Swaying in the balance

Grey’s Anatomy Inner ear viewed from above, the cochlea and vestibule

Imagine attaching a metal screw into a ceiling then tying a cord onto a flashlight to the screw. Place your camera phone directly under the flashlight preferably at night, turn on the camera, turn on the flashlight then hit it. Watch as the random light arc swings wildly around until finding its stable immobile equilibrium. The camera will capture the continuous trail of gravity balance gyrations by tracing skinny lines. A person with a concussion  has trouble holding their posture, they tend to sway, over-correcting while trying to find the vertical as if they are on a tilting floor. Inside the muscles that control our vertical posture, the exquisite middle ear labyrinth orientation apparatus are disturbed in its gravity vector sensing feed-back loop. Researchers have figured out how to analyze the disturbed over-swaying body motion following a concussion with a body balance tracing motion, similar looking to the continuous, dampened flashlight wild  lightline movements.

Balance problems are an early indication for dementia and Alzheimer’s disease, according to Dr Li Wang and fellow researchers from the University of Washington. In an published article entitled : Performance-Based Physical Function and Future Dementia in Older People Li Wang, MS; Eric B. Larson, MD, MPH; James D. Bowen, MD; Gerald van Belle, PhD. Arch Intern Med. 2006;166:1115-1120,  the University of Washington researchers studied 2,288 over 65 year old people who at the onset of the study showed no signs of dementia. People were enrolled from 1994 to 1996 and followed up through October 2003. A 6 year period. After six years 319 individuals had developed dementia, 221 of them had Alzheimer’s disease.

The study tested for physical functioning using a number of tests. It was found that people with good physical performance scores at the beginning of the investigation were three times less likely to develop dementia than those with poor scores.

Dealing with concussions after they occurred is not easy since one of the greatest aspects is: when does the self healing happen for an individual after suffering a concussion? Lets see what happens to brain balance after a stroke. I will be citing from, Shannon and Renyi Entropies to Classify Effectas of Mild traumatic Brain Injury on Postural Sway Jianbo Gao, Jing Hu, Thomas Buckley, Chris Hass PLoS ONE September 2011 /Volume6 /Issue 9 /e24446 http://www.plosone.org

The authors warn, “….premature return to participate, presents an acuter risk of the potentially fatal second impact syndrome as well as elevated risk of repeat concussion and associated long term sequelae including mild cognitive impairment, earlier onset of Alzheimer disease, chronic traumatic encephalopathy and amyotrophic lateral sclerosis. ” The authors settled on studying swaying postural deregulation as a means to assess a sensitive enough test to, ” identify concussion-related neurophysiological abnormality.” Previous studies identified changes as people age, they are less able to maintain postural stability employing a very detailed mathematical analysis using the principles of fractal/chaotic interpretation measuring Center of Pressure (COP) on a balance platform.

How old is the sense of balance in evolution? Do you recall a essay on the hagfish and early life with the importance of bone metabolism development with the early brain? Well, the hagfish only have only a single, vertical canal in their vestibular system, sensing one direction only, up and down in terms of orientation on the sea bed where the hagfish live. Generally all jawed vertebrates have a similar system consisting of two chambers, the saccule and utricle, each of which includes one or two small clusters of sensory hair cells. There are three semicircular canals arising from the utricle, each with an ampulla containing sensory cells at one end.

Nature Vol 446/5 April 2007 Philippe Janvier, Museum National d’Histoire Naturelle, Paris, France

