Amnesia after unilateral temporal lobectomy: a case report

Neurophysiology, Neuropsychology, Epilepsy, 2022: Hills We Have Climbed and the Hills Ahead. Cognition and Sensory Systems in Healthy and Diseased Subjects

This article summarizes selected presentations from a session titled "Cognition and Sensory Systems in Healthy and Diseased Subjects", held to highlight and honor the work of Dr. Marilyn Jones-Gotman. The session was part of a two-day symposium, "Neurophysiology, Neuropsychology, Epilepsy, 2022: Hills We Have Climbed and the Hills Ahead". The session presented research on epilepsy and sensory systems by colleagues and former trainees of Dr. Jones-Gotman. The extended summaries provide an overview of historical and current work in the neuropsychology of epilepsy, neuropsychological and neuroimaging approaches to understanding brain organization, sex differences in brain mechanisms underlying neurological disorders, dietary influences on brain function and cognition, and expertise in olfactory training and language experiences and their implications for brain organization and structure.

How neuropsychology can improve the care of individual patients with epilepsy. Looking back and into the future

Some of the roots of current clinical neuropsychology go back to the early days of epilepsy surgery. Looking back a huge number of publications have dealt with cognition in epilepsy. The major factors driving this work were questions relating to surgery, antiepileptic drugs and, more recently, also to underlying pathology. However, most factors affecting cognition in epilepsy have been discerned many years ago. The body of neuropsychological literature in this field has accumulated much knowledge, raising the question why, apart from epilepsy surgery settings, neuropsychology has still not been fully integrated in the routine care of patients with epilepsy. This review on the occasion of Seizure's 25th anniversary attempts to summarize clinically relevant diagnostic advances following a question guided, modular, and evidence-based approach. In doing so, we hope to attract the interest of readers to an exciting mode of assessment which does not only have theoretical but also practical relevance. The comorbidities of epilepsy are becoming an increasingly relevant topic. It is now widely accepted that, while epilepsy may be defined by the occurrence of epileptic seizures, these seizures represent only one of several possible sources of cognitive impairment. It is well-established that there are complex interactions between epilepsy, cognition and behavior, and that both seizures and problems with cognition or behavior may result from a common underlying pathology requiring treatment. With this review we aim to demonstrate that neuropsychology can make a highly valuable contribution to the care of individual patients by contributing to the diagnostic process and by serving as a tool for the monitoring of disease and treatment, thereby improving the quality and safety of patient care. On a national, European, and international level, first efforts are being made to homogenize diagnostics across epilepsy centers and countries in order to achieve a common language and core standards. This should improve communication within and outside the speciality, and help to generate the data required to allow the field to make further progress.

Music and epilepsy: a critical review

The effect of music on patients with epileptic seizures is complex and at present poorly understood. Clinical studies suggest that the processing of music within the human brain involves numerous cortical areas, extending beyond Heschl's gyrus and working within connected networks. These networks could be recruited during a seizure manifesting as musical phenomena. Similarly, if certain areas within the network are hyperexcitable, then there is a potential that particular sounds or certain music could act as epileptogenic triggers. This occurs in the case of musicogenic epilepsy, whereby seizures are triggered by music. Although it appears that this condition is rare, the exact prevalence is unknown, as often patients do not implicate music as an epileptogenic trigger and routine electroencephalography does not use sound in seizure provocation. Music therapy for refractory epilepsy remains controversial, and further research is needed to explore the potential anticonvulsant role of music. Dopaminergic system modulation and the ambivalent action of cognitive and sensory input in ictogenesis may provide possible theories for the dichotomous proconvulsant and anticonvulsant role of music in epilepsy. The effect of antiepileptic drugs and surgery on musicality should not be underestimated. Altered pitch perception in relation to carbamazepine is rare, but health care professionals should discuss this risk or consider alternative medication particularly if the patient is a professional musician or native-born Japanese. Studies observing the effect of epilepsy surgery on musicality suggest a risk with right temporal lobectomy, although the extent of this risk and correlation to size and area of resection need further delineation. This potential risk may bring into question whether tests on musical perception and memory should form part of the preoperative neuropsychological workup for patients embarking on surgery, particularly that of the right temporal lobe.

