ScienceDaily has an item (here) on a paper by Zeidan, Martucci, Kraft, McHaffie and Coghill; Neural correlates of Mindfulness Meditation-Related Relief, in Social Cognitive and Affective Neuroscience 2013. They compared simple attention-to-breathing with mindfulness meditation in the relief of anxiety to find the brain areas likely to be responsible for the lowering of anxiety after mindfulness meditation.

Here is the abstract:

Anxiety is the cognitive state related to the inability to control emotional responses to perceived threats. Anxiety is inversely related to brain activity associated with the cognitive regulation of emotions. Mindfulness meditation has been found to regulate anxiety. However, the brain mechanisms involved in meditation-related anxiety relief are largely unknown. We employed pulsed arterial spin labeling MRI to compare the effects of distraction in the form of attending to the breath (ATB; before meditation training) to mindfulness meditation (after meditation training) on state anxiety across the same subjects. Fifteen healthy subjects, with no prior meditation experience, participated in 4 d of mindfulness meditation training. ATB did not reduce state anxiety, but state anxiety was significantly reduced in every session that subjects meditated. Meditation-related anxiety relief was associated with activation of the anterior cingulate cortex, ventromedial prefrontal cortex and anterior insula. Meditation-related activation in these regions exhibited a strong relationship to anxiety relief when compared to ATB. During meditation, those who exhibited greater default-related activity (i.e. posterior cingulate cortex) reported greater anxiety, possibly reflecting an inability to control self-referential thoughts. These findings provide evidence that mindfulness meditation attenuates anxiety through mechanisms involved in the regulation of self-referential thought processes.

The aim seems not to be to show that meditation relieves anxiety, which has been shown many times to be the case. Instead they tried to identify the brain activity that led to this relief. “Mindfulness is premised on sustaining attention in the present moment and controlling the way we react to daily thoughts and feelings,” Zeidan said. “Interestingly, the present findings reveal that the brain regions associated with meditation-related anxiety relief are remarkably consistent with the principles of being mindful.”