cr is a hypothesized capacity of mature adult brain to sustain the effects of disease or injury without manifesting clinically .
it accounts for individual differences in the cognitive processes and neural networks which allow one to cope better than others with the brain damage . in earlier period
this construct was a passive model and stated that each individual had a fixed  brain reserve capacity ,  which does not change with time , experience , or training .
it thus implied that an individual has a prefixed amount of brain damage that can be sustained before reaching threshold for clinical expression .
brain reserve capacity was then measured in brain size or the synaptic count , which was understood as a fixed component and thus a nonmodifiable factor .
various researches since the landmark revelation point toward an active construct called  cognitive reserve .
 this reserve is as active as other part of the brain during any activity ; it is functional as it augments the functions of other neurons ; and it is modifiable with time , experience , and training .
neural reserves are those networks which are less susceptible to damage , are more efficient , have greater capacity , and may be invoked while coping with increased task demand .
neural compensation is a process by which individual suffering from brain pathology use brain structures or networks not normally used by intact brain to compensate for brain damage .
 compensation to improve performance ,  the brain recruits additional brain areas which have resilient and healthy networks , i.e. , like similar network on contralateral hemisphere . in
such compensations are more in older age . in general , a better cr implies greater overall cognitive efficiency , greater proliferation of brain neurons , more connection between neurons , enhanced ability to compensate by recruiting generalized neurons for specific task at hand , and better ability to use alternative strategies to solve problems .
these are measured by brain volume , head circumference , synaptic count , dendritic branching , etc .
these measures are intelligence quotient ( iq ) or premorbid iq , level of activation in functional magnetic resonance imaging ( fmri ) , efficiency of neural network , active compensation by alternative / more extensive network after challenge , etc .
these proxy measures are income , occupational attainment , educational attainment , and degree of literacy . although educational attainment is more widely used proxy , the degree of literacy is a more sensitive measure .
it was seen that a higher cr individual was able to activate this network while working on more difficult task , whereas lower cr individual was unable to tap this network .
do these networks degrade during natural aging process ? can this degradation be slowed or halted ?
various literatures suggest that enriched environment ( ee ) , cognitively stimulating activities , cognitive training , and physical training are likely to increase our cr , thus making us more resilient to cognitive decline and damage . 

enriched environment : this term has been given to environmental conditions that facilitate enhanced sensory , cognitive , and motor stimulation .
a)neurogenesis : concept in neurology till last decade held that brain cells can not reproduce .
short - term exposure to ee has led to fivefold increase in new neurons , substantial improvement in learning , exploratory behavior , and locomotor activity .
these effects were seen even beyond the age of 65 years and potential exists throughout the lifespan.b)synaptogenesis : physical activity enhances growth of neurons and learning promotes new connection between the neurons .
neuronal aging diminished by active and challenging life even if starts later in life . 

. these are complex , highly structured enjoyable activity that provide opportunity for self - expression , e.g. , charity , clubs , group games , voluntary work , and caring for sick .
a separate study on cohabitation revealed that single , widowed , or separated had three times higher risk for cognitive impairment and 7.67 higher risk for alzheimer 's disease vis a vis their married / cohabiting counterparts.cognitively stimulating task : in a unique study , 6- to 12-year old learnt in company of older adults in an intergenerational charter school cleveland where older adults contributed by sharing knowledge and experience .
improvement in cognition and qol was seen in these elderlies a china - based study found gardening and other community activities protective for incident dementia .
, the practice of which was associated with reduction in risk for alzheimer 's dementia and slower rates of cognitive decline .
prospective cohort study from new york found that musical instruments , dancing , and leisure activity accounted for reduced risk for incident dementia and memory decline la rue recommendation ( 2008 ) suggests following for better memory : to carve out time for cognitively stimulating activities that one enjoys , to add some new challenging pursuits as time and energy allow , to engage in these pursuits several times a week , and to participate in social interaction.cognitive training : advanced cognitive training for independent and vital elderly ( active ) study undertook training of older adults in areas of reasoning , memory , and processing speed .
improvement lasted at least 5 years with booster training . in experience corps ( ec )
project , elders were taught literacy , mathematics , and conflict resolution in elementary school .
training showed improvement in executive function and memory there are many cognitive training websites available , few of these include www.fitbrains.comnone , www.gamesforthebrain.comnone , www.mybraintrainer.comnone , www.luminosity.comnone , and www.sharpbrains.comnone .
many books are also available which elucidates the concept of cr and ways to improve it .
amen d g 2008 ,   the mature mind : the positive power of ageing brain 
cohen g d 2005 ,   cognitive reserve : theory and application  yakov stern 2006 , 
etc.physical training : aerobic fitness training in older adult promoted significant increase in gray ( cortical neurons ) and white matter ( connecting pathways ) physical and cognitive training combined had multiplier effect . 
 
