Verbal Memory and Learning in Unilateral Posterior Cerebral Infarction

Abstract

Unilateral posterior cerebral infarction, sparing memory-related structures in the diencephalon, may represent a means of investigating the role of hippocampal afferents and the parahippocampal areas in memory processing. Among 30 patients with unilateral posterior cerebral infarction a group of 12 subjects with left-sided lesions suffered from marked verbal memory and learning dysfunction, whereas the remaining subjects with left or right-sided lesions showed no obvious memory deficit. The impairment was most prominent for verbal learning tasks, while recall of isolated and complex verbal information appeared to be less affected. In some cases the memory disturbance could be detected up to one year after the causative event. Analysis by CT scanning revealed a coincidence of mnestic disturbances with lesions around the left collateral sulcus affecting the posterior parahippocampal gyrus and the collateral isthmus. The latter term refers to the fibre stem of the medial temporal lobe limited by the floor of the lateral ventricle and the depth of the collateral sulcus. Through this bottle-neck, bidirectional fibres run between the posterior parahippocampal gyrus and different sensory-specific and multimodal association areas. A lesion within the collateral isthmus or, more particularly, a combined lesion of the collateral isthmus and the posterior parahippocampal gyrus, deprives the hippocampus itself of its main afferent projection source and, on the other hand, prevents dissemination of the hippocampal output to widespread neocortical areas. It cannot be excluded, at least in some cases, that small lesions in the fimbria-fornix route, in the retrosplenial cortex or in the hippocampal formation itself also contribute to the memory and learning dysfunction. However, these small lesions, so far as they could be detected by CT scanning, were present in patients with and without memory disturbances.

Poststroke Memory Function in Nondemented Patients

“…Several studies provided a clear description of the size (volume) 26,39 -43 and the location 4,16,25,33,34,38,[42][43][44][45][46][47][48][49][50][51] of the infarction; however, the relation with PMF was only seldom investigated. In one study, 42 a linear relation between the size of the infarction and the degree of PMF was found.…”

“…46 Four studies 33,38,44,48 found a lower PMF in left-sided stroke compared with right hemispheric stroke. Most studies found left hemispheric stroke to be related to more severe PMD as compared with the right hemisphere, presumably because most memory tasks rely on intact language function, although these studies also included nonverbal memory tasks.…”

Posterior Cerebral Artery Territory Infarcts: Clinical Features, Infarct Topography, Causes and Outcome<footref rid="foot01">¹</footref>

“…Neuropsychological deficits with PCA ischemia are mostly described in case studies; little has been written on their incidence in large series, and to our knowledge, a more reliable clinical data aquisition on a prospective base has not been conducted so far in a large number of patients [3, 32, 33, 34]. In 25% of the patients in the series of Brandt et al [7]specific neuropsychological deficits were found, compared with 29% in the series of Milandre et al [4].…”

Posterior parahippocampal place learning in H.M.

“…Despite the evidence that lesions to the parahippocampal cortex cause disruptions in memory, some investigators have argued that the deficit occurs due to restricted output from the hippocampus to surrounding cortical areas (Von Cramon et al, 1988). Contrary to this claim, researchers have provided evidence that spatial memory can occur despite a lesion to the hippocampus, suggesting that the parahippocampal cortex plays a role above and beyond being a simple gateway to the hippocampus (Bohbot et al, 1998).…”