The hippocampus has an essential role in episodic memory, but its encoding mechanisms remain unclear. Two studies used pattern similarity analysis of functional MRI data from tasks involving learning objects in temporal orders. Hsieh et al. found that hippocampal activity patterns contained information about objects and their sequence positions rather than object or sequence information alone. In addition, they found that activity patterns in the right perirhinal cortex and the parahippocampal cortex were associated with object and sequence position information, respectively. In a different study, Ezzyat and Davachi found that pattern similarity in the left hippocampus was higher when subjects recalled temporally close objects that were presented in different 'scenes'. By contrast, the lateral occipital cortex exhibited higher pattern similarity when recalling objects presented temporally close together in the same 'scene'. Overall, these studies demonstrate that the hippocampus may represent items in specific temporal positions, whereas other nearby brain regions have different roles in encoding objects or temporal information.
References
Hsieh, L.-T. et al. Hippocampal activity patterns carry information about objects in temporal context. Neuron 81, 1165–1178 (2014)
Ezzyat, Y. & Davachi, L. Similarity breeds proximity: pattern similarity within and across contexts is related to later mnemonic judgments of temporal proximity. Neuron 81, 1179–1189 (2014)
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Bray, N. The hippocampus encodes objects in time. Nat Rev Neurosci 15, 281 (2014). https://doi.org/10.1038/nrn3735
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DOI: https://doi.org/10.1038/nrn3735