Electromagnetic correlates of recognition memory processes

Recognition memory is critically dependent on a hierarchically organized network of brain areas including the visual ventral stream, medial temporal lobe structures, frontal and parietal cortices. In recent years, cognitive theories of recognition memory have been helpful to further our understanding of the functional organization of this network. A prominent, although not unchallenged, set of theories proposes that recognition memory is not a unitary phenomenon, but can be based on the recollection of contextual information about events or on familiarity in the absence of recollection. A number of hemodynamic and electromagnetic studies have been undertaken to relate recollection and familiarity to neuronal substrates both in healthy subjects as well as in patients with brain lesions. Today, it is evident that both event-related potential and event-related field (ERP/ERF) data as well as data of oscillatory brain activity (e.g., theta oscillations) are necessary to fully understand the neural dynamics of recollection and familiarity and their relationship to functional anatomy. Ultimately, such data are required from patients with isolated brain injuries to designated components of the networks (such as the hippocampus) to obtain converging evidence for functional relationships between recollection and familiarity and respective neuroanatomic substrates. The complexity of this task is highlighted by findings indicating that recognition memory can already be affected by preparatory processes prior to stimulus onset.