Clinical relevance of memory performance during Wada is stimulus type dependent

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.

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.

Can pentobarbital replace amobarbital in the Wada test?

To investigate the usefulness of pentobarbital (PTB) in the Wada test, 32 patients injected with PTB and 28 patients injected with amobarbital (AMB) were retrospectively analyzed. The AMB and PTB groups did not significantly differ with respect to mean time for recovery to grade III or V motor activity and duration of EEG delta slowing. The incidence of drowsiness or confusion after injection was lower in the PTB group (P=0.043). Language lateralization was well established in both groups. Fifty-three percent of patients in the PTB group and 46.2% in the AMB group with unilateral temporal lobe epilepsy had memory dominance in the nonepileptic hemisphere. The usefulness of PTB in terms of language and memory lateralization was found to be equivalent to that of AMB. Moreover, PTB produced drowsiness and confusion less frequently than AMB, although one patient in the PTB group experienced transient respiratory depression without any sequelae.

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.

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

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