Memory and language impairments and their relationships to hippocampal and perirhinal cortex damage in patients with medial temporal lobe epilepsy

Chronic medial temporal lobe epilepsy (MTLE) is associated with memory loss due to damage in the hippocampal system. To investigate the relationship between volume of medial temporal lobe structures and performance on neuropsychological tests, we studied 39 consecutive patients with MTLE and unilateral hippocampal atrophy (HA) determined by volumetric magnetic resonance imaging (MRI). Structures of interest comprised hippocampus, amygdala, and entorhinal, perirhinal, parahippocampal, and temporopolar cortices. The findings indicated that (1) performance was significantly worse in the group with left HA as compared with the group with right HA on general memory, verbal memory, delayed recall, and verbal fluency tests and the Boston Naming Test (BNT), and (2) the volume of the left hippocampus and also the degree of asymmetry of perirhinal cortex volume were significant and independent predictors of performance on general memory, verbal memory, and verbal fluency tests and the BNT in patients with MTLE.     

Correlates of memory function in community-dwelling elderly: the importance of white matter hyperintensities.

We sought to identify magnetic resonance- (MR)-imaged structures associated with declarative memory in a community-dwelling sample of elderly Mexican-American individuals with a spectrum of cognitive decline. Measured structures were the hemispheric volumes of the hippocampus (HC), parahippocampal gyrus, and remaining temporal lobes, as well as severity of white matter signal hyperintensities (WMH). Participants were an imaged subsample from the Sacramento Area Latino Study of Aging (SALSA), N = 122. Individuals were categorized as normal, memory impaired (MI), cognitively impaired non-demented (CIND), or demented. We show that WMH was the strongest structural predictor for performance on a delayed free-recall task (episodic memory) in the entire sample. The association of WMH with delayed recall was most prominent in elderly normals and mildly cognitively impaired individuals with no dementia or impairment of daily function. However, the left HC was associated with verbal delayed recall only in people with dementia. The right HC volume predicted nonverbal semantic-memory performance. We conclude that WMH are an important pathological substrate that affects certain memory functions in normal individuals and those with mild memory loss and discuss how tasks associated with WMH may rely upon frontal lobe function.     

MRI extrahippocampal volumes and visual memory: correlations independent of MRI hippocampal volumes in temporal lobe epilepsy patients.

Limbic system atrophy and memory dysfunction are common in patients with temporal lobe epilepsy (TLE). However, the relationship between extrahippocampal limbic structures and memory functioning within TLE has received little attention. The present study examined associations of MRI volumetric measurements of the mammillary body, fornix, amygdala, and hippocampus to measures of episodic verbal and visual memory. The Logical Memory and Visual Reproduction subtests from the Wechsler Memory Scale were administered to 47 unilateral TLE patients (25 right, 22 left). Normalized right and left MRI volumes were determined for each patient by cursor tracing 1.5 mm slices from 3D-MRI. Significant associations were found between left hippocampal volume and the immediate, delayed, and percent retention scores of the Logical Memory Test; between the left mammillary body volume and the Logical Memory Test delayed and percent retention scores; immediate Visual Reproduction performance was significantly related to the right and left amygdala volumes, and right mammillary body volume; only the right amygdala and right mammillary body volume were associated with the delayed Visual Reproduction trial. However, neither right nor left hippocampal volumes were related to visual memory performance. Multiple limbic system structural volumes were independently associated with verbal and nonverbal memory performance. Results suggest that visual memory, as measured by the Visual Reproduction Test, may be uniquely associated with extrahippocampal volumes in patients with TLE.     

Compromised memory function in schizophrenia and temporal lobe epilepsy

The purpose of this study was to investigate compromised memory function of schizophrenia patients in comparison with temporal lobe epilepsy patients, whose memory impairments result from a clear lesion. The authors hypothesized that schizophrenia patients would show poorer immediate and delayed recall performances in verbal and visual memory tasks. The study sample consisted of a healthy comparison group of 30 subjects and three patient groups comprising 76 schizophrenia patients, 93 left temporal lobe epilepsy patients, and 72 right temporal lobe epilepsy patients. The authors assessed immediate recall, delayed recall, and delayed retention. Tasks were subdivided into two categories (easy and difficult), and then patient memory dysfunction was compared among the memory tests. The authors observed material-specific memory impairment, where the left temporal lobe epilepsy group showed severe verbal memory impairment and the right temporal lobe epilepsy group showed severe visual memory impairment. A moderate impairment was found in immediate and delayed verbal memory in schizophrenia patients, and the impairment of visual memory was amplified with delayed recall. Such a result can be interpreted not only as a generalized cognitive deficit, but also as an integrative dysfunction involving the mesial temporal and frontal lobes in the left and right hemispheres, whereby the lesion site cannot be determined selectively. Our results show that the selection of a memory task that cannot be influenced by verbal mediation is very important for analyzing memory dysfunction in schizophrenia patients.     

