Brain Plasticity and Aphasia
Plasticity, or neuroplasticity, is the lifelong ability of the brain to reorganize neural pathways based on new experiences. As we learn, we acquire new knowledge and skills through instruction or experience. In order to learn or memorize a fact or skill, there must be persistent functional changes in the brain that represent the new knowledge. The ability of the brain to change with learning is what is known as neuroplasticity.
Facts About Neuroplasticity FACT 1: Neuroplasticity includes several different processes that take place throughout a lifetime. FACT 2: Neuroplasticity has a clear age-dependent determinant. Although plasticity occurs over an individual’s lifetime, different types of plasticity dominate during certain periods of one’s life and are less prevalent during other periods. FACT 3: Neuroplasticity occurs in the brain under two primary conditions: 1. During normal brain development when the immature brain first begins to process sensory information through adulthood (developmental plasticity and plasticity of learning and memory). 2. As an adaptive mechanism to compensate for lost function and/or to maximize remaining functions in the event of brain injury. FACT 4: The environment plays a key role in influencing plasticity.
Developmental Plasticity: Synaptic Pruning For our purpose, developmental plasticity is least important. What is important however, is that following birth, the brain of a newborn is flooded with information from the baby’s sense organs. This sensory information must somehow make it back to the brain where it can be processed. Nerve cells make connections with one another, transmitting the impulses to the brain. Over the first few years of life, the brain grows rapidly. As each neuron matures, it sends out multiple branches, increasing the number of synaptic contacts and laying the specific connections from house to house, or in the case of the brain, from neuron to neuron. At birth, each neuron in the cerebral cortex has approximately 2,500 synapses. By the time an infant is two or three years old, the number of synapses is approximately 15,000 synapses per neuron (Gopnick, et al., 1999). This amount is about twice that of the average adult brain. As we age, old connections are deleted through a process called synaptic pruning. Synaptic pruning eliminates weaker synaptic contacts while stronger connections are kept and strengthened. Experience determines which connections will be strengthened and which will be pruned; connections that have been activated most frequently are preserved. Neurons must have a purpose to survive. Without a purpose, neurons die through a process called apoptosis in which neurons that do not receive or transmit information become damaged and die. Ineffective or weak connections are “pruned”. It is plasticity that enables the process of developing and pruning connections, allowing the brain to adapt itself to its environment.
Plasticity of Learning and Memory It was once believed that as we aged, the brain’s networks became fixed. In the past two decades, however, an enormous amount of research has revealed that the brain never stops changing and adjusting as we learn new things. The capacity of the brain to change with learning is plasticity. So how does the brain change with learning? According to Durbach (2000), there appear to be at least two types of modifications that occur in the brain with learning: 1. A change in the internal structure of the neurons, the most notable being in the area of synapses. 2. An increase in the number of synapses between neurons. Initially, newly learned data are “stored” in short-term memory, which is a temporary ability to recall a few pieces of information. Some evidence supports the concept that short-term memory depends upon electrical and chemical events in the brain as opposed to structural changes such as the formation of new synapses. After a period of time, information may be moved into a more permanent type of memory, long-term memory, which is the result of anatomical or biochemical changes that occur in the brain (Tortora and Grabowski, 1996).
Injury-induced Plasticity: Plasticity and Brain Repair During brain repair following injury, plastic changes are geared towards maximizing function in spite of the damaged brain. In studies involving rats in which one area of the brain was damaged, brain cells surrounding the damaged area underwent changes in their function and shape that allowed them to take on the functions of the damaged cells. Data indicate that similar changes occur in human brains following injury. Implications The implications are that people with damaged brain cells can improve with learning. As leaning takes place new pathways are generated. These new pathways allow the brain to perform lost functions in a new and different way. With repeated practice almost everyone with damaged brain cells should be able to re-gain lost functions by altering the way in which those functions are practiced. The practice must involve a variety of sensory stimuli and must be repeated over and over.