The results suggest a mechanism by which different MTL structures code different types of abstract representations that together represent the content and sequential flow of episodes (Figure 1G). Hence, the identity of viewed objects appears to be coded by TE neurons independent of time and place,
whereas events defined in time and place are coded by the hippocampus independent of object identity. These signals are combined in the entorhinal cortex to represent subsets of objects in sequence and in the perirhinal cortex to distinguish the behavioral context in which identical objects appear. The two studies agree that hippocampal representations evolve in time independent of other external variables and that time cells could signal the unfolding history of experience. These results break new ground and raise Dorsomorphin fundamental questions. What mechanisms drive time cells? Computational models suggest that instantaneous activity
in the hippocampus is determined in part by its prior activity states signaled by recurrent inputs (Howard and Kahana, 2002). Both CA3 and the dentate gyrus include powerful recurrent connections that could maintain similar activity patterns during contiguous intervals yet drive continuous shifts in activity as time proceeds. When and learn more why are hippocampal neurons sensitive to discriminative stimuli? Naya and Suzuki (2011) found that most hippocampal cells coded time, but very few discriminated the visual cues. Perhaps the monkeys were so familiar with the sequences that the hippocampus represented the stimuli only as steps in a routine. Probe trials that include unfamiliar visual cues could be incorporated to disrupt the expected routines and engage hippocampal processing to encode the new cues as distinct episodes in memory. In this case, “object coding” by the hippocampus should be prominent during probe tests. Finally, are hippocampal time fields needed for event memory? The “retiming” described by MacDonald et al. (2011) suggest during that the hippocampus is not merely counting time, but includes duration
and temporal contiguity among task epochs as an intrinsic coding feature. Nonetheless, memory performance did not require memory for time, and time codes did not predict performance levels. Future recording experiments that require animals to compare different durations are needed to test whether time fields contribute to memory for episodes. “
“The vertebrate nervous system is without doubt the most complex organ of the living world, in both morphological organization and cellular diversity. Understanding how this complexity is generated is a topic of obvious interest to developmental biologists, and for neuroscientists it is an important source of insights into the logic of the organization and function of the adult brain.