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
