Effect of Wada memory stimulus type in discriminating lateralized temporal lobe impairment

Diagnostic accuracy of functional magnetic resonance imaging, Wada test, magnetoencephalography, and functional transcranial Doppler sonography for memory and language outcome after epilepsy surgery: A systematic review

OBJECTIVE

The European Union-funded E-PILEPSY project was launched to develop guidelines and recommendations for epilepsy surgery. In this systematic review, we aimed to assess the diagnostic accuracy of functional magnetic resonance imaging (fMRI), Wada test, magnetoencephalography (MEG), and functional transcranial Doppler sonography (fTCD) for memory and language decline after surgery.

METHODS

The literature search was conducted using PubMed, Embase, and CENTRAL. The diagnostic accuracy was expressed in terms of sensitivity and specificity for postoperative language or memory decline, as determined by pre- and postoperative neuropsychological assessments. If two or more estimates of sensitivity or specificity were extracted from a study, two meta-analyses were conducted, using the maximum ("best case") and the minimum ("worst case") of the extracted estimates, respectively.

RESULTS

Twenty-eight papers were eligible for data extraction and further analysis. All tests for heterogeneity were highly significant, indicating large between-study variability (P < 0.001). For memory outcomes, meta-analyses were conducted for Wada tests (n = 17) using both memory and language laterality quotients. In the best case, meta-analyses yielded a sensitivity estimate of 0.79 (95% confidence interval [CI] = 0.67-0.92) and a specificity estimate of 0.65 (95% CI = 0.47-0.83). For the worst case, meta-analyses yielded a sensitivity estimate of 0.65 (95% CI = 0.48-0.82) and a specificity estimate of 0.46 (95% CI = 0.28-0.65). The overall quality of evidence, which was assessed using Grading of Recommendations Assessment, Development, and Evaluation methodology, was rated as very low. Meta-analyses concerning diagnostic accuracy of fMRI, fTCD, and MEG were not feasible due to small numbers of studies (fMRI, n = 4; fTCD, n = 1; MEG, n = 0). This also applied to studies concerning language outcomes (Wada test, n = 6; fMRI, n = 2; fTCD, n = 1; MEG, n = 0).

SIGNIFICANCE

Meta-analyses could only be conducted in a few subgroups for the Wada test with low-quality evidence. Thus, more evidence from high-quality studies and improved data reporting are required. Moreover, the large between-study heterogeneity underlines the necessity for more homogeneous and thus comparable studies in future research.

Memory outcome following left anterior temporal lobectomy in patients with a failed Wada test

PURPOSE

This study aimed to compare the memory outcome following left anterior temporal lobectomy (ATL) between patients with a failed Wada test and patients who passed the Wada test.

METHODS

From 1996 to 2002, we performed the Wada test on all patients with unilateral left mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) and concordant electroclinical data before ATL. We used a 12-item recognition paradigm for memory testing and awarded a score of +1 for each correct response and -0.5 for each incorrect response. No patient was denied surgery on the basis of Wada scores. We assessed cognitive and memory functions using the Wechsler Adult Intelligence Scale and the Wechsler Memory Scale preoperatively and at one year after ATL. We compared the number of patients who showed decline in memory scores, as per the published reliable change indices, between the patients with a failed Wada test and the patients who passed the Wada test.

RESULTS

Out of the 116 eligible patients with left MTLE-HS, 88 underwent bilateral Wada test, while 28 underwent ipsilateral Wada test. None of them developed postoperative amnesia. Approximately, one-third of patients with a failed Wada memory test when the failure was defined as a contralateral score of <4, as an ipsilateral score of >8, and as an asymmetry score of <0. The patients with Wada memory failure had a longer pre-ATL duration of epilepsy (p<0.003). The memory and quality-of-life outcomes did not differ between the group with a failed Wada memory test and the group who passed the Wada memory test. The results remained the same when analyses were repeated at various other cutoff points.

CONCLUSION

The patients with left MTLE-HS with concordant electroclinical, MRI, and neuropsychological data should not be denied ATL solely on the basis of Wada memory test results.

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.

