Engineering a memory with LTD and LTP

A rodent study using optogenetics to induce long-term potentiation and long-term depression provides a causal link between synaptic plasticity and memory. Memories made and unmade It has long been thought that the neural mechanisms underlying memories involve synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD), but demonstrating a causal link between these synaptic processes and memory has been difficult. Now, Roberto Malinow and colleagues claim to have done just that in mice undergoing fear conditioning. The authors use optogenetics to isolate a specific fear memory circuit and then induce LTD or LTP within the circuit to remove or reinstate the memory. It has been proposed that memories are encoded by modification of synaptic strengths through cellular mechanisms such as long-term potentiation (LTP) and long-term depression (LTD) 1 . However, the causal link between these synaptic processes and memory has been difficult to demonstrate 2 . Here we show that fear conditioning 3 , 4 , 5 , 6 , 7 , 8 , a type of associative memory, can be inactivated and reactivated by LTD and LTP, respectively. We began by conditioning an animal to associate a foot shock with optogenetic stimulation of auditory inputs targeting the amygdala, a brain region known to be essential for fear conditioning 3 , 4 , 5 , 6 , 7 , 8 . Subsequent optogenetic delivery of LTD conditioning to the auditory input inactivates memory of the shock. Then subsequent optogenetic delivery of LTP conditioning to the auditory input reactivates memory of the shock. Thus, we have engineered inactivation and reactivation of a memory using LTD and LTP, supporting a causal link between these synaptic processes and memory.