Development of relational reasoning during adolescence

Well, look who hasn't blogged in a really long time!  This gal!

Ah yes, there are all the regular excuses, holidays, families visiting, other work to do, dogs to play with, facebook posts to comment on and, well, you get my point.

But we're back in regular term time now and the Bunge Lab had its first lab meeting yesterday in which we discussed this paper on the development of relational reasoning during adolescence.  It is a very similar task to the one we use in the NORA study and is based on Kalina Christoff's task, first published in this paper in 2003 (as far as I can make out).

The main hypothesis behind the task is that there is an area in anterior prefrontal cortex that works harder during relational integration, than the consideration of single relations. Unfortunately the paper isn't open access so I can't add any figures to this post to explain the task better :(

This paper looked at how different brain areas are recruited by adolescents and adults.  The whole group showed activations which look very similar to other studies involving this task (including this one by Carter Wendelken, a research scientist in the Bunge Lab).  When they look at early adolescence, mid adolescent and adulthood they see that there are non-linear changes with age which are different for the three regions which are most consistently activated by the task (rostrolateral prefrontal cortex, medial superior frontal gyrus and anterior insular/frontal operculum).

The study also incorporates brain structure into their analyzes, investigating whether differences in white matter or gray matter volume in these three regions of interest can explain the differences in functional activation throughout development. They find mixed results, sometimes structure does explain the differences, other regions and age groups don't show the same effect.

It's going to be really exciting for us to see how our study population is similar or different to this paper's sample. It'll be great if we can add to some of their findings. Stay tuned for how our analyses work out!

Longitudinal changes in grey and white matter during adolescence

This paper on the longitudinal changes in grey and white matter during adolescence is the "first study to examine within-subject longitudinal changes in diffusion data in healthy adolescents".  24 teenagers, between 13 and 18 years old (at time one), returned 2.5 years after their first scan and the study investigates changes in their grey and white matter volumes and the fractional anisotropy (FA) of two major white matter tracts.

The results corroborate previous cross-sectional studies which have found increases in white matter volume and FA and decreases in grey matter volume.

Regions of grey (in blue–light blue) and white (in red–yellow) matter where volume shows significant (corrected p < 0.05) decreases and increases, respectively, with age over time.

White matter tracts (in red–yellow) showing significant (corrected p < 0.05) age-related FA increases over time in our group of adolescents.

The main reason I have this paper saved on my desk though, is for the statistical method they use to analyze longitudinal data (because I'm going to have to use them very soon!)  The authors created a design matrix which had regressors for each subject individually, to remove any within subject variance and then a regressor of interest which was their ages.  They orthogonalized that regressor to the subject regressors which (I believe) means that they were looking at the effects of age after the individual subject variance is accounted for, which is, after all, their question of interest :)

I also really liked this figure (below), for two reasons: One, I find it really interesting how little FA changes when you look across the sample.  It's only when you look at the pairs of data that you see an effect of age.  That's great evidence for the power of longitudinal studies: a cross sectional study wouldn't have been as sensitive to these changes. Two, its a change in parallel diffusivity that is driving this change in FA.  Not in perpendicular diffusivity.  I'm now really interested in seeing whether there is a qualitative difference between younger and older subjects.  Maybe myelination is driving a change in perpendicular diffusivity for children and reorganization, decreased tortuosity (curvy-ness) or increased axonal diameter is driving a change in parallel diffusivity in adolescence.  Who knows?  Stay tuned ;)

Scatterplots, with longitudinal data points connected by a line, of mean values of FA, parallel and perpendicular diffusivity from white matter regions showing significant relationship with age over time in adolescents. Orange lines indicate the three left-handed subjects.

Oh, and PS: the paper outlines very clearly how to deliniate the corticospinal tract and the arcuate fasciculus.  That'll be really helpful when I come to draw those tracts because there are so many different ways to do it that it's nice to be able to directly compare with previously published work :)

Longitudinal changes in grey and white matter during adolescence.

Giorgio A, Watkins KE, Chadwick M, James S, Winmill L, Douaud G, De Stefano N, Matthews PM, Smith SM, Johansen-Berg H, James AC.

Neuroimage. 2010 Jan 1;49(1):94-103. Epub 2009 Aug 11.
PMID: 19679191