A recent study by van Dijk, Huijts, and Lodder (2013) studied whether or not Taekwondo can improve cognitive functioning in volunteers over the age of 40. The background for this study was that as individuals age, they do experience declines in various domains of their lives, e.g. dementia and disabilities. It is commonly believed that physical exercise can have positive impact on how fast individuals think and their attention level.
Findings from this study suggest that Taekwondo practice can indeed improve reaction time, cognitive functioning and memory.
Here is the link to the study:
http://www.readcube.com/articles/10.3389/fnagi.2013.00074?locale=en