The contribution of the medial temporal system in humans to semantic processing of words and pictures.

The brain contains several memory systems. Episodic memory deals with episodes in a particular space and time context and is typically associated with structures deep in the temporal lobe (the medial-temporal lobe system). An episodic memory deficit is commonly seen in Alzheimer's disease (AD). Semantic memory refers to our knowledge of the world, the meaning of words and pictures and associations between concepts. Patients with semantic dementia (SD) typically suffer a loss of the meaning of the words, with word finding and comprehension deficits. The anterior part of the temporal lobe is affected. Based on recent findings from our laboratory, we will examine how semantic similarity between concrete words is reflected in the similarity between response patterns in medial temporal cortex, how this differs between medial temporal structures and how this relates to episodic memory. After all, the two memory systems have many operations in common, such as the need to complete a memory pattern when a fragment of a memory trace is encountered, and to bind together memories that are distributed over the neocortex. We will evaluate how the semantic similarity effect in perirhinal cortex is influenced by input modality (such as spoken and written words, sign language), by the type of properties to be retrieved, how it relates to explicit associative-semantic retrieval and whether it can be altered by episodic memory. We will test both healthy volunteers and patients with AD and SD.