Learn Human Brain our brain learns from experiences: confronting our environment alters our behavior through the modification of our nervous system (Carlson, 2010).
Although we are still far from knowing exactly the levels of each of the neurochemical and physical mechanisms involved in this process, the different experimental evidences have accumulated a very broad knowledge about the mechanisms involved in the learning process.
Learn Human Brain
The brain changes throughout our lives. The neurons that compose it can be modified as a consequence of different causes: the development; The suffering of some type of brain injury ; Exposure to environmental stimulation and, fundamentally, as a consequence of learning (BNA, 2003).
Basic Characteristics of Brain Learning
Learning is an essential process that learn human brain, together with memory, is the main means that living beings have to adapt to the recurrent modifications of our environment.
We use the term learning to refer to the fact that experience produces changes in our nervous system (SN) that can be long lasting and involve a behavioral modification (Morgado, 2005).
Experiences in themselves change the way our organism perceives, acts, thinks, or plans through the modification of the SN, altering the circuits involved in these processes (Carlson, 2010).
Thus, at the same time that our organism interacts with the medium, the synaptic connections of our brain will undergo changes, new connections can be established, those that are useful in our behavioral repertoire will be strengthened or others that are not useful or efficient will disappear (BNA, 2003).
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Therefore, if learning has to do with the changes that occur in our nervous system as a result of our experiences, when these changes are consolidated we can talk about memories. (Carlson, 2010). Memory is a phenomenon inferred from those changes that occur in the SN and gives a sense of continuity to our lives (Morgado, 2005).
Due to the multiple forms of learning and memory systems, it is now thought that the learning process and the formation of new memories depends on the synaptic plasticity, a phenomenon through which the neurons alter their communication capacity between them (BNA, 2003 ).
Types of Brain Learning
Before describing the brain mechanisms involved in the learning process , it will be necessary to characterize the different forms of learning, within which we can differentiate at least two basic types of learning: non-associative learning and associative learning.
Non-associative learning refers to the change in the functional response that occurs in response to the presentation of a single stimulus. Non-associative learning in turn can be of two types: habituation or sensitization (Bear et al., 2008).
Habituation: the repeated presentation of a stimulus produces a decrease in the intensity of the response to it (Bear et al., 2008).
Eg: If I lived in a house with a single telephone. When it rings, it runs to answer the call, however, every time it does, the call is for someone else. As this occurs repeatedly, it will stop reacting to the phone and may even stop hearing (Bear et al., 2008).
Sensitization: the presentation of a new or intense stimulus produces a response with an increased magnitude to all the following stimuli.
Ex: Suppose you are walking along a sidewalk on a well-lit street at night, and suddenly a blackout occurs. Any new or strange stimuli that appear, such as hearing footsteps or seeing the headlights of a car approaching, will alter it. The sensory stimulus (blackout) led to a sensitization, which intensifies its response to all subsequent stimuli (Bear et al., 2008).
This type of learning is based on the establishment of associations between different stimuli or events. Within associative learning we can distinguish two subtypes: classical conditioning and instrumental conditioning (Bear et al., 2008).
- Classical conditioning: in this type of learning the association between a stimulus that causes a response (unconditioned response or unconditioned response, RNC / RI), unconditioned or unconditioned stimulus (ENC / EI) and other stimulus Response, conditioned stimulus (EC), and will require a training. The matched presentation of the EC and the IE, will involve the presentation of the learned response (conditioned response, RC) to the trained stimulus. Conditioning will only occur if the stimuli occur simultaneously or if the EC precedes the ENC in a very short time interval (Bear et al., 2008).
Eg: A stimulus ENC / EC, in the case of dogs, may be a piece of meat. Upon visualization of the meat the dogs will emit a salivation response (RNC / RI). However, if a dog is presented as a stimulus the sound of a bell will not present any particular response. If we present both stimuli simultaneously or first the sound of the bell (EC) and then the meat, after a repeated training. The sound will be able to provoke the response of salivation, without being present the meat. There has been an association between food and meat. Sound (EC) is capable of causing a conditioned response (RC), salivation.
- Instrumental conditioning: in this type of learning, one learns to associate a response (motor act) with a meaningful stimulus (a reward). For instrumental conditioning to occur, it is necessary for the stimulus or reward to occur after the individual’s response. In addition, motivation will also be an important factor. On the other hand, there will also be an instrumental type of conditioning if instead of a reward, the individual obtains a disappearance of a aversive valence stimulus (Bear et al., 2008).
Example: If we introduce a hungry rat into a box with a lever that will provide food, when exploring the box the rat will press the lever (motor act) and notice that food appears (reward). After performing this action more times, the rat will associate the lever pressure with obtaining food. Therefore, you will press the lever until it is satiated (Bear et al., 2008).
Neurochemistry of brain learning
Empowerment and depression
As we have previously mentioned, it is thought that learning and memory depend on processes of synaptic plasticity.
