The capacity of the medial temporal lobe to represent memory items in their ordinal position in a sequence is domain-general

Memory systems in humans are less segregated than initially thought as learning tasks from different memory domains (e.g., declarative vs. procedural) can recruit similar brain areas. However, it remains unclear whether the functional role of these overlapping brain regions and the hippocampus in particular is domain-general. Here, we test the hypothesis that the hippocampus encodes and preserves the temporal order of sequential information irrespective of the nature of that information. We used multivariate pattern analyses (MVPA) of functional magnetic resonance imaging (fMRI) data acquired in young healthy individuals during the execution of learned sequences of movements and objects to test whether the hippocampus represents information about the temporal order of items in a learned sequence irrespective of their nature. We also examined such coding in brain regions involved in both motor (primary and premotor cortices) and object (perirhinal cortex and parahippocampus) sequence learning. Our results suggest that hippocampal and perirhinal multivoxel activation patterns do not carry information about specific items or temporal position in a random series of objects or movements. Rather, these regions code for the representation of items in their learned temporal position in sequences irrespective of their nature (i.e., item-position coding). In contrast, although all other ROIs showed evidence of item-position coding, this representation could at least partially be attributed to the coding of other information such as position information. Altogether, our findings indicate that the capacity of regions in the medial temporal lobe to represent the temporal order of sequential information is domain-general. Our data suggest that these regions contribute to the development of item-position maps that might provide a cognitive framework to order sequential behaviors irrespective of their nature.