A way forward for design and analysis of neuroimaging studies of memory consolidation

Abstract

Several novel ideas and suggestions were made in response to our discussion paper (Tallman et al., this issue). Careful consideration of the content and context of memory while accounting for the neuroanatomy and functional specialization of the hippocampus may reveal more consistent patterns in fMRI studies of memory consolidation. Below we address these ideas as well as issues that arise when interpreting the fMRI signal in memory consolidation studies. In addition, we describe new analyses suggested by the commentators that clarify our findings with respect to current theories.

Keywords: Retrograde memory; functional connectivity; functional magnetic resonance imaging.

Figure 1.

Overlap of retrieval-related functional connectivity for the whole hippocampus and hippocampal subregions. Clusters indicate regions where functional connectivity changed as function of memory age when the effects of behavior were minimized for all trials. A. Extensive voxel overlap (green) of anterior hippocampus (yellow) and whole hippocampus (blue, previously reported Tallman et al., this issue). B. Same as A, except posterior hippocampus was used as the seed. There was minimal voxel overlap of posterior hippocampus and whole hippocampus connectivity. Posterior hippocampal and whole hippocampal functional connectivity networks had minimal voxel overlap, yet were generally identified the same brain regions (see Table 2 and Table 2 in Tallman et al., this issue). Voxel-wise p < 0.01, cluster-wise p < 0.05. L, Left.

Figure 2.

Hypothetical examples of brain activity in a region of interest for recent and remote conditions relative to baseline (dashed line). Circles with error bars that do not cross baseline result in significant clusters, but circles with error bars that do cross baseline do not result in significant clusters. Grey and blue examples result in significant clusters (relative to baseline) for the recent and remote conditions and exhibit significant reductions in brain activity. The orange example does not result in significant clusters for the recent or remote conditions, but it does exhibit a significant reduction in brain activity. The green example results in a significant cluster for the recent, but not the remote condition, but brain activity does not change across these conditions.