Preserved hippocampal novelty responses following anterior temporal‐lobe resection that impairs familiarity but spares recollection

Abstract

Although it is well established that the integrity of the medial temporal lobe (MTL) is critical for declarative memory, the functional organization of the MTL remains a matter of intense debate. One issue that has received little consideration so far is whether the hippocampus can function normally in the presence of a lesion to perirhinal cortex that produces noticeable memory impairments. This question is intriguing as the MTL forms a hierarchical system, in which perirhinal cortex represents one of the critical nodes in the reciprocal projections between neocortical association areas and the hippocampus. Here, we used functional magnetic resonance imaging to examine whether NB, an individual who underwent surgical resection of the left anterior temporal lobe that included large aspects of perirhinal and entorhinal cortex but spared the hippocampus, exhibits intact hippocampal novelty responses to auditory sentences. Our results revealed such evidence in NB's left and right hippocampus. They complement previous behavioral work in NB, indicating that recollective processes considered to rely on hippocampal integrity are also preserved. Further analyses revealed intact novelty responses in structures that provide neuroanatomical input to the hippocampus, including remaining perirhinal cortex and surgically spared parahippocampal cortex. These findings point to viable neuroanatomical mechanisms as to how functional integrity in the hippocampus may be maintained in the face of widespread, but incomplete removal of its input structures.

Recall versus familiarity when recall fails for words and scenes: The differential roles of the hippocampus, perirhinal cortex, and category-specific cortical regions

“…To explain our pattern in terms of strong memories selectively increasing hippocampal activity and weak memories selectively increasing Prc activity, one would have to assume that there is something fundamentally different about strong and weak memories that require two different neural mechanisms for each type of memory. This assumption implies two different types of memory, rather than one continuous process, which converges with other evidence suggesting functional heterogeneity in the MTL in both human and rodent models with respect to recollection and familiarity (e.g., Bowles et al, 2010; Cohn et al, 2010; Martin et al, 2011; Sauvage et al, 2008; Winters et al, 2004; Yonelinas et al, 2007). …”

Multiple determinants of lifespan memory differences

“…This is consistent with the hypothesized role of hippocampus in associative memory24, despite mixed findings in prior attempts to associate memory scores with structural brain measures606162 (though see refs 63 and 64). However, any simple dependence of M2 on anterior parahippocampus (as expected from prior association of perirhinal cortex with familiarity65), was not supported; nor was any simple dependence of M3 on fusiform (as expected from prior association of this region with visual priming66). This suggests that there is no simple one-to-one mapping of the memory factors onto single brain regions (or at least, onto the three ROIs considered here).…”

Impaired assessment of cumulative lifetime familiarity for object concepts after left anterior temporal-lobe resection that includes perirhinal cortex but spares the hippocampus

“…NB is a right-handed, university-educated woman whose memory deficits and lesion characteristics have previously been documented in detail elsewhere (Bowles et al, 2007;Bowles et al, 2010;Bowles et al, 2011;Martin, Bowles, Mirsattari, & Köhler, 2011 Bowles et al, 2007). Our past experimental research has revealed that NB exhibits impairments in familiarity assessment for verbal stimuli with respect to a recent experimental study exposure; these impairments contrast with entirely preserved recollection abilities.…”