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The term brain fitness reflects a hypothesis that cognitive abilities can be maintained or improved by exercising the brain, in analogy to the way physical fitness is improved by exercising the body. Although there is strong evidence that aspects of brain structure remain plastic throughout life, and that high levels of mental activity are associated with reduced risks of age-related dementia, scientific support for the concept of "brain fitness" is limited. The term is virtually never used in the scientific literature, but is commonly used in the context of self-help books and commercial products. It first came into play in the 1980s, and appeared in the titles of self-help books in 1989 and 1990.
Brain fitness is the capacity of a person to meet the various cognitive demands of life. It is evident in an ability to assimilate information, comprehend relationships, and develop reasonable conclusions and plans. Brain fitness can be developed by formal education, being actively mentally engaged in life, continuing to learn, and exercises designed to challenge cognitive skills. Healthy lifestyle habits including mental stimulation, physical exercise, good nutrition, stress management, and sleep can improve brain fitness. On the other hand, chronic stress, anxiety, depression, aging, decreasing estrogen, excess oxytocin, and prolonged cortisol can decrease brain fitness as well as general health.
Brain fitness can be measured physically at the cellular level by neurogenesis, the creation of new neurons, and increased functional connections of synapses and dendrites between neurons. It can also be evaluated by behavioral performance as seen in cognitive reserve, improved memory, attention, concentration, executive functions, decision-making, mental flexibility, and other core capabilities.
Like physical fitness, brain fitness can be improved by various challenging activities such as practicing sports, playing chess or bridge, dancing regularly, practicing yoga and tai chi and also by engaging in more structured computer based workouts. Some research shows that brain stimulation can help prevent age-related cognitive decline, reverse behavioral assessment declines in dementia and Alzheimer’s and can also improve normally functioning minds. In experiments, comparing some computer based brain boosting exercises to other computer based activities, brain exercises were found to improve attention and memory in people over age 60. Other studies have evaluated other brain boosting exercises and not found improvements. A study of 67 schoolchildren aged 10 compared 7 week Nintendo brain training to engaging in pen and paper puzzles. The study found that the brain training group suffered a 17 percent decrease in memory tests after the seven-week course, while the pen and paper group saw an increase of 33 percent. Some experts are skeptical with regard to the real value of particular commercial brain boosting products. For example, a panel of experts gathered by Which? Magazine have concluded that ‘Dr Kawashima’s Brain Training’ for the Nintendo DS will not enhance brainpower at all. However, other researchers underline the growing amount of studies indicating that some commercial brain training products have shown measurable results in improving various cognitive skills.
Neurogenesis is the creation of new neurons. The more active a particular brain cell is, the more connections it develops with its neighboring neurons through a process called dendritic sprouting. A single neuron can have up to thirty thousand such connections, creating a dense web of interconnected activity throughout the brain. Each neuron can then be stimulated directly through experience (real or imagined) or indirectly through these connections from its neighbors, which saves the cell from cell death.
Physical exercise boosts the brain’s rate of neurogenesis throughout life, while mental exercise increases the rate at which those new brain cells survive and make functional connections into existing neural networks. Both physical exercise and the challenge from mental exercise increase the secretion of nerve growth factor, which helps neurons grow and stay healthy.
Mental stimulation 
Consistent mental challenge by novel stimuli increases production and interconnectivity of neurons and nerve growth factor, as well as prevents loss of connections and cell death. The Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) nationwide (America) clinical trial is so far the nation's largest study of cognitive training. Researchers found that improvements in cognitive ability roughly counteract the degree of long-term cognitive decline typical among older people without dementia. The results, published in the Journal of the American Medical Association in 2002, showed significant percentages of the 2,802 participants age 65 and older who trained for five weeks for about 2½ hours per week improved their memory, reasoning and information-processing speed.
Joe Verghese, M.D. found that people with higher activity score had lower risks of Alzheimer's and dementia. An open question in the field is whether people who will later develop Alzheimer's are naturally less active, or whether intervening to raise an activity score will delay or prevent Alzheimer's. If the latter hypothesis were true, people could lower their dementia risk by 7% simply by adding one activity per week (such as doing a crossword puzzle or playing a board game) to their schedule. According to the findings of that same study, subjects who did crossword puzzles four days a week had a 47% lower risk of dementia than subjects who did a crossword puzzle just once a week.
Role of neurotrophins 
Brain fitness is purported to be positively influenced through mental and physical exercises that increase levels neurotrophins. Neurotrophins are a small class of proteins that are vital in neuronal development and function. In development, neurotrophins act to protect and warrant the survival of an adequate number of neurons. The survival of ample neurons is vital to ensure that they are match for target innervations. Neurotrophins also assist cell fate decisions, innervations patterns, the development of axons, dendrite pruning, etc. Neurotrophins are also important for regulating neural function and neuronal survival. Neurons are affected most predominantly by neurotrophins; however, they are important for many parts of the body in addition to the nervous system. Neurotrophins are crucial for the survival of neurons in the peripheral nervous system (PNS) as well as neurons in the central nervous system (CNS). The four most common neurotrophins are Nerve Growth Factor (NGF), Brain Derived Neurotophic Factor (BDNF), Neurotrophic Factor-3 (NT-3), and Neurotrophic Factor-4/5 (NT-4/5). In order to understand how neurotrophins affects brain fitness, it is important to understand how they work.
