Stimulus timing effects on Wada memory testing

Functional MRI is a valid noninvasive alternative to Wada testing

Partial removal of the anterior temporal lobe (ATL) is a highly effective surgical treatment for intractable temporal lobe epilepsy, yet roughly half of patients who undergo left ATL resection show a decline in language or verbal memory function postoperatively. Two recent studies demonstrate that preoperative fMRI can predict postoperative naming and verbal memory changes in such patients. Most importantly, fMRI significantly improves the accuracy of prediction relative to other noninvasive measures used alone. Addition of language and memory lateralization data from the intracarotid amobarbital (Wada) test did not improve prediction accuracy in these studies. Thus, fMRI provides patients and practitioners with a safe, noninvasive, and well-validated tool for making better-informed decisions regarding elective surgery based on a quantitative assessment of cognitive risk.

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.

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.

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.

Prediction of Verbal Memory Decline after Epilepsy Surgery in Children: Effectiveness of Wada Memory Asymmetries

PURPOSE

Differences in Wada memory performance after left and right amobarbital injection are powerful predictors of pre- to postoperative memory change among adult epilepsy patients after anterior temporal lobectomy. It is unknown, however, whether these Wada memory asymmetries apply to children who undergo focal cortical resection or to epilepsy surgery patients who undergo resection outside the temporal lobes.

METHODS

To investigate these issues, Wada memory asymmetries and pre- to postoperative neuropsychological memory test performances were examined in 132 children who underwent some form of resective epilepsy surgery. Ninety-three (70%) children showed Wada memory asymmetries in the predicted direction (memory after injection ipsilateral to side of surgery better than memory after contralateral injection), and 39 (30%) did not.

RESULTS

Children with Wada memory asymmetries showed significant improvement in verbal memory after surgery as compared with children without Wada memory asymmetries who showed significant verbal memory decline. This result was also obtained when individual cases were examined: 77% of children with Wada memory asymmetries in predicted direction showed no verbal memory decline after surgery, whereas 80% of children without asymmetries had lower postoperative verbal memory (passage recall) test scores. Wada memory asymmetries had no value in predicting postoperative changes in visual-spatial memory.

CONCLUSIONS

Wada memory asymmetries may be used as one of the factors to assess risk for verbal memory decline after epilepsy surgery in children.

Memory outcome after left anterior temporal lobectomy in patients with expected and reversed Wada memory asymmetry scores

PURPOSE

The ideal candidate for anterior temporal lobectomy surgery shows a Wada memory asymmetry (WMA) score characterized by better memory performance in the hemisphere contralateral to the seizure focus relative to the ipsilateral (surgical) hemisphere. However, some surgical candidates show a reversed WMA or better Wada memory performance in the hemisphere of surgical interest relative to the hemisphere contralateral to the seizure focus. To date, no data are available contrasting memory and seizure outcome for these two Wada groups. The present study compared memory and seizure outcome after left anterior temporal lobectomy (L-ATL) in patients showing expected and reversed WMA scores, and also examined the relationship of the individual hemisphere Wada memory scores for predicting verbal memory outcome after L-ATL.

METHODS

We compared 6-month postoperative verbal memory change scores and seizure outcome in L-ATL patients with either an expected (n=12) or reversed WMA (n=9) pattern on Wada memory testing.

RESULTS

L-ATL patients showing a reversed WMA score had a poorer verbal memory outcome and poorer seizure control after surgery compared with patients showing a WMA score in the expected direction.

CONCLUSIONS

L-ATL patients with a reversed WMA score have a greater risk for memory morbidity and poorer seizure outcome than do patients with a WMA score in the expected direction. The WMA score was the best predictor of memory outcome after L-ATL. When the WMA score is not considered, both individual Wada hemisphere scores (contralateral and ipsilateral) provided significant and independent contribution to predicting postoperative verbal memory functioning. These findings are discussed in the context of the functional reserve and hippocampal adequacy models of memory change after temporal lobectomy.