Clinical magnetoencephalography for neurosurgery

Noninvasive neuroimaging aids in surgical planning and in counseling patients about possible risks of surgery. Magnetoencephalography (MEG) performs the most common types of surgical planning that the neurosurgeon faces, including localization of epileptic discharges, determination of the hemispheric dominance of verbal processing, and the ability to locate eloquent cortex. MEG is most useful when it is combined with structural imaging, most commonly with structural magnetic resonance (MR) imaging and MR diffusion imaging. This article reviews the history of clinical MEG, introduces the basic concepts about the biophysics of MEG, and outlines the basic neurosurgical applications of MEG.

Design considerations for a multicenter randomized controlled trial of early surgery for mesial temporal lobe epilepsy

PURPOSE

To describe the trial design for the multicenter Early Randomized Surgical Epilepsy Trial (ERSET). Patients with pharmacoresistant epilepsy are generally referred for surgical treatment an average of two decades after onset of seizures, often too late to avoid irreversible disability. ERSET was designed to assess the safety and efficacy of early surgical intervention compared to continued pharmacotherapy.

METHODS

ERSET is a randomized controlled, parallel group clinical trial with blinded outcome adjudication. Participants are patients with mesial temporal lobe epilepsy (MTLE) older than the age of 12 who have had pharmacoresistant seizures for not >2 years and are determined by detailed evaluation to be surgical candidates prior to randomization. The primary outcome measure is seizure freedom in the second year of a 2-year follow-up period. Health-related quality of life (HRQOL), neurocognitive function, ancillary outcomes, and adverse events were also measured.

RESULTS

Significant methodologic problems addressed by the study design included the following: recruitment of participants early in the course of epilepsy; establishment of operational definitions for "pharmacoresistant" and "early"; and standardization of diagnostic testing, medical treatment, and surgical interventions across multiple centers.

DISCUSSION

Rigorous trial designs to assess surgical interventions in epilepsy are necessary to provide evidence to guide treatment. This article is the first of a series; trial results will be reported in subsequent publications.

History of neuropsychology through epilepsy eyes

In the 19th century, Hughlings Jackson relied on clinical history, seizure semiology, and the neurologic examination as methods for seizure localization to inform the first epilepsy surgeries. In the 20th century, psychological and neuropsychological tests were first employed as both diagnostic and prognostic measures. The contemporary practice of epilepsy evaluation and management includes neuropsychology as a critical component of epilepsy care and research, and epilepsy and neuropsychology have enjoyed a very special and synergistic relationship. This paper reviews how epilepsy has shaped the practice of neuropsychology as a clinical service by asking critical questions that only neuropsychologists were in a position to answer, and how clinical care of epilepsy patients has been significantly improved based on neuropsychology's unique contributions.

Memory performance is related to language dominance as determined by the intracarotid amobarbital procedure

OBJECTIVE

The goal of this study was to explore the relationship between language and memory lateralization in patients with epilepsy undergoing the intracarotid amobarbital procedure.

METHODS

In 386 patients, language lateralization and memory lateralization as determined by laterality index (LI) were correlated with each other.

RESULTS

Language lateralization and memory lateralization were positively correlated (r=0.34, P<0.01). Correlations differed depending on the presence and type of lesion (chi(2)=7.98, P<0.05). LIs correlated significantly higher (z=2.82, P<0.05) in patients with cortical dysplasia (n=41, r=0.61, P<0.01) compared with the group without lesions (n=90, r=0.16, P>0.05), with patients with hippocampal sclerosis falling between these two groups. Both memory (P<0.01) and language (P<0.01) LIs were higher in right- compared with left-sided lesions.

CONCLUSION

Correlation of language and memory is more pronounced in patients with structural lesions as compared with patients without lesions on MRI.

Use of preoperative functional MRI to predict verbal memory decline after temporal lobe epilepsy surgery

PURPOSE

Verbal memory decline is a frequent complication of left anterior temporal lobectomy (L-ATL). The goal of this study was to determine whether preoperative language mapping using functional magnetic resonance imaging (fMRI) is useful for predicting which patients are likely to experience verbal memory decline after L-ATL.

METHODS

Sixty L-ATL patients underwent preoperative language mapping with fMRI, preoperative intracarotid amobarbital (Wada) testing for language and memory lateralization, and pre- and postoperative neuropsychological testing. Demographic, historical, neuropsychological, and imaging variables were examined for their ability to predict pre- to postoperative memory change.

