Using a virtual-reality arena to present visual targets to walking fruitflies, researchers show that insects share our ability to remember where an object is even when it is temporarily out of sight. By testing flies deleted in specific subsets of neurons and genetically rescuing mutant animals deficient in learning, the researchers pin down the neurons and some of the molecules that are involved in the process.

Visual orientation in a complex environment requires that a target's spatial position be stored, in case it becomes temporarily out of sight - a faculty known as 'spatial working memory' in vertebrates. German researchers show, in this week's Nature, that flies can remember the position of an object for several seconds after it has been removed from their environment. The flies were temporarily lured away from the hidden target, yet were able to resume their aim for it thereafter. The researchers identify the neurons involved - GABAergic ring neurons - and show that the S6KII signalling pathway is required in these neurons for the spatial working memory to function.

The abstract says:

Flexible goal-driven orientation requires that the position of a target be stored, especially in case the target moves out of sight. The capability to retain, recall and integrate such positional information into guiding behaviour has been summarized under the term spatial working memory. This kind of memory contains specific details of the presence that are not necessarily part of a long-term memory. Neurophysiological studies in primates indicate that sustained activity of neurons encodes the sensory information even though the object is no longer present. Furthermore they suggest that dopamine transmits the respective input to the prefrontal cortex, and simultaneous suppression by GABA spatially restricts this neuronal activity. Here we show that Drosophila melanogaster possesses a similar spatial memory during locomotion. Using a new detour setup, we show that flies can remember the position of an object for several seconds after it has been removed from their environment. In this setup, flies are temporarily lured away from the direction towards their hidden target, yet they are thereafter able to aim for their former target. Furthermore, we find that the GABAergic (stainable with antibodies against GABA) ring neurons of the ellipsoid body in the central brain are necessary and their plasticity is sufficient for a functional spatial orientation memory in flies. We also find that the protein kinase S6KII (ignorant) is required in a distinct subset of ring neurons to display this memory. Conditional expression of S6KII in these neurons only in adults can restore the loss of the orientation memory of the ignorant mutant. The S6KII signalling pathway therefore seems to be acutely required in the ring neurons for spatial orientation memory in flies.