Role of dopamine in hippocampal plasticity and hippocampus-dependent memory

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How the brain stores memories is one of the great mysteries in neuroscience. How can we recollect what happened in the past? Scientists believe that memories are stored in the connections between neurons in the brain. These connections are called synapses, and a change in the strength of these connections is known as synaptic plasticity. Whereas synaptic plasticity can account for the immediate storage of information, it is less well understood how different memories are bound together. We have recently discovered a mechanism of synaptic plasticity that can account for such associations over time, with a time scale of many minutes. We have found that activity at a synapse leaves a trace which can be turned into synaptic changes later by activity of the receiver neuron of the synapse if a specific signalling molecule, dopamine, is present. Dopamine is released when we receive an unexpected reward. This mechanism could link together the actions we took prior to the reward with their rewarding outcome, thus making it more likely that we will take the same actions to be rewarded again in the future. Now we want to understand how naturally released dopamine influences synaptic plasticity, whether such release is necessary for new memories to form, and whether dopamine can link memories together. The experiments will be done in a structure in the mouse brain that is known to be important for memory, namely the hippocampus. We will test the hypothesis that release of dopamine is both necessary and sufficient for neuronal activity to convert an initial memory trace into long-term memory. The results of these experiments will be important for our understanding of how memories are linked together. The experiments will give us new insights into memory and could potentially open new avenues for improving our capacity for memory and for treating memory disorder.