Cognitive function changes during a person's lifetime . Elderly people might experience a decline in several cognitive functions such as memory , attention , executive functions [4, 5], and processing speed . Decline in cognitive ability engenders difficulty in performing basic daily living activities [7–9]. Consequently, maintaining or improving cognitive function in older adults is drawing increasing attention [10–25].
Although human cognitive function typically declines with age, earlier studies showed that several cognitive training programs can improve cognitive functions such as memory [18, 26], processing speed [21, 27, 28], executive function [29, 30], and attention  in healthy elderly people. It is particularly interesting that some studies have demonstrated that the effects of cognitive training can impact non-trained cognitive functions or tasks [30, 32–35]. For instance, Schmiedek  conducted a working memory training study for elderly people in which participants were required to perform auditory recognition, discrimination, and memory tasks for about 15 min per day at least 5 days per week, for 8 to 10 weeks. Elderly people in the training group showed improvement of cognitive function in directly trained tasks (for example, alpha span and word list) and in cognitive functions in non-trained tasks (for example, animal span, rotation span, word pairs). Results of earlier studies show that cognitive training (for example working memory training) can improve cognitive functions in elderly people.
In line with previous studies using cognitive training for elderly people, we recently developed a new mode of cognitive training using reading aloud and solving of simple arithmetic calculations, namely learning therapy [30, 36]. Learning therapy is designed for stimulation of the frontal cortex (especially dorsolateral prefrontal cortex) and of the temporal and parietal association cortices by cognitive tasks, thereby engendering improvement of the function of these cortices . We specifically targeted these regions for the following reasons: (1) Previous functional magnetic resonance imaging (MRI) studies showed that task-related activation of these regions in older adults is lower than that in younger adults [37–42]; (2) Previous structural MRI studies using voxel-based morphometry (VBM) showed that regional gray and white matter volumes of these regions decline with age [43–45]; and (3) These activity and regional gray matter volumes of these regions are closely linked to cognitive functions [39, 46–52] such as executive functions, processing speed, and memory, which decrease with age. Therefore, cognitive decline in elderly people might result from reductions of activities and volume in these regions. Based on these facts, we assumed that stimulation of the frontal cortex (especially the dorsolateral prefrontal cortex), as well as those of the temporal and parietal association cortices by cognitive tasks might improve activities and regional gray matter volumes of these cortices. Moreover, they might engender improvement of the functions of these cortices [10, 11, 18, 36, 53].
Learning therapy used two simple and easy training tasks (reading Japanese aloud and solving simple arithmetic calculations) derived from knowledge of neuroscience. Results of brain imaging studies indicate that reading sentences or words aloud [54–58] and simple arithmetic operations [59–61] activate the three associated cortices, especially the prefrontal cortex. Reading aloud is accomplished using a combination of several cognitive processes such as recognition of visually presented words, conversion to phonological representation from graphic representation of words, analysis of the meaning of words, and control of pronunciation. Solving arithmetic problems is also accomplished through the use of numerous cognitive processes such as recognition of visually presented numbers, arithmetic operations, and control of hand movements. Moreover, the bilateral prefrontal cortices are activated even when solving very simple and easy problems. Both reading aloud and solving arithmetic problems require working memory. This prefrontal stimulation might engender the positive transfer effect on other cognitive functions. Learning therapy has outstanding features compared to previous cognitive training. First, training tasks of learning therapy are based on results of neuroscience. Secondly, the training tasks are extremely simple and easy for elderly people to perform. Consequently, elderly people can readily comprehend and perform training tasks.
Previous studies using learning therapy have demonstrated that learning therapy can improve executive functions and processing speed in healthy elderly people. For instance, Uchida and Kawashima  conducted a randomized controlled trial using learning therapy for healthy elderly people. Participants were divided into learning therapy and control groups. The learning therapy group was required to do two training tasks for 5 days a week: reading Japanese aloud and conducting simple calculations. After 6 months, the learning therapy group showed improved scores in the frontal assessment battery (FAB at bedside), which measures executive function [62–64], and a digit-symbol substitution test, which measures processing speed . These results suggest that learning therapy beneficially affects some cognitive functions in elderly people.
Purpose of this study
An earlier study showed effects of learning therapy transferred to executive functions and processing speed . However, it remains unclear whether or not the effects of learning therapy can transfer (improve) other cognitive functions such as memory and attention in elderly people. Consequently, the purpose of this study is to investigate whether or not learning therapy can transfer to a wide range of cognitive functions in elderly people. To reveal transfer effects of learning therapy on cognitive functions, we conduct a single-blinded randomized control trial using learning therapy. Testers are blinded to the study hypothesis and the group membership of participants. To evaluate the transfer effects of the reading aloud and solving simple arithmetic calculations interventions (learning therapy), we assess a broad range of cognitive functions. The measured cognitive functions are divisible into seven categories: executive functions, episodic memory, short-term memory, working memory, reading ability, attention, and processing speed.