Memory relationships between MRI volumes and resting PET metabolism of medial temporal lobe structures

Prior studies of temporal lobe epilepsy (TLE) patients showed that MRI volumes and resting PET scan measures of temporal lobe structures were related to memory. Weintrob and colleagues [Ann. Neurol. 2002;51:442-7] reported that PET glucose uptake in the left perirhinal cortex predicted verbal paired associate (PA) learning, whereas MRI volume of the left hippocampus did not. We investigated whether MRI volumes could account for memory functioning if both PET and volumes were from the same region in 18 TLE patients. Volumes and glucose uptake of the hippocampus and parahippocampal gyrus (PHG) were compared with WMS-III performance. Significant correlations were observed between hippocampal volumes and PA and Logical Memory (LM) Percent Retention, but not between memory and PHG volumes or any PET measures. Multiple regression revealed that hippocampal volumes, but not PHG volumes or PET, significantly predicted PA and LM retention scores. These findings suggest that hippocampal volumes provide unique information regarding memory.     

Medial temporal lobe atrophy in patients with refractory temporal lobe epilepsy

OBJECTIVE: The objective of this study was to assess the volumes of medial temporal lobe structures using high resolution magnetic resonance images from patients with chronic refractory medial temporal lobe epilepsy (MTLE). METHODS: We studied 30 healthy subjects, and 25 patients with drug refractory MTLE and unilateral hippocampal atrophy (HA). We used T1 magnetic resonance images with 1 mm isotropic voxels, and applied a field non-homogeneity correction and a linear stereotaxic transformation into a standard space. The structures of interest are the entorhinal cortex, perirhinal cortex, parahippocampal cortex, temporopolar cortex, hippocampus, and amygdala. Structures were identified by visual examination of the coronal, sagittal, and axial planes. The threshold of statistical significance was set to p<0.05. RESULTS: Patients with right and left MTLE showed a reduction in volume of the entorhinal (p<0.001) and perirhinal (p<0.01) cortices ipsilateral to the HA, compared with normal controls. Patients with right MTLE exhibited a significant asymmetry of all studied structures; the right hemisphere structures had smaller volume than their left side counterparts. We did not observe linear correlations between the volumes of different structures of the medial temporal lobe in patients with MTLE. CONCLUSION: Patients with refractory MTLE have damage in the temporal lobe that extends beyond the hippocampus, and affects the regions with close anatomical and functional connections to the hippocampus.     

Episodic memory impairment in patients with Alzheimer’s disease is correlated with entorhinal cortex atrophy

The aims of this study were to investigate the pattern of cortical atrophy and the relationships between memory performances and the brain regions in Alzheimer's Disease (AD). optimized voxel-based morphometry (VBM) was applied to the MRI brain images of 18 probable AD and 18 healthy subjects (HS). Patients performed verbal and visuo-spatial episodic and shortterm memory tests. Contrasting of AD group with HS, and anatomobehavioural correlations were carried out in order to identify regional atrophic changes and neuro-cognitive aspects in AD group. We found evidence of gray matter (GM) volume reduction in AD in the medial temporal, parietal and frontal areas bilaterally and in the left anterior thalamic nuclei. Performance on the episodic memory delayed recall tests co-varied with GM volume in the left entorhinal cortex. The pattern of cortical atrophy likely reflects the heterogeneous level of dementia severity in our AD group. The anatomical region affected in the left hemisphere indicates a sufferance at multiple levels of the Polysynaptic Hippocampal Pathway, which is involved in declarative memory. Findings on the entorhinal cortex and the delayed memory scores support the role of the entorhinal cortex in episodic memory. Damage to the entorhinal cortex, deafferenting the hippocampus from neocortical inputs, interferes with episodic memory consolidation in AD patients.     

