INTRODUCTION

Previous studies have shown that computerized cognitive training (CCT) targeted at a specific cognitive function such as attention can also improve other cognitive functions such as general intelligence, via near and far-transfer effects. Of the CCT programs, combined CCT is designed to improve several cognitive functions simultaneously. However, only a few studies^1,2 have reported about the effectiveness of combined CCT, and it is not known whether the transfer effect is augmented. We developed a combined CCT program designed to improve working memory and attention training (CCT_wm+at), and evaluated its effect on neurocognitive performance and functional connectivity (FC) of the brain.

METHODS

This prospective study was approved by a local ethical committee, and written informed consent was obtained from all participants. Altogether 29 healthy subjects were included in this study. Each participant was assigned to either the training group or the control group. The training group included 21 subjects (mean age = 27.7 ± 6.0 years, 9 women) and the control group 8 age, gender, and education level-matched subjects (mean age = 31.5 ± 9.5 years, 4 women). All participants underwent a set of neuropsychological tests and resting state functional MRI (rsfMRI) (TR/TE = 3000/30 ms, voxel size = 3.75 × 3.75 × 3.75mm³, 140 dynamic sessions) twice within a six-week period (Figure 1). The neuropsychological tests consisted of 13 tasks designed to reflect task-specific (2 tests), near-transfer (6 tests), and far-transfer (5 tests) effects of the assigned tasks. The rsfMRI data were used to identify the brain voxels which are functionally connected to the salience, dorsal attention, fronto-parietal and default mode networks and the strength of connection in between in terms of functional connectivity (FC). The training group additionally underwent an hour-long CCT_wm+at, which included dual n-back task (DBT) and attention network task (ANT) (Figure 2), five days a week for four weeks, during the period. The effectiveness of the CCT_wm+at was evaluated by comparing the neuropsychological performance as evaluated by the aforementioned neuropsychological tests and FC between the two groups, by using two-way mixed-design ANOVA. The effect size (Cohen’s d) was calculated to identify the magnitude of difference in neuropsychological performance between the trained and control groups and before and after CCT in the training group. The change in neuropsychological performance and that in FC upon CCT were tested for correlation, by using Pearson’s product-moment correlation analyses.

RESULTS

Neuropsychological performance improved significantly after CCT_wm+at in the training group, which was evident in 11 of 13 tasks evaluated (Figure 3). The effect sizes for the performance of neuropsychological tests which evaluated the transfer effect were 0.36 -1.55 and 0.00 - 0.12 in the trained group and the control group, respectively. Those for the training group before and after CCT were 0.08 - 0.41 and 0.43 - 1.70, respectively. FC between the right lateral prefrontal cortex (LPFC) and the left LPFC or the right lingual gyrus also increased after CCT (FWE corrected P<0.05) (Figure 4). The changes in percent correctness of Paced Auditory Serial Addition Task (PASAT) 1.0 and 2.0 s showed significant moderate to strong positive correlation with the change in FC between the right (r=0.595, corrected P=0.04) and left LPFC (r=0.672, corrected P=0.01) (Figure 5).

DISCUSSION

Improved neuropsychological performance, not only in the assigned tasks but also those tasks which involve the transfer effect, implies that the combined CCT also improves neurocognition via near and far-transfer effects. The observation of larger effect sizes for tests which evaluate the transfer effect, compared to those achieved by CCT targeted at a specific cognitive function (0.3-0.7 and 0.3-0.5 for single working memory training³ and single attention training⁴, respectively), is thought to imply augmentation of the transfer effect with combined CCT. Increased FC in the designated brain areas is thought to suggest the role of particular brain networks in modulating cognition. Our observations are in good alignment with previous reports^5,6. Neural connections between the bilateral LPFC have been linked to working memory. Neural connections between the LPFC and lingual gyrus form the fronto-parieto-occipital network, which is known to play an important role in top-down drive of attention and short-term memory maintenance⁶. The correlation between the changes in percent correctness of PASAT and the FC changes between the right and left LPFC may suggest that the far-transfer effect of CCT_wm+at occurs through modification of FC between these areas. FC between bilateral LPFC has been reported as reflective of cognitive functions such as attention and working memory^5,7.

CONCLUSIONS

The effect of combined CCT on neurocognitive performance and FC of the brain was evaluated. Combined CCT improves not only the targeted functions but also the other aspects of neurocognition via augmentation of transfer effect. The LPFC and fronto-parieto-occipital networks are thought to involve in modulation of neurocognition associated with combined CCT.