THE PLASTICITY OF THE BRAIN Neuroplasticity: The ability of the brain to form and reorganise synaptic connections, especially through learning or experience or following injury. This means that the brain… • is adaptive. • changes as a result of experience and learning. • creates new connections between neurons as we learn and experience the world. https://en.oxforddictionaries.com/definition/neuroplasticity A living example of the brain’s plasticity... The story of Jodie, whose right hemisphere had to be removed as a result of epileptic seizures. LINK TO THIS VIDEO Plasticity - More Details ✤ The brain can reorganise and reassign its neural connections and pathways based on which parts of it are used often or used rarely. ✤ Some areas of the brain, such as the sensory and motor cortices, have a higher level of plasticity than others. Especially plastic… Plasticity - Children ✤ A young child’s brain is more plastic than that of an adult, particularly at specific times in development. Strengthened Neural Connections ✤ Whenever you form new memories, the neural connections underlying them are strengthened. Each time these After repeated stimulation,... connections are activated, the neurons involved communicate more efficiently. …a stronger neural connection develops. Long-Term Potentiation ✤ Definition: The lasting strengthening of the synaptic connections of neurons, resulting in their enhanced functioning Long-Term Potentiation ✤ The more a particular neural pathway is activated, the easier it is for information to travel through that circuit. …rather like a bush path that becomes easier to walk along after many other hikers have cleared the way… Winner of the Nobel Prize for Medicine/Physiology in 2000 Eric Kandel If you remember anything about a book (or lecture), it will be because your brain is slightly different after you have finished reading (or hearing) it. When you learn something, your brain changes. That’s plasticity. Effects of Mental Stimulation and Deprivation 1 •Autopsies have shown that the brains of university graduates have 40% more synaptic connections than those of students who do not finish high school (Hockenbury and Hockenbury, 2006). Effects of Mental Stimulation and Deprivation 2 •The risk of cognitive decline in old age has been found to be reduced by doing mentally stimulating tasks, including social interaction and extensive reading. Effects of Mental Stimulation and Deprivation 3 •Studies with sets of identical twins have shown that the twin who was not mentally active or who had a lower level of education was more likely to develop Alzheimer’s Disease. The Story So Far 1: An Either-Or Quiz a The brain is ______ according to learning and experience. able to adapt unable to adapt b Which age group has greater brain plasticity? adults children c Which parts of the brain show the greatest ability to respond to experience? sensory and motor cortices cerebellum d The more often a particular neural pathway is activated the less efficient it becomes. the more efficient it becomes. e The lasting strengthening of synaptic connections, which allows enhanced communication between neurons, is called… consolidation long-term potentiation Two Kinds of Plasticity Developmental Plasticity Adaptive Plasticity occurs as brain is evident when the brain development proceeds recovers from trauma due to according to its normal brain injury and also when maturational blueprint or changes in brain structure plan. enable adjustment to experience. Developmental plasticity refers to changes in the brain’s neural structure in response to experience during the brain’s growth and development. Adaptive plasticity refers to the brain’s ability following brain injury to compensate for the damage done by developing new neural connections. Distinctions Note: A clear line cannot easily be drawn between the two types of plasticity. •Both types of plasticity are influenced by experience. •As Jodie’s recovery after her radical surgery illustrates, the maturing brain of a child has the capacity to adapt to and therefore recover from trauma effectively. Synaptogenesis Synapses are brain structures that permit neurons to send an electrochemical signal to another neuron. The creation of such connections is called synaptogenesis. Each neuron in a baby’s brain at birth already synapses with about 2500 other neurons. By the age of 2 or 3, the number of these connections will have increased dramatically, to around 15,000 per neuron. Link: University of Maine Website - Children’s Development Synaptic Pruning By about 10 years of age, almost 50% of the synapses that were present at the age of 2 will have been pruned or eliminated. This increases