Left Medial Temporal Lobe Epilepsy Research Articles

Glucose Metabolism of Hippocampal Subfields in Medial Temporal Lobe Epilepsy.

Reduced glucose metabolism in the hippocampus is commonly observed in cases of medial temporal lobe epilepsy (MTLE) with hippocampal sclerosis (HS). Glucose metabolism among the various hippocampal subfields has not been thoroughly investigated. This study examined 29 patients (18 females; 15-58 years) diagnosed with HS who underwent surgery for drug-resistant epilepsy. FreeSurfer 7.1.1 was used in the processing of MRI data and 18 F-FDG PET scans to derive volumetric data and the FDG SUVr in the whole hippocampus and hippocampal subfields, including the CA1, CA2-4, granule cell and molecular layer of the dentate gyrus (GC-ML-DG), and subiculum. Asymmetries in the volume and SUVr between the 2 sides from the subfields of the hippocampus were defined in terms of an asymmetry index. Comparisons of the asymmetry index among these regions were performed. The correlations between asymmetry index values and postoperative outcomes and presurgical neuropsychological test results were also evaluated. The CA1, CA2-4, subiculum, GC-ML-DG, and whole hippocampus presented reductions in volume and hypometabolism ipsilateral to MTLE. Asymmetries in volume and SUVr were significantly less pronounced in the CA1 and subiculum than in the CA2-4 or GC-ML-DG. Postoperative seizure outcomes were not correlated with the asymmetry index for volume or SUVr in any hippocampal subfield. In cases of left MTLE, scores of immediate logical memory and delayed logical memory were positively correlated with the asymmetry index for SUVr in the following subfields: CA1 ( R = 0.829, P = 0.021; R = 0.770, P = 0.043), CA2-4 ( R = 0.825, P = 0.022; R = 0.894, P = 0.007), subiculum ( R = 0.882, P = 0.009; R = 0.853, P = 0.015), GC-ML-DG ( R = 0.850, P = 0.015; R = 0.796, P = 0.032), and whole hippocampus ( R = 0.841, P = 0.018; R = 0.822, P = 0.023). In cases of right MTLE, the scores for delayed face memory were positively correlated with the asymmetry index for SUVr in the subiculum ( R = 0.935, P = 0.006). In cases of HS, changes in glucose metabolism levels varied among the hippocampal subfields. Asymmetries in glucose metabolism among the CA-1, CA2-4, subiculum, and GC-ML-DG subregions were correlated with scores for verbal memory among patients with left MTLE. Asymmetric glucose metabolism in the subiculum was also correlated with visual memory scores among patients with right MTLE.

Metabolic Changes in Medial Temporal Lobe Epilepsy Compared to Healthy Controls Using Advanced [18F] FDG PET SPM Analysis Techniques

Objectives: [18F] FDG PET imaging has emerged as an established modality in the evaluation of medically refractory temporal lobe epilepsy. Advanced techniques improve the sensitivity and detection of abnormalities. We sought to measure changes in metabolic activity using [18F] FDG PET in Medial Temporal Lobe Epilepsy (MTLE) patients compared to healthy controls and evaluate changes in the Seizure Onset Zone (SOZ) and remote areas. Methods: We evaluated a cohort of 14 MTLE patients. Following a standard brain [18F] FDG PET acquisition, images were co-registered to a healthy control database using the Neuro-MIM software. Z scores were generated for different temporal and extra-temporal lobe structures for significant p values <0.05. Seizure laterality was determined by experienced epileptologists (>10 years) using intracranial or surface depth electrodes. Results: The mean age of our patient cohort was 33.9 years (range: 9-52 years). We evaluated 7 left MTLE, 1 bilateral MTLE, and 6 right MTLE patients. Significant hypometabolic changes were seen in the amygdala, the hippocampus, and overall, the medial temporal lobe region (Z score of -2.2, -2.3, and -2.1 respectively). There was a smaller decrease in metabolic activity observed in the parahippocampal gyrus, fusiform gyrus, and the lateral temporal lobe (Z score of -1.4, -1.2, and -1.1 respectively). There were no significant differences in the basal ganglia, thalamus, prefrontal cortex, or cingulate gyrus. Conclusions: Measurable significant differences in FDG brain metabolic activity exist in medial temporal lobe epilepsy patients compared to healthy controls. Our study shows the most significant changes are hypometabolism in the amygdala, hippocampus, and overall, the medial temporal lobe region compared to the lateral temporal lobe.

