No abstract

Damage to the human thalamus has been associated with selective anterograde recognition memory impairments. Recently, recognition memory has been subdivided into relational and non-relational memory. The aim of the present study was to assess the potentially differential involvement of the human thalamus in relational and non-relational memory. Ten patients with focal ischemic thalamic lesions were compared to individualized control groups of healthy subjects matched to each individual patient on age and IQ. Six patients showed poorer relational memory than their respective control samples. None of the 10 patients showed a significant deficit on the non-relational memory task. These observations suggest an involvement of the thalamus in relational memory, and are discussed in terms of disruption of mediotemporal-thalamic and thalamic-fronto-striatal circuits.

Human recognition memory shows a decline during normal ageing, which is thought to be related to age-associated dysfunctions of mediotemporal lobe structures. Whether the hippocampus is critical for human general relational memory or for spatial relational memory only is still disputed. The human perirhinal cortex is thought to be critically involved in non-relational memory, but another view postulates hippocampal involvement in both relational and non-relational memory. Investigating whether there is a differential impact of ageing on these memory processes may shed further light into these issues. Thus, in the present study, 106 healthy adults performed three recognition memory tasks in a consecutive age groups design involving a range from age 20 to 76. This allowed the separate assessment of spatial and nonspatial relational memory as well as non-relational memory. Both spatial and nonspatial relational memory declined in the 66-76 yr group. This pattern is consistent with the presumed course of hippocampal changes across normal ageing and points to the hippocampal role in relational memory in general. An impairment of non-relational memory commenced earlier in the 51-65 yr group. This finding is discussed in relation to perceptual/attentional mediation of memory and its potential brain correlates in ageing.

The dissociability of novelty detection in relational (RM) and non-relational memory (NRM) is currently under debate. To further address the time courses and underlying brain correlates of novelty detection, event-related potentials (ERPs) were analysed for encoding and retrieval on three memory tasks in healthy subjects. Spatial and non-spatial RM as well as NRM were assessed separately. The ERPs related to RM and NRM were dissociable for hits and correct rejections in an early and late time window. An early old/new effect was observed for NRM. A late old/new effect replicated the frequently reported recollection-associated old/new effect in terms of direction and amplitudes. Four different novelty types (spatial relational, non-spatial relational, horizontal non-relational and inverted non-relational) were examined. The P3a related to novelty detection differed in horizontal vs. inverted distractors in NRM, but not in spatial vs. non-spatial RM. ERPs for repetition detection (hits during retrieval) and also for subsequent hits (encoding phase) differed between RM and NRM. These findings are discussed in relation to potential brain correlates in RM and NRM during encoding and retrieval.