RESULTS

Verbal memory decline occurred in over 30% of patients. Good preoperative performance, late age at onset of epilepsy, left dominance on fMRI, and left dominance on the Wada test were each predictive of memory decline. Preoperative performance and age at onset together accounted for roughly 50% of the variance in memory outcome (p < 0.001), and fMRI explained an additional 10% of this variance (p <or= 0.003). Neither Wada memory asymmetry nor Wada language asymmetry added additional predictive power beyond these noninvasive measures.

DISCUSSION

Preoperative fMRI is useful for identifying patients at high risk for verbal memory decline prior to L-ATL surgery. Lateralization of language is correlated with lateralization of verbal memory, whereas Wada memory testing is either insufficiently reliable or insufficiently material-specific to accurately localize verbal memory processes.

Repeated Intracarotid Amobarbital Tests

RATIONALE

Our goal was to determine the frequency of repeated intracarotid amobarbital test (IAT) at our center and to estimate the retest reliability of the IAT for both language and memory lateralization.

METHODS

A total of 1,249 consecutive IATs on 1,190 patients were retrospectively reviewed for repeat tests.

RESULTS

In 4% of patients the IAT was repeated in order to deliver satisfactory information on either language or memory lateralization. Reasons for repetition included obtundation and inability to test for memory lateralization, inability to test for language lateralization, no hemiparesis during first test, no aphasia during first test, atypical vessel filling, and bleeding complications from the catheter insertion site. Language lateralization was reproduced in all but one patient. Repeated memory test results were less consistent across tests, and memory lateralization was unreliable in 63% of the patients.

DISCUSSION

In spite of test limitations by a varying dose of amobarbital, crossover of amobarbital from one side to the other, testing of both hemispheres on the same day, practice effects, unblinded observers, fluctuating cooperation of the patients, and a biased sample of patients language lateralization was reproduced in all but one patient. In contrast, repeated memory test results were frequently contradictory. Memory results on IAT therefore seem much less robust than the results of language testing. Gain of reliable information versus the risks of complications and failed tests has to be considered when a patient is subjected to an IAT.

The myth of silent cortex and the morbidity of epileptogenic tissue: implications for temporal lobectomy

This article reviews two commonly held myths regarding temporal lobe epilepsy-it is a static disorder with minimal morbidity and mortality, and epileptogenic tissue impairs only the functions of the seizure focus-and one myth concerning temporal lobe functions-they contain areas of nonfunctional, "silent" cortex. Chronic temporal lobe epilepsy can cause progressive structural, cognitive, and behavioral changes. Aside from the seizure focus, primary epileptogenic cortex may have a deleterious influence on distant brain areas. Removing this "nociferous" cortex and reducing the antiepileptic drug burden can improve cognitive or behavioral and metabolic function in areas remote from the resection. Anterior temporal lobectomy often removes functional tissue that may or may not be epileptogenic. Because normal brain does not contain functionless, "silent" areas, the procedure can have negative as well as positive cognitive or behavioral consequences. To improve the outcomes of focal cortical resections for seizure control, we need to better define functional and nociferous cortex and more clearly understand their boundaries and interactions.

Presurgical assessment of memory-related brain structures: the Wada test and functional neuroimaging

Medial temporal lobe structures are known to play a major role in memory processing. Recent work has revealed that extratemporal structures (e.g. the frontal lobe and thalamus) may also be important in memory function. In candidates for epilepsy surgery, particularly in those with temporal lobe seizures, presurgical evaluation of memory function is essential, since seizures may originate in the neural substrate that is critical for memory. In this article, we review the tools used for presurgical evaluation and their contribution to the understanding of memory function, focusing on the Wada test, [18F]fluorodeoxy-glucose positron emission tomography ([18F]FDG-PET) and functional magnetic resonance imaging (fMRI). We also explore perspectives on future studies that may elucidate the role of the temporal and extratemporal structures in memory function and the mechanisms of cerebral plasticity.

Seizure control and cognitive outcome after temporal lobectomy: a comparison of classic Ammon's horn sclerosis, atypical mesial temporal sclerosis, and tumoral pathologies

PURPOSE

Neuropathologic examination of resected tissue after anterior temporal lobectomy (ATL) for treatment of complex partial seizures revealed several distinct histologic substrates. Our study examined the relation between neuropathology, seizure control, and cognition in ATL patients and described preliminary profiles to aid in the prediction of outcome.

