Abstract: Writing is a complex perceptual-motor process that involves both central cognitive coding and peripheral motor execution. It requires a lot of cognitive resources and is therefore susceptible to physiological aging. Specifically, physiological aging not only weakens the muscle strength of the elderly, but also reduces the coordination between their multi-sensory systems, and leads to a decline in their language cognition. All of these inevitably impact the writing abilities of older adults, reducing the legibility of their written products and their fluency in the writing process.
The legibility of written products is primarily measured by indicators such as the size, alignment, smoothness, and error rates of the letters. Research based on written products has found that older adults always show variations in font size, stroke inversions, reduced smoothness, and increased error rates. Fluency in the writing process is generally measured by indicators such as writing latency, inter-letter interval, whole word duration, writing speed, and pen pressure. Studies on the writing process have revealed that older adults tend to show slower responses, increased pauses, prolonged execution, decreased speed, and uneven pen pressure.
There are three primary reasons for writing aging: The first reason involves the neurodegeneration of the brain. With the decrease in nerve density, the volume of gray matter gets smaller and the integrity of the white matter fiber tract becomes impaired, which inevitably affects the executive function, attention regulation, and processing speed in writing. In addition, the reduction of motor neurons leads to a decline in their function, which weakens the strength of the muscles in the writing-related areas such as the arm, wrist, and fingers. The second reason involves the deterioration of sensory-motor mechanisms. With the tactile and kinesthetic recession, older adults need more time to process the upcoming sensory information, which may affect the fluency in the writing process, the size and layout of the font, the pressure of the pen, and the stability of the writing movements. The third reason involves other physiological processes that may easily affect hand strength. With the interference from hormonal changes or bone loss to hand movements, hand-eye coordination, proprioceptive feedback, sensory perception, grip strength, and the ability to independently control the hand muscles are all adversely affected.
Future research should focus on the following unanswered questions: The first question involved the synchrony and asynchrony of aging in different writing processes. Specifically, are the phases of central cognitive coding and peripheral motor execution simultaneously affected by aging, or do they exhibit independent phase aging? The second question involved the universality and specificity of cognitive aging in writing. On the one hand, from the perspective of language type, it is highly necessary to explore the aging characteristics and patterns exhibited in Chinese character writing, which may show great differences from alphabetic languages. On the other hand, from the perspective of the relationship between writing and other linguistic processes (such as speech and reading) or non-specific motor (such as painting), will the aging of “writing-specific” brain regions exhibit aging-specific characteristics, while the aging of the shared brain regions with other linguistic or motor processes exhibit general patterns? Finally, research should also be conducted to develop and apply clinical diagnostic criteria for cognitive aging in writing, as the kinematic analysis of online and offline writing behavior has become a new perspective for diagnosing and assessing symptoms of AD/PD recently.

Key words: writing, writing cognitive, cognitive aging, neural mechanism