유기용제는 현기증, 행동장애, 주의산만, 말초신경증과 같은 신경 독성을 일으키는 물질로 잘 알려져 있다. 그러나, 이러한 신경 독성물질인 유기 용제에 노출된 근로자들이 작업 기억 기능을 수행할 때 인지 부하에 어떻게 영향을 받는지에 관해서 많이 연구가 되어오지 않았다. 따라서, 본 연구에서는 기능적인 자기공명영상을 이용하여 만성적으로 유기용제에 노출된 근로자들이 인지 부하에 따른 작업 기억 기능을 수행할 때 보여지는 신경 변화의 관계를 살펴보았다. 29명의 유기용제에 노출된 근로자들을 대상으로 언어적 작업 기억 기능(1-back and 2-back)을 수행시켰으며 낮은 인지 부하와 높은 인지 부하의 작업 기억 기능을 수행할 때, 인지 부하의 차이에 따라 활성화 되는 뇌 영역의 차이를 구하였다. 1-back의 반응속도가 증가함에 따라 좌측 하위 두정 피질에서의 뇌 활성화가 점점 증가하는 관계를 보였는데, 이러한 증가되는 양상이 더 높은 인지 부하인 2-back에서는 보여지지 않았다. 이를 통해, 인지 부하가 많이 걸릴수록 활성화 되는 뇌 영역이 많아지며, 유기용제에 노출된 근로자들은 어느 정도 낮은 인지 부하가 걸렸을 때는 그만큼의 뇌 활성화가 증가되는데, 높은 인지 부하가 걸리게 되면 더 이상 뇌 활성화가 증가되지 않고 한계에 다다르는 것을 알 수 있었다.
유기용제는 현기증, 행동장애, 주의산만, 말초신경증과 같은 신경 독성을 일으키는 물질로 잘 알려져 있다. 그러나, 이러한 신경 독성물질인 유기 용제에 노출된 근로자들이 작업 기억 기능을 수행할 때 인지 부하에 어떻게 영향을 받는지에 관해서 많이 연구가 되어오지 않았다. 따라서, 본 연구에서는 기능적인 자기공명영상을 이용하여 만성적으로 유기용제에 노출된 근로자들이 인지 부하에 따른 작업 기억 기능을 수행할 때 보여지는 신경 변화의 관계를 살펴보았다. 29명의 유기용제에 노출된 근로자들을 대상으로 언어적 작업 기억 기능(1-back and 2-back)을 수행시켰으며 낮은 인지 부하와 높은 인지 부하의 작업 기억 기능을 수행할 때, 인지 부하의 차이에 따라 활성화 되는 뇌 영역의 차이를 구하였다. 1-back의 반응속도가 증가함에 따라 좌측 하위 두정 피질에서의 뇌 활성화가 점점 증가하는 관계를 보였는데, 이러한 증가되는 양상이 더 높은 인지 부하인 2-back에서는 보여지지 않았다. 이를 통해, 인지 부하가 많이 걸릴수록 활성화 되는 뇌 영역이 많아지며, 유기용제에 노출된 근로자들은 어느 정도 낮은 인지 부하가 걸렸을 때는 그만큼의 뇌 활성화가 증가되는데, 높은 인지 부하가 걸리게 되면 더 이상 뇌 활성화가 증가되지 않고 한계에 다다르는 것을 알 수 있었다.
Organic solvents are known toxic effects like vertigo, behavioral obstacle, distracting, and peripheral neuropathy in neuron areas. However, there have been few studies how neurotoxic solvents-exposed workers are affected by the cognitive load of preceding working memory tasks. Therefore, we used fM...
Organic solvents are known toxic effects like vertigo, behavioral obstacle, distracting, and peripheral neuropathy in neuron areas. However, there have been few studies how neurotoxic solvents-exposed workers are affected by the cognitive load of preceding working memory tasks. Therefore, we used fMRI as to measure the neural correlates of working memory impairment in occupational workers who had from chronic exposure to organic solvent. Twenty-nine solvent-exposed workers were included in this study. Each participant concluded the verbal N-back tasks (1- and 2-back) during the fMRI acquisition. Within-group analyses showed fronto-parietal networks were active in each condition. Direct comparisons between 1- and 2-back showed higher activation during the 2-back than 1-back. We found that increased activation of these regions at lower task demand is associated with increased cost of implementing.
Organic solvents are known toxic effects like vertigo, behavioral obstacle, distracting, and peripheral neuropathy in neuron areas. However, there have been few studies how neurotoxic solvents-exposed workers are affected by the cognitive load of preceding working memory tasks. Therefore, we used fMRI as to measure the neural correlates of working memory impairment in occupational workers who had from chronic exposure to organic solvent. Twenty-nine solvent-exposed workers were included in this study. Each participant concluded the verbal N-back tasks (1- and 2-back) during the fMRI acquisition. Within-group analyses showed fronto-parietal networks were active in each condition. Direct comparisons between 1- and 2-back showed higher activation during the 2-back than 1-back. We found that increased activation of these regions at lower task demand is associated with increased cost of implementing.
