Recovery From Amnesic Confabulatory Syndrome After Right Fornix Lesion

Abstract

Background. Reports of amnesia due to bilateral fornix lesions are rare. A unilateral right fornix lesion is not known to cause an amnestic confabulatory syndrome. Objective. To investigate the role of right fornix lesion in amnesia, the association of confabulation with executive disorders, and to evaluate the long-term recovery of memory and executive functions after surgical removal of a pilocytic astrocytoma in the right orbitofrontal region extending to the right fornix. Methods. Neuropsychological testing was performed 3 and 17 months after surgery. Results. Severe anterograde global amnesia, mild retrograde amnesia, momentary and spontaneous confabulation, and mild executive deficits were found initially and mostly recovered by 17 months. Conclusions. The authors hypothesize that the lesion of the right fornix was sufficient to cause amnesia by disconnecting the hippocampal formations from the anterior thalamic nuclei and mammillary bodies and interrupting the cholinergic efferents to the hippocampus from the medial septum, according to the extended hippocampal system framework. Sparing of the left fornix may be sufficient to ensure a good recovery of memory. Confabulation is strongly associated with the improvement of executive functions, specifically the ability to suppress irrelevant memory traces.