Long-term forgetting in temporal lobe epilepsy: Is this phenomenon a norm?

ObjectivesThis research investigated forgetting rates of patients with temporal lobe epilepsy (TLE) at brief and longer intervals.MethodsThe sample is formed by 5 patients with TLE and 10 healthy individuals. One of the patients received the diagnosis of transient epileptic amnesia (TEA). All patients underwent a standardized clinical protocol for diagnosis including a comprehensive neuropsychological assessment. In addition, two experimental tasks were used to assess the forgetting rates at 4 intervals (30 s, 10 min, 1 day, and 1 week): a story task to evaluate verbal cued recall and a route task to assess visuospatial cued recall.ResultsThere were no significant differences between groups in forgetting rates.ConclusionsThese findings suggest that forgetting patterns in patients with TLE may be heterogeneous, and the presence of accelerated long-term forgetting is not universal.     

Impact of hippocampal subfield histopathology in episodic memory impairment in mesial temporal lobe epilepsy and hippocampal sclerosis

ObjectiveThe objective of the study was to analyze preoperative visual and verbal episodic memories in a homogeneous series of patients with mesial temporal lobe epilepsy (MTLE) and unilateral hippocampal sclerosis (HS) submitted to corticoamygdalohippocampectomy and its association with neuronal cell density of each hippocampal subfield.MethodsThe hippocampi of 72 right-handed patients were collected and prepared for histopathological examination. Hippocampal sclerosis patterns were determined, and neuronal cell density was calculated. Preoperatively, two verbal and two visual memory tests (immediate and delayed recalls) were applied, and patients were divided into two groups, left and right MTLE (36/36).ResultsThere were no statistical differences between groups regarding demographic and clinical data. Cornu Ammonis 4 (CA4) neuronal density was significantly lower in the right hippocampus compared with the left (p = 0.048). The groups with HS presented different memory performance — the right HS were worse in visual memory test [Complex Rey Figure, immediate (p = 0.001) and delayed (p = 0.009)], but better in one verbal task [RAVLT delayed (p = 0.005)]. Multiple regression analysis suggested that the verbal memory performance of the group with left HS was explained by CA1 neuronal density since both tasks were significantly influenced by CA1 [Logical Memory immediate recall (p = 0.050) and Logical Memory and RAVLT delayed recalls (p = 0.004 and p = 0.001, respectively)]. For patients with right HS, both CA1 subfield integrity (p = 0.006) and epilepsy duration (p = 0.012) explained Complex Rey Figure immediate recall performance. Ultimately, epilepsy duration also explained the performance in the Complex Rey Figure delayed recall (p < 0.001).SignificanceCornu Ammonis 1 (CA1) hippocampal subfield was related to immediate and delayed recalls of verbal memory tests in left HS, while CA1 and epilepsy duration were associated with visual memory performance in patients with right HS.     

Functional substrate for memory function differences between patients with left and right mesial temporal lobe epilepsy associated with hippocampal sclerosis

ObjectiveLittle is known about the functional substrate for memory function differences in patients with left or right mesial temporal lobe epilepsy (mTLE) associated with hippocampal sclerosis (HS) from an electrophysiological perspective. To characterize these differences, we hypothesized that hippocampal theta connectivity in the resting-state might be different between patients with left and right mTLE with HS and be correlated with memory performance.MethodsResting-state hippocampal theta connectivity, identified via whole-brain magnetoencephalography, was evaluated. Connectivity and memory function in 41 patients with mTLE with HS (left mTLE = 22; right mTLE = 19) were compared with those in 46 age-matched healthy controls and 28 patients with focal cortical dysplasia (FCD) but without HS.ResultsConnectivity between the right hippocampus and the left middle frontal gyrus was significantly stronger in patients with right mTLE than in patients with left mTLE. Moreover, this connectivity was positively correlated with delayed verbal recall and recognition scores in patients with mTLE. Patients with left mTLE had greater delayed recall impairment than patients with right mTLE and FCD. Similarly, delayed recognition performance was worse in patients with left mTLE than in patients with right mTLE and FCD. No significant differences in memory function between patients with right mTLE and FCD were detected. Patients with right mTLE showed significantly stronger hippocampal theta connectivity between the right hippocampus and left middle frontal gyrus than patients with FCD and left mTLE.ConclusionOur results suggest that right hippocampal–left middle frontal theta connectivity could be a functional substrate that can account for differences in memory function between patients with left and right mTLE. This functional substrate might be related to different compensatory mechanisms against the structural hippocampal lesions in left and right mTLE groups. Given the positive correlation between connectivity and delayed verbal memory function, hemispheric-specific hippocampal–frontal theta connectivity assessment could be useful as an electrophysiological indicator of delayed verbal memory function in patients with mTLE with HS.     

