Brain Mapping Plasticity
As part of the concept of new synaptic connections being formed during the structural phase of neuronal plasticity , the geographic mapping of the cerebral cortex of the brain can also exhibit neural plasticity . This has been shown with both the primary sensory cortex gyrus located in the parietal lobe and the primary motor cortex gyrus located in the frontal lobe . ( Because the body areas that these cortical regions represent can be mapped by drawing a small figure of a man , they are termed the sensory homunculus and motor homunculus respectively . The term homunculus literally means little man .) With experience , the body learns and reapportions the neurons of these gyri to the areas of the body that are preferentially used . One study involving the primary sensory cortex showed that after amputation of a digit of the hand , the region of the sensory cortex that had represented that digit was now reapportioned to represent adjacent digits that remained . This concept has also been shown to exist with other sensory regions of the brain . In another study involving the primary motor cortex , if an animal was trained to repeatedly use a specific finger , the region of the motor cortex that represented that finger expanded .
Figure 2 . Maturation of a neuron involves proliferation of its dendritic tree
With continued / later repetition , structural changes begin to occur in both the pre- and post-synaptic neurons . The number of active zones present at the synapses of the pathway increases . In addition , the post-synaptic neuron begins to proliferate its dendritic tree by increasing the number of its dendrites ( Figure 2 ). This then allows for the third change , which is that new functional synapses are formed between the pre- and post-synaptic neurons . The result of these structural changes , as with the functional changes , is that more neurotransmitter is picked up by the post-synaptic neuron , increasing the likelihood that it will fire , continuing the impulse down the memory pattern ’ s neuronal pathway . There is a saying in the world of neurology : “ Neurons that fire together wire together .” This describes the concept that when two neurons fire simultaneously , they undergo the functional and structural changes that have been described here as plasticity .
Neuroglial Plasticity
In addition to neuronal plasticity , neuroglial ( glial ) cells also exhibit changes with learning and memory . One type of glial plasticity is manifested by oligodendrocytes . Oligodendrocytes function to insulate neuronal axons in the central nervous system by wrapping layers
In addition to the plasticity of cortical mapping , reapportioning brain regions also occurs with long-term learning . One of the hallmarks of long-term learning , especially of a motor skill , is that it can be performed in an automatic manner . This occurs by preferentially shifting the command of the motor skill from being seated in the cerebral cortex to being seated primarily in subcortical regions , for example the basal ganglia , situated more deeply in the brain . The advantage to this is that it frees up conscious attention space of the cortex to be devoted to other tasks . This is why a person can perform a motor task in an automatic fashion while thinking about something else entirely . A common example is driving home from work in “ autodrive mode ” while lost in thought about the events of the day , only to realize at some point along the way that you have been driving without any conscious attention , and that you have no idea where you are along your route .
Finally , as Charles Leonard , professor of neuroscience of motor control and author , states in The Neuroscience of Human Movement ( Mosby , 1998 ): “ Learning is not all in your head .” The spinal cord of the central nervous system can also exhibit neural plasticity . Sensory-motor stretch reflex synaptic connections can also be changed based upon experience .
of myelin around them . As a neuron repetitively fires , the oligodendrocyte that myelinates it senses this and responds by increasing the number of myelin layers that ensheath it . This results in greater speed and efficiency of the neuron ’ s impulse conduction , which can contribute to the efficiency of a learned memory pattern . Astrocytes and microglial cells can also be involved in neural plasticity . These glial cells have been found to contribute to activity in neuronal pain pathways by secreting substances that help to heal the physical damage of the injury . These substances also stimulate the neurons involved , resulting in greater sensitivity to pain . Unfortunately , it has been found that they continue to secrete these substances even after the physical damage is healed . In this manner , glia are implicated in the process of central sensitization to pain .
Learning Through Repetition
The key to neural plasticity is repetition . With each repetition of a cognitive , motor , emotional , or sensory experience , the central nervous system becomes sensitized to that experience and encodes it into a memory pattern via functional
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