Yet another fascinating Nature article from the research group around Gilles Laurent. This article is built around the mechanisms underlying associative learning and plasticity in the mushroom bodies in insects. The area is known to be crucial for associative learning of odors and contains up to hundreds of thousands of neurons called Kenyon cells.
Here the authors focus on synapses between Kenyon cells and beta lobe neurons in the MBs of locusts that are modifiable by a Hebbian spike-timing-dependent plasticity (STDP) rule. Firing of pre- and postsynaptic neuron within a few tens of milliseconds can result in synaptic change (plasticity). The authors argue that “responses to odours recorded in Kenyon cells during behavioural learning generally occur and end well before reward delivery, indicating that STDP alone cannot support associative conditioning”. Cassenaer and Laurent demonstrate that the local delivery of a reinforcement-mediating neuromodulator, in this case octopamine, following the pre–post pairing causing STDP can specify the synapses that will undergo an associative change. Due to the neuromodulator, at these synapses the STDP rule itself is transformed. Octopamine is a biogenic amine involved in insect learning and memory here applied as an injection one second after spike pairing. Kenyon cells were stimulated in vivo using either electrical impulses or odour delivery, with the same outcome.
This research article is commented by Timothy E. Holy in the same Journal.
Cassenaer, S., & Laurent, G. (2012). Conditional modulation of spike-timing-dependent plasticity for olfactory learning Nature, 482 (7383), 47-52 DOI: 10.1038/nature10776
Holy TE (2012). Neuroscience: Reward alters specific connections. Nature, 482 (7383), 39-41 PMID: 22297965
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