Severe Amnesia in Epilepsy: Causes, Anatomopsychological Considerations, and Treatment

Severe amnesia in epileptic patients is a catastrophic condition that may be due to different etiologies. Because of the striking findings and thorough neuropsychological studies of Patient H.M., the literature has focused on postsurgical occurrence of such memory impairment, with much less emphasis on other causes. Here we summarize, for comparison, the history of H.M. We report five patients with pronounced memory loss who had extensive neuropsychological and electroencephalographic testing. MRI was also performed in four of the patients, MRI volumetric measurements of amygdala and hippocampal formation in three, and measurements of entorhinal cortex in two. The amnesia occurred after head trauma in one patient, following encephalitis in one, after partial status epilepticus in two, and after unilateral surgical resection in a woman with bilateral lesions. On the basis of these studies it was impossible to distinguish the role of recurrent temporal lobe epileptic seizures as distinct from underlying lesions in the genesis and course of the memory loss. We review here the anatomical substrate, neuropsychological, and other investigations and the etiological factors leading to the amnesia in these patients, together with current concepts regarding possible causes of such severe memory dysfunction. In patients with this degree of severity of memory deficit, temporal resection in an attempt to control seizures did not lead to a measurable increase in memory problems. It also, however, did not bring about worthwhile improvement in seizure control.

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.

Wada difference a day makes: interpretive cautions regarding same-day injections

OBJECTIVE

To determine whether memory scores after second intracarotid amobarbital procedure (IAP) injections are affected by the time between the first and second injections.

METHODS

Sixty-two patients received their second IAP injection on the day after the first injection. Forty-three other patients received the second injection on the same day as the first injection. Both groups underwent similar IAP protocols and memory assessments, except for the timing of the second injection.

RESULTS

The second IAP memory scores in the two-day group were significantly higher (p < 0.05) than those in the one-day group. Timing of second injection was a significant correlate of second memory scores, but amobarbital dosage, first IAP memory score, and pre-IAP measures of memory and intelligence were not significant correlates.

CONCLUSION

One-day and two-day IAP protocols do not result in similar memory scores after the second injection. Nineteen percent of a subset of patients in the one-day protocol were misclassified, in terms of IAP memory ratings, because of the deleterious effect of having both injections on the same day. It is recommended that correction scores be considered, for some patients who receive two IAP injections on one day, to approximate what the second IAP memory score would have been had the second injection occurred on a second day.

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.

Use of the intracarotid amobarbital procedure in the evaluation of memory

The intracarotid amobarbital procedure (IAP) involves the temporary inactivation of one cerebral hemisphere by the injection of sodium amobarbital, which allows independent testing of the contralateral hemisphere. Initially used for lateralization of language, IAP later found a role in the evaluation of memory function in patients with intractable temporal lobe epilepsy being considered for resective surgery. IAP technique varies widely across centers, but, in general, memory is assessed by presenting the patient with a number of items during the period of hemispheric inactivation and testing recall or recognition of these items after the effect of the drug has worn off. Because the medial temporal lobe is not directly perfused by the internal carotid artery, concerns have been raised about the ability of the IAP to test hippocampal memory function. Consequently, a variety of selective procedures have been devised. Findings on both intracranial EEG recordings and pathologic and neuroimaging studies support the association of IAP memory results with hippocampal function. The IAP memory test was originally designed to predict the risk for development of global amnesia following unilateral temporal lobectomy. More recently, it also has been used as an adjunct in lateralizing the seizure focus and for predicting postoperative selective memory deficits and seizure outcome.

The intracarotid amobarbital procedure (Wada test) with two protocols combined, Montreal and Seattle

The intracarotid amobarbital procedure was carried out in 8 male and 7 female candidates to temporal lobectomy, and a female candidate to frontal lesionectomy, aged 18-50 (mean 32.5) years. Language and memory were tested after injection in each hemisphere. Both were measured by the Montreal procedure. In 9 patients language and memory were evaluated with the Seattle procedure too. In 12 patients the left hemisphere was dominant for language; three had bilateral dominance. In 1 patient the Seattle procedure demonstrated the dominant hemisphere by relatively slowness of speech during the drug effect in the left hemisphere. Memory was defined to be in the left hemisphere in 12 patients, in the right in 2, bilateral in 1 and in another lateralization was not possible. In 1 patient memory dominance was determined by the Montreal protocol alone because of lack of cooperation. These early results indicate that the methods may be complementary for determination of language and memory dominance in epilepsy surgery candidates.

Wada memory and timing of stimulus presentation

We compared Wada memory performance for stimuli presented at two timing intervals following amobarbital injection in 47 non-lesional patients with complex partial seizures (L = 26; R = 21). A significant interaction between seizure focus and timing of presentation was present (P < 0.03). Memory performance for objects whose presentation began approximately 50-55 s following amobarbital administration differed as a function of ipsilateral vs. contralateral injection at a very high level of statistical significance (P < 0.00001). Items presented approximately 4 min, 30 s post injection were also related to seizure onset literality, but at a lower statistical level (P < 0.01). Presentation of Wada memory stimuli earlier during hemispheric anaesthesia yields results that are more sensitive to lateralized temporal lobe seizure onset than does presentation of items later during the procedure.

