PERIODICUM BIOLOGORUM UDC 57:61

VOL. 116, No 2, 209211, 2014 CODEN PDBIAD

ISSN 0031-5362

Forum

Neuroplasticity

Abstract
VIDA DEMARIN1
SANDRA MOROVI1 Every man can, if he so desires, become the sculptor of his own brain
RAPHAEL BN2
1
Medical Centre Aviva
Santiago Ramon y Cajal (1)
HR-10000, Zagreb, Nemetova 2, Croatia
2
Medical centre Vires Refotae Neuroplasticity can be defined as brains ability to change, remodel and
HR-10000 Zagreb, Hreli~ka 98, Croatia reorganize for purpose of better ability to adapt to new situations. Despite
the fact that the concept of neuroplasticity is quite new, it is one of the most
Correspondence:
Vida Demarin, MD, PhD
important discoveries in neuroscience. The fact is that neural networks are
Medical Director, Medical Centre Aviva not fixed, but occurring and disappearing dynamically throughout our whole
HR-10000, Zagreb, Nemetova 2, Croatia life, depending on experiences. While we repeatedly practice one activity such
E-mail: vida.demarin@zg.t-com.hr as a sequence of movements or a mathematical problem, neuronal circuits
are being formed, leading to better ability to perform the practiced task with
less waste of energy. Once we stop practicing a certain activity, the brain
Key words: Neuroplasticity, Structural will redirect these neuronal circuits by a much known use it or lose it
neuroplasticity, Functional neuroplasticity principle. Neuroplasticity leads to many different occurrences, such as ha-
bituation, sensitization to a certain position, medication tolerance, even
recovery following brain injury.

HISTORICAL OVERVIEW

A bout 120 years ago, William James was the first to suggest the
theory of neuroplasticity in his work Principles of Psychology (2).
He suggested that human brain is capable for continuous functional
changes. Polish neuroscientist Jerzy Konorski was the first to define the
term neuroplasticity in 1948. Konorski suggested a theory by which
neurons which have been activated by closeness of an active neural cir-
cuit, change and incorporate themselves into that circuit (3). Donald
Hebb, a Canadian psychologist established a Hebbs rule, defined also
as pre-post coincidence, implying that changes of biochemical process-
es in one neuron can stimulate neighboring simultaneously activated
synapses, this being the basic principle of synaptic plasticity (4). Paul
Bach-y-Rita is the pioneer in demonstrating neuroplasticity on actual
cases, claiming that healthy regions of the brain can take over the func-
tions of injured parts of the brain. This was the basis of his treatment
for people who suffered vestibular damage. He patented an appliance
which when connected to ones tongue, stimulates receptors by vibra-
tions in a frequency and amplitude in correlation with pixel analysis
from the surroundings (5-7).
Edward Taub supported research and developed first real and ap-
plicable treatments for patients. He proved, first using rhesus monkeys,
Received May 22, 2014.
then on humans, that tying up of healthy half of the body in case of
Vida Demarin et al. Neuroplasticity

hemiplegia, forces the damaged part of the brain to b) Functional neuroplasticity

faster rehabilitation (8-10). Functional neuroplasticity depends upon two basic
Michael Merzenich is yet another neuroscientist who processes, learning and memory. They also represent a
left his mark in the field of neuroplasticity. He designed special type of neural and synaptic plasticity, based on
a software for in order to help people with learning dif- certain types of synaptic plasticity causing permanent
ficulties (11, 12). changes in synaptic effectiveness (15). During learning
and memory permanent changes occur in synaptic rela-
All these scientists had to fight against an academic tionships between neurons due to structural adjustments
dogma which disapproved the existence of adult brain or intracellular biochemical processes.
neuroplasticity, except during developmental phase. Un-
til the Decade of the brain (1990-2000), the word neu-
roplasticity itself, lead to articles not being published in Neurobiological basis of
prestigious journals. When asked, Eric Kandel, a Nobel neuroplasticity
Prize winner in medicine, said that neuroplasticitiy is
When looking at neuroplasticity on molecular level,
what marked the Decade of the brain.
all types of synaptic plasticity share neurotransmitter exo-
cytosis modulation, on the level of one single synapse or
Types of neuroplasticity among a larger neuronal network. Synaptic plasticity
mainly depends on receptors binding neurotransmitters.
Neuroplasticity is a general term, defining the fact that
Mental events activate a large neural molecular cascade,
the brain changes, recognizing the need for further defini-
including regulatory factors referring to DNA and RNA
tion of the term. We distinguish structural from func-
(16). Research on long term changes within the synapse
tional neuroplasticity.
consider different types of memory based on different
a) Structural neuroplasticity mechanisms. Within the cortex, glutamate receptors paly
the key role, as glutamate is the most important excit-
Synaptic plasticity refers to changes in the strength
atory neurotransmitter. If several impulses, from neigh-
between neurons (synapses), chemical or electric meeting
boring neurons, in a very short time, activation of metabo-
points between brain cells. Synaptic plasticity is a general
tropic glutamate receptors (NMDA) occurs. This enables
term, and the name itself has no meaning other that
calcium influx which participates in protein synthesis,
something changed within the synapse, but can include
and permanently changes postsynaptic neuron (17).
many specific processes such as long-term changes in the
number of receptors for certain neurotransmitters, or
changes where some proteins are being synthetized more Remodeling of neuronal circuits
within the cell. following brain damage
Synaptogenesis refers to formation and fitting of syn- After establishing the fact that brain has a possibility
apse or group of synapses into a neural circuit (13). Struc- of remodeling its own neural maps, the main question for
tural plasticity is a normal marking of fetal neurons dur- neurorehabilation medicine is how to direct this neuro-
ing brain development and is called developmental plasticity to regain lost functions caused by a neurologic
plasticity, including neurogenesis and neuronal migration. deficit. This emphasizes the need to neuroanatomically
Neuronal migration is a process in which neurons trav- define every neurologic lesion. When we know which
el from their place of birth in fetal ventricular or subven- neural pathway is damaged, we can start looking for by-
tricular zone, towards their final position in the cortex. passes.
During development, brain areas become specialized a) Movement rehabilitation
for certain tasks such as processing signals form the sur- When we learn complex movements, the brain firstly
rounding areas through sensory receptors. For example, recognizes basic motoric movements, and divides them
in occipital brain area, the fourth layer of cortex hyper- and stores them into a given model which is then remem-
trophies in order to receive signals from the visual path- bered. The same network of neurons will activate every
way (14). time we observe, think, or make a certain movement, or
Neurogenesis is formation of new neurons. It is a pro- hear sounds which remind us of that movement. If we
cess which mainly takes place during brain development, focus on repetitive movements, it is important to under-
even though in the last decade neurogenesis was found in stand the purpose of the movement. For example, for a
adult brain as well. On the other hand, neuronal death patient practicing hand pronation, the movement itself is
occurs throughout life, due to brain damage or pro- not the purpose; the purpose is for him to be able to open
grammed cell death. Other forms of structural neuroplas- the door again. This way we can stimulate other neuronal
ticity include changes in white or gray matter density circuits which can lead to execution of this final goal.
which can be visualized by magnetic resonance. Neurological rehabilitation must focus on expediency of

210 Period biol, Vol 116, No 2, 2014.

Neuroplasticity Vida Demarin et al.

the movement. This makes familiarizing with patients rorehabilitation in the future is finding and defining ma-
habits before stroke very important. Most complex move- jor and minor neural pathways, and then aim to support
ments that we perform, we were first observing during neuroplasticity of compensatory neural circuits.
childhood. It is helpful to repeat these movements during
rehabilitation process. Ventral premotor cortex and base
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