Interictal epileptic discharge correlates with global and frontal cognitive dysfunction in temporal lobe epilepsy

ObjectiveTemporal lobe epilepsy (TLE) with hippocampal sclerosis has widespread effects on structural and functional connectivity and often entails cognitive dysfunction. EEG is mandatory to disentangle interactions in epileptic and physiological networks which underlie these cognitive comorbidities. Here, we examined how interictal epileptic discharges (IEDs) affect cognitive performance.MethodsThirty-four patients (right TLE = 17, left TLE = 17) were examined with 24-hour video-EEG and a battery of neuropsychological tests to measure intelligence quotient and separate frontal and temporal lobe functions. Hippocampal segmentation of high-resolution T1-weighted imaging was performed with FreeSurfer. Partial correlations were used to compare the number and distribution of clinical interictal spikes and sharp waves with data from imagery and psychological tests.ResultsThe number of IEDs was negatively correlated with executive functions, including verbal fluency and intelligence quotient (IQ). Interictal epileptic discharge affected cognitive function in patients with left and right TLE differentially, with verbal fluency strongly related to temporofrontal spiking. In contrast, IEDs had no clear effects on memory functions after corrections with partial correlations for age, age at disease onset, disease duration, and hippocampal volume.ConclusionIn patients with TLE of long duration, IED occurrence was strongly related to cognitive deficits, most pronounced for frontal lobe function. These data suggest that IEDs reflect dysfunctional brain circuitry and may serve as an independent biomarker for cognitive comorbidity.     

Accelerated long-term forgetting in temporal lobe epilepsy: Verbal,nonverbal and autobiographical memory

Patients with temporal lobe epilepsy (TLE) often present with memory complaints despite performing within normal limits on standard memory tests. One possible explanation for this phenomenon is accelerated long-term forgetting (ALF). The present study investigated material‐specific ALF in patients with unilateral TLE and also examined whether ALF could be demonstrated on a novel, standardized anterograde autobiographical memory (ABM) task. Fourteen patients with TLE and 17 controls were administered verbal, nonverbal and ABM event memory tasks. The participants were tested for immediate recall, recall and recognition at 30‐minute delay, and recall and recognition after four weeks. The extent of ALF was calculated based on the percentage decay of memory from the 30‐minute delay trial to the four-week delay trial. Patients with left TLE showed significantly greater ALF for verbal material and a trend towards greater forgetting of ABM. Patients with right TLE showed a non-significant trend towards greater ALF for nonverbal material. Patients with unilateral hippocampal abnormalities showed greater ALF compared to patients without hippocampal abnormalities. Patients with seizures that generalize had more global memory deficits and greater ALF. We conclude that patients with unilateral TLE show material‐specific ALF, which appears to be more pronounced with an abnormal hippocampus or seizures that secondarily generalize.     

Impaired sleep-related consolidation of declarative memories in idiopathic focal epilepsies of childhood

ObjectiveDeclarative memory is consolidated during sleep in healthy children. We tested the hypothesis that consolidation processes are impaired in idiopathic focal epilepsies (IFE) of childhood in association with frequent interictal epileptiform discharges (IEDs) during sleep.MethodsA verbal (word-pair association) and a nonverbal (2D object location) declarative memory task were administrated to 15 children with IFEs and 8 control children 6–12 years of age. Patients had either centrotemporal (11 patients) or occipital (4 patients) IEDs. All but 3 patients had a history of unprovoked seizures, and 6 of them were treated with valproate (VPA). The learning procedure (location of object pairs presented on a grid; association of word pairs) was executed in the evening. Retrieval was tested immediately after learning and on the next morning after a night of sleep. Participants were tested twice, once in natural home conditions and one month later in the unfamiliar conditions of the sleep unit under EEG monitoring.ResultsOvernight recall performance was lower in children with IFE than in control children on both tasks (ps < 0.05). Performance in home conditions was similar to that in hospital conditions. Higher spike–wave index (SWI) during nonrapid eye movement (NREM) sleep was associated with poorer performance in the nonverbal task (p < 0.05). Valproate treatment was not associated with overnight recall performance for both tasks (ps > 0.05).ConclusionMemory consolidation is impaired in IFE of childhood. The association between higher SWI during NREM sleep and poorer nonverbal declarative memory consolidation supports the hypothesis that interictal epileptic activity could disrupt sleep memory consolidation.     

