Biological reward comes from the release of the neurotransmitter, dopamine. Performing working memory tasks promotes dopamine release. In the study of human subjects by Fiona McNab and colleagues in Stockholm, human males (age 20-28) were trained on working memory tasks with a difficulty level close to their individual capacity limit for 35 minutes per day for 5 weeks. After such training, all subjects showed increased working memory capacity. Functional MRI scans also showed that the memory training increased the cerebral cortex density of dopamine D1 receptors, the receptor subtype that mediates feelings of euphoria and reward.
Students who make good grades feel good about their success. Likewise, people who are "life-long learners" have discovered that learning lots of new things makes them feel good. Though this present study did not rigorously test the idea, it is possible that learning how to improve your working memory capacity can also make you feel good.
Source: McNab, F. et al. 2009. Changes in cortical dopamine D1 receptor binding associated with cognitive training. Science. 323: 800-802.
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