Working Memory in the Service of Executive Control Functions

Abstract

Working memory is a type of short-term memory which has a crucial cognitive function that supports ongoing and upcoming behaviors, allowing storage of information across delay periods. The content of this memory may typically include tangible information about features such as the shape, color or texture of an object, and its location and motion relative to the body, as well as phonological information. The neural correlate of working memory has been found in different brain areas that are involved in organizing perceptual or motor functions. In particular, neuronal activity in prefrontal areas encodes task-related information corresponding to working memory across delay periods, and lesions in the prefrontal cortex severely affect the ability to retain this type of memory. Recent studies have further expanded the scope and possible role of working memory by showing that information of a more abstract nature (including a behavior-guiding rule, or the occurrence of a conflict in information processing) can also be maintained in short-term memory, and used for adjusting the allocation of executive control in dynamic environments. It has also been shown that neuronal activity in the prefrontal cortex encodes and maintains information about such abstract entities. These findings suggest that the prefrontal cortex plays crucial roles in the organization of goal-directed behavior by supporting many different mnemonic processes, which maintain a wide range of information required for the executive control of ongoing and upcoming behaviors.

Keywords: executive control; non-human primates; prefrontal cortex; short-term memory; working memory.

Figure 1

Neuronal activity in prefrontal cortex representing abstract entities. (A) Cognitive task paradigm. In each trial, a start cue (a gray circle) appeared when an inter-trial interval (ITI) was over. The monkey had to push a bar after the onset of the start cue. This action changed the start cue to a fixation point, after which a sample stimulus replaced the fixation point. If the monkey maintained eye fixation and bar press three test items appeared (to the left, right and below the sample). The monkeys had to touch the test item that matched the sample in color or shape. The relevant rule for matching (matching by shape or matching by color) was consistent within a block of trials. The relevant rule was not cued and changed without any notice to the monkey when a criterion of 85% correct performance was achieved. (B) Dorsolateral prefrontal cortex cell activity represented conflict level experienced in the previous trial. The rastergram indicates activities in individual correct trials. Each row corresponds to a trial and each dot represents an action potential. Activities in high-conflict trials after low-conflict trials (LH, blue) and those in high-conflict trials after high-conflict trials (HH, pink) are shown. The mean activities are aligned at sample onset. (C) Activity difference between color and shape blocks in a dorsolateral prefrontal cortex cell represented the matching rules. The line graphs on the bottom left show the averaged firing rates in color and shape blocks, aligned at the sample onset. The bar graph on the bottom right represents the mean firing rate during the Sample epoch in consecutive blocks. The red and black dots, lines, and bars indicate color and shape blocks, respectively. The bin size is 50 ms. (A,B) are adapted from Mansouri et al., (Ref. 49). (C) is adapted from Mansouri et al., (Ref. 48).