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.

Effect of focus lateralization on memory assessment during the intracarotid amobarbital procedure

Despite the use of stimuli that can be processed by both hemispheres, a number of studies have reported lower memory scores after the left intracarotid amobarbital procedure (IAP) than after the right IAP. Because of that, failure after ipsilateral IAP is observed more often in patients with a left temporal seizure focus (LT) than in right temporal patients (RT), possibly needlessly excluding some LT patients from surgery. In order to overcome the deleterious effects of anesthetizing the dominant hemisphere, we designed an IAP protocol that did not promote verbal encoding of the stimuli. For this purpose, a large number of visual and tactile stimuli (colored pictures and real objects) were presented to be recognized later. The effect of seizure focus lateralization was examined in 82 temporal lobe epileptic patients who underwent IAP as part of their presurgical evaluation. As expected, for both RT and LT patients, long-term recognition of pictures presented under the effect of amobarbital was highly sensitive to the presence of a contralateral epileptic focus. However, contrary to what is generally reported, LT patients performed better than RT patients when their left (ipsilateral) hemisphere was anesthetized. In RT patients, although memory scores were lower after the left contralateral injection, the disparity in memory scores between the right and left injection was not as marked as in LT patients. These results are discussed in terms of the influence of type of processing required during the initial encoding on later recognition during IAP.

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

PURPOSE

To examine the effects of memory stimulus type on Wada memory performance.

METHOD

Ninety-six patients (left, 47; right, 49) from four epilepsy centers who were candidates for anterior temporal lobectomy (ATL) and who have subsequently undergone surgery were studied. Patients with atypical cerebral language lateralization or with evidence on magnetic resonance imaging (MRI) to suggest a lesion other than hippocampal sclerosis were excluded. Wada memory performance was obtained by using both real objects and line drawings as memory stimuli.

RESULTS

Wada memory laterality scores with either real objects or line drawings as memory stimuli discriminated left from right-ATL groups. However, objects were superior to line drawings in making this differentiation. Further, objects were superior to line drawings in individual patient classification of candidates for left ATL, with no difference in the classification rates using either objects or line drawings in candidates for right ATL.

CONCLUSIONS

Type of memory stimuli is an important factor affecting memory results during the Wada test.

Relation between intracarotid amobarbital memory asymmetry scores and hippocampal sclerosis in patients undergoing anterior temporal lobe resections

The intracarotid amobarbital procedure (IAP) is used to evaluate memory function preoperatively in candidates for anterior temporal lobe resections (ATL). We examined IAP memory asymmetry scores in 30 patients undergoing ATL (17 R, 13 L), as a function of the presence (HS+) or absence (HS-) of hippocampal sclerosis. Ictal onset zones were determined by extraoperative recording with subdural strip electrodes in all but 3 patients in whom magnetic resonance imaging (MRI) scan showed HS. MRI scans were otherwise normal. All patients were left hemisphere dominant for language except 1, in whom language was represented bilaterally. IAP memory testing involved presentation of eight subjects during anesthesia of each hemisphere, followed by recognition testing after patients recovered from amobarbital effects. A score of 1 was given for each correctly recognized object, and 0.5 was deducted for each false-positive identification. There were 16 foils. A total asymmetry score was calculated, which was positive if there was agreement between the direction of the symmetry and side of operation and negative if reversed. The mean asymmetry score for HS- (n = 8) was 0.9; that for HS+ (n = 22) was 4.1 (p < 0.01). IAP memory performance provided lateralizing information (asymmetry score > or = + or -2) in 73% of cases; among these, the lateralization was correct in 91%. Our data indicate that IAP memory asymmetry predicts both laterality of ictal onset and the presence of HS.

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.

Amnesia after unilateral temporal lobectomy: a case report

We report a mixed handed (L > R) patient with exclusive right cerebral language representation who developed a permanent anterograde amnestic syndrome after right anterotemporal lobectomy. Preoperative neuropsychological performance consisted of impaired verbal memory and normal nonverbal memory. Wada memory performance was asymmetrical for objects presented soon after amobarbital injection in conjunction with no memory asymmetry for items presented later in the Wada evaluation. Pre- and postoperative magnetic resonance imaging (MRI) scans showed no structural lesions; however, postoperative MRI hippocampal volume measurements suggested decreased hippocampal volume for the nonresected temporal lobe. These results confirm the risk of anterograde amnesia after unilateral temporal lobectomy and demonstrate that baseline neuropsychological testing may falsely literalize material-specific memory functions in patients with atypical cerebral language dominance.