Neuroplasticity by Moheb Costandi
Neuroplasticity by Moheb Costandi
I have written summaries for a few of the chapters below.
Chapter 1: Introduction
Moheb Costandi starts by suggesting that we have the ability to rewire our own brains. He asserts that the adult brain is not only capable of changing, but it does so continuously throughout life, in response to everything we do and every experience we have [2].
My two sense: This reminds of me of the saying “thoughts are things” by Tony Morrison, because if you believe something strongly enough, you have the ability to manifest it. Sort of like a self-fulfilling prophecy. This strong belief causes changes in your brain. This is one of the reasons some surgeons will not perform some surgeries on patients with “negative” attitudes. They will wait until the patient is thinking more positively before they operate.
This chapter mostly gives the reader a brief history of neuroplasticity by introducing key characters. They are all listed below.
Johann Spurzheim: one of the founders of phrenology
Jean-Baptiste Lamarck: opponent of Charles Darwin and believed that evolution occurs by “the inheritance of acquired characteristics”
Theodore Schwann: one of the founders of cell theory
Matthias Schleiden: one of the founders of cell theory
Santiago Ramon y Cajal: Spanish neuroanatomist that wrote the neuron doctrine (however, he believed that in adulthood, the brain was fixed and incapable of any change) Ramon y Cajal also suggested that plasticity took place between the neurons, in the junctions, alluding to the creation of new synapses
William James: wrote the book “The Principles of Psychology” where plasticity is first mentioned
Charles Sherrington: named the junctions that Ramon y Cajal was talking about “synapses”. He also stated that the synapse is where learning takes place [9].
Tim Bliss and Terje Lomo: reported the discovery of Long Term Potentiation (LTP), a physiological process by which synapses could be strengthened for long periods of time.
LTP, synaptic modification, is now thought of as the basis behind learning and memory, and as Moheb Costandi writes, is the best-known mode of neuroplasticity. Neural stem cells are undifferentiated cells found in the brain. The discovery of these cells in adults is what convinced many scientists that neuroplasticity was a “revolutionary discovery” and should be examined more seriously.
There are two types of neuroplasticity; functional plasticity and structural plasticity. Functional plasticity refers to changes in neurons that lead to the creation of ether stronger or weaker synaptic connections. Structural plasticity refers to “volumetric changes in discrete brain regions”, which are created from new “nerve branches”, or new neuron connections.
Chapter 2: Sensory Substitution
I will start off this section by naming some key characters and terms.
Phrenology is, as Moheb Costandi describes, a pseudoscientific discipline that attempts to determine people’s mental traits from skull measurements.
(attach picture of phrenological example)
Franz Joseph Gall: the anatomist who founded phrenology and localization theory, which was discredited as scientific
Pierre Paul Broca: Worked on stroke patients, all of whom lost the ability to speak. He noticed that it was all do to damage in the same area, in the left frontal lobe. This became known as Broca’s Area
Karl Wernicke: Also worked on stroke patients, who lost the ability to understand language. He noticed it was all due to damage in the same area, in the left temporal lobe. This region became known as Wernicke’s Area.
Gustav Fritz and Eduard Hitzig: Anatomists who electrically stimulated and selectively destroyed parts of animals’ brains. This allowed them to find the motor cortex, and the prefrontal gyrus. They were also able to confirm that each side of the brain controlled the opposite side, with respect to the motor cortex.
Korbinian Brodmann: the neuroanatomist that came up with the Broadmann’s system of neuroanatomical classification, a number system that is still in use today
(attach picture of broadmann’s system)
Widler Penfield: a neurosurgeon who pioneered a technique to electrically stimulate the brains of awake epileptic patients, in order to determine the location of the abnormal brain tissue causing the seizures [21].
Paul Bach-y-Rita: built a device that allowed blind people to see with their tongue
DTI: Diffusion Tensor Imaging
McGurk Effect Video: This is a demonstration of cross-modal processing and multisensory integration.
Paul Bach-y-Rita performed studies that showed that brain localization is not fixed. He showed this with his invention of a device that would help blind people see using their tongue. Before this device, he created a similar device that would help them see with their back. He used a dentist chair with 400 large vibrating pins arranged in a 20 by 20 array on the backrest of the chair. It also consisted of a camera. The camera would capture the image of which the image would be converted to a vibrational pattern. “The [test] subjects learned to use the vibrational patterns as there visual cues” [23]. Paul Bach-y-Rita called this cross-modal mechanism, which is the ability of an area, other than the primary processing area, to process information. You can see elements of this in some blind people’s use of echolocation.
Synesthesia shares characteristics of sensory substitution. It is a neurological condition where sensory information of one type gives rise to percept in another [30]. Usually people are born with this condition, however, non-synesthetes can acquire this ability through cross-modal plasticity. By training the brain to gain this ability, the brain creates new connections that form “haphazardly”. These new connection formations are not entirely understood.
Chapter 3: Developmental Plasticity
The human brain contains between 86 to 100 billion neurons and an even larger number of glial cells. Neurons make up 15% of the brain, while glia make up the other 85% of the brain.
Chapter 3 starts by explaining brain development in infants. We first begin life with way more neurons than we need. As we begin learning, then neurons that we do not use or need, begin to die off. This is called pruning. For example, it is extremely easy for young children to learn a new language without having an accent. However, if they are only exposed to one language, then the neurons necessary for acquiring another language without an accent, die off.
Victor Hamburger, a renowned embryologist, conducted an experiment where he “removed the developing limbs from chick embryos, and noticed that the primary sensory neurons, which extended fibers to the muscles in the limbs, did not survive in the absence of their “target” tissues. He concluded that nerve cells depend largely on their final destination for their maturation into a specific type [34]”. However, Rita Levi-Montalcini, who joined Victor Hamburger’s lab, suspected that removing the tissue, limb tissue, caused the nerve cells to undergo neurodegeneration. Through her studies with Stanley Cohen, they found that nerve growth factor, NGF, was crucial in neuronal survival and differentiation.
Moheb Costandi then goes on to explain synaptic formation and synaptic pruning in the infant brain. First cells form many synaptic connections (possibly over (10000) connections with other cells, except for motor neurons, which form only one connection with one muscle fiber. In order to control redundancy and unused synaptic connections, the neurons undergo synaptic pruning, which destroys those synaptic connections.
Key terms:
NGF: Neuron growth factor- a diffusible protein that is secreted by certain tissues and promotes neuronal survival and differentiation [35]
Neurotrophic Hypothesis: nerve cells are initially overproduced but then compete for a limited supply of target-derived NGF, those that receive the signal survive and undergo maturation, whereas those that do not die off [35]
Caspases: enzyme that promotes genetic cell death
Acetylcholine:
GABA: gamma-aminobutyric acid
Inhibitory Interneurons: synthesize and release GABA
Large Basket Cells: present in primary visual cortex