Emotional asymmetries in refractory medial temporal and frontal lobe epilepsy: Their impact on predicting lateralization and localization of seizures

BackgroundEmotional disturbances have been reported in patients with epilepsy. Although conflicting results emanate from relevant studies, depressive symptoms are seen more often in temporal lobe epilepsy (TLE) whereas, hypomanic/manic symptoms usually accompany frontal lobe epilepsy (FLE); the above psychiatric symptoms are especially seen in refractory epilepsy. However, neocortical TLE and medial TLE are considered as distinct epileptic syndromes, and there is limited literature on comparison of affective traits in medial TLE (MTLE) and FLE. AimIn the present study, we sought to investigate affective traits among epilepsy surgery candidates suffering refractory left medial TLE (LMTLE), right medial TLE (RMTLE), left FLE (LFLE), and right FLE (RFLE). ResultsOur results revealed that patients with MTLE scored significantly higher than the ones with FLE in depression, anxiety, asthenia, and melancholia as measured by the Symptoms Rating Scale for Depression and Anxiety (SRSDA), while patients with FLE scored significantly higher in mania than those with MTLE. Moreover, patients with MTLE scored significantly higher than their FLE counterparts on the anxiety scale of the State Trait Personality Inventory (STPI)-trait version. When laterality of the seizure focus was taken into account, no differences were found among both patients with MTLE and patients with FLE, with exception for the Trail Making Test part B (TMT-B) in which patients with RMTLE performed significantly worse than patients with LMTLE. Seizure frequency was higher for FLE. ConclusionsWe provide evidence for an anterior-frontal versus a posterior-medial temporal cerebral functional asymmetry with regard to the manifestation of manic and depressive emotional traits in FLE and MTLE, respectively. Our results are mainly discussed within the frame of their contribution in localizing and to a lesser extent in lateralizing seizures foci in epilepsy surgery candidates. We suggest that this is of great importance in the context of preoperative monitoring of epilepsy surgery, especially when neuropsychologists are called upon to provide anatomical information in defining the functional deficit zone.

Different neural routes to autobiographical memory recall in healthy people and individuals with left medial temporal lobe epilepsy

Individuals with medial temporal lobe epilepsy (mTLE) are poor at recalling vivid details from autobiographical memories (AM), instead retrieving gist-like schematic memories. Recent research has suggested that this impoverished recall in comparison to controls may reflect (1) differential engagement of anterior vs posterior regions of the hippocampus (HC) and/or (2) differences between the engagement of the HC vs the ventromedial prefrontal cortex (vmPFC). Here we examined these hypotheses by comparing connectivity amongst hippocampal regions and between vmPFC and other brain regions during construction (retrieval of a particular event) vs elaboration (retrieval of perceptual detail) phases of AM recall in 12 individuals with left mTLE and 12 matched controls. Whereas functional connectivity amongst hippocampal regions changed from AM construction to elaboration in controls, the pattern of intra-hippocampal connectivity was unvarying in patients. Furthermore, patterns of connectivity from the vmPFC differed between phases in distinct ways in the two groups of participants. In patients, vmPFC activation was correlated with other prefrontal and lateral temporal cortices during construction and with visual-perceptual cortices during elaboration. While controls did not show a difference in whole-brain connectivity, they did uniquely show a dynamic shift from vmPFC connectivity to anterior HC during construction and to posterior HC during elaboration. Together, these findings suggest that impoverished AM recall in mTLE is a consequence of reduced activation and flexibility of bilateral hippocampal networks and greater reliance on neocortical contributions to memory retrieval.

