While the molecular and cellular mechanisms underlying the acquisition, consolidation, reconsolidation and retrieval of memory have attracted a considerable amount of attention in neuroscience, very little is known about memory allocation, the process that determines which neurons in a network store a given memory. Results from our laboratory have suggested that the transcription factor CREB (cAMP-response element binding protein) has a role in memory allocation in the basolateral amygdala (BLA);increasing the levels of CREB in a subset of neurons of the BLA increased the probability that these neurons were engaged in an auditory-fear memory. More recently, we and others used cell-inactivation techniques to confirm that BLA neurons with higher levels of CREB are preferentially recruited during memory formation. Additionally, we demonstrated that BLA neurons with higher CREB levels are more excitable than other neurons, a finding that provides a potential explanation for why they are especially selected during auditory-fear conditioning. Importantly, we found that increases in synaptic strength thought to be critical for memory are larger in CREB-over expressing neurons, suggesting that these neurons hold a disproportionately large component of the auditory-fear memory trace. Here, I propose to extend and complement these studies with state-of-the-art optogenetic approaches that allow for the activation of specific neurons in the BLA.
The specific aims are: 1-To test the hypothesis that CREB has a key role in memory allocation. I propose to use Herpes Simplex Viral (HSV) vectors that can manipulate CREB levels in 15-20% of BLA neurons, and Channel Rhodopsin 2 (ChR2) that allows for the specific activation of these neurons. My hypothesis predicts that activating BLA neurons with higher CREB levels in trained mice will lead to a behavioral manifestation of the memory, while activating a similar number of neurons with normal CREB levels will not. My very preliminary findings suggest that it is possible to activate an auditory-fear memory with this approach. 2-To examine the hypothesis that increases in excitability are key to memory allocation in the BLA. I propose to manipulate excitability in specific BLA neurons with bi-stable Channel Rhodopsin 2 (ChR2-C128S) delivered with HSV vectors. Unlike the ChR2, light-activation of ChR2-C128S does not necessarily trigger action potentials and instead increases the depolarization of these neurons, thus increasing their excitability. The experiments described in this aim provide an independent test for the hypothesis that CREB affects memory allocation by increasing neuronal excitability. The research proposed here will not only advance our understanding of CREB's role in memory allocation, it will also provide insights into how emotional memories are stored in the amygdala. These insights will aid in the development of treatments for disorders thought to be caused by abnormal emotional memory storage and retrieval in the amygdala, including posttraumatic stress disorder (PTSD).
Traumatic situations often lead to the formation of fear memories that can be debilitating, causing inappropriate fear and anxiety and, in severe cases, posttraumatic stress disorder. This study will elucidate memory mechanisms that could ultimately lead to the development of treatments for the excessive fear and anxiety associated with of emotional trauma.
|Rogerson, Thomas; Cai, Denise J; Frank, Adam et al. (2014) Synaptic tagging during memory allocation. Nat Rev Neurosci 15:157-69|