The Physics of the Brain- Part 3

In the previous post, we discussed the importance of the temporal component in the functioning of the brain.  That neuronal synchrony (or binding) of the seemingly endless bombardment of sensory stimuli reaching our nervous system is achieved via an underlying "beat".  It therefore behooves us to take an exploratory journey into the wild and wacky world of brain research to try and piece together what the source of this "beat" is.  It is here that I reveal to you, what I opine, is one of the greatest and most relevant studies for our profession ever...... and it hasn't gotten a glance by most.

But first, some background and some arousal (not sexual).

Over the years, functional and anatomical studies of the brain has identified the thalamus as the principal relay centre for all sensory information (except olfactory) to the cortex.  It is proposed that the series of networks and circuits which make up the thalamocortical system is responsible for cognition and perhaps even be the foundation for consciousness itself.

The nuclei of the thalamus are subdivided into 2 distinctively different functional units- the specific thalamic nuclei and the non-specific nuclei.  In other words, there are 2 simultaneous systems functioning at the same time:  A baseline non-specific arousal system (via intralaminar and posterior thalamic nuclei) and a sensory specific system (via ventral and lateral nuclei) which is superimposed on the baseline activity.  When we observe lesions to each of these sets of nuclei, we get a clear understanding of their distinct functions.  If, for example, there is a lesion to the specific nuclei there exist a loss of a specific sensory modality (i.e.-visual, auditory etc).  However, if there is a lesion to the non-specific nuclei, patients are unaware of any input by the specific nuclei and even though those pathways still exist and are intact, they cannot  perceive or respond to them.

The perception of any specific sensory stimulus from our environment is absolutely dependent on the constant input from non-specific nuclei.   When measured, via EEG, this constant activity has been observed to occur in bursts or oscillations (~40hz).    When sensory stimuli are presented, these oscillations show a "phase locking" which allows for the cognitive processing and temporal binding of  such sensory stimuli.  Like receiving a "beat" count before beginning to play.

So while we know that there are brain regions with a high degree of localized function and control, we also know that there is no single region responsible for the integration of perception and memories.  When researchers first hypothesized the solution to the binding problem, they discovered thru their experiments that when subjects, for example, recognized faces the electrical activity of different regions of the brain became synchronized for a moment.  The synchrony appeared to be established by brain regions firing in a similar manner, as 40hz gamma oscillations.

This discovery explained that neurons are not only linked in space (as in actual physical synaptic connections) but also time. The brain can now have virtually unlimited possible combinations of neurons with a resultant limitless capacity for retaining information.  There now exists a logical and rational explanation to the mechanisms by which multiple sensory events come together into a single experience.

So what is the source of these thalamocortical oscillations which is so vital for us binding all our sensory information together?  Well, at first it was thought that they were an intrinsic property of the thalamus which was genetically programmed.  But in 1992, two scientists named Pinault and Dechev (published in the journal of Psychological Resarch) found that when they transected the dorsal column of the spinal cords in rats, the rhythmic depolarization of 40hz oscillations in the thalamic nuclei could no longer be recorded.  They showed that the source of this baseline activity was not an intrinsic property of the thalamus but pre-synaptic to the thalamus.  That, in fact, the source of the oscillations were a product of the neurons of the dorsal column and deep midline cerebellum.  Ultimately, they arise mainly from the muscle and joint afferents of the SPINE.

So, in summary, baseline arousal activity, signal to noise ratio and synchronization of the cerebral hemispheres (and hence high level perception) is thought to result from non-specific thalamic nuclei which trace back to the subcortical oscillations originating from the dorsal column and cerebellum, which ultimately receive their input from the non-stop gravitational transductions derived from postural spinal muscles and joints.  This, as we chiropractors know, can be globally deficient and/or specifically decreased in specific areas.  What a unique and powerful set of lenses through which to grasp the impact of our adjustments.  Brings another level of clinical clarity and sense of awe to just how powerful a well delivered and precise adjustment can be- an approach that is rational, scientific and still embraces the time honoured wisdom of our original principles.

So when I first stumbled upon these concepts, this research and this level of understanding of the brain and nervous system, I wondered to myself what would it look like?  If I could peel away the skin and tissues of a living organism and be left with just a bunch of endless activated synapses and circuits lighting up endlessly like an overly lit up Christmas tree, what would that look like?  Well I'm watching a TED talk by Dr. Henry Markram, director of Blue Brain, a supercomputing project that can model components of the mammalian brain to precise cellular detail and simulate their activity in 3D, and he shows a computer simulation of a living rat's brainstem.  See if you can pick up the bursts of 40 hz oscillations responsible for the binding and therefore perception of sensory stimuli....I was stunned.  

So now for a new twist to the Harvey Lillard story as put forth by my Neurology Instructor, Dr. Melillo.  As you know, Harvey Lillard was a janitor who worked in the same building as Daniel David Palmer back in 1895.  Harvey was deaf and D.D. inquired of the man how this came to be.  Harvey proceeded to explain that it happened all of a sudden while lifting something, he heard a pop in his spine and from that time, he could not hear.  As the account goes, D.D. went to the area of the spine pointed out by Harvey and he performed the first chiropractic adjustment.  Harvey's hearing returned and the rest, as they say, is history.  Palmer, at the time, explained that the hearing returned based on the hypothesis that there was a connection between the spine and nervous system...a segmental connection emphasizing interference to the sensory pathways for hearing.  But what if by increasing the movement of spinal joints and allowing those postural muscles to stretch against the forces of gravity on a continuous basis, Harvey's baseline arousal levels was allowed to increase through the cerebellar, thalamic and spinal pathways.  This, in turn, resulted in an increase in the signal to noise ratio such that the same level of sound that could not be perceived previously, now is better able to summate and be processed.  

Food for thought.