Can Neuropsychological Rehabilitation Determine the Candidacy for Epilepsy Surgery? Implications for Cognitive Reserve Theorizing

Objective: The purpose of this study was to explore the effectiveness of a neuro-optimization intervention to determine the suitability for surgery in a patient suffering from left medial temporal lobe epilepsy (MTLE) and hippocampal sclerosis (HS). The rehabilitation program was aimed at amplifying cognitive resources and improving memory functioning, particularly in the non-dominant healthy hemisphere. Method: A preoperative neuro-optimization program, inspired by the functional reserve model and the right hemisphere’s verbal processing potential, was adopted. This neuro-optimization program targeted global cognitive and metacognitive enhancement with an emphasis on memory functions of the right temporal lobe, i.e., the functional upgrade of the healthy right hippocampus and related structures to assist memory after surgery. Results: After a 32 weeks neuro-optimization program, the patient once again underwent intracarotid amobarbital test (IAT). This time his right hemisphere memory functioning yielded a borderline score, allowing us to consider surgery. Immediately after surgery, the patient was seizure free and did not show any clinically significant memory impairment. At six months post-surgery he had largely preserved memory optimization gains. Conclusion: Preoperative optimization interventions aiming at enhancing cognition, in general and memory of the healthy hemisphere, in particular, may contribute to a positive memory outcome after left selective amygdalohippocampectomy.

Relationship between resting state functional magnetic resonance imaging and memory function in mesial temporal lobe epilepsy

ObjectTo study memory impairment mechanisms of the medial temporal lobe epilepsy (MTLE) by analyzing the functional connectivity (FC) through resting state functional magnetic resonance imaging (rs-fMRI). MethodsRs-fMRI data were acquired from 13 patients with left MTLE and 11 patients with right MTLE. Another 13 healthy volunteers were selected as controls. The altered FC pattern between the unilateral hippocampus and other regions of the brain in MTLE patients was compared to that of the normal control group. Then the correlation between the strength of FC and the clinical memory scale scores in patients with MTLE was determined. ResultsThe scores of the following check points of MTLE patients including point to memory, recognition of nonsense figure, associative learning, the image free recall, portrait characteristic recall and memory quotient were significantly lower than those in the normal group (all P<0.05). The scores of point to memory and recognition of nonsense figure were different between R-MTLE and L-MTLE patients. Different correlations between the strength of FC and the clinical memory scale scores were detected between R-MTLE and L-MTLE patients. ConclusionsThe memory function of patients with MTLE was impaired. Patients with L-MTLE showed lower score on pure verbal memory test and those with R-MTLE showed weaker performance on pure visual memory test. Patients with MTLE showed extensive abnormal FC between hippocampus and particular encephalic regions.

Can emotional stress trigger the onset of epilepsy?

The aim of this study was to investigate the potential role of an acute adverse stress as "trigger" for the onset of epilepsy. Among 4618 consecutive patients, twenty-two reported a major life event within three months before the onset of epilepsy. All patients had focal epilepsy except one with idiopathic generalized epilepsy. The temporal lobe was involved in 90% of patients with focal epilepsy. More precisely, 13 patients (62% of patients with focal epilepsy) had medial temporal lobe epilepsy (MTLE), two had lateral temporal lobe epilepsy, four had temporoparietooccipital junction epilepsy, and two patients had central lobe epilepsy. The mean age and the median age at onset of epilepsy for patients with MTLE were both 38 years (range: 9.5-65 years). Ten patients had right and three had left MTLE. Among patients with focal epilepsy, MRI was abnormal in 7 (33%) with hippocampal sclerosis in four, periventricular nodular heterotopia in two, and complex cortical dysgenesis in one. The mean age at onset of epilepsy for patients with brain lesions was 26 years (range: 9.5-49). Twelve patients (54%) reported a death as a triggering factor for the onset of their epilepsy. Seven patients (32%) reported that a relationship of trust had been broken. Three patients (14%) had been subjects of violence. No patient reported sexual abuse as a triggering factor. This study provides evidence that some patients (5/1000 patients) began their seizures in the wake of significant life events. The average age at onset of epilepsy is quite late, around age 30, even in the presence of brain lesions. These patients are emotionally and affectively more prone to have consequences of a stressful life event. The recognition and management of such situations may bring significant relief with improvement of the control of epilepsy.

