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Neuroplasticity: Or...Where did I put my homunculus?

A brief overview of cortical remapping.

Patricia Bockelman

on 31 March 2012

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Transcript of Neuroplasticity: Or...Where did I put my homunculus?

Generally, brain change requires changes in the synapses. Neuroplasticity Cortical Re-mapping
Plastic, in that it is malleable.
challenges the assertion that functions are fixed
both PHYSICAL and FUNCTIONAL changes occur due to experience. How did we get here? "Critical Period"...And beyond. Sources Begley, S. (November 5, 2004). "Scans of Monks' Brains Show Meditation Alters Structure, Functioning". The Wall Street Journal (Washington D.C.): p. B1. Retrieved from:http://psyphz.psych.wisc.edu/web/News/Meditation_Alters_Brain_WSJ_11-04.htm.

Buonomano, D.V.; Merzenich, M.M. (March 1998). "CORTICAL PLASTICITY: From Synapses to Maps". Annual Review of Neuroscience 21: 149186.

Hubel, D.H.; Wiesel, T.N. (February 1, 1970). "The period of susceptibility to the physiological effects of unilateral eye closure in kittens". The Journal of Physiology 206 (2): 419–436.

Purves D, Augustine GJ, Fitzpatrick D,(2001) et al., editors. "Neuroscience: 2nd edition". Sunderland,MA: Sinauer Associates.

Samson, K. (2011) Rep. Giffords' Shooting Underscores Need for Updated Outcomes Data on Penetrating Brain Injury, Neurology Today 11, 4: 1, 20-21. from developmental bio & developmental psych
assumed that the brain didn't really change much after infanthood Hubel & Weisel (1970)
showed vision sensory pathways could tap into "the other side" Decades of research in brain-machine interface, schizophrenia, meditation, lesions, dementia, phantom limbs
...all of these areas showed that our brains do change. TIME is of the essence... We're looking for changes in synaptic strength, presumably responsible for the nervous system's ability to modify behavioral responses. Short-Term Synaptic Plasticity
Lasts seconds to minutes
Facilitation and Depression provide rapid and transient modifications based on altered calcium levels at recent active synapses. Long-Term Potentiation
Calcium & other messengers trigger intercellular events, such as:
protein phosphorylation
changes in gene expression
Synapses continue to increase in strength
Long-Term Depression
To make strengthening useful, some connections are weakened Mechanisms Change in connection strength in pre- or post- synaptic partners.
includes increase or decrease in transmitter release from terminals
changes in number or sensitivity of receptors
fewer or greater synapses in relevant circuits
Different regions evidently use one or more of these strategies to learn and acquire new memories. CHANGES are not learning or memory...But, they provide cellular substrates for these phenomena. a transient increase in synaptic strength which occurs when 2 or more action potentials invade the presynaptic termanl in close succession, resulting in more neurotransmitter release with each succeeding action potential. Results in progressive cells' voltage increases. Action potentials in succession release so much meurotransmitter that the mechanisms for vesicle reuptake and recharging are overwhelmed. Consequently, the pool of avalible vessicles are depleted and the strength of synapse declines until it can be replenished. http://employees.csbsju.edu/ltennison/PSYC340/learning.htm Purves, et al. (1998) But, how does it do that? Some Research Synaptic plasticity
--It's about the strength of connections between synapses. Synaptogenesis and synaptic pruning: whole synapses or groups of synapses can be added or removed, building or destroying neuronal connections. These changes may be permanent!!! Epilepsy & LTP
The mechanisms which support LTP probably contribute to pathologies like epilepsy.
Seizures activate receptors and strengthen connections between excited neurons...possibly promoting ongoing seizures and enabling the spread of seizure activity to other regions.
Supported by animal "kindling". simple nervous systems use sensitization...akin to habituation with stimuli. http://www.epilepsyfoundation.org/about/diagnosis/eeg.cfm An owl monkey was trained in a task that required heavy usage of digits 2, 3, and occasionally 4. The map of the digits in the primary somatic sensory cortex prior to training is shown. Functional expansion of a cortical representation by a repetitive behavioral task. After several months of “practice,” a larger region of the cortex contained neurons activated by the digits used in the task. The cortical map determined in the same animal two months after amputation of digit 3. The map has changed substantially; neurons in the area formerly responding to stimulation of digit 3 now respond to stimulation of digits 2 and 4. Functional changes in the somatic sensory cortex of an owl monkey following amputation of a digit. Diagram of the somatic sensory cortex in the owl monkey, showing the approximate location of the hand representation. The hand representation in the animal before amputation; the numbers correspond to different digits. Merzenich & His Monkey Business... Patricia Bockelman Morrow
Spring 2011
PSB 5005
University of Central Florida
Dr. Shawn Stafford TBI & Plasticity Many factors influence plasticity & recovery following a TBI... Pre-injury factors, like social adaptation prior to injury, matter too... In some studies, bullet survivors have a 50% in hospital mortality and only a 19% "good outcome" with little or no disability. 30% of the remaining survivors will be in a permanent vegetative state. baynews9.com The first 3-6 months are critical in reorganization. Most brain damage is NOT from injury, but from STROKE. ...and stroke seems to be more difficult to bounce back from.
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