Hemispheric differences in hippocampal volume predict verbal and spatial memory performance in patients with Alzheimer's disease

Atrophy of the hippocampal formation, a region important for the acquisition of new declarative knowledge, has been well-documented in Alzheimer's disease (AD), although the relation of such atrophy to the extent of memory dysfunction in these patients has been less clear. In the present study, 18 patients with a clinical diagnosis of probable AD were studied with a high-resolution, quantitative magnetic resonance imaging (MRI) protocol, as well as the verbal and spatial versions of the Buschke controlled learning task. The volumes of the hippocampal formation and, as a control for generalized atrophy, parahippocampal gyrus and temporal neocortex were computed from gapless coronal slices taken perpendicular to the long axis of the hippocampus. To correct for individual differences in brain size, volumes of regions of interest were divided by total intracranial volume. Separate stepwise regression analyses (with age, right and left hippocampal, parahippocampal gyrus, and temporal lobe volumes as the independent variables) showed that left hippocampal volume was the best predictor of free recall and delayed free recall of verbal information (P = 0.0042 and P < 0.0001, respectively). Recall and delayed recall of the spatial location of verbal items were best predicted by right hippocampal volume (P = 0.0054 and P = 0.0118, respectively). Memory scores did not correlate either with parahippocampal gyrus or temporal lobe volume. Furthermore, the relation between hippocampal volume and memory function observed in cases with AD did not hold for healthy aged control subjects.     

Limbic system abnormalities associated with Ammon's horn sclerosis do not alter seizure outcome after amygdalohippocampectomy

PURPOSE: To evaluate whether limbic system abnormalities associated with Ammon's horn sclerosis alter seizure outcome after selective amgydalohippocampectomy. METHODS: In 45 patients with unilateral mesial temporal lobe epilepsy, histologically proven Ammon's horn sclerosis, and uneventful postoperative course, volumes of the hippocampus, hemisphere, amygdala, entorhinal cortex, mamillary body, and fornix were measured by using a T(1)-weighted 3-D gradient-echo sequence with roughly isotropic (1.17 x 1.17 x 1-mm) voxels. In addition, signal intensity of the hippocampus and of the temporal lobe white matter was visually assessed and graded on a coronal T(2)-weighted fast-spin-echo sequence with 2-mm-thick slices. Volumetric measurements and visual analysis were compared between seizure-free and non-seizure-free patients examined 12 months after surgery. RESULTS: Hippocampal, hemispheric, entorhinal cortex, mamillary body, and fornix volumes, but not amygdalar volumes, were significantly smaller on the operated-on than on the non-operated-on side and significantly smaller in patients compared with controls. No volume differences of the hippocampus, hemisphere, amygdala, entorhinal cortex, mamillary body, and fornix existed between seizure-free (Engel class IA) and non-seizure-free patients (Engel class IB-IV). Increased temporal lobe white matter signal was observed in 15 patients but did not alter seizure outcome. CONCLUSIONS: Limbic system abnormalities are not a surrogate marker to predict postsurgical seizure outcome in patients with unilateral Ammon's horn sclerosis.     

Memory and executive function in older adults: relationships with temporal and prefrontal gray matter volumes and white matter hyperintensities

Forty-eight healthy adults aged 65-85 were recruited for structural magnetic resonance scans after an extensive neuropsychological battery that ensured a high degree of variability across the sample in performance on long-term memory tests, and on tests traditionally thought to rely on prefrontal cortex. Gray matter volumes were measured for three gyri in the frontal lobe (superior, middle, inferior), six gyri in the temporal lobe (superior, middle, inferior, fusiform, parahippocampal, and hippocampus), and the occipital lobe. Gray matter volumes declined across the age range evaluated, but with substantial regional variation--greatest in the inferior frontal, superior temporal, and middle temporal gyri but negligible in the occipital lobe. Both memory performance and executive function declined as the number of hyperintense regions in the subcortical white matter increased. Memory performance was also significantly correlated with gray matter volumes of the middle frontal gyrus (MFG), and several regions of temporal neocortex. However, the correlations were all in the negative direction; better memory performance was associated with smaller volumes. Several previous reports of significant negative correlations between gray matter volumes and memory performance are described, so that the possible reasons for this surprising finding are discussed.     

