Bryce Gessell (Duke University)
Many studies on long-term memory formation conceptualize this process as a series of three steps. The first, encoding, is the modification of neural structures in response to incoming information. The second step is consolidation, during which molecular and cellular changes make these earlier modifications more durable. The third step, storage, involves the long-term maintenance of such changes, which preserve a memory trace in a state suitable for reactivation or retrieval. All three steps happen at timescales which can differ by orders of magnitude: encoding may take a single second; consolidation, hours or days or even weeks; storage may continue for many decades. However, it is difficult to find neurobiological correlates whose temporal profiles match those of the steps in longterm memory formation. For example, one form of long-term potentiation (LTP)— a mechanism of memory consolidation and storage—depends on postsynaptic NDMA receptors. But NMDA receptors, as proteins with a short half-life, degrade and recycle frequently, meaning that the temporal stability of consolidation or storage cannot correspond to similarly-stable molecular and cellular structures. Rather, many different neurobiological processes, operating over different timescales, give rise to the three abiding “steps” of long-term memory. In this talk I investigate the extent to which these different neurobiological processes may prompt us to reconsider our analysis of long-term memory formation. In particular, I argue that alternative pathways of early consolidation, such as those enhanced by sleep (Yang et al. 2014; Feld and Born 2017), suggest a more nuanced decomposition. I outline one possible decomposition, paying special attention to how variability at neural substrates across time can culminate in meaningful behavioral and cognitive consequences. I conclude with a self-conscious reflection on the method of my talk, and on the role of molecular and cellular findings in cognitive neuroscience more generally.
