Contributions of occipital, parietal and parahippocampal cortex to encoding of object-location associations.

Events are stored in our episodic memory in varying degrees of accessibility for conscious retrieval and combined with varying amounts of associated information. A crucial aspect of episodic memory is to bind information together, e.g. linking an object to a certain location. Spontaneous or experimenter-induced variance in the allocation of attentional resources during encoding critically determines the strength of the resulting memory trace especially for associative information as measured in subsequent memory tests. The neural correlates of associative memory encoding were investigated by lesion, PET- and fMRI-studies. So far no study aimed to assess the memory for associative information in a non-categorical way. Such a parametric assessment opens the possibility for a closer inspection of the relationship between brain activity and memory trace formation. We established a novel associative object-location memory paradigm, together with a parametric assessment of subsequent memory performance for spatial location which allows: (i) to determine if associative information is retrieved in a continuous or discontinuous manner during recognition and (ii) to investigate the relationship between activity during encoding and the resulting memory trace. Such correlations were observed in the occipital, parietal and the parahippocampal cortex, areas known to be involved in processing either objects and/or locations. The analysis of response functions revealed for the majority of areas involved in encoding a continuous relationship between brain activity during encoding and the confidence in a subsequent memory test.