Spatiotemporal imaging of cortical activation during verb generation and picture naming

One hundred and fifty years of neurolinguistic research has identified the key structures in the human brain that support language. However, neither the classic neuropsychological approaches introduced by Broca (1861) and Wernicke (1874), nor modern neuroimaging employing PET and fMRI has been able to delineate the temporal flow of language processing in the human brain. We recorded the electrocorticogram (ECoG) from indwelling electrodes over left hemisphere language cortices during two common language tasks, verb generation and picture naming. We observed that the very high frequencies of the ECoG (high-gamma, 70-160 Hz) track language processing with spatial and temporal precision. Serial progression of activations is seen at a larger timescale, showing distinct stages of perception, semantic association/selection, and speech production. Within the areas supporting each of these larger processing stages, parallel (or "incremental") processing is observed. In addition to the traditional posterior vs. anterior localization for speech perception vs. production, we provide novel evidence for the role of premotor cortex in speech perception and of Wernicke's and surrounding cortex in speech production. The data are discussed with regards to current leading models of speech perception and production, and a "dual ventral stream" hybrid of leading speech perception models is given.

Stimulus type affects Wada memory performance

The effects of amytal injection side, seizure focus laterality, and stimulus type (real and line-drawn objects, printed words, and faces) on recognition memory were studied during the Wada procedure. To-be-remembered stimuli were presented during cerebral anesthesia to 35 patients with left temporal lobe epilepsy (LTLE) and 28 patients with right temporal lobe epilepsy (RTLE), all with left hemisphere language dominance. In both groups, recognition of real and line-drawn objects was best after anesthetization of the lesional hemisphere. Recognition of faces was poor after either injection in patients with RTLE, but only after right injection in patients with LTLE. Conversely, recognition of words by patients with LTLE was impaired equally after either injection, but more so after left than right injection in patients with RTLE. The findings suggest that (1) real and line-drawn objects are "dually encoded" and memory accuracy depends on seizure focus laterality, and (2) accuracy in recognition of words and faces is related to seizure focus laterality, but may also depend on the language dominance of the hemisphere being assessed.

Clinical relevance of memory performance during Wada is stimulus type dependent

OBJECTIVES

This study aimed to investigate whether different types of memory stimulus provide different information during the Wada or intracarotid amytal procedure (IAP) in patients with refractory medial temporal lobe epilepsy (MTLE).

METHODS

Eighty nine surgical candidates with documented MTLE and selected for left hemispheric language dominance underwent memory assessment with verbal and dually encodable stimuli during a presurgical IAP.

RESULTS

The overall IAP memory performance with the left hemisphere is significantly better than with the right hemisphere regardless of lesion side. This can be explained by the left hemispheric advantage of encoding all stimuli, whereas the right hemisphere has only limited resources to encode verbal stimuli. More importantly, it appeared that dually encodable items remain more readily recognised following injection ipsilateral to the lesion, whereas verbal items are always better recognised following right hemisphere injection regardless of lesion side.

CONCLUSIONS

Verbal IAP stimuli show left hemispheric sensitivity in left language dominant MTLE patients. The dually encodable items of the IAP appear lesion sensitive.

Alternatives to the Wada test: a critical view of functional magnetic resonance imaging in preoperative use

PURPOSE OF REVIEW

The Wada or intracarotid amobarbital procedure is already in its fifties and, despite its invasive character, still routine for determining the lateralization of language and memory prior to epileptic surgery. Among the new techniques available, functional magnetic resonance imaging is one of the most promising alternatives. This non-invasive method has several advantages including the possibility of mapping relevant areas within the hemispheres and being able to prolong examination time in case of discordant results.

RECENT FINDINGS

Many functional magnetic resonance imaging studies have focused on correlations with the intracarotid amobarbital procedure as the gold standard and found an agreement of about 90%. More importantly, recent studies demonstrated a significant correlation between presurgical functional magnetic resonance imaging testing and postsurgical outcome for functional magnetic resonance imaging activations in frontal language areas. In some studies, prediction for outcome is already higher for functional magnetic resonance imaging than for the intracarotid amobarbital procedure.

