Amnesia after a discrete basal forebrain lesion

Abstract

Destructive lesions of the basal forebrain are often associated with memory impairment and this structure is thought to contribute to memory function by providing a cholinergic input to critical structures associated with memory such as the hippocampus and amygdala. In previously reported cases of amnesia associated with damage in the basal forebrain, multiple neuroanatomical regions were damaged, and the critical lesion responsible for amnesia has not been identified clearly. We report a patient who developed primarily anterograde amnesia after clipping of an unruptured anterior communicating artery aneurysm. Postoperative magnetic resonance imaging showed a discrete lesion, centring in the right diagonal band of Broca and including the anterior hypothalamus, septal nucleus, lamina terminalis, and paraterminal gyrus, and an indiscrete patchy lesion in the corresponding area on the opposite side. The nucleus basalis of Meynert was minimally aVected and the diencephalon was not damaged. Single photon emission computed tomography showed marked hypoperfusion in the midline frontobasal region corresponding to the MRI lesion and hypoperfusion in the hippocampus bilaterally. It is concluded that disconnection of the pathway between the diagonal band of Broca and the hippocampus contributed to memory impairment. (J Neurol Neurosurg Psychiatry 1998;65:126-130) Keywords: diagonal band of Broca; amnesia; time taggingThe amnesic syndrome has been found in patients with relatively discrete lesions in several cerebral sites including (a) the medial temporal lobes including the hippocampus, (b) median thalamic nuclei, (c) anterior thalamic nuclei, (d) basal forebrain, (e) fornix, (f) mammillary bodies, and (g) retrosplenial cortex. 1-3The basal forebrain has been considered to contribute to memory function by way of the pathways between nuclei of the diagonal band or the septal nucleus and the hippocampal region, thus providing a cholinergic input to the hippocampus. [1][2][3][4] In most previously reported cases of amnesia 4-14 associated with basal forebrain lesions, multiple neuroanatomically identified areas were damaged, and it has been diYcult to identify the minimal lesion necessary to produce an amnesic syndrome except for patients in whom basal forebrain lesions were relatively well circumscribed. 5We describe a patient who developed anterograde amnesia as the result of a discrete lesion in the basal forebrain after clipping of an unruptured anterior communicating artery aneurysm. Case reportA 61 year old right handed high school teacher, who had taught science for more than 35 years and had had good memory function, experienced a sudden onset of weakness in the right upper and lower limbs in July 1993, but recovered the next day. He was admitted to a hospital elsewhere and underwent MRI, which showed a small haemorrhage in the left external capsule. He underwent cerebral angiography, which showed an aneurysm 5 mm in diameter in the anterior communicating artery. He underwent surgical clipping of the aneur...

The Role of the Mammillary Bodies in Memory: A Case of Amnesia Following Bilateral Resection

“…This finding is similar to previous cases (e.g., Dusoir et al 1990, Abe et al 1998, Tucker et al 1988, in which global amnesia resulted from disconnection of the hippocampus from the MB and basal forebrain. The presence of significant temporal disorientation, which has been associated with the anterior nuclei (Clarke et al 1994), and other thalamic and fornix lesions (Shuren et al 1997, Yasuno et al 1999) further supports our contention of a functional disconnection of the hippocampus and thalamus.…”

“…Following resection, the patient improved on immediate memory, but remained amnestic after delays. Executive functions and other skills were largely unimpaired and there was no retrograde amnesia.Anterograde amnesia is typically associated with mesial temporal lobe damage, such as in the patient HM (Scoville & Milner 1957), but has been described in association with other forms of pathology, such as lesions to the thalamus (Malamut et al 1992), transection of the fornix and mammillothalamic tracts (Dusoir et al 1990), and basal forebrain lesions (Abe et al 1998). The capability of discrete MB lesions to produce amnesia is unclear.…”

Spontaneous acute hemorrhage within a subependymoma of the lateral ventricle: successful emergent surgical removal through a frontal transcortical approach

“…This kind of basal forebrain lesion, mainly seen after removal of tumors and hemorrhage from anterior communicating aneurysms, tends to produce memory deficits which are less severe than those observed in patients with medial diencephalic or mesial temporal lobe damage, and characteristically do not affect non -declarative memory 10,16 . It has been postulated that the amnesia following basal forebrain damage can be a consequence of the interruption of the cholinergic innervation that the nuclei located in this anatomical region provide to the hippocampus and neocortical areas 1,3,10,16 . Nevertheless, the presence of clinically evident memory dysfunctions seems to depend on a combination of basal forebrain nuclei and fiber tracts lesions rather than on damage to a single structure 16 .…”

Stereotaxic probabilistic maps of the magnocellular cell groups in human basal forebrain

“…It has been long known that basal forebrain lesions in humans, including those from trauma, tumor, or rupture of the anterior cerebral or anterior communicating arteries result in impaired memory functions (Damasio et al, 1985;Morris et al, 1992;Diamond et al, 1997;Abe et al, 1998). Since multiple anatomic regions were often damaged in these cases, it has been difficult to determine the exact area of the lesion that caused the cognitive symptoms.…”