Category Archives: Neuroimaging

Yoga, A Cognitive Exercise

In August 2009 Annals of the New York Academy of Sciences Volume 1172 was released, containing within it 31 peer-reviewed articles which attempt to “study the impact of Indo-Tibetan practices on longevity and health.” If our brain cells are rewiring themselves based on our habits and thought patterns, suddenly our hobbies and pastimes are rocketed to the center stage of mental health. What you or I do in our free time is habitual and over time can optimize our brains for said activities while allowing other regions to decay. Yoga as a physical exercise has demonstrated incredible ability to affect mental health, including but not limited to focus and emotional regulation. The following papers contained within the volume are of particular interest:

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Feed Your Head – Aβ, Tau & APOE

Aβ plaques & Tau tangles

Fig 1: Pathology of AD showing plaques and tangles.

Some would say a soul is the collective memories and personality traits of an individual. So, what is left if those memories and traits are erased? You and I might be far from old and senile (well I’m not old). But you know someone near & dear to you, who will have to deal with this existential crisis in their golden years. Alzheimer’s disease currently has two culprits, Beta amyloid (Aβ) which can form plaques on the brain and Tau protein, whose over expression can cause neurons to tangle up (NFT).

These pathologies appear to be affected by the APOE gene, certain variations of which are now recognized as dead-ringers for Alzheimer’s. The mechanism however is still very much in the process of being understood. More so, when considering the role of Tau.

Fig 2: Constant expression of plaque causing Aβ with varying levels of Tau shows little difference in pathology. Plaques and tangles remain present. Thus deletion or over expression of Tau is not enough to prevent AD pathology.

Although the signs of Alzheimer’s on a cellular level remained steady while playing with the knobs of Tau expression, the authors did find a difference is the cell & organism survivability. Hypothesizing that Tau helps the neuron deal with excitotoxicity, the damage to nerve cells through stimulation.

Don’t lose hope, although it’s difficult to get a full picture, we may have enough glimpses to make a clinical difference. Eventhough, we don’t quite understand the role between APOE, lipoproteins and Alzheimer’s pathology, on a higher symbolic level APOE is a great predictor of who is at risk for AD and sometimes even when. Best move for now is probably just to get your parents genotyped and planning active mental lifestyles for them, there should be a fix by the time I’m grey.

Citations: Reducing endogenous tau ameliorates amyloid beta-induced deficits in an Alzheimer’s disease mouse model by Roberson, et al.

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Neurophysiology of Meditation, 2 of 2

These articles have taken steps to identify and understand physiological differences in well-focused minds compared to lay people, it is analogous to a study showing that professional athletes have more muscle mass, in a manner communicating to those of us who seek to perform better at either a physical sport or become better problem solvers, that the mind, like the body must be trained and shaped to overcome difficult challenges. The papers in these two posts converge in that both studies show meditation increases activity and over long-term practice, cause structural changes in regions associated with focus and concentration.

Fig 1 Larger GM volumes in meditators (co-varied for age). Views of the right orbito-frontal cortex, right thalamus, and left inferior temporal gyrus, where GM is larger in meditators compared to controls. The color intensity represents T-statistic values at the voxel level.

Where the last post attempts to capture a snapshot of the mind during a meditative act the paper in the following post attempts to show structural changes caused by long-term, regular meditation. The underlying anatomical correlates of long-term meditation-Larger hippocampal and frontal volumes of gray matter, by Luders, et al., asked a simple question: does regular meditation over many years cause any neuroanatomical changes in the meditator.

Image from National Geographic magazine

To find the answer the authors took 22 meditators with mean meditation experience of 24.18 years and acquired images of their brains using MRI. The images were then passed through Voxel-based GM volume analysis, at a local and global level. Next the images passed through Parcellated volume analysis software, combined the various software analysis would help to distinguish grey matter volume differences between the 22 long-term meditators and 22 control subjects with no meditation experience. As a result, this would to some degree, help the authors identify regions with grey matter (GM) differences, however it is not so clear how those changes can be specifically attributed to meditation alone. The data in figure 1 reveals increased GM differences in areas shown as activated by meditation in previous studies. The authors believe the results of this study provides enough positive data to continue to examine the relationship between meditation and GM volume, they nevertheless do acknowledge that on a global level there was no GM difference, only on a local level.

The future for neurophysiological research of focus and the clarity of thought relies significantly on better imaging technology; we must be able to see what pathways are becoming activated, when and during which thoughts. With increased complexity in our everyday lives, less time and more tasks to complete, being able to focus on the everyday problems and the overarching issues that are inherent with existence will become more relevant, research such as this may help to aid individuals and societies alike.