SUMMARY

Current data support functional magnetic resonance imaging as a valid alternative to the intracarotid amobarbital procedure. Small sample sizes in outcome studies and restrictions to certain sites of operation, however, still call for caution. A standardized series of tasks to activate the whole language and memory system paired with good comparability between medical centres is needed.

Lateralization of Epileptic Foci by Neuropsychological Testing in Mesial Temporal Lobe Epilepsy

This study investigated the lateralizing value of neuropsychological testing in presurgical evaluation of mesial temporal lobe epilepsy (MTLE). This study differed from previous ones in that the cutoff values were determined to yield high positive predictive values (PPVs), multiple neuropsychological predictors were considered in combination, and patients with atypical language dominance or low intelligence were not excluded from the sample. The participants were 92 patients with MTLE (left, n = 47; right, n = 45) who showed good postoperative seizure control. With a stringent cutoff criterion, the multiple neuropsychological predictors considered in combination yielded a sensitivity of 15% and a PPV of 93%, and with a less stringent cutoff criterion, a sensitivity of 37% and a PPV of 83%.

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.

Lateralising value of neuropsychological protocols for presurgical assessment of temporal lobe epilepsy

PURPOSE

To estimate the value of neuropsychological measurements in determining the side of seizure onset for presurgical assessment in patients with temporal lobe epilepsy. The lateralising value of neuropsychological protocols was evaluated for all patients and in subpopulations depending on surgical outcome with regard to seizure control, speech dominance, neuropathology, and need for intracranial EEG recordings.

METHODS

A battery of neuropsychological procedures was carried out preoperatively in 125 patients who underwent left (n = 66) or right (n = 59) temporal lobectomies. Binary logistic regression analysis was performed to find sets of variables that allowed the best prediction of the side of seizure onset (assumed to be the operated-on side).

RESULTS

Combinations of noninvasive neuropsychological tests and Wada subscores showed the highest lateralising values: 80.8% for all patients, 79.4% in seizure-free patients, 86.0% in patients not rendered seizure free, 85.7% in left speech patients, 77.8% in non-left speech patients, 89.3% in patients with mesial temporal sclerosis (MTS), 78.1% in non-MTS patients, 80.3% in patients who underwent intracranial EEG recordings, and 77.3% in those who did not.

CONCLUSIONS

The lateralising value (80-90%) of neuropsychological protocols appears similar to that of other tests widely accepted for lateralisation (ictal and interictal scalp EEG and neuroimaging). Attention should be paid to neuropsychological results, particularly from the Wada test, during presurgical assessment of temporal lobe epilepsy, as they can provide strong support for findings from other lateralising tests, particularly in patients with presumed MTS or in left-speech patients.

Effect of Wada methodology in predicting lateralized memory impairment in pediatric epilepsy surgery candidates

Because Wada evaluations are not standardized, it is impossible to know to what degree method variance accounts for reported differences in results. To examine this problem, three comprehensive epilepsy surgery centers compared the efficacy of two Wada memory methods to predict seizure onset laterality in 152 children being considered for epilepsy surgery. Wada memory asymmetries were evaluated using either real objects with no verbal response required or more mixed stimuli requiring a verbal response. When using real objects, Wada memory performance was significantly worse when relying on the side of seizure onset in both left and right seizure onset children. In contrast, Wada memory performance using mixed stimuli was worse on the side of seizure onset only among patients with seizures originating in the left-hemisphere. The superiority of real objects was most apparent in younger children with left side seizure onset. Results suggest the use of mixed stimuli is less sensitive to the effects of unilateral seizure onset, and thus, diminishes the capacity of the Wada test to predict lateralized seizure onset in children.