Janvier describes the embryonic shape changing of the hagfish, “…was the odd development of the ‘neural crest,’  a unique vertebrate structure that has possible precursors in other chordates. During the embryonic development of lampreys and gnathostomes, the brain and spinal cord form a dorsal infolding of the ectoderm (the future epidermis of the skin), which then closes into a ‘neural tube.’ Where the two lips  (or crests) of this infolding meet to close to the neural tube, some cells of the ectoderm delaminate, becoming free, and then migrate to contribute to essential organs of the vertebrate body, such as the branchial apparatus, part of the brain case, and the dermal bones, scales, teeth, nerve ganglia and pigment cells. The neural crest thus generates a ‘new head,’ which possibly made vertebrates more competitive in the early stage of evolution.”  The reason for all this interest in hagfish is still not established definitively, but defining its single labyrinth canal as the most primitive, the intense focus is the question: are hagfish the common ancestor to all vertebrates? That’s why this hagfish is very interesting. We are back to the basics of the oldest vertebrate communication between brain with bone and now a simple version of balance sensing. So as we jump back from the mists of early evolution, looking at a brain concussion may be the way into breaking open the understanding of how concussions change things in the brain; is to look at the oldest existing signalling systems, which in a nutshell is our logic for our concussion work. Lets get back to the Center of Pressure, (CAP) apparatus for trying to establish: has the brain healed sufficiently after a concussion?

Ten varsity intercollegiate student athletes with mild concussion, basically mild traumatic brain injury (mTBI), or with recent diagnosis of concussion participated in the study. The volunteers stepped onto a force platform barefooted in the biomechanics laboratory for their testing session. Ground reaction forces measured medial/lateral, anterior/posterior and vertical and center of pressure data were collected from a single force platform.

Three Kistler force platforms imbedded in a laboratory walkway

The athletes stood on the platform for a period of time generating a COP trajectory.  To get a better sense of the analysis using COP trajectories I’ll be referring to a technical research article Dynamical structure of center-of-pressure trajectories inpatients recovering from stroke Exp Brain Res (2006) 174: 256-269 by M. Roerdink, M De Haart, A Daffertshofer, S.F. Donker, A.C.H. Geurts, P.J. Beek. These authors describe the appropriate differences as, ” the nature of postural sway has been characterized both as deterministic chaotic. They have used the fractal analysis since Nature uses fractal behavior to regulate complex control systems, describing things as, “Chaotic time series appear random and unpredictable but arise from deterministic non-linear processes, whereas stochastic time series are governed by chance alone (e.g., Brownian motion, see
below) or by a combination of deterministic and random processes (e.g., biased random walk). Although conceptually different, these approaches both focus on the dynamical structure of COP trajectories, which may contain information about the postural control exerted. The ‘smoothness’ of the COP trajectories hints at strong deterministic components in the stochastic postural sway dynamics and comparatively weak influences of noise.”

Any time a measurement is made on a biological system there is inherent noise as part of the process of recording. However the authors were very concerned about, “…the importance of the repeatedly demonstrated non-linear character of the COP dynamics.” So the authors decided in effect, “…in order to identify the stochastic dynamics of postural sway, COP analyses that account for the non-linear and stochastic temporal evolution of postural sway appear appropriate,” as the detail for their assessment of sway posture measuring brain control. The specifics involved their resolution to get at the detail of the postural control, “Since a plethora of measures may be used to analyze the temporal structure underlying COP trajectories, we restricted the analysis to four: the correlation dimension, the largest Lyapunov exponent, the sample entropy, and the Hurst exponent. This particular choice was motivated from the consideration that these measures are all defined operationally in terms of readily interpretable and complementary (i.e., deterministic and stochastic) properties of motor control, namely, number of degrees of freedom, local stability, regularity, and scaling behavior.”

Lets get a better grasp of some of these important terms like, correlation dimension. The dimensionality treats the COP data as a time series which may provide as an estimate the, ‘number of (active)  dynamical degrees of freedom involved in the postural control.’ Lyapunov exponents, ‘…quantify the convergence or divergence of nearby points in the postural state space. With the largest Lyapunov exponent characterizing a system’s local stability,’ which is, ‘the sensitivity of the postural control system to  local perturbations.’ Next is sample entropy, which, ‘ …quantifies the regularity (or predictability) of a time series, while scaling factors like the Hurst exponent, which is determined by detrended fluctuation analysis (DFA) quantifies the extent to which a recorded COP time series exhibits long-range correlations.’ So lets get the authors conclusions in less scientific terms without getting bogged down with all the intricacies of the fractal mathematical interpretations.

