The number of new things you can hold in your mind – like the digits of a telephone number or street address – is dictated by a tiny spot on the posterior parietal cortex of the brain. Scientists suggest that locating such an important aspect of intelligence in so small an area may set humans up for a cognitive bottleneck.
A joint study conducted at University of Oregon and Vanderbilt University in Tennessee tested subjects’ retention of information about images of which they were only given quick glimpses. Most people can hold just three or four such details in their minds. This capacity, known as working memory, is directly related to intelligence – the larger one’s working memory, the more quickly one can reason and solve problems.
Dr Edward Vogel and colleagues at Oregon measured electrical brain activity in subjects shown a series of colored dots. One image flashed each second, and subjects were asked whether the image had changed. When two-dot comparisons shifted to four-dot comparisons, a large brain activity increase occurred. Graphic depiction of data determined the exact size of each individual’s working memory, and showed the four-dot test pushed most to full capacity.
Dr Reni Marois and colleagues at Vanderbilt used MRI scans to identify the specific brain area used during such short-term visual memory tasks. When the teams compared results, both agreed that the same tiny spot in the parietal lobe determined working memory capacity. The collaborative study was reported in the journal Nature (2004;428:748-751 and 751-754).