enriched environment : this term has been given to environmental conditions that facilitate enhanced sensory , cognitive , and motor stimulation .
a)neurogenesis : concept in neurology till last decade held that brain cells can not reproduce .
short - term exposure to ee has led to fivefold increase in new neurons , substantial improvement in learning , exploratory behavior , and locomotor activity .
these effects were seen even beyond the age of 65 years and potential exists throughout the lifespan.b)synaptogenesis : physical activity enhances growth of neurons and learning promotes new connection between the neurons .
neuronal aging diminished by active and challenging life even if starts later in life . 
 
neurogenesis : concept in neurology till last decade held that brain cells can not reproduce . however , adequate evidences suggest that brain structures could generate new cells .
short - term exposure to ee has led to fivefold increase in new neurons , substantial improvement in learning , exploratory behavior , and locomotor activity .
these effects were seen even beyond the age of 65 years and potential exists throughout the lifespan .
synaptogenesis : physical activity enhances growth of neurons and learning promotes new connection between the neurons .
these are complex , highly structured enjoyable activity that provide opportunity for self - expression , e.g. , charity , clubs , group games , voluntary work , and caring for sick .
a separate study on cohabitation revealed that single , widowed , or separated had three times higher risk for cognitive impairment and 7.67 higher risk for alzheimer 's disease vis a vis their married / cohabiting counterparts .
cognitively stimulating task : in a unique study , 6- to 12-year old learnt in company of older adults in an intergenerational charter school cleveland where older adults contributed by sharing knowledge and experience .
improvement in cognition and qol was seen in these elderlies a china - based study found gardening and other community activities protective for incident dementia .
, the practice of which was associated with reduction in risk for alzheimer 's dementia and slower rates of cognitive decline .
prospective cohort study from new york found that musical instruments , dancing , and leisure activity accounted for reduced risk for incident dementia and memory decline la rue recommendation ( 2008 ) suggests following for better memory : to carve out time for cognitively stimulating activities that one enjoys , to add some new challenging pursuits as time and energy allow , to engage in these pursuits several times a week , and to participate in social interaction .
cognitive training : advanced cognitive training for independent and vital elderly ( active ) study undertook training of older adults in areas of reasoning , memory , and processing speed .
( ec ) project , elders were taught literacy , mathematics , and conflict resolution in elementary school .
training showed improvement in executive function and memory there are many cognitive training websites available , few of these include www.fitbrains.comnone , www.gamesforthebrain.comnone , www.mybraintrainer.comnone , www.luminosity.comnone , and www.sharpbrains.comnone .
many books are also available which elucidates the concept of cr and ways to improve it .
amen d g 2008 ,   the mature mind : the positive power of ageing brain 
physical training : aerobic fitness training in older adult promoted significant increase in gray ( cortical neurons ) and white matter ( connecting pathways ) physical and cognitive training combined had multiplier effect .
it lays stress on the structural neuronal complexity as well as the dynamic functional processing capacity and efficacy . from the above ,
it is obvious that the cr has a role to play in almost all aspects of cognitive and at all stage of development .
improving cr will not only improve the function capacity but also delay the expressions of cognitive disorders such as alzheimer 's disease significantly [ figure 2 ] .
life course model for better memory factors affecting cognitive reserve at various stages of human development crs have implications in various other disorders .
common neurological disorders include traumatic brain injury , epilepsy , multiple sclerosis , huntington 's disease , and parkinson 's disease .
psychiatric disorders where cr was found to have positive role were schizophrenia , affective disorders , substance abuse , sleep apnea - related cognitive deficits , etc .
these are measured by brain volume , head circumference , synaptic count , dendritic branching , etc .
these measures are intelligence quotient ( iq ) or premorbid iq , level of activation in functional magnetic resonance imaging ( fmri ) , efficiency of neural network , active compensation by alternative / more extensive network after challenge , etc .
these proxy measures are income , occupational attainment , educational attainment , and degree of literacy .
although educational attainment is more widely used proxy , the degree of literacy is a more sensitive measure .
it was seen that a higher cr individual was able to activate this network while working on more difficult task , whereas lower cr individual was unable to tap this network .
do these networks degrade during natural aging process ? can this degradation be slowed or halted ?
various literatures suggest that enriched environment ( ee ) , cognitively stimulating activities , cognitive training , and physical training are likely to increase our cr , thus making us more resilient to cognitive decline and damage . 

