Building memory by not building molecules

Honeybees are clever wee beasties. If you give a honeybee a scent, then give her food, she can quickly learn to extend her mouthparts when she smells the scent alone. And they can remember this for at least a whole 24 hour day. This is a classic learning test made famous by Pavlov’s dogs. So honeybees are at least as smart as dogs, for this test anyway.

What’s going on in that tiny little head as they learn that some arbitrary smell means food? Usually, neurons need to make new “stuff” to form a memory. Making proteins, for instance, is usually needed for long term memory, but not short term memory.

Actin is a protein that is best known as half of the machinery that powers muscles (myosin in the other), but actin is also a more general component of a cell’s skeleton. In rats and mice and other furry mammals, you need to make actin to get long-term potentiation (LTP), which is a strengthening of the connections between two neurons.

Ganeshina and colleagues injected honeybees with chemicals that blocked the making of actin. You would expect that this would mess up the poor little honeybee’s memory.

But expectations were dashed. These actin-inhibiting drugs made the honeybees remember better, not worse.

The authors’ aren’t sure what’s going on here, but they have a guess.

The parts of the honeybee’s nervous system that learns smell are called the mushroom bodies. These mushroom bodies grow a little as the honeybee gets older, adding in new connections between neurons all the time, regardless of whether the honeybee learns anything or not. These new connections, because they aren’t related to anything the bee learns, would mostly add noise to the neural pathway. And that could drown out some of connections between neurons that are formed or strengthened as the honeybee learns.

The authors seem to think that knocking out the actin production prevents “random” new connections that would form just during normal aging. As a result, the honeybee gets more memory signal and less noise.

This is a story of diversity. This paper reminds us that even when animals can learn the same kinds of tasks, they may not be learning them in the same ways.

Reference

Ganeshina O, Erdmann J, Tiberi S, Vorobyev M, Menzel R. 2012. Depolymerization of actin facilitates memory formation in an insect. Biology Letters 8(6): 1023-1027. DOI: 10.1098/rsbl.2012.0784

Photo by BugMan50 on Flickr; used under a Creative Commons license.