Bilateral Memory Dysfunction in Epilepsy Surgery Candidates Detected by the Intracarotid Amobarbital Procedure (Wada Memory Test)

The intracarotid amobarbital procedure (IAP) is widely used in the evaluation of candidates for resective epilepsy surgery, in part to identify patients at risk for postoperative amnesia. Yet there is no widely accepted standardized protocol, and there is a paucity of quantitative data to assess the factors associated with poor IAP performance. This report summarizes our findings on 110 patients with intractable focal epilepsy who underwent IAP testing at our center. Ipsilateral IAP scores for patients with left-sided seizure foci were significantly lower than those for patients with right-sided seizure foci. Falsely and poorly lateralizing scores were also significantly more common in subjects with left-sided seizure onsets. Twenty-four percent of subjects failed the IAP bilaterally, and patients who failed the IAP bilaterally had significantly lower scores on neuropsychologic measures. There was no difference between patients who passed and failed in the location, etiology, duration, or age of onset of epilepsy. We conclude that bilateral memory dysfunction is common in patients with intractable partial epilepsy. Whether memory dysfunction detected by IAP testing as performed at our center is predictive of functionally limiting postoperative amnesia remains to be determined.

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.

Chemical shift imaging spectroscopy and memory function in temporal lobe epilepsy

PURPOSE

Hippocampal neuron loss and associated memory deficits are characteristic of intractable temporal lobe epilepsy (TLE). Proton chemical shift imaging (CSI) spectroscopy is a sensitive tool for detecting neuronal loss. The aim of this study was to investigate the correlation between memory functions and results provided by CSI spectroscopy of the hippocampal structures.

METHODS

Ten patients with cryptogenic TLE participated. The study protocol involved both the acquisition of high-spatial-resolution CSI spectroscopy and neuropsychological evaluation, including memory testing and intracarotid sodium amytal test (IAT). The analysis of the CSI data was based on normative data obtained in 30 healthy volunteers. Memory functions were represented by verbal, visual, and general memory indices.

RESULTS

A significant correlation was found between CSI spectroscopy of the hippocampal formation and the verbal memory indices for the dominant hemisphere. In addition, there was a significant correspondence of the qualitative judgment "hippocampal pathology indicated by CSI spectroscopy" and both "material specific memory deficit" and "memory deficit in the IAT."

CONCLUSIONS

Our results demonstrate that CSI spectroscopy of the hippocampal structures is strongly related to lateralized memory deficits in patients with TLE. This suggests that CSI spectroscopy may be useful in the prediction of postoperative outcome in respect of seizure control and memory.

Interpretation of Wada memory test for lateralization of seizure focus by use of (99m)technetium-HMPAO SPECT

PURPOSE

Although the intracarotid amobarbital procedure (IAP) or Wada test is useful in lateralizing seizure focus in patients with temporal lobe epilepsy (TLE), the results of the IAP memory test are frequently nonlateralizing. An insufficient suppression of the medial temporal region contralateral to the seizure focus may contribute to the failure of lateralization. We tried to correlate IAP memory results with the functional changes in the contralateral medial temporal region as measured by single photon emission computed tomography (SPECT) during IAP.

METHODS

We performed a (99m)technetium-(Tc) hexamethylene-propylene-amine-oxime (HMPAO) brain SPECT in 19 medial TLE patients during a contralateral IAP (sodium amobarbital injected contralateral to the seizure focus). Regional cerebral blood flow (rCBF) was measured in the contralateral medial temporal region. The amount of decrease in the rCBF was calculated by subtracting the previous measurement from the one obtained with the interictal SPECT.

RESULTS

Ten (53%) patients passed and nine (47%) failed the contralateral IAP. The mean percentage decrease in rCBF was 5.3+/-5.3%. There was a significant negative correlation between a decrease in the rCBF and the IAP memory-retention score by Spearman correlation (p = -0.53: p<0.021). Patients with smaller decreases in rCBF (<5%) more frequently passed the contralateral IAP memory test than did those with larger decreases (80 vs. 22%; p<0.023).

CONCLUSIONS

We suggest that an insufficient suppression of the contralateral medial temporal function is partly responsible for nonlateralizing IAP memory tests. An IAP-SPECT may be useful in interpreting IAP memory tests for the lateralization of seizure focus in TLE patients.