enriched environment : this term has been given to environmental conditions that facilitate enhanced sensory , cognitive , and motor stimulation .
a)neurogenesis : concept in neurology till last decade held that brain cells can not reproduce .
short - term exposure to ee has led to fivefold increase in new neurons , substantial improvement in learning , exploratory behavior , and locomotor activity .
these effects were seen even beyond the age of 65 years and potential exists throughout the lifespan.b)synaptogenesis : physical activity enhances growth of neurons and learning promotes new connection between the neurons .
neuronal aging diminished by active and challenging life even if starts later in life . 

ees are meaningful social engagement and activities that provide a sense of mastery . these are complex , highly structured enjoyable activity that provide opportunity for self - expression , e.g. , charity , clubs , group games , voluntary work , and caring for sick .
a separate study on cohabitation revealed that single , widowed , or separated had three times higher risk for cognitive impairment and 7.67 higher risk for alzheimer 's disease vis a vis their married / cohabiting counterparts.cognitively stimulating task : in a unique study , 6- to 12-year old learnt in company of older adults in an intergenerational charter school cleveland where older adults contributed by sharing knowledge and experience .
improvement in cognition and qol was seen in these elderlies a china - based study found gardening and other community activities protective for incident dementia .
, the practice of which was associated with reduction in risk for alzheimer 's dementia and slower rates of cognitive decline .
prospective cohort study from new york found that musical instruments , dancing , and leisure activity accounted for reduced risk for incident dementia and memory decline la rue recommendation ( 2008 ) suggests following for better memory : to carve out time for cognitively stimulating activities that one enjoys , to add some new challenging pursuits as time and energy allow , to engage in these pursuits several times a week , and to participate in social interaction.cognitive training : advanced cognitive training for independent and vital elderly ( active ) study undertook training of older adults in areas of reasoning , memory , and processing speed .
( ec ) project , elders were taught literacy , mathematics , and conflict resolution in elementary school .
training showed improvement in executive function and memory there are many cognitive training websites available , few of these include www.fitbrains.comnone , www.gamesforthebrain.comnone , www.mybraintrainer.comnone , www.luminosity.comnone , and www.sharpbrains.comnone .
many books are also available which elucidates the concept of cr and ways to improve it .
amen d g 2008 ,   the mature mind : the positive power of ageing brain 
etc.physical training : aerobic fitness training in older adult promoted significant increase in gray ( cortical neurons ) and white matter ( connecting pathways ) physical and cognitive training combined had multiplier effect . 
 
enriched environment : this term has been given to environmental conditions that facilitate enhanced sensory , cognitive , and motor stimulation .
a)neurogenesis : concept in neurology till last decade held that brain cells can not reproduce .
short - term exposure to ee has led to fivefold increase in new neurons , substantial improvement in learning , exploratory behavior , and locomotor activity .
these effects were seen even beyond the age of 65 years and potential exists throughout the lifespan.b)synaptogenesis : physical activity enhances growth of neurons and learning promotes new connection between the neurons .
neuronal aging diminished by active and challenging life even if starts later in life . 
 
