Memory encoding processes in young and old adults

Context: Information processing requires a series of mental operations from encoding to storage and retrieval. A large number of studies have examined the retrieval process, but less attention has been paid to the encoding process. Evidence Acquisition: The aims of this paper were to provide an overview of perceptual and semantic encoding processes as well as identify and compare the structural and functional changes in the memory encoding process of young and old adults. A review of encoding was conducted based on findings from two recent memory encoding studies and a literature search on memory encoding. It included studies published from January 1980 to December 2013 and appeared in the databases of CINAHL, MEDLINE, AMED, Journals@Ovid and the ISI Web of Science. Results: Five stages of encoding were identified. They were: 1) early perceptual processing; 2) prelexical feature detection and early lexical processing; 3) initial selection of information from competing information for processing in the working memory; 4) semantic, syntactic, or lexical processing; and 5) updating of working memory with the newly created item representation and elaborate processing. Perceptual encoding appears to be modulated by sensory cortices, in which stimuli are initially perceived and processed, whereas semantic encoding involves the left prefrontal cortex temporal regions by both verbal and nonverbal stimuli. Conclusions: Early perceptual processing and the selection of information processes associated with memory encoding are comparable between young and old adults. However, they showed differences in semantic processing, updating of working memory, and elaborate processing. These differences might be due to reduced volume and functional capacity of the hippocampus and frontal lobes, shrinkage in the white matter and its associated tracts, as well as inability of the aging brain to produce levels of dopamine comparable to its previous levels.