Neuroplasticity

Melody MyDowel

• Editorial: Payhip
• Año: 2013
• ISBN:
  9783955775933
• Categoría: Sciences biologiques
• Categoría: Anatomie humaine et physiologie

This e-book covers everything you wanted to know about neuroplasticy. All the new data that is available, all the new research covering the theme of brain plasticity. The book starts with general anatomy and physiology needed to understand the information in the book. The next chapter is about history and you would be surprised to see that therm neuroplasticity is not new! What is new is the research being more widespread. Book also contains information about brain damage, mental health and addictions. There are really interesting findings in the fields of learning and memory, those are the biggest chapters! Also if you want to know more about habits that influence central nervous system - both bad and good things, there is all the new data in it. Book includes interesting facts that will convince you to take a better care about your brain. It is never too late to start working in yourself and improving yourself.

1. Definition

Neuroplasticity or brain plasticity stands for the brains ability to reorganize itself by forming new neural connections. The term is derived from two words: Neuron and Plastic.

Neuron is a nerve cell in our brain and it consists of stoma (or the body), an axon and dendrites. Neuron cells are electrically excited cells that process and transmit information through electrical and chemical signals. The cells are connected with each other by synapses, which transmit chemical signals and allow neurons to form neural networks. All neurons are electrically excitable. They maintain voltage gradients across their membranes by ion channels and ion pumps. What that means is that when there is a high voltage change, ion pumps generate action potential and the information travels through network of neurons, from one cell to another.

Now, how does action potential work? When there is a signal from another neuron, there is a polarity change across the membrane. Polarity changes due to sodium and potassium ions and ion pumps that open and close as the membrane reaches the threshold potential. What happens is that sodium ions enter the membrane, causing depolarization and when potassium channels open, potassium ions travel out of the axon and repolarization accurse. This creates the change in polarity and allows an impulse to travel through the axon, to the axon terminal where it passes the signal to other neurons.

There are different types of neural cells, like sensory neurons, motor neurons and interneurons and they are the core components of the brain, spinal cord and peripheral ganglia and all together they form the nervous system.

The word “Plastic” doesn’t mean it has plastic consistency as one my think but it refers to the ability of change. Plastic stands for mold, modify or sculpt. Brain has an ability to modify its structure and function, caused by bodily and environmental changes.

To understand the next chapters there is also some brain anatomy you should know about. Brain is the center of nervous system. It contains about a 100 billion neurons! And some glia cells but I will not give you too much information yet. So, the brain has white matter and grey matter, the difference is not just in color but also in its structure and function. Grey matter mostly stands for nucleus or I should say the body of cells and the white matter is mostly made of axons and glial cells. Meaning, white matter modulates the distribution of action potentials and is enabling communication and coordination between different brain regions whilst the gray matter is mostly associated with processing and cognition.

The brain has two hemispheres that are connected by corpus callosum which is the largest white matter in the brain. Important information is that the brain is divided in 4 lobes on each side. Frontal, parietal, occipital and temporal lobe:

These lobes are divided by gyri and sulci, those are the cortical folds of the cortex and these wrinkles exist to create a bigger surface. In some literature they count insula as an additional lobe. But that doesn’t matter now. Here are some basic functions of individual lobes:

• Frontal lobe is associated with planning, reasoning, parts of speech, movements, emotions and problem solving
  
  
• Parietal lobe is associated with orientation, recognition, perception of stimuli and movement
  
  
• Occipital lobe is associated with visual processing and
  
  
• Temporal lobe is associated with perception and recognition of auditory stimuli, memory and speech

I should also give you some information about the complex limbic system. Limbic system is responsible for behavior, memory, emotions and olfaction. All in all it is believed to have an important role for our emotional life and the formation of memories. There are two parts of the system that will be mentioned in this book. The first one is hippocampus. Hippocampus is a horseshoes shaped paired structure. It is located in the temporal lobe and its function is connected with memory, emotional response, spatial orientation and navigation. Hippocampus is communicating with amygdala, almond shaped structure also located in the temporal lobe. Its functions are referred to memory modulation, emotional learning, hormonal secretions, arousal and autonomic response to fear.

The structure of the nervous system is complex and so is its function. Modern technology is helping us in discovery of its potential, but there is still a lot that has been unrevealed and unexplained.

