Abstracts

Rationale: The hippocampal formation is essentially involved in the formation of conscious memories for facts and events and hippocampus sclerosis (HS) is associated with memory deficits in a variable scale. But HS is not a unitary phenomenon, cluster analysis revealed different patterns of cell loss in the different hippocampal subfields CA1 - CA4 and the dentate gyrus, constituting characteristic types of HS, who seems to be related to the time, when the hippocampal damage is acquired (Blümcke et al. 2007). We could recently demonstrate, that the dentate gyrus plays a critical role within the neuronal network responsible for memory formation (Pauli et al. 2006). In this study we investigated the impact on memory functions of different types of HS.Methods: We studied the degree of declarative memory dysfunction in 61 patients, suffering from unilateral mesial temporal lobe epilepsy, using the possibility to access memory performance of each isolated hippocampus by the intracarotid amobarbital test. Subsequently, surgical treatment for intractable seizures were performed and the hippocampal specimens were neuropathologically analysed and grouped in accordance to normal hippocamus, type 1 (CA1 sclerosis), type 2 (endfolium sclerosis), type 3 (classical hippocampal sclerosis) and type 4 ( severe hippocampal sclerosis). Results: Memory performance was significantly different in the different types of HS. Whereas HS type 1 (CA1 sclerosis) as well as normal hippocampal cell densities where not associated with memory deficits, type 2 (endfolium sclerosis) as well as type 3 (classical HS) and type 4 (severe HS) showed significantly reduced memory capacity. The commonality of these three types is found in a more extensive cell loss in the endfolium (dentate gyrus and CA4) in contrast to HS type 1 (CA1-sclerosis), characterized in selective and severe cell loss restricted to CA1, whereas the endfolium, especially the dentate gyrus is spared. Conclusions: This data may contribute to explain, why HS is associated with memory impairment in a highly variable degree, and postoperative memory loss may also occur in cases with evident HS in MRI.