Preserved hippocampal novelty responses following anterior temporal‐lobe resection that impairs familiarity but spares recollection

Although it is well established that the integrity of the medial temporal lobe (MTL) is critical for declarative memory, the functional organization of the MTL remains a matter of intense debate. One issue that has received little consideration so far is whether the hippocampus can function normally in the presence of a lesion to perirhinal cortex that produces noticeable memory impairments. This question is intriguing as the MTL forms a hierarchical system, in which perirhinal cortex represents one of the critical nodes in the reciprocal projections between neocortical association areas and the hippocampus. Here, we used functional magnetic resonance imaging to examine whether NB, an individual who underwent surgical resection of the left anterior temporal lobe that included large aspects of perirhinal and entorhinal cortex but spared the hippocampus, exhibits intact hippocampal novelty responses to auditory sentences. Our results revealed such evidence in NB's left and right hippocampus. They complement previous behavioral work in NB, indicating that recollective processes considered to rely on hippocampal integrity are also preserved. Further analyses revealed intact novelty responses in structures that provide neuroanatomical input to the hippocampus, including remaining perirhinal cortex and surgically spared parahippocampal cortex. These findings point to viable neuroanatomical mechanisms as to how functional integrity in the hippocampus may be maintained in the face of widespread, but incomplete removal of its input structures. © 2010 Wiley‐Liss, Inc.     

Extrahippocampal gray matter atrophy and memory impairment in patients with medial temporal lobe epilepsy

Memory impairment observed in patients with medial temporal lobe epilepsy (MTLE) is classically attributed to hippocampal atrophy. The contribution of extrahippocampal structures in shaping memory impairment in patients with MTLE is not yet completely understood, even though atrophy in MTLE extends beyond the hippocampus. We aimed to evaluate the neuropsychological profile of patients with MTLE focusing on memory, and to investigate whether gray matter concentration (GMC) distribution within and outside the medial portion of the temporal lobes would be associated with their neuropsychological performance. We performed a voxel based morphometry study of 36 consecutive patients with MTLE and unilateral hippocampal atrophy. We observed a significant simple regression between general and verbal memory performance based on Wechsler Memory Scale-Revised and the GMC of medial temporal and extratemporal structures in patients with left MTLE. We also performed a "regions of interest analysis" of the medial temporal lobe, and we observed that the GMC of the hippocampus, entorhinal, and perirhinal cortices were consistently associated with general and verbal memory performance in patients with MTLE. We also observed that the GMC of the cingulate and orbito-frontal cortex are independently associated with verbal and general memory performances. Our results suggest that general and verbal memory impairments in patients with left MTLE are associated with atrophy of the hippocampus, the entorhinal, and the perirhinal cortex. We also suggest that atrophy and dysfunction of limbic and frontal structures such as the cingulate and the orbito-frontal cortex contribute to memory impairment in MTLE.     

Glucocorticoid-induced impairment of declarative memory retrieval is associated with reduced blood flow in the medial temporal lobe

Previous work indicates that stress levels of circulating glucocorticoids can impair retrieval of declarative memory in human subjects. Several studies have reported that declarative memory retrieval relies on the medial temporal lobe. The present study used H(2)(15)O-positron emission tomography to investigate whether acutely elevated glucocorticoid levels affect regional cerebral blood flow in the medial temporal lobe, as well as in other brain regions, during declarative memory retrieval in healthy male human subjects. When measured over four different declarative memory retrieval tasks, a single, stress-level dose of cortisone (25 mg) administered orally 1 h before retention testing, induced a large decrease in regional cerebral blood flow in the right posterior medial temporal lobe, the left visual cortex and the cerebellum. The decrease in the right posterior medial temporal lobe was maximal in the parahippocampal gyrus, a region associated with successful verbal memory retrieval. Cortisone administration also significantly impaired cued recall of word pairs learned 24 h earlier, while drug effects on performance in the other tasks (verbal recognition, semantic generation and categorization) were not significant. The present results provide further evidence that acutely elevated glucocorticoid levels can impair declarative memory retrieval processes and suggest that such impairments may be related to a disturbance of medial temporal lobe function.     

