Limitations on working memory

08/05/2009 by admin.

A paper has been published by a large multidisciplinary group from Sweden and Spain, using computer simulations and fMRI scans to look at working memory. The research is reported in Science Daily (here) and (here).

The working memory, which is our ability to retain and process information over time, is essential to most cognitive processes, such as thinking, language and planning. It has long been known that the working memory is subject to limitations, as we can only manage to “juggle” a certain number of mnemonic items at any one time. Functional magnetic resonance imagery (fMRI) has also revealed that the frontal and parietal lobes are activated when a sequence of two pictures is to be retained briefly in the visual working memory. However, just how the nerve cells work together to handle this task has remained a mystery…

For their project, the researchers used techniques from different scientific fields, applying them to previously known data on how nerve cells and their synapses function biochemically and electrophysiologically. They then developed, using mathematical tools, a form of virtual or computer simulated model brain. The computations carried out with this “model brain” were tested using fMRI experiments, which allowed the researchers to confirm that the computations genuinely gave answers to the questions they asked.

With their model brain, the team was able to discover why the working memory is only capable of retaining between two and seven different pictures simultaneously. As the working memory load rises, the active neurons in the parietal lobe increasingly inhibit the activity of surrounding cells. The inhibition of the inter-neuronal impulses eventually becomes so strong that it prevents the storage of additional visual input, although it can be partly offset through the greater stimulation of the frontal lobes. This leads the researchers to suggest in their article that the frontal lobes might be able to regulate the memory capacity of the parietal lobes…This finding was also replicable in follow-up experiments on humans.

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