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. 2017 Mar 8;93(5):1227-1235.e6.
doi: 10.1016/j.neuron.2017.02.003.

Mnemonic Training Reshapes Brain Networks to Support Superior Memory

Martin Dresler  1 , William R Shirer  2 , Boris N Konrad  3 , Nils C J Müller  4 , Isabella C Wagner  4 , Guillén Fernández  4 , Michael Czisch  5 , Michael D Greicius  2
Affiliations

Mnemonic Training Reshapes Brain Networks to Support Superior Memory

Martin Dresler et al. Neuron. .

Abstract

Memory skills strongly differ across the general population; however, little is known about the brain characteristics supporting superior memory performance. Here we assess functional brain network organization of 23 of the world's most successful memory athletes and matched controls with fMRI during both task-free resting state baseline and active memory encoding. We demonstrate that, in a group of naive controls, functional connectivity changes induced by 6 weeks of mnemonic training were correlated with the network organization that distinguishes athletes from controls. During rest, this effect was mainly driven by connections between rather than within the visual, medial temporal lobe and default mode networks, whereas during task it was driven by connectivity within these networks. Similarity with memory athlete connectivity patterns predicted memory improvements up to 4 months after training. In conclusion, mnemonic training drives distributed rather than regional changes, reorganizing the brain's functional network organization to enable superior memory performance.

Keywords: brain networks; cognitive training; dynamics; memory; memory championships; memory sports; method of loci; mnemonic; resting state.

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Figures

Figure 1
Figure 1
Top: study schema. All participants underwent at least one experimental session; participants of the training arm underwent a second experimental session after six weeks, plus a retest after four months. Bottom: Sequence of MRI scans and memory tasks performed in pre- and post-training sessions.
Figure 2
Figure 2
Mnemonic training has potent and enduring effects on memory capacity. Participants in the mnemonic condition showed significantly greater improvement in memory performance after training than participants of the active and passive control groups (p<.001, η2=.3 each, no significant difference between control groups). Mean changes from pre- to post-training sessions in free recall of 72 learned words ± standard error of the mean are shown. During a four month follow-up, subjects re-encoded the list of words from their baseline visit and were asked to recall the list after a 15 minute delay.
Figure 3
Figure 3
Brain networks examined with resting-state fMRI analyses: Six networks based on Shirer et al. 2012 were selected due to their hypothesized recruitment by the memory task: (A) ventral (dark blue) and dorsal (light blue) default mode network, (B) higher visual (dark red) and visuospatial (light red) network, (C) left (dark green) and right (light green) medial temporal lobe.
Figure 4
Figure 4
Similarity of training-induced connectivity changes with athlete-control connectivity differences. (A) Brain network connectivity differences between memory athletes and controls. (B) Connectivity changes from pre- to post-training assessment for each training condition. (C) Scatterplots and correlations between the memory athlete vs. control connectivity difference matrix and the pre- vs. post-training connectivity difference matrices. The pattern of connectivity differences between memory athletes and controls correlates significantly with the pattern of connectivity changes in the mnemonic training condition (r=.222, p=.005), but does not correlate significantly with the connectivity pattern changes in the active (r=.011, p=.943) or passive (r=−.061, p=.632) control groups.
Figure 5
Figure 5
Memory performance is correlated with functional connectivity changes. The spatial correlation strength of change-in-FC matrices to the athletes-controls matrix was significantly related to the participants’ performance on the free-recall tasks at 20 minutes, 24 hours, and in an additional learning session at 15 minutes for the baseline list of words re-encoded at the 4 month follow-up visit.
Figure 6
Figure 6
The top 1% of differential connections between memory athletes and matched controls are shown. Red connections depict stronger and blue connections weaker functional connectivity in memory athletes as compared to controls.
Figure 7
Figure 7
During resting state, similarity between mnemonic training-induced connectivity changes and athlete/control connectivity differences is mainly driven by between brain network connectivity. During encoding, in contrast, similarity between mnemonic training-induced connectivity changes and athlete/control connectivity differences is mainly driven by within brain network connectivity.
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