Uncorrelated functional and structural connectivity during insula and parietal cortex development

The relationship between the anterior insula and the posterior parietal cortex is believed to play a role in linking the default mode network. In their Feb ’12 study, Supekar et al. used resting-state fMRI as well as DTI to hone in on the multimodal connection between these two brain regions.

One of their findings is that the overall fiber density between these regions is about 1.5x greater in adults (mean age of ~20) than in children (mean age of ~8).

fiber density = number of fibers / unit area; red = right posterior parietal cortex, yellow = right anterior insula; doi:10.1371/journal.pcbi.1002374

The reconstructed nerve bundles in cyan are part of the superior longitudinal fasciculus. The age differences are relatively unsurprising because myelination is a well-regulated process depending upon many growth factors and transcriptional events, which surely encompasses many years.

They also found a dependency between fiber density (i.e., structural connectivity) and instantaneous correlations in activity (i.e., functional connectivity) between the anterior insula and posterior parietal cortex in adults but not children.

rAI = right anterior insula, rPPC = right posterior parietal cortex; they found a correlation in adults (r = 0.44) but not children (r = 0.02); doi:10.1371/journal.pcbi.1002374

The same group previously made a similar finding relating the posterior cingulate cortex and the medial prefrontal cortex. Thus it seems to be a trend that structure-function relationships become more abiding as development progresses.

This makes sense to me within an energy savings framework. It only seems worth it to spend valuable energy tuning the synaptic weights between regions when the structural connections are stable. Still, we’ll have to wait for more data to judge this hypothesis.

Reference

Supekar K, Menon V (2012) Developmental Maturation of Dynamic Causal Control Signals in Higher-Order Cognition: A Neurocognitive Network Model. PLoS Comput Biol 8(2): e1002374. doi:10.1371/journal.pcbi.1002374

Supekar K, et al. 2010 Development of functional and structural connectivity within the default mode network in young children. Neuroimage. http://dx.doi.org/10.1016/j.neuroimage.2010.04.009