METHODS

Of the 149 patients who underwent ATL from 1980 to 1999, long-term follow-up was available for 145. Specimens from 124 of the 145 patients had histologic findings consistent with one of three diagnoses: classic Ammon's horn sclerosis (cAHS; n = 75), atypical mesial sclerosis (Atypical; n = 21), or low-grade tumor (Tumor; n = 28). The other 20 patients had diverse pathologies that were insufficient for analysis. ATL patients underwent a complete preoperative and 68 underwent a postoperative neuropsychological evaluation.

RESULTS

Of the 145 patients, 84% of cAHS, 57% of Tumor, and 29% of Atypical patients had a > or =95% reduction in seizure frequency. Neuropsychological testing suggested that cAHS patients demonstrate more generalized preoperative cognitive impairment than do the Atypical or Tumor patients. The Atypical group recalled significantly less nonverbal material after surgery than did the cAHS or Tumor groups. Stratification by both pathology and surgery side revealed that the right Atypical patients declined more on information processing and set shifting.

CONCLUSIONS

Patients with cAHS or Tumor demonstrated better seizure control and fewer declines in cognitive functioning after ATL than did the Atypical patients, highlighting the need to investigate this group as a distinct entity.

Epilepsy surgery. Presurgical evaluation

The presurgical evaluation should result in a clear understanding of whether surgery can be undertaken and its associated risks and potential for benefit. The results of surgery are best when there is congruence in the seizure semiology, the irritative zone on interictal EEG, and the ictal onset zone with the epileptogenic lesion as defined on MRI and PET, and when there is a clear understanding of the ictal onset zone's relationship to eloquent cortex as defined by neuropsychologic evaluation, the intracarotid amobarbital test, and cortical functional mapping.

Prediction of seizure-onset laterality by using Wada memory asymmetries in pediatric epilepsy surgery candidates

PURPOSE

Because the capacity of intracarotid amobarbital (Wada) memory assessment to predict seizure-onset laterality in children has not been thoroughly investigated, three comprehensive epilepsy surgery centers pooled their data and examined Wada memory asymmetries to predict side of seizure onset in children being considered for epilepsy surgery.

METHODS

One hundred fifty-two children with intractable epilepsy underwent Wada testing. Although the type and number of memory stimuli and methods varied at each institution, all children were presented with six to 10 items soon after amobarbital injection. After return to neurologic baseline, recognition memory for the stimuli was assessed. Seizure onset was determined by simultaneous video-EEG recordings of multiple seizures.

RESULTS

In children with unilateral temporal lobe seizures (n = 87), Wada memory asymmetries accurately predicted seizure laterality to a statistically significant degree. Wada memory asymmetries also correctly predicted side of seizure onset in children with extra-temporal lobe seizures (n = 65). Although individual patient prediction accuracy was statistically significant in temporal lobe cases, onset laterality was incorrectly predicted in < or =52% of children with left temporal lobe seizure onset, depending on the methods and asymmetry criterion used. There also were significant differences between Wada prediction accuracy across the three epilepsy centers.

CONCLUSIONS

Results suggest that Wada memory assessment is useful in predicting side of seizure onset in many children. However, Wada memory asymmetries should be interpreted more cautiously in children than in adults.

Material-specific memory changes after anterior temporal lobectomy as predicted by the intracarotid amobarbital test

PURPOSE

The intracarotid amobarbital test (IAT) has been shown to predict verbal memory changes after anterior temporal lobectomy (ATL). Seeking to extend these findings, we examined two questions: (a) What is the relationship between material-specific aspects of IAT memory and material-specific memory changes after ATL? and (b) Which IAT memory score(s) optimally predict memory changes after surgery, the memory score after injection ipsilateral to the seizure focus, the memory score after injection contralateral to the seizure focus, or the IAT asymmetry score, comprising the ipsilateral minus contralateral injection scores?

METHODS

Seventy left hemisphere language-dominant patients undergoing ATL for treatment of medically refractory seizures were administered a verbal and visuospatial recognition memory test before surgery and 3 weeks after surgery. IAT memory recognition scores for words and designs were used to predict verbal and visuospatial memory changes after surgery.

RESULTS

After surgery, left ATL patients declined in verbal memory, whereas right ATL patients declined in visuospatial memory. IAT total recognition memory scores (collapsed across all types of materials) and IAT word memory scores were associated with postoperative verbal memory decline. This relationship was significant for the IAT ipsilateral injection memory scores and the IAT hemispheric asymmetry scores. IAT memory performances were not related to visuospatial memory changes.

