Brain plasticity refers to the changes that occur in the organisation of the brain, and in particular changes that occur to the location of specific information processing functions, as a result of the effect of experience. The term cortical plasticity is more commonly used, however there is no particular restriction of the phenomenon to the cortex. A common and surprising consequence of plasticity is that the location of a given function can "move" from one location to another in the brain. Comparative brain sizes In animals, the brain, or encephalon (Greek for in the head), acts as the control center of the central nervous system. ... Cortex (Latin for bark) has different meanings, depending on the context: In neuroanatomy: the cerebral cortex (often simply called cortex) is the thin wrinkled outermost layer of the brain. ...

The concept of plasticity can be applied to molecular as well as to environmental events. The phenomenon itself is complex and involves many levels of organization. To some extent the term itself has lost its explanatory value because almost any changes in brain activity can be attributed to some sort of "plasticity". Plasticity should be more restricted to adaptive events in the central nervous system rather than merely indicating any change in response to environmental input. For example, after a traumatic brain injury, if the organism can recover to normal levels of performance, that adaptiveness could be considered an example of "positive plasticity". However, an excessive level of neuronal growth leading to spasticity or tonic paralysis, or an excessive release of neurotransmitters in response to injury which could kill nerve cells, would have to be considered perhaps as a "negative or maladaptive" plasticity.

The main thing to know is that even the adult brain is not "hard-wired" with fixed and immutable neuronal circuits. Many people have been taught to believe that once a brain injury occurs, there is little to do to repair the damage. This is simply not the case and there is no fixed period of time after which "plasticity" is blocked or lost. We simply do not know all of the conditions that can enhance neuronal plasticity in the intact and damaged brain, but new discoveries are being made all of the time. There are many instances of cortical and subcortical rewiring of neuronal circuits in response to training as well as in response to injury. There is now solid evidence that neurogenesis, the formation of new nerve cells, is possible in the adult, mammalian brain--and such changes can persist well into old age.

Brain plasticity and cortical maps

Cortical organization, especially for the sensory systems, is often described in terms of maps. For example, sensory information from the foot projects to one cortical site and the projections from the hand target in the other site. As the result of this somatopic organization of sensory inputs to the cortex, cortical representation of the body resembles a map (or homunculus). Interestingly, cortical maps are not fixed, but rather plastic. The work of John, Pomeranz, Kaas, Merzenich, Diamond, Ebner, Nicolelis and many other researchers has shown that cortical maps change after manipulations with peripheral inputs (e.g., sensory nerve transection): cortical representations deprived of sensory input are 'filled' by adjacent representations. Similar plasticity of cortical maps results from changes in sensory experience. Hartsoekers homunculus The concept of a homunculus (Latin for little man, sometimes spelled homonculus) is often used to illustrate the functioning of a system. ...

Brain plasticity during operation of brain-machine interfaces

Brain-machine interface (BMI) is a rapidly developing field of Neuroscience. According to the results obtained by Mikhail Lebedev, Miguel Nicolelis and their colleagues (Lebedev, M.A., Carmena, J.M., O’Doherty, J.E., Zacksenhouse, M., Henriquez, C.S., Principe, J.C., Nicolelis, M.A.L. (2005) Cortical ensemble adaptation to represent actuators controlled by a brain machine interface. J. Neurosci. 25: 4681-4693), operation of BMIs results in incorporation of artificial actuators into brain representations. The scientists showed that modifications in neuronal representation of the monkey's hand and the actuator that was controlled by the monkey brain occurred in multiple cortical areas while the monkey operated a BMI. Initially, monkeys moved the actuator by pushing a joystick. After the monkey started using its brain activity to directly control the actuator, the activity of individual neurons and neuronal populations became less representative of the animal's hand movements while representing the movements of the actuator. Presumably as a result of this adaptation, the animals could eventually stop moving their hands yet continue to operate the actuator. Thus, during BMI control, cortical ensembles plastically adapt to represent behaviorally significant motor parameters, even if these are not associated with movements of the animal's own limb. A brain-computer interface (BCI) or direct neural interface is literally a direct technological interface between a brain and a computer not requiring any motor output from the user. ... A brain-computer interface (BCI) or direct neural interface is literally a direct technological interface between a brain and a computer not requiring any motor output from the user. ... Neuroscience is a field of study that deals with the structure, function, development, genetics, biochemistry, physiology, pharmacology, and pathology of the nervous system, divided into the central nervous system (the brain and spinal cord), and the peripheral nervous system, consisting of the myriad nerve pathways running throughout the body. ... Mikhail A. Lebedev (Михаил Альбертович Лебедев) is a Russian-born (1963) Neuroscientist known for his neurophysiological studies of cerebral cortex. ... Miguel Nicolelis, MD, PhD, is a Brazilian scientist best known for his pioneering work in reading monkey thought. He implanted electrode arrays into the monkey brain that were able to detect monkeys motor intent and thus able to control reaching and grasping movements performed by a robotic arm. ...

Suggested reading

• Lebedev, M.A., Carmena, J.M., O’Doherty, J.E., Zacksenhouse, M., Henriquez, C.S., Principe, J.C., Nicolelis, M.A.L. (2005) [http://www.jneurosci.org/cgi/content/full/25/19/4681 Cortical ensemble adaptation to represent actuators controlled by a brain machine interface.
• Monkeys Treat Robot Arm as Their Own
• Monkeys treat robot arm as bonus appendage
• Monkey See, Robotics Do

See also

• Brain-machine interface

A brain-computer interface (BCI) or direct neural interface is literally a direct technological interface between a brain and a computer not requiring any motor output from the user. ...

External links

• http://faculty.washington.edu/chudler/plast.html
• http://www.crossroadsinstitute.org/plastic.html
• http://www.birf.info/artman/publish/article_454.shtml