Nerve growth factor (NGF) was the first neurotrophin to be discovered and is the most famous. The effects of NGF are present in a multitude of tissues through human development as well as adulthood. NGF is associated with immunity, stress reaction, nerve maintenance and neurodegenerative diseases. NGF is known have a predominant effect on the sympathetic ganglion cells and dorsal root ganglion cells with free nerve endings and the cholinergic neurons of the basal nucleus. Sympathetic ganglion cells are masses of neuronal cell bodies in the in the sympathetic branch of the visceral (autonomic) nervous system. Dorsal root ganglion are masses of neuronal cell bodies in the posterior portion of the spinal cord where sensory information is processed. Cholinergic neurons are profuse in parts of the brainstem, the base of the forebrain, and the basal ganglia. They are thought to play a role in regulating the general level of activity of CNS neurons, especially during the different phases of wakefulness and sleep and also during learning. Therefore, it can be purported that increased secretion of NGF can stimulate the sympathetic nervous system, the sensory portion of the spinal cord, parts of the brainstem, the base of the forebrain, and the basal ganglia. Perhaps the roles of these individual structures can be facilitated or preserved with increased NGF.
Secretion of brain derived neurotrophic factor (BDNF) is stimulated by cortical neurons, and is essential for permanence of striatal neurons in the brain. Patients with both Alzheimer's and Huntington disease exhibit reduced levels of BDNF. Striatal neurons are the nerve cells that make up the stratium. The stratium is an inclusive term for several structures of the midbrain. The stratium is the major point of entry for receiving input from most or all cortical areas and analyzing inhibitory outputs to the various parts of the midbrain. Therefore, it may be deduced that secretion of BDNF can have an influence on many parts of the cerebral cortex and coincidentally the functions of the areas influenced.
Spiral ganglion neurons are particularly sensitive to neurotrophic factor-3 (NT-3). The spiral ganglion neurons contain the cell bodies of the auditory primary afferent fibers. The central process of these cells collect at the base of the cochlea to form the cochlear division of the eight nerve  These afferent fibers carry auditory impulses toward the central nervous system. Therefore, it may be reasoned that healthy levels of NT-3 can preserve the function of these cells that are crucial for processing auditory information in the brain.
An article entitled “Neurotrophin 4/5 is a trophic factor for mammalian facial motor neurons” summarizes a study that was conducted on the researchers’ findings in 1993. The research suggests that NT-4/5 prevents injuries that cause death of facial motor neurons in neonatal rats. Additionally, there is functional receptor for NT-4/5 in facial motor neurons that can be serviceable thought embryonic development and even postnatal life. Thus, both NT-4/5and brain-derived neurotrophic factor (BDNF) may be physiological survival factors for facial motor neurons and may serve as restorative means for motor neuron disease.
Activities presumed to promote brain fitness 
Not all brain activity exercises the brain in the same way.
- Activities that require you to use all your senses, break your routines and engage in novel experiences which can create BDNFs(neurotrophins) as explained in the book Keep Your Brain Alive, Workman Publishing.
- Activities that involve planning ahead, like chess, stimulate the Frontal lobe area of the brain.
- Activities like ballroom dance and basketball, train short range spatial skills, used when one walks through a short limited space, like the interior of a house.
- Activities that combine intellectual and physical demands improve spatial and reasoning skills 
- Activities like learning a new language or painting require the coordinating of multiple regions of the brain.
- Physical exercise promotes BDNF.
Practical effects 
A significant issue in brain fitness work has been establishing that brain training exercises have impacts on brain function that exist outside the context of the training task. For example, in the ACTIVE studies, subjects were trained only in one of these three modalities: speed of processing, reasoning, or memory. Subjects did not significantly improve in non-trained modalities.
Other studies, however, have looked at changes in tests of everyday function that occur after brain-based training. In a review of these studies, the following significant effects were noted. Improvements on speed of processing training tests were related to improvements in the Timed Instrumental Activities of Daily Living test (TIADL). Evidence of ceiling effects were also noted, indicating that subjects who were further below normal at the beginning of training had the largest expected gains. Further, the effect sizes may be related to customizing the training difficulty to the performance level of the trainee. Subjects trained with one training strategy, the Useful Field of View test (UFOV), showed significant improvements in an on-the-road driving test designed to evaluate driver response during potential dangerous situations. Specifically, subjects trained with UFOV made fewer dangerous maneuvers after training. In another study, the researchers have found that action video game experience is shown to improve trainees’ probabilistic inference. These results were established both in visual and auditory tasks, indicating generalization across modalities.
See also 
- Serious game
- Environmental enrichment
- Mental exercise
- Brain Fitness Program
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