” In stroke patients, maintaining balance is more difficult due to neuromuscular impairments, resulting in reduced postural stability. To cope with this reduced stability, postural control is actively (i.e., cognitively) increased, resulting in more regular yet higher dimensional COP trajectories. In the course of rehabilitation, postural stability improves, allowing the patients to relax their cognitive involvement in postural control, which leads to less regular COP trajectories. This process is reminiscent of that of automatization in skill acquisition. In line with this interpretation, the introduction of a cognitive dual task reduced the cognitive contribution to postural control, resulting in less regular COP trajectories of larger dimension but similar stability. Thus, by combining findings gathered from a complementary set of dynamics-related analyses under various task conditions and its recovery during rehabilitation after stroke, we could make readily interpretable inferences about (changes in) the underlying postural control. All in all, it is fair to conclude that the results of the present study supported our expectation that the use of dynamical measures would have surplus value in the analysis of COP trajectories. The implication of this overall conclusion is that, in future studies of postural control, it should be deemed worthwhile to incorporate both dynamical and conventional measures in the analysis of COP trajectories.”Now lets get back to the concussion COP trajectories.

What concerned the concussion researchers was the essentially the use of their algorithm for,’… detrending, denoising, multiscale decomposition, and multfractal analysis. The measurement problems appear to be better than simple linear filters with wavelet and chaos-based approaches.’ The authors were basically looking at if a long-term trend could be accurately determined, in terms of understanding the mechanism for the trend signal itself. They conclude with, ….”nonstationarity associated with longer data will not pose a challenge in data analysis.” These authors used the are of COP to make their analysis. Their primary propose for evaluating the concussed athletes was to help, ‘assess recovery from minor traumatic brain injury (mTBI). Here are their pertinent conclusions.

“We have found that immediately following concussion, the area of the COP data increases with data length at least linearly for data length up to 2 minutes, therefore at least 2 minutes of data recording is required in order to reliably quantify the effects of fractal analysis for assessing postural instability. ” The utility of fractal analysis, …” appears applicable to sway power above about 0.5 Hz, thus fractal characterization is only quantifying the secondary effects (as a small fraction of total power) in the sway time series, and not effective in indicating recovery following mTBI. ” Using the authors own Shannon and Renyi entropies from COP they describe what they term as appealing properties, which includes, …” capacity for determination of the optimal length of the time series for analysis plus new interpretation of the area of COP. Most importantly, entropy analysis can readily detect postural instability in athletes at least 10 days post-concussion, so that it appears promising as a sensitive measure of effects of mTBI on postural sway.”

Covered a lot of material in this essay. Lets recapitulate. Postural sway if measured as a fractal time series of COP appears to get at a sensitive evaluation for post concussion healing time. Balance deregulation is an early signpost for Alzheimer disease occurrence. Balance is an ancient evolutionary characteristic from primal sensing found in Nature. Early life used brain formation in the embryo linking to coordinated bone metabolism to build a head for evolutionary advantage. Brain bone communication with balance sensing is conserved from the Mother species, the hagfish, through all vertebrates. Strange- that Sidney Crosby sped up his recovery from his concussions by being strapped in a astronaut chair loading his balance- organ brain, stimulating his vestibular system with Dr Ted Carrick, I don’t think it’s strange at all any more.

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Montreal Grandmother, Agnes Kent was saved by Raul Wallenberg from certain death, when he provided papers for her and her Mom to escape away from the Nazis. Today when asked what that escape meant, she replied,"Remind people, that while statesmen and whole countries remained silent and did nothing, a single individual chose to act, with ramifications that proved enormous. Similar choices confront us today. Write that simple truth she said, it can never be repeated often enough because the world keeps forgetting it."
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