Sunday, 8 January 2012

Neuroplasticity

I am sure most people in the paleoshere are aware of the concept of neuroplasticity; the ability of your brain to change and adapt (both structurally and functionally) to various input in your environment.  In the UK a commonly cited example of this is in the brains of London cab-drivers who develop an evolved hippocampus as their knowledge of The Knowledge grows.  Other common examples are concerned with phantom limbs where the amputated limb can be stimulated aead of 'remapping' in the brain of those neurological parts formally accomodating the lost appendage.

In 'The Brain That Changes Itself', Norman Doidge looks in to the Brain Science behind neuroplasticity.  I am only half way through it but one paragraph leapt off the page to do with the work of Posit Science who are,
  • "...working on 'gross motor control'.  A function that declines as we age, leading to loss of balance, the tendency to fall, and difficulties with  mobility.  Aside from the failure of the vestibular processing, this decline is caused by the decrease in sensory feedback from our feet.  According to [Dr] Merzenich, shoes, worn for decades, limit the sensory feedback from our feet to our brain.  If we went barefoot, our brains would receive many different kinds of input as we went over uneven surfaces.  Shoes are a relatively flat platform that spreads out the stimuli, and the surfaces we walk on are increasingly artificial and perfectly flat.  This leads us to dedifferentiate the maps for the soles of our feet and limit how touch guides our foot control.  Then we may start to use canes, walkers, or crutches or rely on other senses to steady ourselves.  By resorting to these compensations instead of exercising our failing brain systems, we hasten their decline.

    As we age, we want to look down at our feet while walking down stairs or on slightly challenging terrain, because we're not getting much information from our feet.
    "
I know this is cherry-picking, but it is great to see different disciplines tie an idea together from their respective angles.

I intend to blog a bit more about kinaesthetic awareness and neuroplasticity in general.  There seem to be a great many mental consequences to how you live your life and how you train in general.  It is easy to think that your mind is rather static, and compartmentalised.  But Doidge suggests it is highly plastic and adaptable - even in to old age.  More importantly, as with any other muscle in the body there is a 'use it or lose it' principle at work, but things go a bit further with the brain.

Unlike a muscle that will atrophy with a lack of use, brain function can be co-opted for processing of sensor input from other sources.

This is actually quite profound.  In the great Taubes vs Guyenet debate (and I continually find both of their arguments quite persuasive - lipodystrophy is one curious feature that make me think that a reward hypothesis is limited), we have to consider the dose and response of hormones, and how these are managed, and consequently how neuroplasticity might affect outcomes (and given that these maps repond to stimulus, you have to wonder what the neural implication is of seldom if ever draining muscle glycogen stores - could this be the real value of exercise on bodyfat levels rather than the idea that we simply exercise to 'burn fat').  Sure we know quite a bit about sensitivity to ghrelin, insulin etc... - thresholds can change over time, but throw in the fact that measures and triggers themselves might also be subject to a loss of control as brain function is co-opted or neural maps maladapt, it is no surprise that fat loss is such a contentious subject.

UPDATE: I blogged earlier about how thoughts can manifest in physical behaviour over VERY short timescales, which you can read about here.

2 comments:

Christine said...

Very interesting!
Some time ago I injured a foot, tearing tendons and making quite a mess of it all. My physio gal advised me to stay away from uneven ground and get good shoes. The injury plagued me for years. Now I've quit working and spent spring, summer and well into fall in bare feet in my garden, very uneven ground. The result is that my foot no longer troubles me and lower back problems have also diminished.

Asclepius said...

Hi Christine. I am still ploughing my way through the book but there is an incredible section on stroke rehabilitation (which I may post on). Suffice to say that even the most debilitating of injuries (which includes severe spinal injuries), seem to prompt remapping and an attempt by the bod to regain control. One caveat is that without appropriate stimulation, the new 'post trauma map' can be compromised and leave residual loss of control (manifest as a limp or similar - depending on the limb affected). After a period of time the post trauma remapping is less active, and repeated use of the badly mapped limb appears to re-enforce the condition. All is not lost though. Immobilisation of the limb appears to allow the malformed map to atrophy and you can almost 'start again'. (I am skeptical about some of this stuff as it really does seem to be just too incredible!) Personally I think there are LOADS of benefits to going barefoot and tackling challenging terrain; no need to wait for enfored rehabilitation!