Search

The aim of this study was to explore the effects of preoperative and postoperative lateralized mesial temporal damage on three measures of spatial learning: navigation, object location and plan drawing, and to determine the relationship between volumetry of the hippocampus and memory performance. Fifteen patients with well-characterized unilateral hippocampal sclerosis, 15 patients who had undergone unilateral anterior temporal lobectomy (ATL), and a comparison group consisting of 15 patients with idiopathic generalized epilepsy and 25 neurologically healthy participants explored a novel virtual environment. Volumetric analyses of both hippocampi were conducted on unilateral hippocampal sclerosis and idiopathic generalized epilepsy patients’ T1-weighted magnetic resonance imaging scans. Performance of temporal lobe epilepsy (TLE) patients (either unilateral hippocampal sclerosis or anterior temporal lobectomy) on the different spatial memory variables, namely navigation, object location and plan drawing, was significantly worse relative to the comparison groups (either idiopathic generalized epilepsy or controls). Patients with right TLE did not differ from patients with left TLE on any of the spatial memory measures. An index of absolute hippocampal asymmetry did not correlate with any of the spatial memory measures. Together, our lesion and volumetry findings suggest that the domain of spatial memory is systematically related to the integrity of both right and left mesial temporal lobe, and is unlikely to be a strongly lateralized function. From the standpoint of cerebral organization (lateralization), the notion of material-specificity, which postulates that all components of verbal and spatial memory are lateralized in their entirety to the left and right hemispheres, respectively, requires modification. Instead it would appear that the notion of task-specificity is a more accurate description of patterns of lateralization of spatial memory. [ABSTRACT FROM AUTHOR]

Some patients considered for left temporal lobectomy for epilepsy present with normal verbal learning and no MRI evidence of hippocampal pathology. In order to preserve learning function, the surgical approach in these cases often aims at sparing the hippocampus. Parahippocampal structures, including the left perirhinal region, however, also appear to contribute to some forms of verbal learning. We studied aspects of verbal learning in four patients with left temporal lobe resections that preserved the hippocampus, but which included perirhinal/entorhinal cortices in two cases. Pre- and postoperative T1-weighted MRI scans were spatially normalized and residual mesial temporal structures identified. The two patients whose resection included perirhinal and entorhinal cortices exhibited a marked decrement in the ability to acquire arbitrarily related word pairs that persisted at 12-month follow-up. Word list learning showed an early postoperative impairment, but recovered to normal levels within 12 months. In two patients, resection encompassed anterolateral and inferior temporal neocortex but spared the perirhinal and entorhinal cortices, amygdala and hippocampus. No postoperative change in verbal learning was evident. We concluded that hippocampal-sparing left temporal lobe resections result in task-specific verbal learning deficits when perirhinal/entorhinal tissue is included in the resection. [ABSTRACT FROM AUTHOR]