Double dissociation of selective recollection and familiarity impairments following two different surgical treatments for temporal-lobe epilepsy

Research has firmly established that the integrity of the medial temporal lobe (MTL) is critical for recognition memory. This ability is supported by recollection, which involves recovery of contextual details of a past stimulus encounter, and familiarity assessment, which leads to awareness of prior occurrence without such recovery. Dual-process models of MTL organization posit that recollection and familiarity are supported by the hippocampus and perirhinal cortex, respectively. Alternatively, it has been argued that both structures support these recognition processes similarly as part of a more integrated declarative memory system; from this perspective, reported selective recollection impairments with circumscribed hippocampal lesions may reflect differential sensitivity to overall memory strength, rather than a deficit in a distinct recognition process. Findings from past neuropsychological research remain inconsistent and controversial, in part due to biases in patient selection, variability in clinical etiology, and limited lesion documentation. Here, we administered a verbal recognition-memory task in combination with remember-know judgements to 10 individuals who had undergone left- or right-sided stereotactic amygdalo-hippocampotomy as a surgical treatment for intractable temporal-lobe epilepsy. Comparisons with healthy control participants revealed isolated impairments in recollection with preserved familiarity, regardless of hemispheric site of lesion. In addition, we show that this impairment can be observed at a comparable level of memory strength (i.e., overall recognition performance) as the selective familiarity impairment we previously described in N.B. – an individual who underwent a tailored surgical resection of the left anterior temporal lobe with hippocampal sparing for treatment of temporal-lobe epilepsy. By revealing a double dissociation concerning temporal-lobe mechanisms for recollection and familiarity, this evidence argues against a unitary, strength-based account of MTL organization.