Citations:
Luders E, Toga AW, Lepore N, & Gaser C (2009). The underlying anatomical correlates of long-term meditation: larger hippocampal and frontal volumes of gray matter. NeuroImage, 45 (3), 672-8 PMID: 19280691

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Neurophysiology of Meditation, 1 of 2

Fig 1. Expert meditators & non-meditators asked to focus on a dot for extended time. A) 12 expert meditators had greater overlap of increased activation of attention-related brain regions. B) 12 non-meditators had less overlap and activation. Orange hues equal higher correlation between individuals & activation. Blue hues equal little to no correlation between regions of activation.

We have all found ourselves struggling to concentrate on a thought through all the chatter and imagery in our minds. Often, it is a work related problem, other times we try to understand our relationships and throughout our lives we attempt to ponder existence itself. The predicament with focus and the clarity of thought presents itself as an enticing case for study at a neurophysiological level. Meditation as a set of techniques that requires the practitioner to regularly conduct thought exercises or hold steady attention on an internal/external stimuli, can help to identify & understand neural structures implicated in concentration. There are several recent research papers which provide some excellent insight into the contemporary study of how the brain behaves and is ultimately changed through meditation. In Neural correlates of attentional expertise in long-term meditation practitioners by J. A. Brefczynski-Lewis & A. Lutz, et al. the authors scanned the brains of 3 groups as they were asked to concentrate on a dot, using fMRI.  The groups consisted of 16 non-meditators (NM), 11 non-meditators who were given an incentive of $50 if they were able to hold their attention (INM) and 14 expert Buddhist meditators (EM). Furthermore, the EM group was sub-divided into those with most hours of practice, with a mean of 44,000 hours (MHEM) and those meditators with less, mean of 19,000 hours (LHEM);each subgroup containing 4 meditators. Compared to NMs & INMs, EMs were found to have increased activation of attention-related brain regions of interest (ROI), while simultaneously having far less activation of regions unassociated with the task at hand, Fig 1. One of the most interesting results came from the comparison between expert meditator groups MHEMs and LHEMs; whereas LHEMs showed increased activation of ROIs & decreased activation of unassociated regions, MHEMs showed less activation of all brain regions while maintaining the most attention.

Fig 2. Bar graphs for amplitude of activation in the ‘‘early’’ part of the meditation block (the first 10 sec, excluding the first 2 sec because of hemodynamic delay) and the ‘‘late’’ part of the meditation block (120 sec to 200 sec)

What this all means- with a decent amount of practice one can cause greater activation of attention-related regions of the brain, while simultaneously reducing the level of “chatter” and the activation of unrelated brain regions. More interestingly, we see that even amongst expert meditators those with a mean 44,000 hours of meditative practice shows far less activation of all brain regions, including attention related ROIs, compared with meditators who have half as much practice(Fig 2); this demonstrates networks involved in meditation become optimized with increased use, that is it requires less activation, less resources to have the same concentration. Whatever goal one has, having greater focus with more ease will ensure greater success. This paper gives some live data of what is happening in the brain as one performs meditative tasks while showing us that those with extensive practice have a significantly different response, hinting at structural changes. What those changes could possibly be, is discussed in part two of this post.

Citations:
Brefczynski-Lewis JA, Lutz A, Schaefer HS, Levinson DB, & Davidson RJ (2007). Neural correlates of attentional expertise in long-term meditation practitioners. Proceedings of the National Academy of Sciences of the United States of America, 104 (27), 11483-8 PMID: 17596341

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BOLD fMRI, a clear new view of the brain

Hemoglobin carries the oxygen to our cells, which use it as energy. Our neurons use incredible amounts of energy when they fire electrical currents, which create our thoughts, actions, memories and senses. When a neuron fires, it takes up large amounts of oxygen from nearby hemoglobin molecules. As oxygen leaves it causes a change in the iron-rich structure of hemoglobin, which can be detected by Magnetic Resonance Imaging.

Blood-oxygen-level dependent fMRI allows us to see where in the brain oxygen is being consumed, correlating it with nearby neurons firing. This allows us now to literally map the brain based on activity. Which part of the brain is active during certain thoughts? Memories? Motor actions? BOLD fMRI can and has answered many of these questions. Contemporary studies with this technology has touched the edge of what we once thought possible, from algorithms that can scan our brains to guess what our eyes are seeing; to showing how meditation decreases the number of neurons firing in random areas of the mind.  As we begin to settle into a comfortable pace of understanding and uncovering the functions of the brain in-terms of neurotransmitters and receptors, functional imaging of the mind provides a new horizon of understanding the mind as a complete neural network.

Citation:
Aguirre, G. (2002). Experimental Design and the Relative Sensitivity of BOLD and Perfusion fMRI NeuroImage, 15 (3), 488-500 DOI: 10.1006/nimg.2001.0990
Kay KN, Naselaris T, Prenger RJ, & Gallant JL (2008). Identifying natural images from human brain activity. Nature, 452 (7185), 352-5 PMID: 18322462

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Filed under Neuroimaging, Neurophysiology, Neuroscience