New Neuroscience Findings

BRAIN IMMUNE SYSTEM: It was always supposed that constituents of the immune system didn’t exist in the brain. The blood/brain barrier was supposed to keep foreign objects out of the brain. Scientists have been surprised to find proteins that are involved in the immune response in the brain as well as the peripheral nervous system. Proteins, such as Major Histocompatibility Complex (MHC) which cells have coated on their membranes to identify themselves have been found in fetal cat brains. Another immune system protein, PirB, has also been found. It is thought that these proteins prune away unwanted synapses. If there are too many connections, chaos ensues with impulses going in every direction. There is excessive synaptic plasticity when there are no checks on synapse formation.

C1q is another protein that appears to have a similar function. It is found to work with thrombospondin, a synapse formation stimulator that is formed by astrocytes. The two work together to break and build synapses, respectively. C1q that is found elsewhere binds to bacteria and foreign substances to identify them for destruction. C1q has been found in overabundance in the brain of Alzheimer’s patients and in retinas of those with glaucoma. It is surmised that part of the neuropathology of Alzheimer’s is excessive severing of synapses.

MHC has also been found in peripheral nerves. Those found in motor neuron are thought to aid in nerve repair. MHC severs excitatory nerve synapses between neurons and muscles. Inhibitory synapses are maintained as they stop the neurons from firing. The synaptic stripping and the quelling of excitatory synaptic firings frees damaged neurons to use their energy for repair.

Numerous neurological disorders may have dysfunction of MHC expression as part of their pathological process.

– Trivedi B. “Thought Control.” New Scientist, 1 March 2008

MYELIN: White matter or myelin is more than just nerve insulation. As we know, myelinated nerves have bare spots about 1 mm apart called Nodes of Ranvier. These nodes allow nerve impulses to travel faster than in comparable non-myelinated nerves. In the brain and spinal cord, glial cells called oligodendrocytes form myelin. In the peripheral nervous system, a different glial cell, Schwann cell, forms myelin.

At birth, little myelin has formed in the brain. The process is completed by age 25 to 30  years. Myelination in the brain occurs from back to front. The higher reasoning centers of the frontal lobes are the last to be myelinated. Teens are really mentally immature as the brain is not fully myelinated – the current and constant use of cellular phones by youth cannot be good for brain development either. The reason that it takes until adulthood to form myelin is probably to maintain plasticity in the developing brain as myelinated nerves are not as plastic.

The big question today is: Is myelin formation programmed or can life experiences have an impact on myelination?

One study of professional pianists used diffusion tensor imaging (DTI) which is a imaging process that uses MRI machines to create special 3-D images. In professional pianists, certain regions of the cerebral cortex were more highly developed than in non-musicians. One area of white matter that was more highly developed was in areas associated with finger movement coordination. Other areas were associated with cognitive processes associated with music. The more that the musician practices each day, the greater the DTI signal in these white matter regions – the axon density was greater and myelination was thicker. Animal studies have found that animals in “enriched” environments had a greater degree of myelination on neurons in the corpus callosum.

There are “windows of opportunity” for learning. Learning occurs more readily when myelination is still occurring, i.e., it is best to learn languages or a musical instrument early in life. Myelination was greater in those who took up music at an early age. Those who took up musical instruments later had increased white matter development only in the forebrain. Scientists are still trying to understand why mental exercises in later life helps delay Alzheimer’s disease.

How does learning affect myelination? In the brain, astrocytes listen in to the impulses traveling down neurons. With increased impulse traffic down neurons, these astrocytes release a chemical that stimulates the oligodentrocytes to lay down more myelin.

It appears that myelin formation is both programmed and altered by life experiences. It is best to pick up a skill early in life, but it is not too late for those of us who are long past youth to learn. It’s just harder and synaptic-based, it is unlikely that one can achieve the level of someone who begins a skill in childhood. For chiropractic students in their 20s-30s, practice, practice, practice so that you can gain the extra myelination in those areas associated with adjusting skills and in those cognitive and memory areas associated with clinical skills.

  • Fields RD. “White Matter.” Scientific American, March 2008
  • Ishibashi T, et al. “Astrocytes Promote Myelination in Response to Electrical Impulses.” Neuron, 16 March 2006.
  • Fields RD. Myelination: An Overlooked Mechanism of Synpatic Plasticity. The Neuroscientist, December 2005.

GLIA: We were taught that glia was filler and covering material in the nervous system. It appears that they have important roles and communicate with each other and neurons. As new research tools are developed, neuroscientists have been better able to understand the various functions of glia.

Studies of a glial cell in the brain called astrocytes found that these cells can “listen in” on adjacent neurons. Astrocytes wrap around synapses. What is the importance of this function? How does it occur?

It has been found that communications between glia and between glia and neurons are via ATP – adenosine triphosphate. It’s size is small and its rapid diffusion and breakdown makes it ideal. ATP was found to inhibit myelin formation but its end product, adenosine was found to be stimulatory. Astrocytes were found to have both large scale and focal intercommunications. Focal intercommunications may cause astrocytes to release the same neurotransmitter being released by the synapses that they surround. This probably amplifies the impulse signal. The glial intercommunications probably allow distant glial to contribute to the release of neurotransmitters from distant synapses. This would have an impact in learning and memory – helps to form associations between different stimuli that are processed by different neural circuits.

  • Fields RD. “White Matter.” Scientific American, March 2008.
  • Ishibashi T, et al. “Astrocytes Promote Myelination in Response to Electrical Impulses.” Neuron, 16 March 2006.
  • Fields RD. “The Other Half of the Brain.” Scientific American, April 2004