The way that your heart rate increases in response to alertness in the brain has been recently discovered by researchers. Specifically, this study looked at the interactions between neurons that fire upon increased attention and anxiety and neurons that control heart rate to discover the "why," "how," and "where to next" behind this phenomenon. The results may have important implications for how certain conditions are treated in the future, such as post-traumatic stress disorder, chronic anxiety, or even stress, the researchers note.