Cognitive training is grounded in the idea that the brain is plastic. Brain plasticity refers to the ability for the brain to change and develop based on life experiences. Evidence for neuroplasticity includes studies on musical expertise and London taxicab drivers that have demonstrated that expertise leads to increased volume in specific brain areas. A  2008 study that trained older adults in juggling showed an increase in gray matter volume as a result of the training. A study attempting to train the updating component of executive function in young and older adults showed that cognitive training could lead to improvements in task performance across both of the groups, however, general transfer of ability to new tasks was only shown in young adults and not older adults. It has been hypothesized that transfer effects are dependent on an overlap in neural activation during the trained and transfer tasks. Cognitive training has been shown to lead to neural changes such as increased blood flow to the prefrontal cortex in attention training and decreased bilateral compensatory recruitment in older adults.