Neural correlates of verbal semantic memory in patients with temporal lobe epilepsy

Functional imaging data suggest that the core network engaged in verbal semantic memory (SM) processing encompasses frontal and temporal lobe structures, with a strong left lateralization in normal right handers. The impact of long term temporal lobe epilepsy (TLE) on this network has only partly been elucidated. We studied verbal SM in 50 patients with chronic, intractable TLE (left TLE = 26, right TLE = 24) and 35 right handed normal controls using a verbal fMRI semantic decision paradigm. All patients had language lateralized to the left hemisphere, as verified by the intracarotid amobarbital procedure. Within and between group analyses showed remarkable, group-specific activation profiles. The control group activated frontal and temporal areas bilaterally, with a strong left predominance. Left TLE patients showed a shift of activations of left frontal and medial temporal areas to homologous regions in the right hemisphere. Furthermore, left TLE subjects utilized subcortical structures such as the thalamus and putamen to accomplish the verbal SM task. Contrastively, the activation pattern of right TLE patients resembled that of normal controls, but exhibited ‘hypofrontality’ with a shift from frontal to posterior regions in the temporal, parietal and occipital lobe. Our results show that chronic epileptic activity originating from temporal seizure foci is associated with an alteration of neural circuits which support semantic language processing and that side of seizure focus has a specific impact on the resulting activation network. These findings presumably result from morphological changes and from functional reorganization which are both inherent to chronic TLE.     

Le Test des cinq mots dans les formes légères de maladie d’Alzheimer : comparaison du score total,du Score Total Pondéré, du Score d’apprentissage et du Score de mémoire dans trois classes d’âge (60 ans, 70 ans, 80 ans)

IntroductionThe five-word test (5WT) is a serial verbal memory test with semantic cuing. It is proposed to rapidly evaluate memory of aging people and has previously shown its sensitivity and its specificity in identifying patients with AD. It measures the efficacy of free and cued recalls during a procedure of immediate and delayed recalls.MethodsThe 5WT was compared in a group of 202 normal subjects and a group of 302 mild AD patients (MMS of 20 or more) aged from 60 to 92 years, in three age classes (60 years, 70 years, 80 years). Nine scores were measured (Total Score, Total Weighted Score, Free Immediate Recall, Learning Score = total of Immediate Recalls, Free Delayed Recall, Memory Score = total of Delayed Recalls, Forgetting Rate, Percentage of Immediate Cuing, Percentage of Delayed Cuing) as well as the presence of intrusions. For each age class, Receiver Operating Characteristic curves determined the most significant cut-off scores.ResultsFor each score of the 5WT, AD patients differed significantly from controls. The cut-off scores were not the same according to age. For the Total Score, the cut-off scores were 10 (60 years), 9 (70 years) and 8 (80 years), whereas the cut-off scores of the Total Weighted Score were 17 (60 years), 16 (70 years) and 14 (80 years). As suggested by Cowppli-Bony et al. (2005), the Total Weighted Score (which gives a higher coefficient to free recalls) was better than the Total Score for discriminating mild AD. The 5WT is useful to discriminate normal controls and mild AD patients. Normal aged subjects displayed good encoding, efficient stocking and consolidation (few forgetting, efficient cued recall), intrusions were rare. Mild AD patients were characterized by weak encoding of words and severe deficit for stocking and consolidation (important forgetting, impaired cued recall), they made numerous intrusions. This psychometric profile is characteristic of the amnestic hippocampal syndrome found in AD.ConclusionThe 5WT is a simple and reliable test for investigating memory in elderly people above 60 years old. According to age, different cut-offs are needed for the Total Score and the Total Weighted Score, the latter appearing more discriminating than the Total Score for the diagnosis of mild AD. It is also interesting to evaluate the presence of intrusions. Lastly, it is important to consider the forgetting rate (between Learning and Memory Scores) in order to confirm the presence of a hippocampal amnesia.     