Thus, different studies have shown that learning processes (among which are described above) and memory, lead to changes in synaptic connectivity that alter the strength and ability of communication between neurons.
These changes in connectivity would be the result of molecular and cellular mechanisms that regulate this activity as a consequence of excitation and neuronal inhibition that regulates structural plasticity. Thus, one of the main characteristics of the excitatory and inhibitory synapses is the high level of variability in their morphology and stability that occurs as a consequence of their activity and the passage of time (Caroni et al., 2012).
Scientists specializing in this area are particularly interested in the long-term changes in synaptic strength as a result of long-term potentiation (PLP) and long-term depression (DLP).
- Long-term potentiation : there is an increase in synaptic strength as a consequence of stimulation or repeated activation of the synaptic connection. Therefore, a consistent response will appear to the presence of the stimulus, as in the case of sensitization.
- Long-term depression (DLP): There is an increase in synaptic strength as a consequence of the absence of repeated activation of the synaptic connection. Therefore, the magnitude of the response to the stimulus will be less or even zero. We could say that there is a process of habituation.
Habituation and awareness
Early experimental studies interested in identifying the neural changes that underlie learning and memory used simple forms of learning such as habituation, sensitization, or classical conditioning.
In this scenario, the American scientist Eric Kandel focused his studies on the reflex of gill retraction of the Aplysia Californica, starting from the premise that the neural structures are analogous between these and the superior systems.
These studies provided first evidence that memory and learning are mediated by the plasticity of synaptic connections between neurons involved in behavior, revealing that learning leads to profound structural changes accompanying memory storage (Mayford et al. Al., 2012).
Kandel, like Ramón and Cajal , concludes that synaptic connections are not immutable and that structural and / or anatomical changes are the basis of memory storage (Mayford et al., 2012).
In the context of neurochemical learning mechanisms, different events will occur for both habituation and sensitization.
As mentioned above, the habituation consists in the decrease of the intensity of the response, consequence of the repeated presentation of a stimulus. When a stimulus is sensed by the sensory neuron, an excitatory potential is generated that allows an effective response.
As the stimulus repeats, the excitatory potential decreases progressively, until finally it fails to exceed the threshold of minimum discharge necessary to generate a potential for postsynaptic action , which makes possible the contraction of the muscle.
The reason why this excitatory potential decreases is because, as the stimulus is continually repeated, there is an increasing output of potassium ions (K + ), which in turn leads to the closure of the calcium channels ( Ca 2+ ), which prevents the entry of calcium ions. Therefore, this process is produced by a decrease in the release of glutamate (Mayford et al, 2012).
Sensitization is a more complex form of learning than habituation, in which an intense stimulus produces an exaggerated response to all the following stimuli, even to those that previously caused little or no response, which can also be seen in the retraction reflex Of the Aplysia gill, caused by an excess of glutamate release in the presence of a new stimulus (Mayford et al, 2012).
Despite being a basic form of learning, it presents different stages, both short and long term. While short-term sensitization would involve rapid and dynamic synaptic changes, long-term sensitization would lead to long-lasting and stable changes resulting from profound structural changes.
In this sense, in the presence of the sensitizing stimulus (intense or new), a release of glutamate will occur, when the amount released by the presynaptic terminal is excessive, it will activate the postsynaptic AMPA receptors.
This fact allows the entry of Na2 + into the postsynaptic neuron allowing its depolarization as well as the release of the NMDA receptors, which until now were blocked by Mg2 + ions, both events will allow a massive entry of Ca2 + into the postsynaptic neuron.
If the sensitizing stimulus occurs continuously, it will cause a persistent increase in the Ca2 + entry, which will activate different kinases , giving rise to the early expression of genetic factors and the synthesis of proteins. All this will lead to structural changes in the long term.
Therefore, the fundamental difference between both processes is in the synthesis of proteins. In the first case, in short-term sensitization, its action is not necessary for it to occur, whereas in the long-term sensitization it is essential that a synthesis of proteins is produced to produce lasting and stable changes that have As a goal the training and maintenance of new learning.
Consolidation of learning in the brain
Learning and memory are the result of structural changes that occur as a consequence of synaptic plasticity.
In order for these structural changes to occur, a long-term potentiation or synaptic strength consolidation process must be maintained.
As in the induction of long-term sensitization, both protein synthesis and expression of genetic factors are required which will lead to structural changes. For these events to occur, a number of molecular factors must occur:
- The persistent increase in the Ca 2+ entry in the terminal will activate different kinases, giving rise to the early expression of genetic factors and the synthesis of protein that will lead to the induction of new AMPA receptors that will be inserted into the Membrane and will maintain PLP.
These molecular events will result in alteration of the size and dendritic form, being able to give increases or decreases in the number of dendritic spines of certain zones.
In addition to these localized changes, current research has shown that changes also occur globally, since the brain acts as a unified system. Therefore, these structural changes are the basis of learning, in addition, when these changes tend to last in time, we will be speaking of memory.