Human Oscillatory EEG Activities Representing Working Memory Capacity

Abstract

We can flexibly process and make decisions regarding multiple types of information in daily situations such as driving and cooking. However, human error is increased in complex or combined tasks (relative to simple tasks) because our information processing capacity is limited. This limited cognitive function is associated with working memory (WM), which is proposed to be a higher-level human ability to memorize, maintain, and manipulate mental representations in mind for a short time (Baddeley, 1986). Most theorists think that WM function includes active manipulation as well as passive short-term maintenance. An oftenused metaphor for working memory is the blackboard of mind. For example, imagine that you are rearranging furniture in your room. You can move around furniture in your mind, that is, transform imagination any number of times. To guide behavior and make decisions about what to do next, WM temporarily selects and retains task-relevant information such as recently processed sensory input, retrieved information from long-term memory, or mentally manipulated images. Thus, WM is directly linked to any and all other brain functions, including perception, movement, emotion, and problem solving. Baddeley & Hitch (1974) proposed a basic psychological model in which WM is divided into separate components, “storage system” and “central executive“. The “storage system“ consists of 2 temporary storage buffers for visual information (visuospatial sketch pad, i.e., visual working memory) and auditory-verbal information (phonological loop, i.e., verbal working memory) and an episodic buffer for long-term memory, whereas “central executive“ controls allocations of attention, selects relevant information, and manipulates information held in storage systems (Baddeley, 1986; Baddeley & Hitch, 1974; Phillips, 1974; Baddeley, 2000). Extensive experimental evidence from behavioral performance of normal subjects, lesion studies, and neuroimaging studies supports this view. For example, performance in dual tasks requiring 2 separate perceptual domains (i.e., a visual and a verbal task, or a mental processing task and a maintenance task) is nearly as efficient as performance of individual tasks (for a review, Cowan, 2001; Della Sala & Logie, 1993). These findings indicate that visual and verbal WM are separated. Both visual and verbal WM have 3 phases: encoding, which imports relevant information in memory; maintenance, which stores encoded information; and retrieval (or rehearsal), which briefly uses information for a task. To investigate neural substrate for WM, previous electrophysiological studies in nonhuman primates and human