University of Texas Southwestern Medical Center, Dallas

A psychiatrist talks about finding answers that add up across all levels.

Often when we study the brain and behaviour, we fail to tie molecular events to higher-order changes in composition, to shifts in the organ's circuitry, or all the way up to changes in actions or broad mental abilities. Many scientific fields suffer from this problem of scale, but the recent explosion in techniques available for molecular biology and quantitative behavioural analysis has given neurobiology the potential to bridge many conceptual gaps.

An excellent example is a study carried out by Roberto Malinow of Cold Spring Harbor Laboratory, New York, and his colleagues (H. Hu et al. Cell 131, 160–173; 2007). They elucidated a molecular mechanism by which emotional stress and arousal promote long-term memory formation. In doing so, they brought together two well-characterized phenomena: that noradrenaline stimulates memory formation in the brain's hippocampus, and that the trafficking of a type of glutamate receptor is important for a form of plasticity in the same brain region.

Malinow's team shows that, by stimulating noradrenaline release in the hippocampus, emotional stress leads to phosphorylation of glutamate receptors. This boosts the incorporation of these receptors at the synapse — the junction between nerve cells — which, in turn, enhances synaptic function and improves memory formation. Crucially, mice with a mutation that prevents phosphorylation of the relevant part of the glutamate receptor do not show noradrenaline-mediated memory enhancement.

Impressively, this study begins with a clinically important phenomenon — memory enhancement by emotional stress — and establishes a detailed biological pathway that underlies a behavioural endpoint in an animal model. Studies such as this are what the field needs.