neurogenesis : concept in neurology till last decade held that brain cells can not reproduce .
short - term exposure to ee has led to fivefold increase in new neurons , substantial improvement in learning , exploratory behavior , and locomotor activity .
these effects were seen even beyond the age of 65 years and potential exists throughout the lifespan .
synaptogenesis : physical activity enhances growth of neurons and learning promotes new connection between the neurons .
these are complex , highly structured enjoyable activity that provide opportunity for self - expression , e.g. , charity , clubs , group games , voluntary work , and caring for sick .
a separate study on cohabitation revealed that single , widowed , or separated had three times higher risk for cognitive impairment and 7.67 higher risk for alzheimer 's disease vis a vis their married / cohabiting counterparts .
cognitively stimulating task : in a unique study , 6- to 12-year old learnt in company of older adults in an intergenerational charter school cleveland where older adults contributed by sharing knowledge and experience .
improvement in cognition and qol was seen in these elderlies a china - based study found gardening and other community activities protective for incident dementia .
, the practice of which was associated with reduction in risk for alzheimer 's dementia and slower rates of cognitive decline .
prospective cohort study from new york found that musical instruments , dancing , and leisure activity accounted for reduced risk for incident dementia and memory decline la rue recommendation ( 2008 ) suggests following for better memory : to carve out time for cognitively stimulating activities that one enjoys , to add some new challenging pursuits as time and energy allow , to engage in these pursuits several times a week , and to participate in social interaction .
cognitive training : advanced cognitive training for independent and vital elderly ( active ) study undertook training of older adults in areas of reasoning , memory , and processing speed .
improvement lasted at least 5 years with booster training . in experience corps ( ec )
project , elders were taught literacy , mathematics , and conflict resolution in elementary school .
training showed improvement in executive function and memory there are many cognitive training websites available , few of these include www.fitbrains.comnone , www.gamesforthebrain.comnone , www.mybraintrainer.comnone , www.luminosity.comnone , and www.sharpbrains.comnone .
many books are also available which elucidates the concept of cr and ways to improve it .
amen d g 2008 ,   the mature mind : the positive power of ageing brain 
cohen g d 2005 ,   cognitive reserve : theory and application  yakov stern 2006 ,  etc .
physical training : aerobic fitness training in older adult promoted significant increase in gray ( cortical neurons ) and white matter ( connecting pathways ) physical and cognitive training combined had multiplier effect .
it lays stress on the structural neuronal complexity as well as the dynamic functional processing capacity and efficacy . from the above ,
it is obvious that the cr has a role to play in almost all aspects of cognitive and at all stage of development .
improving cr will not only improve the function capacity but also delay the expressions of cognitive disorders such as alzheimer 's disease significantly [ figure 2 ] .
life course model for better memory factors affecting cognitive reserve at various stages of human development
common neurological disorders include traumatic brain injury , epilepsy , multiple sclerosis , huntington 's disease , and parkinson 's disease .
psychiatric disorders where cr was found to have positive role were schizophrenia , affective disorders , substance abuse , sleep apnea - related cognitive deficits , etc .
ee and cognitively and physically stimulating activities affect the cr positively in all stages of life and development .
these reserves are determined by efficiency and capacity of existing brain networks and ability to enlist new compensatory networks and pure cr networks .
cr has prophylactic and therapeutic implication in a wide range of neuropsychiatric conditions across all ages . improving cr may delay or reverse the effects of aging or brain pathology .
 dementia is characterized by progressive and mostly irreversible memory loss . 
 other neuropsychiatric disorders affect cognition in varying manner . 
 are all people affected with such disorders manifest clinically in similar manner or does our brain have some reserve to tolerate insults ? relevant researches over the last two decades were scrutinized to understand brain reserve , appreciate the conceptual change in the same over years , and how the same can be improved for better cognition and memory over the year . 
 literature evidence suggests that the cognitive reserve ( cr ) is a dynamic and functional concept . 
 there is adequate evidence to suggest that enriched environment and various other measures are likely to improve cr across all age . improving cr may delay or reverse the effects of aging or brain pathology . 
COGNITIVE RESERVE
Measures of cognitive reserve
How to improve the cognitive reserve
Role of cognitive reserve in other disorders
CONCLUSION