One way that drumming has an impact on us is through “entrainment”. Entrainment is one effect of drumming that defines the relationship between external rhythms and your inner rhythms. It effects both your heart and your brain.

The relationship between the external rhythms and your inner rhythms or pulses is inseparable. In fact, our internal rhythms will speed up or slow down to match a stronger external rhythm.   (Frank Lipman, M.D.)

So what is it that is so captivating about the rhythm of the drum particularly as it relates to past and present?  There is some quantifiable research done by Dr. Melinda Mayfield at Stanford University.  

How long should I listen?

Her research suggests that “the use of the drum by indigenous cultures in ritual and ceremony has specific neurophysiological effects and the ability to elicit temporary changes in brain wave activity, and thereby facilitates imagery and possible entry into an ASC (altered state of consciousness), especially the SSC (shamanic state of consciousness)”.

It turns out that that listening to a drum beat at 4- 4.5 beats per second for 13-15 minutes will result in a temporary change in the brain pattern. As most cultures have known, drumming can help get us in a Shamanic or meditative state.

Source: http://web.stanford.edu/group/brainwaves/2006/Maxfieldabstract.html