False recognition of objects following MTL damage

A recent rat study suggests that recognition memory impairments following medial temporal lobe (MTL) damage are caused by the misidentification of novel stimuli as familiar, but this impairments can be eliminated by reducing perceptual interference (McTighe et al., 2010). This finding challenges a fundamental assumption underlying most accounts of amnesia - that memory impairments arise because previously studied information is either lost rapidly, or made inaccessible - and lends support to an alternative account in which object-level representations in MTL are critical for recognition memory because they shield from perceptual interference (Cowell et al., 2006 ). In this study, we investigated whether these findings extend to humans with focal MTL lesions. With eye movements recorded as an indirect measure of perceived novelty (observers make more fixations to novel items), participants incidentally viewed familiar (previously studied) and novel (previously unstudied) objects from the same semantic category (e.g., lamps). The novel objects were either perceptually similar (high-interference) or perceptually dissimilar (low-interference) to the familiar objects. An amnesic individual with a unilateral temporal lobe resection showed normal novelty detection for low-interference novel objects, but false recognition for high-interference novel objects. This supports the counterintuitive notion that recognition memory impairments following MTL damage are driven by the misidentification of novel items as familiar, rather than by the mis-identification of familiar items as novel. This adds support to a 'representational-hierarchical' account of MTL amnesia, in which memory loss is explained in terms of increased susceptibility to interference due to impoverished object-level representations in the MTL.