We as humans have
the memory. This is an ability which
we posses to comprehend our reality through our experiences. We can recognize
our thoughts, consciousness and language due to this ability. Also we can
classify memories. There are two types of memories. These are the short-term
and the long-term ones. We understand the memories that occurred in the present
or the past thanks to the transient memories. These are the essential
memoirs that we carry out by some processes that allow us to comprehend the
meaning of our experiences.
Likewise, there
is a kind of transient memory called the
working memory. This is known as the memory that takes place in the
present. Its information capacity is very low but it has an important role as
well. It permits us to comprehend spoken and written language. The researches
have stated that more or less significant memories depend on the reactions.
They could be physical or mental reactions that happen within the brain.
On the other
hand, our experiences don’t have to be considered relevant to be long-term
remembered. There is a phenomenon known as the
flash bulb memory, which is not an important lived memory but it is still
kept within the long-term memory. Also, in normal circumstances, these memories
are not quickly forgotten.
In addition, the
brain is altered. We have been talking about the short-term and long-term
memories. Thanks to this we can say that there are different mechanisms for
their information. Within the brain, the synapses in the neural circuits are
altered to conform the formation of the memory. The long-term memory requires
dialogue between neurons and genes for its functional work. But the short-term
memory does not require any of those factors.
Our brain has a
lot of knowledge inside it. One of the most particular characteristics in that
the brain is able to “classify” information, so we can know exactly for
example, which is capital of a country, how to give address and even the name
of our friends. We possess all kind of simple and complex skills at the same
time. Our brain’s memory banks, it means that when we learn something we
acquire it even if we don´t practice often we never forgot it, like for example
riding a bicycle or knitting, it means that those things stays in our memory
store. The parts that involved our complex motor skills in the brain are
located in the basal ganglia and the cerebellum. Motor skills are an essential
part of our memory store, we have also an “episodic” memory to remember things
that happened in the past, which is not easily to verified and that can be
recalled. Some sort of studies made it by scientific aware that memory has
recollected details of past events, it means that not only specific memory has
a physical basis but that each also has a particular physical location in the
brain.
The
"where" of memory.
Different kinds
of memory have different positions in our brain. The explicit working memory is
associated with the pre-frontal cortex. The hippocampus is where the long-term
explicit memory is. The hippocampus is related with the navigation too because this
part of our brains help us to create detailed maps. With more information the
hippocampus becomes larger. Learning complex motor tasks engages the motor and
sensory cortex.
The
how of memory.
There are many
experiments in animals about that because we use the same genetic code as
worms’ flies and other animals or insects. In the 60's Eric Kandel doesn't knew
which this method will work in sophisticated kinds of memory like in the human.
He won the prize on 2000 about memory research.
Sensation is
another type of learning seen in humans and the sea slug.
It occurs when we are exposed to an unexpected or
strongly unpleasant stimulus.
After that our attention is sensitized as an innocuous
stimulus.
Generally the
sensitizing effect last perhaps for just a few minutes. But if the alarm
stimulus is repeated a number of times our senses maybe heightened for days and
now sensitization is a form of long-term memory.
Kandel has
studied the two most basic types of memory, short-term and long-term using the
paradigm of habituation and sensitization. He could observe what was going on
in individual neurons and at individual synapses while the memory was being
form. Kandel showed that the gill withdrawal reflex of Aplysia can be
sensitized by a single strong electric shock to the tail. Thus a single shock
gives rise to a memory in the form of sensitize responsiveness, lasting just a
few minutes.
Next Kandel
repeated it five times in spaced trials and converted the short-term memory
into a long-term memory that last days. These experiments demonstrated that
Aplysia displays form of learning leading to short- and long- term memory
similar to humans. What was required now was evidence that there was indeed a
true conservation of the physical or molecular mechanism of memory formation
between Aplysia and mammals.
The neuronal
network controlling the gill reflex is very simple. The sensitizing stimulus to
the tail excites these neurons and when they are inhibited the sensitizing
effects of stimulating the tail are blocked. The activation of these neurons is
necessary for the creation of memory. These key cells are named “modulatory
neurons”. With these cells inactivated the sea slug is capable to perform the
gill withdrawal, but the strength of touching the siphon is not capable in
short- long- term by shocks to the tail.
The roles of the
modulatory neurons are crucial to explain how the strength of the gill reflex
was modified by experience.
Kendel’s experiments showed that the activation of the
modulatory neuron strengthened the pre-existing synapses between the sensory
neurons and the motor neurons.
They showed that
when a puff of serotonin is directed to the sensory motor of the synapse, it
was strengthened for a few minutes just like the tail.
The serotonin can substitute the tail shock and
produce short- long- term memory.
So now the question is how serotonin, a
neurotransmitter, found in all animals, strengthens a synaptic connection in
short-long- term.
Kandel showed
that the common denominator in Aplysia is the ubiquitous second messenger
called cyclic-AMP, whose synthesis is triggered by serotonin released by the
modulatory neurons.
When cyclic AMP is injected into the sensory neurosis
mimics the effects of serotonin.
Now we must ask
how cyclic-AMP operates. It activates a very important enzyme called Kinaze.
The target of this enzyme is the potassium channel.
Thus the sensory neurons synapsis with the gill motor
neuron is strengthened.
Finally we have
arrived to the strengthened synapse modifying the animal behavior in
short-term. This is only in short-term memory because the special enzyme
removes phosphates from proteins and return to their original state restoring
the synaptic strength. There is requirement of new proteins to be synthetized
and the blocking of this prevents long-term memory formation and this is true
in Aplysys as it is true in us.
The synapse must
involve the cell body and its nucleus. The relation between synapse and nucleus
cause the stimulation of the necessary genetic information that is needed for
the synthesis of the new protein required to the strength of the long term
memory. The beginning process is the same as short-term memory, it´s different
only because of the time that serotonin is delivered. When is delivered several
times, its long- term memory formation.
When the cell body is activated it modifies proteins,
those ones interact with the DNA and determinate the manifestation of
particular genes. In Aplysia the converting process of short-term into long
term memory, requires the strengthening of short term changes in synaptic
strength and thee development of new synapses. Those processes need the synthesis
of new proteins
Memory
mechanisms are universal.
From all the
experiments, we get two conclusions. First, the synapse is crucial for adaptive
change in the brain, learning and memory. Chemical synapse´s function is to
modify the strength of that process. Also involves the ability of communication
with the cell´s genome which has the purpose of making and finishing possible
changes. Summing up, synapse makes evolution and adaptation possible. Behavior
is determinate by the last experiences in our environment.
Secondly, it´s
always told that upbringing influence our mental skills, but the ability to
learn from nurture is determinate by how our genes are intended to answer to
experience.
Different species
and human beings can have similar and even the same mechanisms of memory
formation. Also, between a hippocampus and a snail they both have the same
mechanism of synaptic strengthening.
The advanced
knowledge of the components of memory allows the development of advanced drugs,
which can help us to improve our learning ability and the efficiency of our
neurotransmitters. On the other hand, we have to be careful with those drugs,
because in a future they might help on the memory loss. That’s why we need to
be aware of our mechanisms of memory formation.
Brain is a
flexible machine and very responsive, so if we are looking for a better memory
we only need to keep learning. This machine will develop a new storage if we
give it new information. As we grow older neurons die and we cannot replace
them, so, we lose brain ability. Nevertheless, mental exercise can reduce this
dramatic time effect.
Daniel Andrades
Alan Becar
Francisca Arellano
Sebastian Aravena
Camila Contreras