Neuropsychological correlates of hippocampal and rhinal cortex volumes in patients with mesial temporal sclerosis

Considerable progress has been made toward understanding the function of the primate rhinal cortex, comprising the entorhinal (ErC) and perirhinal (PrC) cortices. However, translating animal models to human memory has been limited by the technological problems associated with characterizing neural structures in vivo. Functional correlates of hippocampal and rhinal cortex volume changes were examined in a sample of 61 temporal lobe epilepsy patients with mesial temporal sclerosis (MTS; 33 left, 28 right). Patients were administered the Wechsler Adult Intelligence Scale (revised or third edition), the Wechsler Memory Scale (revised or third edition), and a spatial maze task. Neuropsychological data, together with rhinal cortex and hippocampal volumes, collected in our earlier study (O'Brien CE, Bowden SC, Whelan G, Cook MJ, unpublished observations), were analyzed using multiple regression. The only significant predictor of verbal memory function was the difference score between the volume of left hippocampus and the left PrC. Spatial maze scores were predicted by the bilateral sum of ErC volume. The difference score between the left hippocampus and left PrC volumes was the most powerful predictor of verbal episodic memory. Right hippocampal volume was not a significant predictor of nonverbal episodic memory. Verbal and nonverbal semantic memory were not significantly predicted by any combination of rhinal cortex structures. This quantitative study suggests a lateralized or material-specific memory function for the left hippocampus and left PrC, in contrast to the bilateral role of the ErC. The left hippocampus and left PrC appear to act on verbal memory function through an opposing relationship. Finally, differentiation between hippocampal and subhippocampal components in terms of episodic and semantic memory, respectively, could not be supported by the current data.     

Is the right amygdala involved in visuospatial memory? Evidence from MRI volumetric measures

Quantitative MRI measurement of hippocampal sclerosis in patients suffering from temporal lobe epilepsy (TLE) have, as yet, failed to evidence any correlation between the right hippocampus and visuospatial memory. In this report, word learning and design learning tasks were carried out as well as MRI volumetric measurements of the hippocampus and amygdala in order to verify possible modality-specific correlations between function and structure. Delayed recall indices in our memory tasks provided significant results. Visuoverbal ratios differed between right and left TLE groups, as did laterality indices of hippocampal and amygdalar volumes. Furthermore, correlations were found between the left hippocampal volume and verbal memory, and between the right amygdala and visuospatial memory. We suggest that the difficulty encountered in establishing a correlation between right temporal structures and visuospatial memory could come both from the type of test employed and the structures considered.     

A case of right mesial temporal lobe epilepsy accompanied with ictal polyopsia]

A 59-year-old, right-handed woman had a paroxysmal polyoptic visual illusion, in which multiple copies of the object she saw spread horizontally in the left hemi-visual field. Polyopsia appeared for a few seconds. Neurological examination was normal. Magnetic resonance imaging (MRI) showed a tumor-like lesion involving the cortical and subcortical matters in the right mesial temporal regions. An interictal EEG showed frequent spikes in the right mesial temporal area and intermittent theta waves in the right fronto-temporal area. Video-EEG monitoring using the sphenoidal electrodes showed the seizure discharges originating in the right sphenoidal lead accompanying the polyoptic visual illusion. The seizure discharges were restricted within the right mesial temporal lobe. Paroxysmal visual illusion disappeared after administration of anti-epileptic drugs. EEG showed rare spikes in the right mesial temporal area. Polyopsia in this patient presumed to be associated with right mesial temporal lobe epilepsy because polyopsia and seizure activities on the ictal EEG were coupled and polyopsia ceased after administration of anti-epileptic drugs. Polyopsia is recognized as visual perseveration in space and a rare visual illusion. The lesion causing polyopsia has been reported to be mostly within posterior cerebral areas including occipital, parietal and temporal regions. This patient whose ictal polyopsia associated with mesial temporal lobe epilepsy is a very rare case because most reported cases presenting ictal polyopsia are neocortical temporal lobe epilepsy. The precise mechanism of polyopsia remains unknown. The mesial temporal lobe includes the hippocampus and parahippocampal formation that have been reported to receive information from the diverse association cortex and work as memory controllers. Ictal polyopsia may result from dysfunction of the visual association cortex or visual memory systems induced by the epileptic activities in the mesial temporal lobe. Polyopsia is a rare ictal semeiology of mesial temporal lobe epilepsy and may be one of the important ictal symptoms.     

