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Neuroplasticity 4/14/2019 Brain: Important Facts • CNS begins from 2 • Uses 20% of the body weeks gestation energy • At birth, human brain • Consume 20 % of the weighs 350 g, at 1 year body oxygen 1000 g • All parts of brain are ISTE 2012 • 10% of the cells are involved in learning, neurons (100 billion) some more than other • Each neuron makes 1,000 to 20,000 connections Copyright@ Pradip Ghosh 2019 1 Copyright@ Pradip Ghosh 2019 2 Tractography of Whole Brain Brain Growth • The number of neurons that a child is born with is largely fixed around four months before birth. • The most important mechanisms involved in the massive brain spurt that occurs in the early years of life are: – Myelination – Production of glial cells – Synaptogenesis: Formation of new synapses Copyright@ Pradip Ghosh 2019 3 Copyright@ Pradip Ghosh 2019 4 Neuroplasticity Developmental Plasticity vs Adaptive Plasticity Developmental Plasticity Adaptive Plasticity • It can be described as brain’s ability to reorganize Definition Changes in neural connections as a The brain’s ability to compensate result of interactions with the for lost functionality due to brain itself by forming new neural connections throughout environment (our experiences during damage as well as in response to the life. childhood) as a consequence of interaction with the environment developmental processes. by reorganizing its structure • Neuronal connections are continuously being created e.g. Development of visual cortex and broken and all modeled by our experiences, and Occurs in It is predetermined and occurs in Compensation for brain injury our states of health or diseases. response to response to the initial processing of and in adjustment to new sensory information by the immature experiences. • Neuroplasticity allows neurons in the brain: brain – To adjust neural activities in response to new situations or Neuronal Synaptogenesis, synaptic pruning, Sprouting to changes in their environment (developmental plasticity) changes neural migration, myelination Rerouting – To compensate the loss from injury and neural diseases When it occurs Over the lifespan, but diminishes with Over the lifespan, but is more (adaptive plasticity) age efficient and effective during infancy/early childhood Copyright@ Pradip Ghosh 2019 5 Copyright@ Pradip Ghosh 2019 6 1 4/14/2019 Neuroplasticity Neuroplasticity in Normal Brain • It involves forming neuronal connections (synapses • It is now clear that mammalian brain is and pathways) in response to information derived capable of change throughout the life time in from experiences in the environment, sensory stimulation, and normal development. response to the environment and subsequent sensory experience. • Plasticity occurs on a variety of levels: – Cellular changes involved in learning – Large-scale changes involved in cortical remapping in • Numerous research studies examined the response to injury effects of sensory and social stimulation • Widely recognized forms of plasticity are learning, memory, and recovery from brain damage through enrichment of environment on the rodent brain. Copyright@ Pradip Ghosh 2019 7 Copyright@ Pradip Ghosh 2019 8 Neuroplasticity in Normal Brain Neuroplasticity in Normal Brain: Environment and Neuroplasticity Synaptogenesis • Environmental stimulation and exercise has • Black et al in 1990 examined the cerebellar neurons of rats after placing them in 4 housing conditions. significant influence in neuroplastic changes – Obstacle course (AC) in the brain. – Forced treadmill exercise (FX) • – Voluntary running wheel (VX) Van Praag and his group have shown – In a cage (IC) increased number of neurons in the • Observations: hippocampus when mice were housed in – increased capillary density in the cerebellum of rats from FX and VX. enriched environment with free access to the – increased synapses per neuron of the Purkinje cells of cerebellum of rats from AC running wheel. • Van Praag H, Kemperman G, Gage FH. Nature Neurosci 1999; 2: 266-270 Black JE, Isaacs KR, Anderson BJ, Alcantara AA, Greenough WI. Proc Natl Acad Sci 1990; 87: 5568-72 Copyright@ Pradip Ghosh 2019 9 Copyright@ Pradip Ghosh 2019 10 Neuroplasticity in Normal Brain Neuroplasticity in Normal Brain Synaptic Configuration Enriched Environment • Plastic changes in the brain are associated with changes in synaptic configurations. • Comery et al conducted studies by housing one group of rats in a toy- and object-filled environment and by keeping the other group in the standard cages for 30 days. • They observed an increased number of bifurcating and multi- headed spines in neurons of the caudate nucleus of rats housed in enriched environments. Comery TA, Stadmondia CX, Irwin SA, Greenough WT. Neurobiol Learn Mem. 1996; 66: 93-96 Copyright@ Pradip Ghosh 2019 