Effects of incorporating memory confidence ratings and language handicap modifications on intracarotid amobarbital procedure (Wada test) memory asymmetry scores

PURPOSE

Intracarotid amobarbital procedure (IAP) memory asymmetry scores are often considered in determining lateralization of temporal lobe seizure foci. Additionally, these scores sometimes influence treatment plans for epilepsy surgery candidates. We examined the effects of two scoring modifications on IAP asymmetry scores: incorporating memory confidence ratings (MC), and use of a language handicap (LH) (i.e., adding a point to the memory score with anesthetization of the language-dominant hemisphere), both of which could be applied to most IAP protocols despite variations in testing methods among epilepsy surgery programs.

METHODS

Sixty-nine consecutive unilateral temporal lobe epilepsy (TLE) patients with subsequent good surgical outcomes (Engel I or II) underwent bilateral IAP testing. Confidence ratings were obtained for all memory responses. The incorporation of confidence ratings and the application of a language handicap for dominant-hemisphere injections were applied to memory asymmetry scores in all combinations, resulting in four scoring methods. Results of the four methods were compared with respect to the proportion of patients lateralized accurately by each method.

RESULTS

No patients were falsely lateralized with any method. Percentage of patients correctly lateralized with each scoring method is shown in Table 2. The results obtained with MC and with MC + LH (67% and 64% of patients accurately lateralized, respectively) were significantly better than results obtained with LH (55%, p<0.05). No other differences were significant.

CONCLUSIONS

Although not statistically superior to standard methods, these results suggest that incorporating memory confidence ratings into IAP protocols may increase the likelihood of obtaining asymmetry scores that accurately lateralize to the hemisphere of seizure onset. In contrast, inclusion of a language handicap for scores obtained with the language-dominant ICA injection were not helpful and may even decrease the probability of obtaining clinically useful lateralizing data. These scoring modifications can be applied to most IAP protocols.

Lateralizing value of the Wada memory test in non-Western patients with temporal lobe epilepsy

The Wada memory test measures a psychological construct (i.e. memory), which is widely acknowledged to be under the influence of a vast array of moderating variables including culture. Thus, the lateralizing value of the Wada memory test for epileptogenic foci may potentially differ for Western versus non-Western patients with temporal lobe epilepsy (TLE). In the present study, the lateralizing value of the Wada memory test was investigated in 17 Korean patients with medically intractable TLE who were post-operatively seizure-free. The Wada memory stimuli were composed of eight drawings of common objects, animals, and fruits. A clinical criterion of at least 2 points difference between left and right injections correctly classified 14 patients (82%) into left and right TLE groups, with only one patient (6%) falsely classified. This diagnostic accuracy is at least as high as that reported for Western TLE patients. These results indicate that whatever culture-specific factors Korean TLE patients may bring to the Wada memory test, they do not significantly reduce the lateralizing value of the test.

Prediction of presence of hippocampal sclerosis from intracarotid amobarbital procedure memory asymmetry scores and epilepsy on set age

Identification of the pathological status of the hippocampus prior to surgery is important since the absence of hippocampal sclerosis (HS) carries risks to memory function following anterior temporal lobectomy (ATL). We studied 62 patients undergoing ATL (31 L, 31 R) for intractable epilepsy of temporal lobe origin in whom no pathology was identified apart from HS. An intracarotid amobarbital procedure (IAP) was performed as part of the preoperative evaluation. All patients were left hemisphere dominant for language. IAP memory testing was according to the protocol of Loring. We examined IAP memory asymmetry scores at four levels of difference (<2, > or =2, > or =4, > or =6) as a function of the presence (HS+) or absence (HS-) of HS. A logistic regression analysis was performed with HS+ as the dependent variable, and age at onset of epilepsy, age at time of surgery, gender, side of surgery and significant IAP memory asymmetry as independent variables. At each level of memory asymmetry, onset age and memory asymmetry were the only predictors of HS+. Younger age at onset was associated with HS+. Curves were constructed showing probability of HS+ for age at onset for each level of asymmetry. These can be used to predict the likelihood of presence of HS based on age at onset of epilepsy and the IAP memory asymmetry score. It is concluded that IAP memory asymmetry scores reflect the functional and pathological status of the hippocampus, and greater asymmetry increases the probability of finding HS in the resected hippocampus.