The effect of medial temporal lobe epilepsy on visual memory encoding

Effective visual memory encoding, a function important for everyday functioning, relies on episodic and semantic memory processes. In patients with medial temporal lobe epilepsy (MTLE), memory deficits are common as the structures typically involved in seizure generation are also involved in acquisition, maintenance, and retrieval of episodic memories. In this study, we used group independent component analysis (GICA) combined with Granger causality analysis to investigate the neuronal networks involved in visual memory encoding during a complex fMRI scene-encoding task in patients with left MTLE (LMTLE; N=28) and in patients with right MTLE (RMTLE; N=18). Additionally, we built models of memory encoding in LMTLE and RMTLE and compared them with a model of healthy memory encoding (Nenert et al., 2014). For those with LMTLE, we identified and retained for further analyses and model generation 7 ICA task-related components that were attributed to four different networks: the frontal and posterior components of the DMN, visual network, auditory-insular network, and an “other” network. For those with RMTLE, ICA produced 9 task-related components that were attributed to the somatosensory and cerebellar networks in addition to the same networks as in patients with LMTLE. Granger causality analysis revealed group differences in causality relations within the visual memory network and MTLE-related deviations from normal network function. Our results demonstrate differences in the networks for visual memory encoding between those with LMTLE and those with RMTLE. Consistent with previous studies, the organization of memory encoding is dependent on laterality of seizure focus and may be mediated by functional reorganization in chronic epilepsy. These differences may underlie the observed differences in memory abilities between patients with LMTLE and patients with RMTLE and highlight the modulating effects of epilepsy on the network for memory encoding.

Hyperactivation of parahippocampal region and fusiform gyrus associated with successful encoding in medial temporal lobe epilepsy

Performance in recognition memory differs among patients with medial temporal lobe epilepsy (MTLE). We aimed to determine if distinct recognition performances (normal vs. impaired) could be related to distinct patterns of brain activation during encoding. Event-related functional magnetic resonance imaging (fMRI) activation profiles were obtained during successful encoding of non-material-specific items, in 14 MTLE patients tested for recognition of stimuli afterward. Findings were compared to those of 25 healthy subjects, and voxel-based correlations were assessed between brain activation and performance. Patients with left and right MTLE showed similar activations and similar performances. As a whole, the group of patients demonstrated altered recognition scores, but three of the seven patients with left MTLE and three of the seven patients with right MTLE exhibited normal performance relative to controls. In comparison to healthy subjects and patients with impaired recognition, patients with normal recognition showed weaker activations in left opercular cortex, but stronger activations in bilateral parahippocampal region/fusiform gyrus (PH/FG). By contrast, patients with impaired performance showed weaker activations in bilateral PH/FG, but stronger activations in a frontal/cingulate and parietal network. Recognition performance was correlated positively to bilateral PH/FG activations, and negatively correlated to bilateral frontal/cingulate activations, in the whole group of patients, as well as in subgroups of patients with either left or right MTLE. These results suggest occurrence of effective functional compensation within bilateral PH/FG in MTLE, allowing patients to maintain recognition capability. In contrast, impairment of this perceptive-memory system may lead to alternative activation of an inefficient nonspecific attentional network in patients with altered performance.

