. Cortical hubs revealed by intrinsic functional connectivity: mapping, assessment of stability, and relation to Alzheimer's disease. J Neurosci. 2009 Feb 11;29(6):1860-73. PubMed.

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  1. As is usually the case with work from Buckner, Sperling, and Johnson, this is very interesting and innovative work. It’s similar in some respects to the 2005 J. Neurosci paper comparing the topography of the default mode network to amyloid deposition. Indeed, many of the hubs lie in this region, and hub activity may be at the root of default mode activity and, in turn, may exacerbate Aβ deposition. It’s not completely clear to me whether this hub-vulnerability is simply a function of activity level (of any type) or whether it’s more a function of some form of connectivity and activity that is unique to hubs and may be less dependent on the actual level of activity (as might be measured by fMRI or FDG, for example).

    The implications to this work appear rather ominous to me. If there is this arrangement of hubs, it’s highly likely that this architecture and its normal functioning are essential to normal cognition. Therefore, it may be very difficult to affect the hub network without bad consequences. However, it may be that some people have hyperactive hubs and they may benefit from some downregulation without noticing any untoward effects.

    One thing is sure: this is an elegant and innovative hypothesis and could suggest novel avenues of treatment that would be most welcome in our current efforts against AD.

  2. This paper takes the previous associations between brain function and β amyloid deposition a step further. These investigators have previously noted the interesting similarity between regions of β amyloid deposition and the default mode network. Using a different computational approach they defined hubs as brain regions with unusually high connectivity, and they find that it is these areas that are particularly predisposed to β amyloid accumulation. The idea essentially parallels molecular studies that have shown how neural activity stimulates Aβ production.

    So basically, the idea is that persistent, high levels of neural activity may be responsible for Aβ deposition. This is an attractive argument as it explains not only why β amyloid tends to occur in some regions but not others, and also because it might explain age-dependence of the disease and its ubiquity. On the other hand, it is somewhat difficult to reconcile with epidemiological data showing that cognitive activity reduces the risk of AD. The data do not also seem to fully correspond to the deposition of β amyloid in subcortical structures and to some regions of prefrontal cortex. Nevertheless, as the authors point out, these data provide further testable approaches to exploring the pathogenesis of AD.