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

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.