CONCLUSIONS

Results indicate IAT memory measures to be related to postoperative verbal, but not visuospatial, memory change. A specific relationship was found between postoperative verbal memory change and IAT verbal memory after injection ipsilateral to the seizure focus, when relying primarily on the contralateral hemisphere. This finding is consistent with the functional reserve model of memory change in ATL.

Does the intracarotid amobarbital procedure predict global amnesia after temporal lobectomy?

PURPOSE

The intracarotid amobarbital procedure (IAP) is widely used to help predict who might be at risk for postoperative amnesia after unilateral temporal lobectomy for intractable seizures. We describe the memory outcome in 10 patients who underwent standard temporal lobectomy, including mesial temporal structures, despite failing the memory portion of the IAP after injections both ipsilateral and contralateral to the resected seizure focus.

METHODS

Data for seven of the study subjects were obtained through a retrospective review of patients assessed on a surgical epilepsy unit during a 15-year period who failed the Montreal Neurological Institute IAP memory protocol after both ipsilateral and contralateral injections and subsequently underwent unilateral temporal lobectomy. More recently, we have studied temporal lobectomy patients who failed the Medical College of Georgia memory protocol after both ipsilateral and contralateral injections (n = 3). Preoperative and postoperative memory test scores were compared, and data regarding seizure outcome and self-perception of postoperative memory were collected.

RESULTS

At follow-up, none of the patients presented with a pattern indicative of a global amnesia, and 80% demonstrated >90% improvement in their seizure disorder or were seizure-free.

CONCLUSIONS

These findings indicate that bilateral memory failure on the IAP does not preclude the removal of an epileptogenic temporal lobe or a successful surgical outcome. In addition, the findings raise questions regarding the validity of the IAP and the possibility that memory may be reorganized in patients with a long history of temporal lobe epilepsy.

Pediatric epilepsy surgery: neuroimaging, neuropsychology, and anticonvulsants

Neuroimaging and the neuropsychological evaluation are important components of the presurgical evaluation for epilepsy surgery. Advances in neuroimaging over the last decade, to a large part, underlie improvements in pediatric epilepsy surgery outcomes. The neuropsychological evaluation plays an important role in the evaluation of the older child and adolescent, particularly in the evaluation of mesial temporal sclerosis. However, its role in the young child being considered for surgery remains to be defined. This section reviews the definition of medical intractability, issues related to medication withdrawal during video-EEG monitoring, recent neuroimaging advances, and the neuropsychological evaluation.

The wada test: prediction of focus lateralization by asymmetric and symmetric recall

PURPOSE

The intracarotid amytal test is commonly used as a predictor of memory dysfunctioning after anterior temporal lobe resection (ATL) for intractable epilepsy. Asymmetry in memory scores can provide focus lateralizing information. In this study the predictive value of a set of Wada test parameters was analyzed, including patients with symmetrical memory scores.

METHODS

The Wada test was carried out in 226 patients undergoing ATL (94 L, 132 R). Data were collected on item recognition (five items), story recall, amytal dose, presentation time, EEG and arterial filling of amytal. A logistic regression analysis was performed on these data in order to find a set of variables which could best predict the side of seizure onset.

RESULTS

The analysis yielded four variables, i.e. both memory scores, story recall after right-sided injection and presentation time of stimuli after left-sided injection which could correctly predict seizure lateralization in 85% of the cases. Misclassification was lower for right foci than for left foci. Seizure outcome was four times more favourable in the correctly classified patients.

CONCLUSIONS

The results suggest that prediction of focus lateralization in temporal lobe epilepsy can be fairly exact even if left/right memory scores are equal. Performing the Wada test with only five memory items keeps the time window of active amytal short enough and gives accurate information about contralateral temporal lobe functioning. The classification scheme can be useful in predicting a lowered chance of seizure freedom.

Neuropsychological assessment for temporal lobe epilepsy surgery

Neuropsychological assessment consists of a comprehensive evaluation of cognitive functioning and most often some evaluation of motor skills and sensory status also. Cognitive functions sampled typically include "intelligence" (IQ tests), attention, language skills, visuospatial abilities, "executive skills" and other abilities associated with frontal-lobe function, and learning and memory. Thus, the assessment samples vary widely among a variety of functions, providing a comprehensive picture of an individual's strengths and weaknesses. The resulting pattern points to the probable site of epileptic focus. Neuropsychological findings also serve to predict the risk for postsurgical cognitive decline and, when performance before and after operation is compared, they provide data on the impact of surgery upon cognitive functioning. Comprehensive evaluation of learning and memory is particularly important in this context, because of the frequency of temporal lobe epilepsy and the prominence of memory dysfunction associated with it. In addition, patients slated for elective surgery may also undergo an intracarotid amobarbital procedure (IAP), which is performed to determine the side of cerebral dominance for language and to test the memory capabilities of each hemisphere alone. All of these specialized neuropsychological tools are discussed in this paper.

