Descending Post-commissural Fornix Lesions Produce Impaired Spatial Working Memory in a 12-arm Maze

Memory is supported in the brain by a distributed neural network, comprised of cortical, limbic and brainstem structures and fibre pathways. The descending component of the post-commissural fornix (dPCFx) conveys hippocampal efferents to the mammillary bodies (MB), and so presents as a critical pathway along the hippocampal-MB-anterior thalamic axis, structures all crucial to memory function. However, two previous studies have reported surprisingly mild, if any, effect of selective dPCFx lesions on spatial memory in an 8-arm radial arm maze (RAM). To examine the impact of dPCFx lesions on electrophysiological activity in the anterior thalamus, dorsal hippocampus and prefrontal cortex, and in an effort to substantially increase task difficulty, we trained rats postoperatively in a 12-arm RAM. We found that dPCFx lesions produced a severe RAM impairment, showing that the RAM can elicit spatial working memory deficits after dPCFx lesions when task demands are high and suggesting that the dPCFx may indeed play an important mnemonic role