The Effects of Working Memory Training on Brain Activity

Abstract

This study aimed to investigate if two weeks of working memory (WM) training on a progressive N-back task can generate changes in the activity of the underlying WM neural network. Forty-six healthy volunteers (23 training and 23 controls) were asked to perform the N-back task during three fMRI scanning sessions: (1) before training, (2) after the half of training sessions, and (3) at the end. Between the scanning sessions, the experimental group underwent a 10-session training of working memory with the use of an adaptive version of the N-back task, while the control group did not train anything. The N-back task in the scanning sessions was relatively easy (n = 2) in order to ensure high accuracy and a lack of between-group differences at the behavioral level. Such training-induced differences in neural efficiency were expected. Behavioral analyses revealed improved performance of both groups on the N-back task. However, these improvements resulted from the test-retest effect, not the training outside scanner. Performance on the non-trained stop-signal task did not demonstrate any transfer effect. Imaging analysis showed changes in activation in several significant clusters, with overlapping regions of interest in the frontal and parietal lobes. However, patterns of between-session changes of activation did not show any effect of training. The only finding that can be linked with training consists in strengthening the correlation between task performance accuracy and activation of the parietal regions of the neural network subserving working memory (left superior parietal lobule and right supramarginal gyrus posterior). These results suggest that the effects of WM training consist in learning that, in order to ensure high accuracy in the criterion task, activation of the parietal regions implicated in working memory updating must rise.

Keywords: N-back task; neural efficiency; stop-signal task; training; working memory.

Figure 1

Schematic representation of the tasks used in the three scanning sessions. (A) shows an example of the stimuli the subject would see when performing the N-back task. (B) shows an example of the stimuli the subject would see when performing the Stop-Signal task. (C,D) respectively show the variables recorded for each run of the N-back and Stop-signal tasks (‘Outcome’ column), while also offering an explanation for when a response was considered correct.

Figure 2

Contrast maps showing changes in brain activation associated with the correct identification of targets (‘Hits’, 3A), corrects rejection of distractors (‘Correct rejection’, 3B), and accuracy of N-back task performance (‘Correct vs. Incorrect’, 3C). Only the significant ROIs that survived the FDR correction are shown. (A) 1—superior parietal lobule; 2—inferior parietal lobule (SMG posterior); 3—superior frontal gyrus. (B) 1—superior parietal lobule; 2—superior frontal gyrus (paracingulate gyrus); 3—inferior parietal lobule (SMG posterior). (C) 1—superior parietal lobule; 2—inferior parietal lobule (SMG posterior); 3—superior frontal gyrus (paracingulate gyrus). Coordinates are presented in Table 2.

Figure 3

Contrast estimates in superior parietal lobule depending on the scanning session and accuracy in the N-back task. Contrast 1 (‘Hits’). Visualization has been prepared independently of the statistical computations, in which the accuracy variable was kept continuous.

Figure 4

Contrast estimates in superior parietal lobule depending on the scanning session and accuracy in the N-back task. Contrast 3 (‘Correct vs. Incorrect’). Visualization has been prepared independently of the statistical computations, in which the accuracy variable was kept continuous.