Beyond speech lateralization: a review of the variability, reliability, and validity of the intracarotid amobarbital procedure and its nonlanguage uses in epilepsy surgery candidates

While the intracarotid amobarbital procedure (IAP) was originally utilized to lateralize speech functions as an aid in the surgical treatment of epilepsy, additional uses for the IAP have emerged including: (1) the use of the IAP to predict post-surgical memory changes, including both global amnesia and smaller, yet significant, material-specific memory deficits; (2) the use of the IAP to provide confirmatory evidence of lateralization of seizure focus; and (3) the use of the IAP to predict post-surgical relief from seizures. While the literature on the IAP is extensive and growing, its utility is marred by the wide variability associated with the procedure itself from epilepsy center to center. This variability renders comparisons among IAP studies problematic and conclusions about IAP efficacy difficult. The variability associated with the amobarbital procedures, as well as the reliability and the validity of the IAP in its nonlanguage uses is reviewed here. A special emphasis is devoted to research conducted in the last decade. Also discussed is the future of the IAP including anticipated research directions.

Criterion-based validity of an intracarotid amobarbital recognition-memory protocol

PURPOSE

We tested whether the behavioral components of an Intracarotid Amobarbital Protocol (IAP) had criterion validity. It was hypothesized that a recognition-memory test designed for intracarotid injections and used to predict the risk of global amnesia before an elective temporal lobectomy should also identify persons who are severely amnesic due to other neurologic causes. Divergent validity predicts that speech tasks would be unaffected by amnesia. Test-retest reliability also was measured.

METHODS

Fifteen persons with severe amnesia were administered four alternate forms of a yes/no recognition-memory protocol and a speech protocol. No drug injection occurred. Standardized neuropsychological tests were used to divide the amnesic group into those with Global Amnesia (i.e., retain no ongoing memories), Severe Amnesia (i.e., memory impaired), and Amnesia Plus (severe amnesia plus other neuropsychologic deficits).

RESULTS

Two persons with Global Amnesia obtained scores at or below chance (i.e., failed) on the memory protocol. Unexpectedly, 12 of 13 severely amnesic persons obtained near-perfect memory scores. Amnesia had no impact on the speech protocol. Pass/Fail outcomes were highly correlated across all four sets.

CONCLUSIONS

A four-item IAP memory protocol showed good reliability and criterion validity in identifying the rare condition of Global Amnesia, but it was insensitive to other disabling, severe amnesic disorders. This IAP memory protocol might have validity in predicting a postsurgical Global Amnesic disorder, but it did not identify and therefore could not predict other more common severe amnesic disorders.

Evaluation of functional changes in the medial temporal region during intracarotid amobarbital procedure by use of SPECT

PURPOSE

Because the main blood supply to the medial temporal region is through the posterior cerebral artery, the validity of the intracarotid amobarbital procedure (IAP) is still debated. To verify clinical validity of the IAP, we investigated changes in neuronal function in the medial temporal region during IAP.

METHODS

Brain single photon emission computed tomography (SPECT) was performed during IAP (IAP-SPECT) in 22 patients with temporal lobe epilepsy (TLE), and regional cerebral blood flow (rCBF) in the medial and lateral temporal regions of interest (ROIs) was measured quantitatively. To determine the distribution of sodium amobarbital, in another 20 patients with TLE, SPECT images were obtained after intracarotid injection of 99mTc-HMPAO mixed with sodium amobarbital.

RESULTS

Mean rCBF was 89.2% in the medial temporal region and 81.6% in the lateral temporal region: in the former region, it was significantly lower than that shown by the results of interictal SPECT (99.1%; p < 0.001). In a few patients, however, rCBF did not decrease in the medial temporal region. In only 25% of patients, the medial temporal region was visualized in SPECT images obtained after intracarotid injection of 99mTc-HMPAO.

