The impact of auditory working memory training on the fronto-parietal working memory network

Abstract

Working memory training has been widely used to investigate working memory processes. We have shown previously that visual working memory benefits only from intra-modal visual but not from across-modal auditory working memory training. In the present functional magnetic resonance imaging study we examined whether auditory working memory processes can also be trained specifically and which training-induced activation changes accompany theses effects. It was investigated whether working memory training with strongly distinct auditory materials transfers exclusively to an auditory (intra-modal) working memory task or whether it generalizes to a (across-modal) visual working memory task. We used adaptive n-back training with tonal sequences and a passive control condition. The memory training led to a reliable training gain. Transfer effects were found for the (intra-modal) auditory but not for the (across-modal) visual transfer task. Training-induced activation decreases in the auditory transfer task were found in two regions in the right inferior frontal gyrus. These effects confirm our previous findings in the visual modality and extents intra-modal effects in the prefrontal cortex to the auditory modality. As the right inferior frontal gyrus is frequently found in maintaining modality-specific auditory information, these results might reflect increased neural efficiency in auditory working memory processes. Furthermore, task-unspecific (amodal) activation decreases in the visual and auditory transfer task were found in the right inferior parietal lobule and the superior portion of the right middle frontal gyrus reflecting less demand on general attentional control processes. These data are in good agreement with amodal activation decreases within the same brain regions on a visual transfer task reported previously.

Keywords: auditory; fMRI; n-back task; plasticity; training; visual; working memory.

Figure 1

Schematic description of the experimental design. Both groups performed the same auditory and visual 2-back and 0-back control task in the pretest and posttest fMRI session. During the training interval, the auditory training group was trained on an adaptive n-back task using auditory tonal sequences, whereas the control group did not receive any training.

Figure 2

Schematic description of the adaptive auditory n-back task during training illustrated for a 2-back condition. Targets were defined as tonal sequences comprising the same sequence that was transposed in pitch. Non-targets were defined as tonal sequences comprising a different sequence that was also transposed in pitch.

Figure 3

Schematic description of the auditory and visual 2-back transfer tasks in the pre and posttest fMRI sessions. In the auditory task equivalent auditory tonal sequences as during training were used. In the visual black-and-white pattern stimuli were used.

Figure 4

Performance increase in the n-back task for the auditory training group. (A) The mean level of n as an indicator of the participants' performance for each session and corresponding standard errors of the mean are shown. (B) Mean Pr scores and corresponding standard errors of the mean of the auditory transfer task (left panel) and of the visual transfer task (right panel) for both groups during fMRI pretest and posttest.

Figure 5

Intra-modal training-related activation changes during the performance of the auditory transfer task (left panel). The activation changes for the visual transfer task are shown in the right panel. Percent signal change values of functional volumes of interests thresholded at p < 0. 005 (135 voxel extend) are shown for the training and the control groups [left inferior frontal gyrus at BA 46 (A upper panel) and left inferior frontal gyrus at BA 47 (B lower panel)]. Note that the activation decrease in the training group from pre to posttest was larger in the auditory than in the visual transfer task. See results section for details.

Figure 6

Amodal training-related activation changes during the performance of the auditory (left panel) and visual transfer task (right panel). Percent signal change values of functional volumes of interests thresholded at p < 0. 005 (135 voxel extend) are shown for the training (solid line) and the control group (dotted line) [right inferior parietal lobule at BA 40 (A upper panel) and superior part of the right middle frontal gyrus at BA 6 (B lower panel)].