Executive functions in individuals with intellectual disability

The aim of the present study was to investigate executive functions in adults with intellectual disability, and compare them to a closely matched control group longitudinally for 5 years. In the Betula database, a group of adults with intellectual disability (ID, n = 46) was defined from measures of verbal and non-verbal IQ. A control group, with two people for every person with intellectual disability (n = 92), was chosen by matching on the following criterion in order of priority: IQ higher than 85, age, sex, sample, level of education, and years of education. Three types of tasks of executive functions were included on two occasions, with 5 years between testing sessions: The Tower of Hanoi, executively loaded dual task versions of word recall, and verbal fluency. Adults with ID showed significant impairments on verbal fluency and on the executively loaded dual task word recall task (at encoding but not at recall). There were no group differences on the Tower of Hanoi. No significant differences between the two test occasions were found. The results are interpreted in terms of individuals with ID having problems with speed of accessing lexical items and difficulties with working memory-related executive control at encoding, which includes shifting between tasks. There are, however, not necessarily problems with inhibition. The dual task results additionally imply that the adults with intellectual disability were more sensitive to strategy interruptions at encoding, but that dividing attention at recall did not have such detrimental effects.     

Distribution of regional gray matter abnormalities in a pediatric population with temporal lobe epilepsy and correlation with neuropsychological performance

ObjectiveThe goals of the work described here were to determine if hippocampal and extrahippocampal atrophy in children with temporal lobe epilepsy (TLE) follows a pattern similar to that in adult patients, and to assess the clinical and neuropsychological relevance of regional brain atrophy in pediatric TLE.MethodsChildren with symptomatic TLE (n = 14: 9 with mesial TLE due to hippocampal atrophy and 5 with TLE due to neocortical lesions), healthy children (n = 14), and 9 adults with mesial temporal lobe epilepsy (MTLE) were compared using voxel-based morphometry (VBM) of brain magnetic resonance imaging (MRI). The children underwent a comprehensive neuropsychological battery.ResultsChildren with MTLE with unilateral hippocampal atrophy (n = 9) exhibited a significant reduction in gray matter in the hippocampus ipsilateral to the seizure origin and significant atrophy in the ipsilateral cingulate gyrus and contralateral middle frontal lobe. Children with TLE (n = 14) exhibited a significant reduction in the gray matter of the ipsilateral hippocampus and parahippocampal gyrus. There was a correlation between gray matter volume in children with TLE and scores on several neuropsychological tests. Atrophy in pediatric patients with MTLE was less extensive than that in adults, and involved the hippocampi and the frontal cortex.ConclusionsSimilar to adult MTLE, pediatric MTLE is associated with hippocampal and extrahippocampal cell loss. However, children display less intense quantifiable gray matter atrophy, which affects predominantly frontal lobe areas. There was a significant association between volume of gray matter in medial temporal and frontal regions and scores on neuropsychological tests. In childhood, TLE and the concomitant cognitive/behavior disturbances are the result of a damaged neural network.     

Interictal serum brain-derived neurotrophic factor level reflects white matter integrity,epilepsy severity,and cognitive dysfunction in chronic temporal lobe epilepsy

ObjectiveMost patients with temporal lobe epilepsy (TLE) have epileptic foci originating from the medial temporal lobe, particularly the hippocampus. Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin growth factor mainly expressed in the hippocampus, though it is not known whether the circulating level of BDNF reflects cognitive performance or white matter structural changes in chronic TLE.MethodsThirty-four patients with TLE and 22 healthy controls were enrolled for standardized cognitive tests, diffusion tensor imaging, and serum BDNF measurement. The patients were further divided into a subgroup with unilateral TLE (n = 23) and a subgroup with bilateral TLE (n = 11) for clinical and neuroimaging comparisons.ResultsThere were significantly lower BDNF levels in the patients with TLE compared with the controls, with significance contributed mainly from the subgroup with bilateral TLE, which also had more frequent seizures. The BDNF levels correlated with epilepsy duration (σ = − 0.355; p = 0.040) and fractional anisotropy (FA) in the left temporal lobe, left thalamus, and right hippocampus. Using a regression model, BDNF level predicted verbal memory score. Further, design fluency scores were predicted by serum BDNF level via the interactions with left temporal FA.ConclusionsSerum BDNF levels reflected longer epilepsy duration, impaired white matter integrity, and poor cognitive function in patients with chronic TLE.     

