including the cerebral cortex. the specific details of how this process occurs at the molecular and ultrastructural levels are topics of active neuroscience research. the way experience can influence the synaptic organization of the brain is also the basis for a number of theories of brain function including the general theory of mind and neural darwinism. the concept of neuroplasticity is also central to theories of memory and learning that are associated with experience-driven alteration of synaptic structure and function in studies of classical conditioning in invertebrate animal models such as aplysia. there is evidence that neurogenesis (birth of brain cells) occurs in the adult, rodent brain—and such changes can persist well into old age. the evidence for neurogenesis is mainly restricted to the hippocampus and olfactory bulb, but research has revealed that other parts of the brain, including the cerebellum, may be involved as well. however, the degree of rewiring induced by the integration of new neurons in the established circuits is not known, and such rewiring may well be functionally redundant. treatment of brain damage a surprising consequence of neuroplasticity is that the brain activity associated with a given function can be transferred to a different location; this can result from normal experience and also occurs in the process of recovery from brain injury. neuroplasticity is the fundamental issue that supports the scientific basis for treatment of acquired brain injury with goal-directed experiential therapeutic programs in the context of rehabilitation approaches to the functional consequences of the injury. neuroplasticity is gaining popularity as a theory that, at least in part, explains improvements in functional outcomes with physical therapy post-stroke. rehabilitation techniques that are supported by evidence which suggest cortical reorganization as the mechanism of change include constraint-induced movement therapy, functional electrical stimulation, treadmill training with body-weight support, and virtual reality therapy. robot assisted therapy is an emerging technique, which is also hypothesized to work by way of neuroplasticity, though there is currently insufficient evidence to determine the exact mechanisms of change when using this method. one group has developed a treatment that includes increased levels of progesterone injections in brain-injured patients. "administration of progesterone after traumatic brain injury (tbi) and stroke reduces edema, inflammation, and neuronal cell death, and enhances spatial reference memory and sensory-motor recovery." in a clinical trial, a group of severely injured patients had a 60% reduction in mortality after three days of progesterone injections. however, a study published in the new england journal of medicine in 2014 detailing the results of a multi-center nih-funded phase iii clinical trial of 882 patients found that treatment of acute traumatic brain injury with the hormone progesterone provides no significant benefit to patients when compared with placebo. binocular vision for decades, researchers assumed that humans had to acquire binocular vision, in particular stereopsis, in early childhood or they would never gain it. in recent years, however, successful improvements in persons with amblyopia, convergence insufficiency or other stereo vision anomalies have become prime examples of neuroplasticity; binocular vision improvements and stereopsis recovery are now active areas of scientific and clinical research. phantom limbs a diagrammatic explanation of the mirror box. the patient places the intact limb into one side of the box (in this case the right hand) and the amputated limb into the other side. due to the mirror, the patient sees a reflection of the intact hand where the missing limb would be (indicated in lower contrast). the patient thus receives artificial visual feedback that the "resurrected" limb is now moving when they move the good hand. main articles: phantom limb and mirror box in the phenomenon of phantom limb sensation, a person continues to feel pain or sensation within a part of their body that has been amputated. this is strangely common, occurring in 60–80% of amputees. an explanation for this is based on the concept of neuroplasticity, as the cortical maps of the removed limbs are believed to have become engaged with the area around them in the postcentral gyrus. this results in activity within the surrounding area of the cortex being misinterpreted by the area of the cortex formerly responsible for the amputated limb. the relationship between phantom limb sensation and neuroplasticity is a complex one. in the early 1990s v.s. ramachandran theorized that phantom limbs were the result of cortical remapping. however, in 1995 herta flor and her colleagues demonstrated that cortical remapping occurs only in patients who have phantom pain. her research showed that phantom limb pain (rather than referred sensations) was the perceptual correlate of cortical reorganization. this phenomenon is sometimes referred to as maladaptive plasticity. in 2009, lorimer moseley and peter brugger carried out an experiment in which they encouraged arm amputee subjects to use visual imagery to contort their phantom limbs into impossible configurations. four of the seven subjects succeeded in performing impossible movements of the phantom limb. this experiment suggests that the subjects had modified the neural representation of their phantom limbs and generated the motor commands needed to execute impossible movements in the absence of feedback from the body. the authors stated that: "in fact, this finding extends our understanding of the brain's plasticity because it is evidence that profound changes in the mental representation of the body can be induced purely by internal brain mechanisms—the brain truly does change itself." chronic pain main article: chronic pain individuals who have chronic pain experience prolonged pain at sites that may have been previously injured, yet are otherwise currently healthy. this phenomenon is related to neuroplasticity due to a maladaptive reorganization of the nervous system, both peripherally and centrally. during the period of tissue damage, noxious stimuli and inflammation cause an elevation of nociceptive input from the periphery to the central nervous system. prolonged nociception from the periphery then elicits a neuroplastic response at the cortical level to change its somatotopic organization for the painful site, inducing central sensitization. for instance, individuals experiencing complex regional pain syndrome demonstrate a diminished cortical somatotopic representation of the hand contralaterally as well as a decreased spacing between the hand and the mouth. additionally, chronic pain has been reported to significantly reduce the volume of grey matter in the brain globally, and more specifically at the prefrontal cortex and right thalamus. however, following treatment, these abnormalities in cortical reorganization and grey matter volume are resolved, as well as their symptoms. similar results have been reported for phantom limb pain, chronic low back pain and carpal tunnel syndrome. meditation main article: research on meditation a number of studies have linked meditation practice to differences in cortical thickness or density of gray matter. one of the most well-known studies to demonstrate this was led by sara lazar, from harvard university, in 2000. richard davidson, a neuroscientist at the university of wisconsin, has led experiments in collaboration with the dalai lama on effects of meditation on the brain. his results suggest that meditation may lead to change in the physical structure of brain regions associated with attention, anxiety, depression, fear, anger, and compassion as well as the ability of the body to heal itself. artistic engagement and art therapy there is substantial evidence that artistic engagement in a therapeutic environment can create changes in neural network connections as well as increase cognitive flexibility. in one 2013 study, researchers found evidence that long-term, habitual artistic training (e.g. musical instrument practice, purposeful painting, etc) can "macroscopically imprint a neural network system of spontaneous activity in which the related brain regions become functionally and topologically modularized in both domain-general and domain-specific manners". in simple terms, brains repeatedly exposed to artistic training over long periods develop adaptations to make such activity both easier and more likely to spontaneously occur. some researchers and academics have suggested that artistic engagement has substantially altered the human brain throughout our evolutionary history. d.w zaidel, adjunct professor of behavioral neuroscience and contributor at vaga, has written that "evolutionary theory links the symbolic nature of art to critical pivotal brain changes in homo sapiens supporting increased development of language and hierarchical social grouping". fitness and exercise