Selective familiarity deficits after left anterior temporal-lobe removal with hippocampal sparing are material...

Research has firmly established a link between recognition memory and the functional integrity of the medial temporal lobes (MTL). Dual-process models of MTL organization maintain that there is a division of labour within the MTL, with the hippocampus (HC) supporting recollective processes and perirhinal cortex (PRc) supporting familiarity assessment. An older neuropsychological literature suggested a different type of division of labour within the MTL, with left-sided structures playing a critical role in memory for verbal materials and right-sided structures being differentially involved in memory for material that cannot easily be verbalized. Research that has related predictions made by these two accounts to each other is limited. Evidence from research in patients with selective recollection impairments and fMRI data in healthy individuals suggests that lateralization of recollection for verbal materials is not clear-cut. Here we examined lateralization of familiarity processes in the MTL by asking whether selective familiarity impairments after unilateral anterior temporal-lobe removal with hippocampal sparing are material specific. We examined this issue in NB, an individual who was previously shown to exhibit selective familiarity impairments with such a lesion (Bowles et al., 2007). We administered three similar recognition memory tests in combination with the same Remember-Know procedure for three different types of novel stimuli without pre-existing semantic representations. Analyses focused on discrimination and on possible differences in response criterion, and included an ROC based approach as well. We found that NB exhibited a deficit in overall recognition of aurally presented pronounceable non-words that reflected a specific impairment of familiarity assessment with preservation of recollective processes. Examination of recognition memory for visually presented abstract pictures and faces did not reveal any impairment, neither at the level of overall recognition nor, more specifically, at the level of familiarity assessment. These findings suggest that the neural mechanisms that support familiarity assessment in the temporal lobe operate in a manner that is tied to the specific stimulus class being assessed.