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The breakthrough came in 1972, when psychologist Jonathan Winson came up with a simple theory: The rabbit brain exhibited the same pattern of activity when it was scared and when it was dreaming because it was dreaming about being scared. The theta rhythm of sleep was just the sound of the mind processing information, sorting through the day's experiences and looking for any new knowledge that might be important for future survival. They were learning while dreaming, solving problems in their sleep.

Wilson began his experiment by training rats to run through mazes. While a rat was running through one of these labyrinths, Wilson measured clusters of neurons in the hippocampus with multiple electrodes surgically implanted in its brain. As he'd hypothesized, Wilson found that each maze produced its own pattern of neural firing. To figure out how dreams relate to experience, Wilson recorded input from these same electrodes while the rats were sleeping. The results were astonishing. Of the 45 rat dreams recorded by Wilson, 20 contained an exact replica of the maze they had run earlier that day. The REM sleep was recapitulating experience, allowing the animals to consolidate memory and learn new things. Wilson's lab has since extended these results, demonstrating that "temporally structured replay" occurs in both the hippocampus and visual cortex.

Using a translational reporter, a fluorescent protein that can be easily detected and tracked, we directly visualized the increased local translation, or protein synthesis, during memory formation.

Importantly, this translation was synapse-specific and it required activation of the post-synaptic cell, showing that this step required cooperation between the pre and post-synaptic compartments, the parts of the two neurons that meet at the synapse.

This study provides evidence that a mechanism that mediates this gene expression during neuronal plasticity involves regulated translation of localized mRNA at stimulated synapses.

In the traditional view, the brain becomes frozen with the onset of adulthood, after which few new connections form. In the past 20 years, though, scientists have discovered that intensive training can make a difference. For instance, the portion of the brain that corresponds to a string musician's fingering hand grows larger than the part that governs the bow hand - even in musicians who start playing as adults. Davidson's work suggested this potential might extend to emotional centers

But Davidson saw something more. The monks had responded to the request to meditate on compassion by generating remarkable brain waves. Perhaps these signals indicated that the meditators had attained an intensely compassionate state of mind. If so, then maybe compassion could be exercised like a muscle; with the right training, people could bulk up their empathy. And if meditation could enhance the brain's ability to produce "attention and affective processes" - emotions, in the technical language of Davidson's study - it might also be used to modify maladaptive emotional responses like depression.

Davidson and his team published their findings in the Proceedings of the National Academy of Sciences in November 2004. The research made The Wall Street Journal, and Davidson instantly became a celebrity scientist.