the efficiency of neural transmission and brain communication. This process is called synaptic pruning. Source: Santos E., Noggle C.A. (2011) Synaptic Pruning. In: Goldstein S., Naglieri J.A. (eds) Encyclopedia of Child Behavior and Development. Springer, Boston, MA The Story So Far 2: An Either-Or Quiz a The creation of new neural connections is called… synaptic pruning synaptogenesis b The elimination of unused neural connections is called… synaptic pruning synaptogenesis c Which type of plasticity refers to the brain’s ability to recover after trauma or injury? adaptive plasticity developmental plasticity d Synaptic pruning is essential because it makes neural transmission… less efficient. more efficient. e When does synaptogenesis occur most rapidly? 0-2 years of age 10-12 years of age f Which factor determines which synapses are retained? age of synapses use of synapses A Sensitive Period A sensitive (or critical) period is a specific period of time in development when an organism is more ‘sensitive’ or responsive to certain environmental stimuli or experiences. For example, another language is most easily acquired during a sensitive period in development and is more difficult and time-consuming to learn outside this ‘window of opportunity’. A Sensitive Period In relation to language learning, psychologists are not in complete agreement about the age limits for the sensitive period. Generally, the sensitive period for our native language is up to the age of about 12 years, with the window gradually closing from about age seven. The Importance of the Sensitive (or Critical) Period 1 Genie Genie, a girl who was deprived of language in the first 12 years of life through living in a kind of enforced solitary confinement, learned to speak yet was not able to develop all the standard language structures. It is however very difficult to determine which factors influenced this outcome. The Importance of the Sensitive (or Critical) Period 2 This child developed a haemangioma on her right eye as a young baby. The Importance of the Sensitive (or Critical) Period 2 Doctors warned that if this growth obscured her vision in the first year or two of life, there might never be sight in that eye. The eye itself would have been intact but the time when the brain makes connections with that eye’s input would have passed. The Importance of the Sensitive (or Critical) Period 2 Lack of stimulation during this sensitive period can lead to a long-term deficit. For instance, a closed eye from birth leads to later blindness in that eye, even when the eye eventually opens. A Happy Ending This child was lucky. Her haemangioma never did obscure her vision and she is now a fully sighted child. Adaptive Plasticity: Neuronal Changes Re-routing: Damaged parts of the brain begin to “rewire”, creating new neural pathways to replace older, damaged ones. Sprouting: The growth of new bushier nerve fibres with more branches on axons and dendrites. This facilitates new neural connections. When an accident occurs on a major road, travellers have to detour… Example: from this blog on MS research: https://drkarenlee.ca/rewiring-neurons-how-the-brain-copes-with-ms/ Another Form of Adaptive Plasticity When we learn a skill, this learning is becomes evident in the brain’s structure. In one study, the grey matter in the mid- temporal lobes of people who developed juggling skills increased by 3-4%. See also: http://faculty.washington.edu/chudler/jugg.html Adaptive Plasticity and Experience 1 Neuroimaging studies show that in musicians who play string instruments, the area of the somatosensory cortex that represents the fingers of the left hand is larger than the area that represents the fingers on the right hand. Adaptive Plasticity and Experience 2 MRI scans of London taxi drivers show that the rear of their hippocampus, the part involved in spatial navigation and consolidation of memories, is clearly larger than those of bus drivers, whose navigation skills are far less challenging. The Story So Far 3: Matching Concepts a long-term potentiation • b motor and sensory cortices • c plasticity • d rerouting • e synaptic pruning • f synaptogenesis 1 The lasting strengthening of synaptic connections of neurons, resulting in their enhanced functioning 2 The process of forming new synapses 3 An undamaged neuron, having lost a connection with a neuron, connects with another 4 The particularly plastic parts of the brain that are responsible for processing of movement and touch 5 The brain’s ability to rewire and adapt its neurons and its neural network as a result of learning and experience 6 The elimination of unused neural connections, particularly evident between ages 2 and 10.