11 Copyright@ Pradip Ghosh 2019 12 2 4/14/2019 Neuroplasticity in Normal Brain Neuronal changes in the Brain Changes in the strength of Synaptic Connections Copyright@ Pradip Ghosh 2019 13 Copyright@ Pradip Ghosh 2019 14 Role of BDNF on Reaching Functions after Role of BDNF on Reaching Functions after Focal Focal Ischemia Ischemia • It is also known that exercise can increase brain Infused antisense BDNF to lateral Rehabilitation derived neurotrophic factor (BDNF) in the brain ventricle after inducing ischemia in (Running, (Neeper et. al, 1995) one group of rats while no infusion Skilled to the 2nd group (control) reaching) • Ploughman et al tested the hypothesis by evaluating the contribution of BDNF to motor skill relearning after endothelin-1–induced middle Found reaching skills Rats ran for 10 min in cerebral artery occlusion in rats. diminished in antisense BDNF motorized running infused rats while reaching wheel followed by Neeper SA, Gomez-Pinilla F, Choi J, Cotman C. Nature. 1995; 373: 109 improved in non infused rats reach training Ploughman M, Windle V, MacLellan CL, White N, Doré JJ, Corbett D. Stroke. 2009;40:1490-1495 Copyright@ Pradip Ghosh 2019 15 Copyright@ Pradip Ghosh 2019 16 Plastic Changes in Human Brain Influence of Repetitive Movements • Motor tasks are accomplished by using repetitive sensory feedback to learn and refine the skill. • Pascual-Leone et al trained adult human volunteers on finger/thumb repetitive movements. • Observations: – Training groups had progressively larger cortical output to the involved muscles along with improved performance. – They also observed an increase in cortical map size followed by a subsequent decrease to baseline after the motor sequence was learned indicating possible contribution of other brain structures rather than primary motor cortex. • Pascual-Leone A, Grafman J, Hallerr M. Science 1994; 263: 1287-89 Copyright@ Pradip Ghosh 2019 17 Copyright@ Pradip Ghosh 2019 18 3 4/14/2019 Plastic Changes in the Human Brain Plastic Changes in the Human Brain Deafferentiation Influence of Immobilization • Brasil-Neto and associates examined the speed and topography of cortical plasticity during short term • Liepert et al examined individuals with ankle deafferentiation using blood pressure cuff on the arm and immobilization following ankle injury with no peripheral leg of human subjects. nerve damage. • They have shown a decreased cortical map representation • They found an increased motor evoked potential (MEP) from for the tibialis anterior muscle. the proximal muscles to the tourniquet within minutes. • So, cortical maps change on a daily and even minute-to minute basis depending on increase or decrease in sensory • They also observed an enlarged cortical representation area input and motor activity. for those proximal muscles. • Therefore movement along with sensation from periphery is essential for maintaining cortical map. Brasil-Neto JP, Cohen LG, Pascual-Leone A, Jabir FK, Wall RT, Hallett M. Neurol 1992; 42: 1302-06 Liepert J, Tegentoff M, Malin JP. Electroencephal Clin Neurophysiol 1995; 97: 382-86 Copyright@ Pradip Ghosh 2019 19 Copyright@ Pradip Ghosh 2019 20 Plastic Changes in Grey Matter Thickness Plastic Changes in Grey Matter Thickness Licensed London taxi drivers with extensive navigation 3 months of intensive juggling training is performed in a group of 12 individuals whereas 12 controls are experience were analyzed and compared with those of control subjects who did not drive taxis provided as “non-jugglers” (experiment: 3-ball cascade juggling) Voxel-based morphometry was employed to reveal fine changes of grey matter volume on anatomical MR images Voxel-based morphometry was employed to reveal fine changes of grey matter volume on anatomical MR Key findings were: images The posterior hippocampi of taxi drivers were significantly larger Hippocampal volume correlated with the amount of time Transient changes take place in grey matter in specific spent as a taxi driver (positively in the posterior and motion-selective areas. negatively in the anterior hippocampus) Draganski B, Gaser C, Busch V, Schuierer G, Bogdahn U, May A . Nature 2004; 427: 311-312 Maguire EA, Gadian DG, Johnsrude IS, Good CD, Ashburner J, Frackowiak RSJ, Frith CD Proc Natl A Sci 2000; 97: 4398-4403. Copyright@ Pradip Ghosh 2019 21 Copyright@ Pradip Ghosh 2019 22 Two current concepts Types of Neuroplasticity Type Mechanism Duration Enhancement of existing Formation of new connections connections 1. Enhancement of existing connections A. Synapse development Physiological ms-1 to hours B. Synapse strengthening Biochemical hours to days 2. Formation of new connections A veryVery active researchresearch area; area; concepts concepts are are continually continually being being updated
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