Longitudinal data on cortical thickness before and after working memory training

The data and supplementary information provided in this article relate to our research article “Task complexity and location specific changes of cortical thickness in executive and salience networks after working memory training” (Metzler-Baddeley et al., 2016) [1]. We provide cortical thickness and subcortical volume data derived from parieto-frontal cortical regions and the basal ganglia with the FreeSurfer longitudinal analyses stream (http://surfer.nmr.mgh.harvard.edu [2]) before and after Cogmed working memory training (Cogmed and Cogmed Working Memory Training, 2012) [3]. This article also provides supplementary information to the research article, i.e., within-group comparisons between baseline and outcome cortical thickness and subcortical volume measures, between-group tests of performance changes in cognitive benchmark tests (www.cambridgebrainsciences.com [4]), correlation analyses between performance changes in benchmark tests and training-related structural changes, correlation analyses between the time spent training and structural changes, a scatterplot of the relationship between cortical thickness measures derived from the occipital lobe as control region and the chronological order of the MRI sessions to assess potential scanner drift effects and a post-hoc vertex-wise whole brain analysis with FreeSurfer Qdec (https://surfer.nmr.mgh.harvard.edu/fswiki/Qdec [5]).


a b s t r a c t
The data and supplementary information provided in this article relate to our research article "Task complexity and location specific changes of cortical thickness in executive and salience networks after working memory training" (Metzler-Baddeley et al., 2016) [1]. We provide cortical thickness and subcortical volume data derived from parieto-frontal cortical regions and the basal ganglia with the FreeSurfer longitudinal analyses stream (http:// surfer.nmr.mgh.harvard.edu [2]) before and after Cogmed working memory training (Cogmed and Cogmed Working Memory Training, 2012) [3]. This article also provides supplementary information to the research article, i.e., within-group comparisons between baseline and outcome cortical thickness and subcortical volume measures, between-group tests of performance changes in cognitive benchmark tests (www.cambridgebrainsciences.com [4]), correlation analyses between performance changes in benchmark tests and training-related structural changes, correlation analyses between the time spent training and structural changes, a scatterplot of the relationship between cortical thickness measures derived from the occipital lobe as control region and the chronological order of the MRI sessions to assess potential scanner drift effects and a post-hoc vertex-wise whole Longitudinal randomized controlled intervention study

Experimental features
Longitudinal randomized controlled intervention study comparing the effects of adaptive working memory training relative to non-adaptive control activities (n ¼ 20 healthy adults per group) on cognition and MRI derived cortical thickness indices in cognitive control networks. Data source location Cardiff University Brain Research Imaging Centre, Cardiff, UK Data accessibility Data is provided in this article

Value of the data
Transparency and comparability of research results. Calculation of effect sizes for future apriori sample size and power calculations. Information about potential confounding factors that may affect the interpretation of similar studies.

Data
We provide data on cortical thickness and subcortical volume in regions of interest of cognitive control networks [1]. These structural data were acquired on a 3 Tesla GE Magnetic Resonance Imaging (MRI) system [1] and were derived with the FreeSurfer longitudinal analyses stream [2].

Experimental design, materials and methods
48 healthy participants (19-40 years of age) were pseudo-randomly (with the provision to match groups for age and sex) allocated to an adaptive training or an active control group [1]. Both groups underwent structural MRI scanning on a 3 Tesla GE system at the Cardiff University Brain Research Imaging Center (CUBRIC) as well as cognitive assessment [4] before and after two months of working memory training (40 sessions in total) [3]. The training group performed the working memory tasks in an adaptive way, i.e., training demands increased with performance levels whilst the control group performed the same tasks but in a non-adaptive way, i.e., task difficulty was held at a low level and never exceeded an item span of 3. Participants could train from home and their progress and compliance was monitored throughout the training time. Eight participants dropped out so the final sample size for both groups was n ¼20 each (n ¼40 in total). Training-related changes in working memory span and executive functioning as well as in cortical thickness and subcortical volume in regions of interest of cognitive control networks (executive, salience, basal ganglia networks) were assessed. Cortical thickness and subcortical volume indices were derived with the FreeSurfer longitudinal analyses stream [2]. Training-specific effects were investigating with group by time interaction effects in the structural and cognitive outcome measures [6,7] (Tables 1 and 2). Brain-function relationships and potential artefacts in the MRI data due to scanner drift effects were studied with correlational analyses (Fig. 1 and Tables 3 and 4).    Table 3 Spearman's rho correlation coefficient ρ (p-values) between performance changes in the backwards digit span and spatial span tasks and changes in cortical thickness in the right caudal middle frontal gyrus, the right pars triangularis and the right insula and changes in subcortical volume in the left pallidum for the training and the control group (n¼ 20 2.1. Vertex-wise whole brain analysis of group and time effects on cortical thickness in FreeSurfer Qdec [5] We conducted a post-hoc whole brain vertex-wise analyses in Qdec to test for the effects of group (adaptive training versus active control group) and time of assessment effects (baseline versus outcome) on cortical thickness measures. Cortical thickness indices were derived from the T 1 -weighted anatomical images smoothed with a kernel of 10. Multiple comparisons were controlled with a False Discovery Rate (FDR) of 5%. There were regions on both hemispheres with significant clusters of group effects across time (see Fig. 2) but no region demonstrated main effects of time or interaction effects between time and group, in either the right or the left hemisphere.