Hippocampal atrophy in temporal lobe epilepsy: the ‘generator’ and ‘receiver’

Some patients with unilateral medial temporal lobe epilepsy (MTLE) display bilateral hippocampal atrophy on MRI, even though seizures originate in only one hippocampus. The correct identification of the epileptogenic hippocampus (the 'generator') vs the non-epileptogenic (the 'receiver') may lead to better surgical planning and results. We studied 14 patients with MTLE (eight left and six right) who became seizure free after unilateral hippocampal resection, with hippocampal sclerosis confirmed by histology. Hippocampal tridimensional morphometry was performed comparing patients and healthy controls employing a voxel-wise Wilcoxon test. Results were corrected for multiple comparisons with the application of a False Discovery Rate (FDR)-corrected threshold for q < 0.05. Patients with MTLE showed atrophy involving the ipsilateral hippocampus and the contralateral hippocampus, more pronouncedly within the ipsilateral hippocampus in the anterior-inferior aspect of the hippocampal head (left MTLE, left hippocampus x = -28, y = -16, z = -24, Z = 3.6; right MTLE, right hippocampus x = 22, y = -11, z = -27, Z = 2.9). On the contralateral hippocampus, the atrophy was more noticeable in the posterior head and body areas. The epileptogenic hippocampal atrophy has an anatomically distinct pattern compared with the contralateral hippocampus. This information may help guide the presurgical assessment of MTLE.

A functional MRI study of language networks in left medial temporal lobe epilepsy

Purpose The purpose of this study was to investigate the abnormality of language networks in left medial temporal lobe epilepsy (MTLE) using fMRI. Materials and methods Eight patients with left MTLE and 15 healthy subjects were evaluated. An auditory semantic judgment (AJ) paradigm was used. The fMRI data were collected on a 3T MR system and analyzed by AFNI (analysis of functional neuroimages) to generate the activation map. Results Behavioral data showed that the reaction time of the left MTLE patients was significantly longer than that of controls on the AJ task ( t = −3.396, P < 0.05). The left MTLE patients also exhibited diffusively decreased activation in the AJ task. Right hemisphere dominance of Broca's and Wernicke's areas was demonstrated in left MTLE patients. Conclusions Long-term activation of spikes in left MTLE patients results in language impairment, which is associated with an abnormality of the brain neural network.

Hippocampal removal affects visual but not auditory naming.

Dominant, left anteromedial temporal lobe resection (AMTLR) for seizure control carries risks to verbal episodic memory and visual object naming. Consistent with traditional thinking, verbal memory decline is considered a consequence of hippocampal removal and naming decline has been attributed to lateral temporal resection. Interestingly, recent findings suggest a potential relation between visual naming and hippocampal integrity, which is consistent with studies that link the hippocampus with higher level visual processing. Historically, naming has been evaluated using visual object naming tasks; however, naming can also be assessed using auditory verbal descriptions. Recent cortical stimulation studies have shown a neuroanatomic distinction between visual naming and auditory description naming. We speculated that unlike visual naming, the hippocampus is not involved in auditory naming, and hypothesized that left AMTLR would not result in auditory naming decline, despite visual naming and verbal memory decline. In this cohort study, we tested auditory naming, visual naming, and verbal memory in 25 left medial temporal lobe epilepsy (MTLE) and 20 right MTLE patients pre-AMTLR and 1 year post-AMTLR. Left AMTLR patients declined in visual naming and verbal memory, with no decline in auditory naming. Right AMTLR patients exhibited no decline. Results suggest that left anteromedial temporal lobe resection presents a greater risk to visual naming than auditory naming in patients with left medial temporal lobe epilepsy.