CONCLUSIONS

The results in this study demonstrate that IAP is valid because the medial temporal region is inactivated in spite of infrequent delivery of sodium amobarbital. We assume that intratemporal diaschisis is operating for the inactivation of neuronal function. IAP-SPECT with intratemporal ROIs may be useful for monitoring changes in neuronal function in the medial temporal region during IAP.

Prediction of verbal memory loss in individuals after anterior temporal lobectomy

PURPOSE

Decreased memory function represents the area of greatest neuropsychological morbidity after anterior temporal lobectomy (ATL), particularly for left ATL candidates. We wished to identify easily derived demographic and neuropsychological predictors of risk of pre- to postoperative memory decline using only information available preoperatively.

METHODS

We assessed decline in memory as measured by the California Verbal Learning Test (CVLT) by deriving multiple regression equations using the following measures as independent variables: age at onset, chronological age at time of surgery, sex, Full Scale IQ (FSIQ), level of education, and preoperative memory scores. In all, 203 patients (93 males, 110 females), undergoing ATL (107 left, 96 right) with preoperative and 6-month postoperative testing, were examined.

RESULTS

The combination of age, FSIQ, sex, side of surgery and preoperative score was highly predictive (p-values < 0.0001) of postoperative memory scores. Higher postoperative scores were associated with higher preoperative score, younger chronological age, higher FSIQ, female sex, and right side of resection. Reliable change index (RCI) values were used to estimate meaningful decline on the total score across five trials. Logistic regression analysis showed preoperative score and age to be predictors of RCI decline for left-sided resections. Sensitivity of decline (> or =90th centile RCI) prediction was 56%, and specificity was 95%. Validation in 30 patients from a separate population of patients undergoing left ATL produced similar figures.

CONCLUSIONS

The derived regression equations can accurately predict verbal memory decline on a list-learning task in approximately 50% of individual patients undergoing ATL, and false-positive prediction errors are very rare.

Anterior temporal lobectomy, hippocampal sclerosis, and memory: recent neuropsychological findings

Anterior temporal lobectomy (ATL) is an effective and increasingly utilized treatment for nonlesional, intractable mesial temporal lobe epilepsy. However, this surgery results in domain-specific neuropsychological morbidity for a subset of patients. Within the past decade, multidisciplinary studies have revealed that left ATL patients without significant sclerosis in the resected hippocampus are most at risk for a substantial postacute decline in the ability to encode new verbal information. These patients are also at risk for a significant decrement in confrontation naming and other retrieval-based language abilities. The memory deficit is not attributable to this disruption of language. A relationship between hippocampal sclerosis (HS) status and memory performance has not been identified consistently in right ATL patients, but investigation of new visuospatial measures continues. The influence of variables other than HS on neuropsychological outcome is also discussed.

Unilateral medial temporal lobe memory impairment: type deficit, function deficit, or both?

Previous research has characterized memory deficits resulting from unilateral hippocampal system damage as 'material specific', suggesting that left damage results in verbal memory impairment with preservation of visuospatial function and the converse with right damage. Implicit within this hypothesis are the assumptions that the systems are independent and memory is lateralized for each type of material. To test the verbal component of this hypothesis, unilateral hippocampal lesion and commissurotomy patients were compared with controls on a multiple-list free-recall task. The material specific hypothesis predicts severe impairment only with left lesions; right lesions and commissurotomy patients should be only minimally impaired. However, secondary memory was compromised at immediate recall for all patient groups, with both unilateral groups showing comparable and severe verbal episodic memory deficits. Final testing across all lists also revealed severe impairment in commissurotomy patients. Finding both unilateral groups to be similarly impaired for verbal material is taken as evidence against a material specific deficit during this verbal episodic memory task. Although previous data suggest that left patients are considerably more impaired during some verbal tasks, this may not be specific to the material, but rather the combination of material and task demands. Implications for the material specific hypothesis are discussed.

Amnesia in temporal lobectomy patients: historical perspective and review

Profound memory loss is a rare but serious complication of temporal-lobe surgery for the relief of medically intractable epilepsy. This paper examines the characteristics of the patients who have been reported to become amnesic following temporal-lobe surgery over the last four decades. The critical role of the hippocampi in memory function are implicated in autopsy studies and MRI investigations, but these cases suggest that a range of memory impairments result from bilateral hippocampal damage, rather than a pure amnesic syndrome in every case. There is some evidence that bilateral structural hippocampal abnormalities may not necessarily be associated with significant memory problems, if these abnormalities have a developmental basis. However, whilst not necessarily profound, any post-operative deterioration in memory function remains a significant consideration in the presurgical evaluation of temporal-lobe epilepsy patients.

