The medial temporal lobe and the attributes of memory

Abstract

Neuroimaging and lesion studies have seemed to converge on the idea that the hippocampus selectively supports recollection. However, these studies usually involve a comparison between strong recollection-based memories and weak familiarity-based memories. Studies that avoid confounding memory strength with recollection and familiarity almost always find that the hippocampus supports both recollection and familiarity. We argue that the functional organization of the medial temporal lobe (MTL) is unlikely to be illuminated by the psychological distinction between recollection and familiarity and will be better informed by findings from neuroanatomy and neurophysiology. These findings indicate that the different structures of the MTL process different attributes of experience. By representing the widest array of attributes, the hippocampus supports recollection-based and familiarity-based memory of multiattribute stimuli.

Figure 1

Hippocampal activity associated with strong recollection and strong familiarity. In the left hippocampus activity associated with Source-Correct decisions (item-correct plus source-correct items) was greater than the activity associated with Forgotten items. In the same region, activity associated with Incorrect Source decisions (item-correct plus source-incorrect items) was also greater than the activity associated with Forgotten items. To equate for memory strength, the source correct and source incorrect data were based on old decisions made with relatively high confidence (5 or 6 on a 6-point rating scale). Error bars for the two source categories represent the standard error of the mean (s.e.m.) of the difference scores for each comparison, whereas the error bar for the forgotten items represents the root mean square of the s.e.m. values associated with the two individual comparisons (* denotes a difference relative to forgotten items, p-corrected< 0.05). Reproduced, with permission, from [27].

Figure 2

Cortical afferents to the medial temporal lobe in the nonhuman primate based on earlier findings [51]. The diagram shows the percentage of cortical input from the“what” (blue) and“where” (red) pathways to the perirhinal and parahippocampal cortices in the medial temporal lobe (black boxes). The box for hippocampus also includes dentate gyrus and subiculum. The data suggest that parahippocampal cortex might be important for spatial memory (red lines and boxes), while perirhinal cortex might be important for visual memory (blue lines and boxes). Perirhinal cortex may also be involved in spatial memory based on the strong input it receives from parahippocampal cortex. Figure adapted from [87].