2. History

It has been believed for a long time that we are born with a certain amount of neurons and during the life time, the number decreases and there is no possibility to generate new neural cells. It was thought that passed the age of mid-childhood, new neurons could not develop, meaning that in the period of mid-childhood and death, the brain does not possess the ability of regeneration and formation of new pathways and neurons. Common belief was that the mind started as a blank slate from which intelligence and personality were developed, the notion of tabula rasa.

First mention of neuroplasticity was in 1890 made by William James and his seminal work “the principles of Psychology” where he says that “Organic matter, especially nervous tissue, seems endowed with a very extraordinary degree of plasticity”. There is a paper from The American Journal of Psychology in 1897 which discusses how “intelligence enables the organism to make better adaptation. Its neural pre-requisite is plasticity”. In 1923, Karl Lashley preformed experiments on rhesus monkeys demonstrating changes in neural pathways. Lashly concluded that these changes were the roof of brain plasticity. There was a parallel study about recovery of function after brain injury. In 1948 a Polish neuroscientist named Jerzy Konorski suggested that over time neurons that had coincidal activation due to the vicinity to the firing neuron would after time create plastic changes in the brain.

A very important name in field of neuroplasticity is Donald Hebb, Canadian psychologist who in 1940’s wrote that if the axon of one cell was close enough to another cell, it could excite the neighboring cell. If this interaction occurred on a repetitive basis, there would be some type of structural or chemical change in one or both of the cells so that the first cell’s efficiency would be increased. His famous sentence is: “Neurons that fire together, wire together”.

Evidence was brought to the scientific world in 1960’s, when Bach-y-Rita contented that if one sense were to sustain damage, a person’s other senses might be able to compensate. He stated: “We see with our brains, not with our eyes”. Paul Bach-y-Rita’s work was mostly concentrated to stroke patients and balancing issues due to vestibular damage. His interest in helping developing treatment for stroke came from his father, who had physical impairment after having a stroke. Paul developed exercises for his father and was able to help him make almost full recovery of the language and physical impairments he had incurred. He has also developed device called a “brainport” that when connected to the patient’s tongue will stimulate certain areas of it through vibrations. The effects of the treatment happen miraculously fast. Patients treated could stand on their own almost immediately while being connected to the device and after several weeks of treatment the patients were able to stand without being connected to the device.

Very notable scientist that helped to further the study of treating people that have had strokes and who created advanced technological methods was Edward Taub. In his clinic he changed many people’s lives by reorganizing their brains and helped them to become more independent.

A pioneer in proposing that brain exercise might be useful in treating mental illness was Michael Merzenich, who believed that the brain retains plasticity from birth to dead and that even seniors could improve their cognitive function. Merzenich developed software which improves cognitive functioning.

Fernando Nottebohm found that birds could learn new songs all through their lives. Joseph Altman discovered that adults could regenerate new nerve cells, but his discovery was ignored until the 1990’s. At that time, Elizabeth Gould proved that the brains of primates could demonstrate neurogenesis.

Throughout history there has been evidence of brain plasticity and with modern technology they were able to prove it. The fact that the brain possesses an ability of re-mapping has changed our perspective and helped many people to show a degree of recover after sustaining brain damage. Therefore I believe there were two important facts that made us believe we can influence on our brain from birth to death. First of all there was evidence of recovery in patients who survived brain damage. The other factor that contributed to the fact that brain has plastic quality is modern technology. With PET (positron emission tomography) and MRI (magnetic resonance imaging) scans, neuroscientists were able to visualize the changes in nervous system.

3. Neuroplasticity through lifetime

Eighteen days after fertilization there is a rapid growth of the young brain system. Neurons are produced at the rate of 250,000 to one million per minute and it is influenced by genetics and the baby’s events (experience) in the womb. After the birth, the brain of a newborn is flooded with information. Suddenly there is a lot of sensory information that has to make it to the brain in order to be processed. Impulses have to be transmitted to the brain and for that reason; nerve cells make connections with one another. Those connections or “pathways” from a particular neuron to the correct area of the brain are instructed by genes and environment. For instance, neurons in the retina of the eye send impulses to the primary visual area in the occipital lobe and not to the left posterior temporal lobe where is the area of language production. These connections form rapidly and as each neuron cell matures, it sends out axon and dendrites, increasing the number of synaptic contact and laying specific connection from one cell to another. The baby is born with approximately 2,500 synapses and by reaching two or three years of life, the number of synapses is approximately 15,000 per neuron. The number of synapses then decreases through life by a process called synaptic pruning. Synaptic pruning eliminates the weaker contac...

Índice

• 1. Definition