Is a meditative brain a more folded brain?

Eileen Luders

Some research which has gotten a lot of press the last two weeks has been the work done @ UCLA by Eileen Luders, Florian Kurth, Emeran Mayer, Arthur Toga, Katherine Narr and Christian Gaser.  The paper is "The Unique Brain Anatomy of Meditation Practitioners: Alterations in Cortical Gyrification", which was published in Frontiers In Human Neuroscience, 29 Feb 2012.

Much of what we have been looking at in cognitive neuroscience has been focused on individual brain centers and how they are activated, or deactivated, and how they operate together, or not, with different types and duration of meditation.  Earlier research demonstrated that there were increases in cortical thickness with meditation as in "Meditation Experience is Associated With Increased Cortical Thickness" by Sarah Lazar, et. al. in November 2005.  However, the UCLA work is the first that i am aware of that has focused on increases in the actual folding (gyrification) of the cortex with meditation.

As the first work on cortical folding variation with meditation, it is important to remember the huge advantage the fMRI folk have in their current studies based upon the many careful, and well-designed, studies that have been done on fMRI vs meditation.  If one reads the literature on the "research on meditation", of the 3,000 studies done since the 1950s, most were poorly designed and inconclusive.  Roughly coinciding with the Dalai Lama's push on mindfulness meditation and fMRI has the research become more rigorous, sophisticated, and conclusive.   It is not surprising then, that this, the first effort at looking at "folding" of the cortex, has some areas that need more work.  

What does cortical folding look like and why does it matter?  Cortical folding results in hills (gyri) and valleys (sulci) on the external surface of the brain.   Cortical folding varies greatly across mammals and increases slightly with brain size, as shown in the figure.  It is not totally clear what factors determine the extent of cortical folding.  Genetics are generally believed to be of primary significance but the biomechanical factors are not fully understood.  

This paper has a good "nature vs nurture" discussion which highlights the difficulty of assigning specific meaning to cortical folding.  It was pointed out that as we age, the gyri/peaks get more sharp and steep and the sulci/valleys become flatter, which may confuse a "years of meditation" gyrification analysis.

The main advantage of folding, as the cerebral cortex is relatively laminar like a sheet of rubber, is just to pack more neurons into an existing volume by increasing surface area, which roughly corresponds to neuron density, in the available brain mass and volume.  More folding = more neurons = more intelligence.

Measuring gyrification

Different ways have been proposed to measure gyrification, shown on the left.  Those used in this paper are shown on the right.  

Cortical folding or gyrification

It is obvious that it can be a simple two dimensional peak/valley measurement or a more complex three dimensional approach such as that used in this paper in which thousands of "vertices" are used to calculate a mean curvature with complex statistical data handling.

This approach demonstrated that there were some significant positive correlations between number of meditation years and gyrification in certain regions.   In the graphic at the left remember that the large furrow that divides the brain into two halves, the "interhemispheric fissure" is so deep that cross sections of the brain will show this well below the nominal spherical surface of the brain.  There are folds here as well as shown in the graphic.
 

Correlations of gyrification by region
with years of meditation 

It is obvious that at this correlation level of p < .05 there are numerous regions that have positive correlations (red/orange) across the left and right lateral (sides) regions and in some medial regions.  As you can see, the medial/central plane actually shows some negative (blue) correlations with increasing meditation years, i.e. the cortex is smoothed out, rather than more extensively folded, with increased meditation years in some parts of the interhemispheric fissure.

If the statistical correlation criteria are made more difficult by changing to p < 0.01, virtually all of these correlations disappear.  In this graphic, which is shown in the paper, only the right temporal lobe, and the left and right anterior (top) insula, the right cuneus and right fusiform gyrus remained.  The paper focused on the right insula, which has often been identified in fMRI studies, such as Farb, et. al as being a key element in meditation-induced effects, particularly those having to do with shifting from a default mode network (wandering mind), to a "now-now-now" mode.

The popular press has covered this widely, but not well, IMHO.  There is much here that is good for a first paper in an area, but there is much to question.  The listing of years of meditation, type of meditation, frequency and duration, shows that this is a very heterogeneous population of meditators from which it would be hard to draw any specific conclusions, particularly with regard to something as complex and poorly understood as cortical folding.  This difference is particularly striking when  compared to some recent fMRI studies which have been covered in this blog which drew upon a carefully selected group from one meditation tradition doing meditation they knew well.  

The key "take aways" would be that there is work now being conducted on cortical folding, and that it did indicate that probably the right insula, which is critical in default mode network functioning, is somehow impacted by cortical folding enhanced by meditation.  Given the press coverage that it has received, i am certain there will be more papers in the area building upon this ground-breaking  work.