||
General score | 99.12 | 13.720 | 84.77 | 15.970 | 164.0 | .032* |
An analysis of covariance was subsequently conducted to analyze the effect of demographic and clinical variables of the sample. It is noted that the level of education (F = 16,327, p <.05), diagnosis (F= 9.154, p <0.05) and number of hospitalizations (F= 7.537, p <.05) have a significant effect on the total scores on the NEUROPSI (table 3).
Origin | Type III sum of squares | gl | Quadratic mean | F | Sig. | Partial eta squared |
Corrected model | 4448,834a | 7 | 635.548 | 6.426 | .000 | .577 |
Intersection | 9217.172 | 1 | 9217.172 | 93.190 | .000 | .738 |
Age | 231.400 | 1 | 231.400 | 2.340 | .136 | .066 |
Hospitalizations | 745.483 | 1 | 745.483 | 7.537 | .010 | .186 |
Time of illness months | 9.070 | 1 | 9.070 | .092 | .764 | .003 |
Years of instruction | 1614.909 | 1 | 1614.909 | 16.327 | .000 | .331 |
Diagnostic | 905.382 | 1 | 905.382 | 9.154 | .005 | .217 |
Background | 1.133 | 1 | 1.133 | .011 | .915 | .000 |
Diagnostic * background | 326.152 | 1 | 326.152 | 3.298 | .078 | .091 |
Error | 3263.947 | 33 | 98907 | |||
Total | 355289.000 | 41 | ||||
Total corrected | 7712.780 | 40 | ||||
to. R Squared = 577 (R square = the set, 487) |
Discussion
The main finding of this study was that patients with the diagnosis of alcoholism performed cognitively better than those with schizophrenia in memory and executive function. These results were similar to those of other investigations 25,26,27,28, also reporting on several factors that could mediate the degree of cognitive impairment in both groups. However, it has also been mentioned that in addition to memory and executive functions, other processes such as attention are severely affected in both groups of patients. This would be associated with the alteration level of the circuits that underly these processes 20.
It is known that the brain involvement of a patient with schizophrenia includes the prefrontal and medial temporal cortices 21, whereas in the case of alcoholics, the medial temporal involvement is greater 29. Thus, the profile of alterations observed in executive functions and memory, correspond to these areas; which may even be associated with alterations in executive memory components, including encoding and retrieval of information. In the case of alcoholic patients, the main impact would be on consolidation 30.
In the same context, Landa, et al., 27, and Barrera 25 maintain that deficiencies in both alcoholic and patients with schizophrenia, focus on working memory which, in turn, affects declarative episodic long-term memory. Yet, Landa et al., also assert that semantic memory seems to remain preserved in alcoholic patients 27, but not so in patients with schizophrenia who, rather, show severe impairment of verbal and spatial declarative memory. It is important to note that, as stated by Bustamante-Quiroz 31 and Barrera 25, these alterations are associated with chronicity and other aspects of the clinical course in schizophrenia. This would explain the impact of the number of hospitalizations in the patient’s cognitive performance. Conversely, as seen above, in patients with schizophrenia the disorder in declarative memory has been attributed to a dysfunction of the medial temporal lobe 26, while in alcoholic patients, it may be due to a deficiency in the memory circuit that includes structures vulnerable to thiamine deficit reaching, on occasions, clinical levels of Wernicke - Korsakoff encephalopathy 32.
On the other hand, the executive functions are clearly affected in both conditions. Neuropsychological explanations can be found in underactive frontal lobes, measured by functional neuroimaging techniques 33. For schizophrenia, the most significant dysfunction occurs in the dorsolateral prefrontal cortex (DLPFC), which would be associated with deficits in working memory 34. An abnormality in the functional connectivity between frontal and temporal lobe has also been pointed out, implying a hyperconnectivity between these regions although at a random and very inefficient activation level 35. In addition, dysfunctions have been observed in subcortical regions, with failures in the thalamus-cortical integration 32. These studies conclude that schizophrenia would be a pathology linked to a progressive disengagement of the brain.
We have observed that the pattern of cognitive impairment is strongly influenced by the education level of patients. This has been corroborated in other studies, conducted in contexts like ours 36. As it is known, exposure to formal schooling changes the brain circuits making them more efficient, and preparing them for increasingly complex and/or abstract tasks 37. This has frequently been observed in studies with healthy samples of varying schooling levels 36, and even in clinical samples 39. Therefore, it is necessary to measure the pattern and degree of involvement considering this factor and assessing its actual weight when facing the implementation of intervention strategies.
To conclude, these initial data show an interesting cognitive pattern that should be extended to a wider battery of neuropsychological assessments, including follow-up studies. In addition, it would be relevant to deepen the neurophysiological foundations of these pathologies, especially to clarify the link between memory tasks and executive function, as well as to analyze patterns of disconnection between different brain structures. In this respect, assessments that evaluate the degree of participation of the different processes have been developed, considering that brain connectivity is more relevant than an individual process assessment, especially for outset strategies 40. Likewise, assessments must be expanded to all cognitive processes, attempting to deep in the connections between the two conditions in order to clarify the presence of dual pathology or comorbidity. Finally, it is relevant to develop intervention strategies that target the rehabilitation of cognitive processes, particularly in the area of executive functions, which seem to show very interesting prospects in the patients’ functional and social reintegration processes 41,42.