Chris Chatham posted a brief overview of the classic working memory model and offered a new diagram for that model. There are several interesting points, but I'd like to emphasize two of them: processing and memory are two sides of the same coin and gating functions are likely to be present at every intersection of arrows on the working memory diagram.
Having said that, I side with O'Reilly and his collaborators who proposed a completely different working memory model outlined in their article Banishing the Homunculus: making working memory work. The model is based on tripartite architecture, which is composed of the posterior cortex (PC) that performs majority of "automatic" sensory and motor processing, the hippocampus (HC) that is responsible for rapid learning that binds together arbitrary information, and the prefrontal cortex and the basal gandlia (PFC/BG) system that maintains internal contextual information (PFC), which can be dynamically updated by the BG.
In this model working memory is defined as an emergent property of the interactions between these three brain areas. These mechanisms not only support those basic memory functions that are generally associated with working memory, but also those controlled processing functions that are typically associated with a "central executive". The critical difference between this model and the model covered in Chris's post is that all information is viewed to be distributed in a relatively stable configuration throughout the cortext with working memory being represented by the controlled activation of those distributed representations. Authors' view is that working memory and executive function are two sides of the same coin, based on the fact that processing and memory functions are typically distributed within and performed by the same neural substrates.
As a side note, while a framework that separates working and long-term memory may look familiar and computantionally appealing, think about "simple" operation of copying a concept from long-term to working memory. What mechanism would support this copying that (to properly reproduce the concept) would need to include not only sensory and motor information associated with it, but also (potentially) large number of related concepts? How would "activation" of such a copy look like?
The authors also identify six key functional demands underlying working memory and describe how those are addressed in the proposed model:
- Rapid updating
- Robust maintenance
- Multiple, separate working memory representations
- Selective updating
- Top-down biasing of processing
- Learning what and when to gate
There is one more interesting point in the paper that I'll expand on later:
...it is likely that working memory may represent a kind of phylogenetic extension of the same kinds of mechanisms that underlie all forms of complex motor coordination and planning. (emphasis mine)
update 2006/03/20: More on working and long-term memory processes and assessment from Intelligence Testing.