Memory, simple and complex language, and the temporal lobe

Nineteen patients with intractable temporal lobe epilepsy who underwent anterior temporal lobectomy were given a highly specific memory battery (23 tests) pre- and post- (1 week; 1, 2, and 6 months; 1 and 2 years) resection. Sixteen of 23 tests revealed that memory performance of temporal lobe epilepsy patients was worse than normal controls prior to surgery (p < .001), while the most profound differences were seen in the remembering and generation of inferences from connected discourse. Almost no differences were observed in delayed nonmatching to sample tasks (recognition without language task). MRI results revealed that anterior, middle, and posterior hippocampal abnormality was extensive in 12 of 19 patients, and 12 also showed medial temporal lobe abnormalities and volume loss. Hippocampal damage was negatively correlated with extended delay memory performance for connected discourse: worse performance was associated with greater damage. Few differences in less complex memory performance were observed pre-postsurgery. While ordinary recognition functions were preserved, results demonstrated that dominant medial temporal lobe structures appeared heavily involved in language-generated memory, and hippocampus is heavily implicated in both simple and complex language.

The relation between quantitative MRI measures of hippocampal structure and the intracarotid amobarbital test

PURPOSE

The increasing sophistication of quantitative magnetic resonance imaging (MRI) techniques has generated hopes that they may eventually supersede the intracarotid amobarbital procedure (IAP) in the presurgical screening for bilateral abnormalities in prospective candidates for temporal lobe epilepsy surgery. As the first step toward this aim, the purpose of this study was to examine the relationship between these measures of structural and functional integrity.

METHODS

We examined the relation between memory performance and pass/fail rates on the IAP and two MRI measures of hippocampal integrity: hippocampal volumes, adjusted for intracranial volume (HCvol) and hippocampal T2 relaxometry (HCT2), in 48 patients with medically intractable temporal lobe epilepsy, who underwent the IAP as part of their presurgical evaluation for temporal lobectomy.

RESULTS

The unilateral memory scores from the IAP were not significantly correlated with the corresponding HCvol or HCT2 measures in the right- and left-temporal-lobe groups. However, the MRI measures of hippocampal asymmetry (right minus left HCvol, right minus left HCT2) were significantly correlated with our measure of functional asymmetry, the right minus left hemisphere memory score from the IAP, supporting the role of the IAP in lateralising temporal lobe dysfunction. Forty-six patients with unilateral hippocampal sclerosis and concordant EEG studies passed the IAP. Two patients failed the memory component of the IAP. In both cases, other presurgical investigations suggested bilateral abnormalities.

CONCLUSIONS

We conclude that patients with unilateral hippocampal sclerosis, established by a rigorous quantitative MRI protocol, and concordant ictal and interictal EEG findings may not be at risk for postoperative amnesia, despite baseline neuropsychological deficits suggestive of bilateral disturbance.

Sodium amobarbital memory tests: what do they predict?

Severe transient postoperative memory deficits among epilepsy patients with resection from one temporal lobe may be indicative of increased risk for amnesia had more extensive removal of mesial structures occurred. Immediate postoperative testing may provide some validation for risk of amnesia as predicted by the intracarotid sodium amobarbital memory test (IAP-M). Thirty patients (24 not considered at risk for amnesia and 5 who failed the IAP-M) were tested on the first, second, and third days following resection from the right or left temporal lobe. Results suggest that the IAP-M paradigm used does not necessarily predict postoperative memory performance.

Memory for objects presented early after intracarotid sodium amytal: a sensitive clinical neuropsychological indicator of temporal lobe pathology

Results from a simple test of post-recovery recognition of objects presented immediately after intracarotid sodium amytal (ISA) injection were compared with those obtained using the 'Montreal' anterograde memory test procedure of post-recovery recognition of items presented later after injection in 16 patients with unilateral temporal lobe pathology undergoing routine bilateral ISA testing prior to epilepsy surgery. All 16 patients were given both memory tests following injection on both sides. Significantly fewer 'early objects' were recognized when injection was contralateral to pathology than when injection was ipsilateral to pathology (i.e. contralateral to an intact hemisphere), whereas there was no significant difference in the number of 'Montreal' anterograde items recognized regardless of side of pathology. Memory for objects presented early after ISA appears to be a sensitive measure although its potential as a valid indicator of temporal lobe pathology needs to be further refined.