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문제 정의
In this study, employing the N-back task with varying levels of load, our goal was to investigate activation patterns of cognitive load in individuals with chronic occupational exposure to solvent. As hypothesized, we found that solvent-exposed subjects exhibited significantly higher activation of the bilateral DLPFC, IPC, and cerebellum with increased cognitive demands during the N-back tasks.
제안 방법
However, no investigations have directly examined that how solvents-exposed subjects are influenced by the cognitive load of a preceding working memory task. Accordingly, in this study, we used fMRI to evaluate the neural correlates of organic solvent induced memory impairment in occupational workers with subclinical dysfunction in working memory networks as a consequence of chronic exposure to this neurotoxicant. We supposed that memory functional deficits were related to an increased cognitive demand on the working memory system.
Blood oxygenation level dependent (BOLD) contrast was collected for each subject using a 3.0 T GE EXCITE scanner (Milwaukee, WI) equipped with a transmit-receive body coil and a commercial eight-element head coil array. T2*-weighted echo-planar imaging was used for fMRI acquisition.
uk). Data were converted from DICOM to NIFTII format, processed using a slice timing correction with the first acquired slice to correct for temporal offsets in the acquisition of slices and spatially realigned and unwarped to the first image for correction movement and distortion. The mean fMRI volume and FSPGR were coregistered using mutual information, and normalized to the Montreal Neurological Institute (MNI) brain.
To ensure that the participants understood the task demands, they received instructions and rehearsed before they entered the MRI suite. The experiment utilized a blocked design with two epochs for each of the two experimental conditions (4 epochs in total). Each stimulus letter was visible for 500 ms and was followed by a fixation cross that randomly appeared for 2500 or 3500 ms.
In the within-group analyses, the N-back working memory tasks revealted that a network of frontal and parietal cortical areas was active in both two conditions (1- and 2-back). The network included activations in the dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), inferior parietal cortex (IPC), precuneus, and cerebellum (Fig. 2). Direct comparisons between two conditions (1- and 2-back) showed that, during the 2-back working memory task, the organic solvent-exposed subjects showed higher activation than performing the 1-back working memory task in the bilateral DLPFC, IPC, and cerebellum (Fig.
8) The normalized data were smoothed with isotropic Gaussian kernel of FWHM 8 mm. The pre-processed fMRI data were then entered into the first-level individual analysis by comparing fMRI activity during the N-back task with that during the 0-back (N-back＞0-back). In the second-level within-group analysis, contrast images from the analysis of individual subjects were analyzed by one-sample t-tests, there by generating a random-effects model, allowing inference to the general population.
대상 데이터
A total 29 solvent-exposed workers were recruited in this study. The subjects were 45.
The following acquisition parameters were used in the fMRI protocol: echo time (TE)=40 ms, repetition time (TR)=3000 ms, field of view (FOV)=22×22 cm, acquisition matrix=64×64. Using a midsagittal scout image, 31 contiguous axial slices with 4 mm thickness were placed along the anterior-posterior commissure (AC-PC) plane covering the entire brain. A 3-dimensional T1- weighted anatomical scan was obtained using fast spoiled gradient echo (FSPGR) for structural reference.
데이터처리
In the second-level within-group analysis, contrast images from the analysis of individual subjects were analyzed by one-sample t-tests, there by generating a random-effects model, allowing inference to the general population. And for the direct comparison between the conditions (2-back＞1-backand 2-back＜1-back), contrast images for the main effects were assessed using a two-sample t-test. The significant level of p＜0.
We used t-tests to examine N-back accuracy and reaction time in solvent-exposed subjects. Pearson correlation analyses were used to determine the correlations between mean percentage changes in BOLD fMRI signals in the activation brain regions and working memory performance in individual subjects. All statistical analyses were performed using SPSS software.
성능/효과
2). Direct comparisons between two conditions (1- and 2-back) showed that, during the 2-back working memory task, the organic solvent-exposed subjects showed higher activation than performing the 1-back working memory task in the bilateral DLPFC, IPC, and cerebellum (Fig. 3). No region showed significantly higher activation in the performing the 1-back task compared to the 2-back task.
The increased percentage BOLD signal change in the left inferior parietal cortex of the 1-back task compared to 0-back control condition showed a strong positive correlation (R=0.370, p＜0.05) with increased 1-back response time compared to 0-back control condition (Fig. 4). For the high-load-cognitive task (2-back), however, such a positive trend was not founded for any of the activated brain areas.
And for the direct comparison between the conditions (2-back＞1-backand 2-back＜1-back), contrast images for the main effects were assessed using a two-sample t-test. The significant level of p＜0.01 was used with correcting multiple comparisons by using the false discovery rate (FDR) method across the whole brain and clusters of fewer than 32 voxels were ignored.
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