Executive Function Impairment Of Schizophrenia:a Graded Tower Of London Study

BackgroundSchizophrenia is a common psychological disorder without exact causes, which is usually conjugated with unique perception, thought, emotional and behavioral dysfunction, lacking of coordination between psychological activities and the surroundings, lengthening of the morbid condition, and displaying variable in clinical. Cognitive impairment is one of the core symptoms in schizophrenia, while execution is the overall display of cognitive function; executional dysfunction mainly comes from the abnormalities in prefrontal cortex (PFC), which could display as difficulty in formation, planning, completion and execution, thus ending in difficulty in problem-solving and lowered problem correction skill. The Tower of London (TOL) is one of the classic tasks that examine an individual’s problem-solving skill. An individual’s result in TOL is in relation to one’s executional skill level, as well as the difficulty of TOL. Near-infrared spectroscopy (NIRS), the other means of examination in this study, is a pragmatic, non-invasive functional imaging technique; it may measure the shift of blood-oxygen and local blood volume in different cortical region under real-time basis, thus achieve the brain dynamic monitoring under real cognitive processing.Objective①To compare the executional function between schizophrenia patients and healthy subjects as well as the correlation with the subjects’relative psychological symptoms.②To study schizophrenia and healthy individuals’PFC activity level and activity mode under different difficult levels of TOL tasks, and the effect of TOL task difficulty on PFC activity; moreover, we will discuss the relationship between the change in PFC and the executional dysfunction.Methods①40schizophrenia patients and40healthy individuals were divided into two groups and performed electronic TOL task to record the response time and the number of correct answer. For the psychological symptoms, we used positive and negative symptoms scale (PANSS) to rate the individuals. Based on the necessary moving steps, we compared the TOL results between the healthy and the schizophrenic group, as well as analyzing the relationship between the PANSS score and the TOL result.②Ranking the TOL tasks into easy, medium, and difficult task as stimulus of the block design in this experiment, we recorded the response time and the number of correct response, simultaneously collected signals with28-channel NIRS system in order to monitor the hemodynamic changes and hemoglobin concentrations, established the different show under the different TOL level and compared the TOL results with PANSS scores to analyze the difference of PFC activity level and activity mode between the two groups.Result①Schizophrenia patients had a significantly lower numbers of correct response in the1-4step TOL tasks compared to the healthy (P＜0.05), while the numbers of correct response were showed no significant difference in5-step and6-step tasks. In all levels, patients had significantly longer response time than the healthy (P＜0.05). The response time for1-4step TOL task had a positive relation to both the score of negative symptoms and the score of cognitive impairment (P＜0.05), while the number of correct response in3-step and4-step TOL tasks was negatively related to negative symptom score and cognitive impairment score(P＜0.05) and furthermore the overall number of correct response is negatively related to cognitive impairment score (P＜0.05).②Behavioral tests’ data implied that in the schizophrenic group, the numbers of correct response in all three levels were significantly lower than the control group (P<0.05), while the response time were all significantly longer(P＜0.05). For the schizophrenic group, the number of correct response in medium level was negatively related to the negative symptom score, and the response time was positively related to negative symptom score in easy and medium level. NIRS results stated that most regions of PFC in healthy group were distinctively activated but in schizophrenic individuals, most PFC activations were apparent in easy tasks, nearly one-third of the PFC regions were not clearly activated in medium level, while in difficult level, only a small portion of the PFC regions were activated in obvious. The difference in activation mode is neither related to left and right hemisphere nor dorsolateral/mid-PFC partitioning under TOL stimulus. The hemoglobin concentrations in most regions of PFC of schizophrenia patients were lower than the control in all three tasks, and the difference was even more evident in dorsolateral prefrontal cortex (DLPFC) with no dominance. The shift in hemoglobin concentration indicated that DLPFC was greater than mid-PFC. In the health, the mid-PFC hemoglobin concentration was greatest in the medium level, and minimal in the difficult level, while, in DLPFC, the easy and medium level had a similar hemoglobin concentration shift, both being greater than the difficult level. In schizophrenia patients, the mid-PFC hemoglobin concentration differences between difficulties were insignificant; in DLPFC, the hemoglobin concentration decreased as task difficulty increases. In the time for [oxy-Hb] to reach its peak, the result showed that the hemoglobin concentration change was slower than the healthy individual.Conclusion①In schizophrenia patients, the executional skill is impaired, and it is mainly displayed as difficulties in formulating and completing plan, as well as lowered efficiency in executing plans, especially in relatively more complex and difficult problem-solving tasks.②The negative symptoms of schizophrenia are related to executional skill impairment, but the impairment is only apparent in appropriate task difficulties (i.e.3-and4-step, medium level TOL tasks).③Lowered PFC function is one of the brain function anomalies that differ schizophrenia patients from healthy individuals, which is mainly represented as changes in PFC hemodynamics and brain activation level and mode during task performance.④DLPFC is the main portion participating in execution, which may be the top brain region and temporary information storage area of relative information in top-down execution.⑤The difficulty in TOL has a great effect in task performance and NIRS brain function monitoring; comparing to the easy and the difficult task levels, the medium level task is more suitable and effective for the comparison between healthy and schizophrenic individuals.⑥NIRS is a very practical method for brain function examination; it has effective spatial and temporal resolution; the combination of NIRS and neuropsychological tests may reflect real-time changes in blood flow and hemoglobin concentrations in different cerebral regions, which is highly applicable in studies relating to brain function impairment and etiology of psychological disorders.