Neuroscience/Cognitive Neuroscience/Memory Networks

White matter tracts

Transection of the fornix results in a temporal lobe amnesia. A much more severe and dense amnesia than that produced by fornix transection is seen when other subcortical pathways, in addition to the fornix, are cut (Gaffan 2001). In naturally occurring lesions in the human brain these other pathways are damaged only in conjunction with the medial temporal cortex itself. Dense amnesia can be produced in monkeys experimentally by a surgical procedure that destroys the subcortical white matter pathways while leaving intact the medial temporal cortical areas (namely the hippocampus, the entorhinal and perirhinal cortex, and the parahippocampal gyrus (Gaffan 2001)). The crucial pathways that are interrupted in dense amnesia are thought to be the ascending axon projections from the basal forebrain and brainstem that pass through the anterior medial temporal lobe on their way to widespread cortical targets (Easton & Gaffan 2001 and Easton et al 2002 ).