Strategic verbal rehearsal in adolescents with mild intellectual disabilities: A multi-centre European study

BackgroundThere is a long-held view that verbal short-term memory problems of individuals with intellectual disabilities (ID) might be due to a deficit in verbal rehearsal. However, the evidence is inconclusive and word length effects as indicator of rehearsal have been criticised.Aim & methodThe aim of this multi-site European study was to investigate verbal rehearsal in adolescents with mild ID (n = 90) and a comparison group of typically developing children matched individually for mental age (MA, n = 90). The investigation involved: (1) a word length experiment with non-verbal recall using pointing and (2) ‘self-paced’ inspection times to infer whether verbal strategies were utilised when memorising a set of pictorial items.ResultsThe word length effect on recall did not interact with group, suggesting that adolescents with ID and MA comparisons used similar verbal strategies, possibly phonological recoding of picture names. The inspection time data suggested that high span individuals in both groups used verbal labelling or single item rehearsal on more demanding lists, as long named items had longer inspection times.ConclusionsThe findings suggest that verbal strategy use is not specifically impaired in adolescents with mild ID and is mental age appropriate, supporting a developmental perspective.     

List-learning and verbal memory profiles in childhood epilepsy syndromes

Findings of material-specific influences on memory performance in pediatric epilepsy are inconsistent and merit further investigation. This study compared 90 children (aged 6 years to 16 years) with childhood absence epilepsy (CAE), frontal lobe epilepsy (FLE), and temporal lobe epilepsy (TLE) to determine whether they displayed distinct list-learning and verbal memory profiles on the California Verbal Learning Test — Children's Version (CVLT-C). Group comparison identified greater risk of memory impairment in children with TLE and FLE syndromes but not for those with CAE. While children with TLE performed worst overall on Short Delay Free Recall, groups with TLE and FLE performed similarly on Long Delay Free Recall. Contrast indices were then employed to explore these differences. Children with TLE demonstrated a significantly greater retroactive interference (RI) effect compared with groups with FLE and CAE. Conversely, children with FLE demonstrated a significantly worse learning efficiency index (LEI), which compares verbal memory following repetition with initial recall of the same list, than both children with TLE and CAE. These findings indicated shallow encoding related to attentional control for children with FLE and retrieval deficits in children with TLE. Finally, our combined sample showed significantly higher rates of extreme contrast indices (i.e., 1.5 SD difference) compared with the CVLT-C standardization sample. These results underscore the high prevalence of memory dysfunction in pediatric epilepsy and offer support for distinct patterns of verbal memory performance based on childhood epilepsy syndrome.     

Right hippocampal impairment in the recall of spatial location: encoding deficit or rapid forgetting?

The recall of spatial location in patients with left or right temporal-lobe lesions was studied in two experiments, in which recall was tested either immediately after presentation of an array of objects, or after an intervening verbal task, a spatial task or an unfilled interval. Deficits were found only in patients with right temporal-lobe lesions that included extensive removal of the hippocampal region, and only when recall was tested after a delay. The presence of an intervening task in the delay interval did not accentuate the deficit. The results show that, despite a normal ability to encode location, patients with large right hippocampal lesions demonstrate an abnormally rapid forgetting of such information.     

Clinical utility of the Wechsler Memory Scale — Fourth Edition (WMS-IV) in patients with intractable temporal lobe epilepsy

IntroductionThe Wechsler Memory Scale (WMS) is one of the most widely used test batteries to assess memory functions in patients with brain dysfunctions of different etiologies. This study examined the clinical validation of the Dutch Wechsler Memory Scale — Fourth Edition (WMS-IV-NL) in patients with temporal lobe epilepsy (TLE).MethodThe sample consisted of 75 patients with intractable TLE, who were eligible for epilepsy surgery, and 77 demographically matched healthy controls. All participants were examined with the WMS-IV-NL.ResultsPatients with TLE performed significantly worse than healthy controls on all WMS-IV-NL indices and subtests (p < .01), with the exception of the Visual Working Memory Index including its contributing subtests, as well as the subtests Logical Memory I, Verbal Paired Associates I, and Designs II. In addition, patients with mesiotemporal abnormalities performed significantly worse than patients with lateral temporal abnormalities on the subtests Logical Memory I and Designs II and all the indices (p < .05), with the exception of the Auditory Memory Index and Visual Working Memory Index. Patients with either a left or a right temporal focus performed equally on all WMS-IV-NL indices and subtests (F(15, 50) = .70, p = .78), as well as the Auditory–Visual discrepancy score (t(64) = − 1.40, p = .17).ConclusionThe WMS-IV-NL is capable of detecting memory problems in patients with TLE, indicating that it is a sufficiently valid memory battery. Furthermore, the findings support previous research showing that the WMS-IV has limited value in identifying material-specific memory deficits in presurgical patients with TLE.     

