Researchers from the Karolinska Institutet in Sweden, using computational methods and biophysical modeling, seem to have identified why we are only able to hold a few things in mind at a time.
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.
"It´s like a computer programme for aircraft designers," says Fredrik Edin, PhD in computational neuroscience. "Before testing the design for real, you feed in data on material and aerodynamics and so on to get an idea of how the plan´s going to fly."
With their model brain, the team was able to discover why working memory is only capable of retaining between two and seven different pictures simultaneously. As 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.
"The model predicts, for instance, that increased activation of the frontal lobes will improve working memory," continues Dr Edin. "This finding was also replicable in follow-up fMRI experiments on humans. Working memory is a bottleneck for the human brain´s capacity to process information. These results give us fresh insight into what the bottleneck consists of."
Here’s Albert Compte of Karolinska Institutet explaining the mechanism of top-down control of working memory capacity at the 5th European Conference on Complex Systems in Jerusalem, Israel:
Press release: Computer simulations explain the limitations of working memory