Memory Takes Time

Memory is an adaptation to particular temporal properties of past events, such as the frequency of occurrence of a stimulus or the coincidence of multiple stimuli. In neurons, this adaptation can be understood in terms of a hierarchical system of molecular and cellular time windows, which collectively retain information from the past. We propose that this system makes various timescales of past experience simultaneously available for future adjustment of behavior. More generally, we propose that the ability to detect and respond to temporally structured information underlies the nervous system's capacity to encode and store a memory at molecular, cellular, synaptic, and circuit levels. What is a memory? Kukushkin and Carew envision memory and synaptic plasticity as “Fourier transforms of experience”, whereby multiple timelines of the external world are simultaneously represented in the brain by a nested, hierarchical system of dynamic processes, limited in time.