Disruption of learning and long-term retention of prose passages in patients with focal epilepsy

Recent investigations of accelerated long-term forgetting, a condition in which newly acquired memory is normal initially but decays rapidly over days or weeks, indicate that multiple factors might influence whether this phenomenon is seen in patients with epilepsy. Test-based differences such as learning condition or type of memory measure (e.g., recall vs recognition) as well as epilepsy variables (e.g., side, site, or frequency of epileptiform activity) may be important. The present study sought to characterize factors affecting learning and memory for prose passages in patients with focal epilepsy. We enrolled 21 patients with temporal lobe epilepsy, with and without hippocampal lesions, 11 patients with extratemporal epilepsy (ETE), and 29 healthy controls. Two matched passages were used to compare effects of initial learning condition (one exposure versus learning-to-criterion) on subsequent patterns of retention. Recall and recognition were tested at different delays (i.e., immediately, 30 min, 24 h, and 4 days). Regression analyses and one-way ANOVAs indicated that having a left-hemisphere epileptic focus had a negative impact on learning, whilst presence of a hippocampal lesion (irrespective of side) was associated with deterioration in recall for intervals up to 24 h postencoding. Learning condition affected patterns of memory decay in that the ETE group showed significant decline in recall between 24 h and 4 days only when stories were learned to criterion. In contrast with recall, no changes over time were evident in recognition memory, as patients with hippocampal lesions were impaired from 30 min onward. Epilepsy variables other than side and site of epilepsy/lesion did not influence performance. In conclusion, the left hemisphere is involved in learning of prose material, and the hippocampus is involved in the consolidation of this material mainly for the first 24 h. After this, cortical regions outside the hippocampus become important for recall.     

Is there a creative functional paradoxical facilitation in juvenile myoclonic epilepsy?

ObjectiveIn patients with juvenile myoclonic epilepsy (JME), a specific personality profile suggestive of frontal lobe dysfunctions has been described. From a neurobiological point of view, the frontal lobe seems to be crucial for creative processes, although the exact role remains unclear. The theory of creative paradoxical functional facilitation (PFF) assumes that disinhibited frontal lobe function can enhance creative abilities. The aim of the current study was to explore our hypothesis that JME is associated with higher artistic creativity based on the theory of PFF.MethodsWe assessed 25 patients with JME aged 18 to 40 years in regard to neuropsychological creativity testing. Results were compared with those of 25 age-, sex-, and level of education-matched healthy control subjects (HC) and patients with temporal lobe epilepsy (TLE). Creative abilities were assessed using two validated and standardized tests: 1) nonverbal: the incomplete figure task of Torrance Test of Creative Thinking and 2) verbal: verbal creativity test. Additionally, a basic assessment of fluid intelligence (test for problem solving) and frontal lobe function (trail-making test) was administered to all participants.ResultsVerbal creativity was impaired in both groups with epilepsy compared with that in HC (specific score: JME vs. HC, p = 0.008; TLE vs. HC, p = 0.003). In regard to nonverbal creative abilities, both groups with epilepsy exhibited fair performance. Level of fluid intelligence was even in all groups (p = 0.433). Only patients with JME showed deficits in the frontal lobe test of psychomotor speed (time in seconds: 67.7 JME vs. 54.6 TLE vs. 52.8 HC; p = 0.045).ConclusionsOverall, our study did not reveal increased creativity in JME. The current findings provide insights into creative abilities in two different epilepsy syndromes. Knowledge on specific neuropsychological strengths or deficits in patients with epilepsy may be useful for treatment or counseling.     

