The Role of Diencephalic Pathology in Human Memory Disorder

Abstract

A patient (B.J.) is reported who developed severe memory impairment following a penetrating brain injury caused by a snooker cue which entered through his left nostril into the basal regions of the brain. Initially, his memory disorder had the clinical features of a dense amnesic syndrome, with both anterograde and retrograde amnesia, but B.J. subsequently showed significant recovery of memory function. Formal memory testing was carried out 21 months after injury. This demonstrated marked verbal memory impairment, as severe as that seen in patients with the amnesic syndrome. On nonverbal memory tests, his impairment was relatively mild and patchy. His retrograde amnesia had regressed mainly to affect a 6 month period before the injury. On other cognitive tasks, he performed at an average or above average level, and there was no neuropsychological evidence of frontal lobe dysfunction. Neuroradiological investigations at various stages after his injury failed to demonstrate a lesion in any of the thalamic nuclei. Magnetic resonance imaging showed a lesion in the hypothalamus in the region of the mamillary bodies. Our study demonstrates that marked, relatively focal, memory disorder after diencephalic injury can occur without direct pathology to the body of the thalamus. It also indicates that structures in or adjacent to the hypothalamus, such as the mamillary bodies, may play a more important role in human memory functioning than has hitherto been considered.

The performance of amnesic subjects on tests of delayed matching-to-sample and delayed matching-to-position

“…In this regard the findings are consistent with other studies of spatial memory in mixed amnesic groups [20,31]. The performance of B.J.J., who had sustained bilateral damage to the mamillary bodies [10], was however of especial interest. Descriptions of the effects of selective mamillary body lesions in rats and monkeys clearly indicate that damage in this region leads to deficits on spatial tasks even though nonspatial recognition is little affected [2,3,37].…”

“…Consistent with this, B.J.J. performed remarkably well on the nonspatial DMS task (overall 55 out of 60) and this agreed with his normal performance on the Warrington Recognition Memory task [10]. His scores on the spatial task (overall 43) were, however, considerably poorer.…”

“…An additional subject (B.J.L) was, however, included in the mixed amnesic group. This subject was of particular interest as he had suffered a bilateral traumatic accident in the region of the mamillary bodies [10]. His performance on a range of psychometric tests is shown in Table 1.…”

“…In the case of Experiment 2 special interest focused on the performance of subject BJJ on the spatial and nonspatial stimuli. This man had suffered quite selective bilateral damage to the mamillary body region [10], and in the light of this region's close association with the hippocampus and in view of evidence from lesion studies in monkeys [3,16] it might be expected that this subject would perform disproportionately worse on the spatial task.…”

Impaired recollection but spared familiarity in patients with extended hippocampal system damage revealed by 3 convergent methods

“…The mammillothalamic tract carries projections from the MBs to the anterior thalamus, making these findings highly relevant, a view reinforced by studies in rats showing comparably severe memory impairments following lesions to the MBs or mammillothalamic tract (32). In a clear advance over these single-case studies (20,31), the present study involved 2 patient subgroups matched for surgical procedure as well as age, IQ, and time since surgery. It also was possible to compare the volumetric status of brain sites outside the MBs.…”