Facial emotion recognition impairment in chronic temporal lobe epilepsy

To evaluate facial emotion recognition (FER) in a cohort of 176 patients with chronic temporal lobe epilepsy (TLE). FER was tested by matching facial expressions with the verbal labels for the following basic emotions: happiness, sadness, fear, disgust, and anger. Emotion recognition performances were analyzed in medial (n = 140) and lateral (n = 36) TLE groups. Fifty healthy subjects served as controls. The clinical and neuroradiologic variables potentially affecting the ability to recognize facial expressions were taken into account. The medial TLE (MTLE) group showed impaired FER (86% correct recognition) compared to both the lateral TLE patients (FER = 93.5%) and the controls (FER = 96.4%), with 42% of MTLE patients recording rates of FER that were lower [by at least 2 standard deviations (SDs)] than the control mean. The MTLE group was impaired compared to the healthy controls in the recognition of all basic facial expressions except happiness. The patients with bilateral MTLE were the most severely impaired, followed by the right and then the left MTLE patients. FER was not affected by type of lesion, number of antiepileptic drugs (AEDs), aura semiology, or gender. Conversely, the early onset of seizures/epilepsy was related to FER deficits. These deficits were already established in young adulthood, with no evidence of progression in older MTLE patients. These results on a large cohort of TLE patients demonstrate that emotion recognition deficits are common in MTLE patients and widespread across negative emotions. We confirm that early onset seizures with right or bilateral medial temporal dysfunction lead to severe deficits in recognizing facial expressions of emotions.

Decreased basal fMRI functional connectivity in epileptogenic networks and contralateral compensatory mechanisms

A better understanding of interstructure relationship sustaining drug-resistant epileptogenic networks is crucial for surgical perspective and to better understand the consequences of epileptic processes on cognitive functions. We used resting-state fMRI to study basal functional connectivity within temporal lobes in medial temporal lobe epilepsy (MTLE) during interictal period. Two hundred consecutive single-shot GE-EPI acquisitions were acquired in 37 right-handed subjects (26 controls, eight patients presenting with left and three patients with right MTLE). For each hemisphere, normalized correlation coefficients were computed between pairs of time-course signals extracted from five regions involved in MTLE epileptogenic networks (Brodmann area 38, amygdala, entorhinal cortex (EC), anterior hippocampus (AntHip), and posterior hippocampus (PostHip)). In controls, an asymmetry was present with a global higher connectivity in the left temporal lobe. Relative to controls, the left MTLE group showed disruption of the left EC-AntHip link, and a trend of decreased connectivity of the left AntHip-PostHip link. In contrast, a trend of increased connectivity of the right AntHip-PostHip link was observed and was positively correlated to memory performance. At the individual level, seven out of the eight left MTLE patients showed decreased or disrupted functional connectivity. In this group, four patients with left TLE showed increased basal functional connectivity restricted to the right temporal lobe spared by seizures onset. A reverse pattern was observed at the individual level for patients with right TLE. This is the first demonstration of decreased basal functional connectivity within epileptogenic networks with concomitant contralateral increased connectivity possibly reflecting compensatory mechanisms.

Sensory gating in the human hippocampal and rhinal regions: Regional differences

To further explore the roles of medial temporal structures in mediating sensory gating of incoming irrelevant or redundant auditory input, twenty-seven patients with intractable epilepsy with depth electrodes implanted in the medial temporal lobe for presurgery evaluation underwent evoked response recording to auditory paired-stimuli (S1-S2). Seventeen subjects were diagnosed with left medial temporal lobe epilepsy (MTLE) and 10 with right MTLE. Only data from the nonlesion side were included. Twenty-three records from rhinal and anterior hippocampal regions, and 21 from posterior hippocampal regions were included in the analysis. The rhinal region had two prominent components (a negativity peaking around 200 ms followed by a positivity peaking around 400 ms). Both the anterior and posterior hippocampal regions exhibited a dominant negative potential peaking around 400 ms. These components were all composed predominantly of slower frequencies. In contrast, a negativity in the posterior hippocampus at around 100 ms was composed of slow and fast frequencies. All components but the early rhinal negativity were attenuated by stimulus repetition. This is the first report documenting that different regions of the medial temporal area are differentially involved in the processing of auditory input, most likely reflecting separate steps of processing. The data support the need for further exploration of the contribution of these regions to sensory gating. This information helps to increase our understanding of this basic but important and complex function.