Impaired cerebral blood flow networks in temporal lobe epilepsy with hippocampal sclerosis: A graph theoretical approach

Graph theory is an emerging method to investigate brain networks. Altered cerebral blood flow (CBF) has frequently been reported in temporal lobe epilepsy (TLE), but graph theoretical findings of CBF are poorly understood. Here, we explored graph theoretical networks of CBF in TLE using arterial spin labeling imaging. We recruited patients with TLE and unilateral hippocampal sclerosis (HS) (19 patients with left TLE, and 21 with right TLE) and 20 gender- and age-matched healthy control subjects. We obtained all participants' CBF maps using pseudo-continuous arterial spin labeling and analyzed them using the Graph Analysis Toolbox (GAT) software program. As a result, compared to the controls, the patients with left TLE showed a significantly low clustering coefficient (p = 0.024), local efficiency (p = 0.001), global efficiency (p = 0.010), and high transitivity (p = 0.015), whereas the patients with right TLE showed significantly high assortativity (p = 0.046) and transitivity (p = 0.011). The group with right TLE also had high characteristic path length values (p = 0.085), low global efficiency (p = 0.078), and low resilience to targeted attack (p = 0.101) at a trend level. Lower normalized clustering coefficient (p = 0.081) in the left TLE and higher normalized characteristic path length (p = 0.089) in the right TLE were found also at a trend level. Both the patients with left and right TLE showed significantly decreased clustering in similar areas, i.e., the cingulate gyri, precuneus, and occipital lobe. Our findings revealed differing left–right network metrics in which an inefficient CBF network in left TLE and vulnerability to irritation in right TLE are suggested. The left–right common finding of regional decreased clustering might reflect impaired default-mode networks in TLE.     

The effects of temporal lobe epilepsy on scene encoding

Forty-four patients with temporal lobe epilepsy (TLE) (25 left) and 40 healthy control participants performed a complex visual scene-encoding fMRI task in a 4-T Varian scanner. Healthy controls and left temporal lobe epilepsy (LTLE) patients demonstrated symmetric activation during scene encoding. In contrast, right temporal lobe (RTLE) patients demonstrated left lateralization of scene encoding which differed significantly from healthy controls and LTLE patients (all p ≤ .05). Lateralization of scene encoding to the right hemisphere among LTLE patients was associated with inferior verbal memory performance as measured by neuropsychological testing (WMS-III Logical Memory Immediate, p = 0.049; WMS-III Paired Associates Immediate, p = 0.036; WMS-III Paired Associates Delayed, p = 0.047). In RTLE patients, left lateralization of scene encoding was associated with lower visuospatial memory performance (BVRT, p = 0.043) but improved verbal memory performance (WMS-III Word List, p = 0.049). These findings indicate that, despite the negative effects of epilepsy, memory functioning is better supported by the affected hemisphere than the hemisphere contralateral to the seizure focus.     

Short-term neurocognitive outcomes following anterior temporal lobectomy

Changes in cognitive function are a well established risk of anterior temporal lobectomy (ATL). Deficits in verbal memory are a common postoperative finding, though a small proportion of patients may improve. Postoperative evaluation typically occurs after six to 12 months. Patients may benefit from earlier evaluation to identify potential needs; however, the results of a formal neuropsychological assessment at an early postoperative stage are not described in the literature. We compared pre- and postoperative cognitive function for 28 right ATL and 23 left ATL patients using repeated measures ANOVA. Changes in cognitive function were compared to ILAE seizure outcome. The mean time to postoperative neuropsychological testing was 11.1 weeks (SD = 6.7 weeks). There was a side × surgery interaction for the verbal tasks: immediate memory recall (F(1,33) = 20.68, p < 0.001), short delay recall (F(1,29) = 4.99, p = 0.03), long delay recall (F(1,33) = 10.36, p = 0.003), recognition (F(1,33) = 5.69, p = 0.02), and naming (F(1,37) = 15.86, p < 0.001). This indicated that the left ATL group had a significant decrement in verbal memory following surgery, while the right ATL group experienced a small but significant improvement. For the right ATL group, there was a positive correlation between ILAE outcome and improvement in immediate recall (r = − 0.62, p = 0.02) and long delay recall (r = − 0.57, p = 0.03). There was no similar finding for the left ATL group. This study demonstrates that short-interval follow-up is effective in elucidating postoperative cognitive changes. Right ATL was associated with improvement in verbal memory, while left ATL resulted in a decrement in performance. Improvement in the right ATL group was related to improved seizure outcome. Short-interval follow-up may lend itself to the identification of patients who could benefit from early intervention.