The slowing in cognitive processing speed is associated with age and it reflects cognitive decline in elderly individuals [18]. Working memory (WM) involves the capacity to temporarily hold information and manipulate it for short period of time. WM can be divided into three stages: the initial encoding of information, the maintenance of WM items, and the retrieval of WM items [19]. Prominent age-related differences were seen in older adults in WM tasks compared to a short-term memory task that required only the maintenance and storage of information [20]. Several studies have utilized the n-back test to investigate age-related alterations in the brain, revealing the underlying mechanism by applying functional magnetic resonance imaging (fMRI) [21,22] and EEG [23,24]. The brain oscillatory responses vary during the phases of working memory while engaging in a WM task. Studies using the Sternberg item recognition task found distinct patterns for activation in the encoding, storage, and retrieval of WM, which were found to be sensitive to WM load levels [25,26,27,28].