Whole-brain voxel-based morphometry of white matter in medial temporal lobe epilepsy

Purpose The purpose of this study was to analyze whole-brain white matter changes in medial temporal lobe epilepsy (MTLE). Materials and methods We studied 23 patients with MTLE and 13 age- and sex-matched healthy control subjects using voxel-based morphometry (VBM) on T1-weighted 3D datasets. The seizure focus was right sided in 11 patients and left sided in 12. The data were collected on a 1.5 T MR system and analyzed by SPM 99 to generate white matter density maps. Results Voxel-based morphometry revealed diffusively reduced white matter in MTLE prominently including bilateral frontal lobes, bilateral temporal lobes and corpus callosum. White matter reduction was also found in the bilateral cerebellar hemispheres in the left MTLE group. Conclusion VBM is a simple and automated approach that is able to identify diffuse whole-brain white matter reduction in MTLE.

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.

Asymmetrical extra-hippocampal grey matter loss related to hippocampal atrophy in patients with medial temporal lobe epilepsy

Background: Structural neuroimaging studies have consistently shown a pattern of extra-hippocampal atrophy in patients with left and right drug-refractory medial temporal lobe epilepsy (MTLE). However, it is not yet completely...

Memory performance during the intracarotid amobarbital procedure and neuropsychological assessment in medial temporal lobe epilepsy: The limits of material specificity

We investigated the relationship between material-specific memory performance elicited during the Wada test, or intracarotid amobarbital procedure (IAP), and classic neuropsychological assessment in 89 surgical candidates with refractory medial temporal lobe epilepsy (MTLE). The neuropsychological battery included measures of simple and complex verbal and visual memory, whereas the IAP material consisted of verbal and dually encodable stimuli. Neuropsychological testing revealed that reduced verbal memory performance was associated with left-sided MTLE, whereas visual memory tasks revealed no differences between patients with left-sided and right-sided MTLE. During IAP, memory performance was worse with the ipsilesional hemisphere, regardless of lesion side. Most importantly, performance on verbal memory tests was significantly, but moderately, correlated with left hemispheric IAP performance, indicating that memory tasks using verbal material are a valid marker of left hemispheric integrity in left language-dominant MTLE patients and significantly predict left hemispheric memory performance during IAP. In contrast, performance on classic visual memory tests is unrelated to right hemispheric IAP performance, suggesting that the currently used visual memory stimuli do not reflect right hemispheric sensitivity.

Sensory gating in the human hippocampal and rhinal regions

Objective: The objective of this work was to ascertain if sensory gating can be demonstrated within the human medial temporal lobe Methods: Eight patients with intractable epilepsy with depth electrodes implanted in the medial temporal lobe for presurgery evaluation underwent evoked response recording to auditory paired-stimuli (S1–S2). Each of the eight subjects had a diagnosis of left medial temporal lobe epilepsy (MTLE) Results: Data from the non-focal right hippocampi revealed a large negative response on S1 (starting at about 190 ms and lasting for approximately 300 ms from stimulus onset). Rhinal region recordings revealed a positive response (starting at about 240 ms with a rapid incline, followed by a long-lasting decline). A significant attenuation of both responses to S2 stimuli was observed. Conclusions: Data are suggestive of an involvement of the human medial temporal lobe in the processing of simple auditory information which occurs in a time frame later than the neocortical auditory evoked components. The exact role of these anatomical structures in the sensory gating process remains to be defined. Significance: This study provides the first evidence of an activation of the rhinal cortex after simple auditory stimulation and provides new evidence that the activation of the medial temporal lobe structures occurs at a later stage than that of the neocortex.