Entorhinal cortex atrophy in epilepsy patients exhibiting normal hippocampal volumes

OBJECTIVE: To determine whether MRI volumetric measurement of the entorhinal cortex could detect structural damage and lateralize the seizure focus in patients with temporal lobe epilepsy in whom no measurable hippocampal abnormalities were found. BACKGROUND: A reduction in the volume of the entorhinal cortex ipsilateral to the seizure focus in patients with intractable temporal lobe epilepsy and hippocampal atrophy was recently shown. METHODS: MRI volumetric analysis of the entorhinal cortex was performed using a T1-weighted three-dimensional gradient echo sequence in 24 control subjects and 22 patients with temporal lobe epilepsy and normal hippocampal volumes. Thirteen patients underwent surgery, with a mean postoperative follow-up of 36 months. RESULTS: Group analysis (multivariate analysis of variance) showed a reduction in the volume of the entorhinal cortex ipsilateral to the seizure focus in patients with left (p < 0.0001) and right temporal lobe epilepsy (p < 0.0001). Lateralization of the seizure focus could be done in 14 of 22 patients (64%) based on entorhinal cortex volumetry. CONCLUSION: Entorhinal cortex atrophy ipsilateral to the seizure focus supports the presence of structural damage in the mesial temporal lobe in patients with temporal lobe epilepsy and normal hippocampal volumes and emphasizes the participation of the entorhinal cortex in the pathogenesis of this disorder.     

A volumetric MRI study of the hippocampus and the parahippocampal region after unilateral medial temporal lobe resection

Segmentation guidelines on high-resolution MRI designed to assess remaining volumes of the hippocampus and the parahippocampal cortices after medial temporal lobe (MTL) surgery could provide a useful tool to investigate the involvement of these anatomical regions in surgical outcomes and in human memory. For this purpose, we implemented an MRI volumetric analysis, already applied to healthy population or epileptic patient before surgery, to quantify the volume of the hippocampus, the temporopolar cortex and the regions of the parahippocampal gyrus (perirhinal, entorhinal and parahippocampal cortices) spared after unilateral MTL resection carried out to treat medically uncontrolled temporal lobe epilepsy (TLE). Based on the locations of remaining anatomical landmarks, we quantified the volume of these regions in 24 patients after MTL resection and in 16 control participants. Our results show that (1) mean volumes of these regions contralateral to the epileptic focus were similar to those of normal subjects, (2) volumetric measures obtained from the resected side were much smaller than those from the non-resected side or from normal values and (3) the extent of MTL resection was comparable in right or left MTL surgery. Individual analysis of patients showed that the parahippocampal cortex, as opposed to the other regions, was not systematically removed across patients. As a post-operative MRI-based method, it therefore proves valuable to assess group data as well as to explore differences between individual patients.     

Comprehensive dissection of the medial temporal lobe in AD: measurement of hippocampus, amygdala, entorhinal, perirhinal and parahippocampal cortices using MRI

Background Early pathological involvement of specific medial temporal lobe areas is characteristic for Alzheimer’s disease (AD). Objective To determine the extent of regional medial temporal lobe atrophy, including hippocampus, amygdala, and entorhinal, perirhinal, and parahippocampal cortices in mild AD patients and healthy controls, and to compare diagnostic accuracy across volumetric markers. Methods We studied 34 patients with clinically probable AD and 22 healthy elderly control subjects. Regional volumetric measures were obtained from volumetric T1–weighted MRI scans after accounting for global brain atrophy using affine transformation into standard space. Results Volumes of medial temporal lobe structures were significantly smaller in AD patients than in controls with exception of the left entorhinal cortex. The degree of atrophy was comparable between all structures. Diagnostic accuracy (number of correctly allocated cases divided by number of all cases) was highest for the right parahippocampal cortex with 85%, but only slightly lower for the right hippocampus and right entorhinal cortex with 82% and 84%. Using a linear combination of markers, the unilateral volumes of the right hippocampus, parahippocampal cortex and perirhinal cortex yielded an accuracy of 93%. Conclusion Extent of atrophy is similar between the different regions of the medial temporal lobe in mild AD.Volume measurements of medial temporal lobe structures in addition to the hippocampus only yield improved diagnostic accuracy if a combination of these structures is used.     

A controlled quantitative MRI volumetric investigation of hippocampal contributions to immediate and delayed memory performance

MRI volumetric TLE studies show inconsistent evidence of hippocampal involvement in memory. Prior studies have not dissociated hippocampal and temporal lobe contributions to memory. We measured hippocampal and temporal lobe volumes and immediate/delayed memory performances in 64 TLE patients. Regression was used to dissociate hippocampal from temporal lobe contributions to memory. Results revealed reliable evidence for dominant hippocampal involvement in delayed verbal recall across three separate measures and less consistent evidence for nondominant hippocampal involvement. The findings point to a consistent relationship of dominant hippocampal volumes to delayed verbal recall but no involvement of the temporal lobe or nondominant hippocampus in memory.