Synaptome of a Memory
A longstanding question in neuroscience concerns the cellular mechanisms of learning and memory. Since synapses were first discovered as the sites of communication between neurons, scientists have thought that changes in their number or structure would be a likely substrate of memory. Although evidence has accumulated, proof of this hypothesis has been elusive. Addressing this question requires substantial improvement in understanding how the brain is wired, namely, the “connectome”. Ultimately, the connectome will contain a map of the location and type of every synapse in the brain. The synaptome of a memory, sensation, or behavior is quite different from the co nectome of a brain region because these experiences likely involve a subset of synapses distributed across different brain regions. Hence, to understand mechanisms, it is necessary to know which specific synapses were involved. Detecting synapses and their subcellular components requires the nanoscale resolution of serial section electron microscopy, an approach that has been pioneered in my laboratory. We propose new strategies that will for the first time, provide specific identification of the progression and ultrastructural consequences of activity-dependent synapse remodeling in a cellular mechanism of learning and memory, a crucial first step in defining the synaptome of a memory. Nothing like this has ever been done before and the findings are crucial not only to understand the basic neuroscience and development of learning and memory, but also to illuminate synaptic dysfunction in prominent disease states, such as autism and Alzheimer’s disease.