A note by Sara Lazar et al. in Neuroreport proposes that mindful awareness meditation causes increases in the thickness of areas of the frontal lobes associated with attention, interoception and sensory processing (the sample size is small). It is known that brain areas associated with other skilled activities such as juggling or playing the piano increase in size with practice.
I find it difficult to communicate my experience of mindful awareness. It seems like a contentless animal kind of openness that observes mind products such as thoughts, feelings, and emotions as they rise and decay, sensing itself as distinct from completely being them. This is very different from my usual more immersed self that feels itself to be completely defined by those thoughts, feelings, and emotions. This losing of a normal self, paradoxically, yields a platform for acting in the real world that others experience as a strong presence of self. One description would be that this platform is continually making such distinctions as that between being an angry person and noting the process of angry-ing as it appears and disappears. (I try to expand on this in Mindstuff: a guide for the curious user)