Antiepileptic drug clearance and seizure frequency during pregnancy in women with epilepsy.

The aims of the study were to characterize the magnitude of clearance changes during pregnancy for multiple antiepileptic drugs (AEDs) and to assess seizure frequency and factors increasing seizure risk in pregnant women with epilepsy. A retrospective analysis was performed for 115 pregnancies in 95 women with epilepsy followed at the Emory Epilepsy Center between 1999 and 2012. Antiepileptic drug blood levels (ABLs) obtained during routine clinical practice were used to calculate AED clearance at multiple points during pregnancy. Antiepileptic drug doses and seizure activity were also recorded. The data were analyzed for changes in clearance and dose across pregnancy and for an association between ABL and changes in seizure frequency. Significant changes in clearance during pregnancy were observed for lamotrigine (p<0.001) and levetiracetam (p<0.006). Average peak clearance increased by 191% for lamotrigine and 207% for levetiracetam from nonpregnant baseline. Marked variance was present across individual women and also across repeat pregnancies in individual women. Despite increased AED dose across most AEDs, seizures increased in 38.4% of patients during pregnancy. Seizure deterioration was significantly more likely in patients with seizures in the 12 months prior to conception (p<0.001) and those with localization-related epilepsy (p=0.005). When ABL fell >35% from preconception baseline, seizures worsened significantly during the second trimester when controlling for seizure occurrence in the year prior to conception. Substantial pharmacokinetic changes during pregnancy occur with multiple AEDs and may increase seizure risk. Monitoring of AED serum concentrations with dose adjustment is recommended in pregnant women with epilepsy. Further studies are needed for many AEDs.

Differential effects of antiepileptic drugs on neonatal outcomes.

Offspring of women with epilepsy (WWE) on AEDs are at increased risks for major congenital malformations and reduced cognition. They may be at risk for other adverse neonatal outcomes. Women with epilepsy on carbamazepine (CBZ), lamotrigine (LTG), phenytoin (PHT), or valproate (VPA) monotherapy were enrolled in a prospective, observational, multicenter study of the neurodevelopmental effects of AEDs. The odds ratio for small for gestational age (SGA) was higher for VPA vs. PHT, VPA vs. LTG, and CBZ vs. PHT. Microcephaly rates were elevated to 12% for all newborns and at 12 months old, but normalized by age 24 months. Reduced Apgar scores occurred more frequently in the VPA and PHT groups at 1 min, but scores were near normal in all groups at 5 min. This study demonstrates increased risks for being born SGA in the VPA and CBZ groups, and transiently reduced Apgar scores in the VPA and PHT groups. Differential risks among the AEDs can help inform decisions about AED selection for women during childbearing years.

The effect of topiramate plasma concentration on linguistic behavior, verbal recall and working memory.

This is the first study of the effect of topiramate on linguistic behavior and verbal recall using a computational linguistics system for automated language and speech analysis to detect and quantify drug-induced changes in speech recorded during discourse-level tasks. Healthy volunteers were administered a single, 100-mg oral dose of topiramate in two double-blind, randomized, placebo-controlled, crossover studies. Subjects' topiramate plasma levels ranged from 0.23 to 2.81 µg/mL. We found a significant association between topiramate levels and impairment on measures of verbal fluency elicited during a picture description task, correct number of words recalled on a paragraph recall test, and reaction time recorded during a working memory task. Using the tools of clinical pharmacology and computational linguistics, we elucidated the relationship between the determinants of a drug's disposition as reflected in plasma concentrations and their impact on cognitive functioning as reflected in spoken language discourse.

Effects of fetal antiepileptic drug exposure: outcomes at age 4.5 years.

OBJECTIVE: To examine outcomes at age 4.5 years and compare to earlier ages in children with fetal antiepileptic drug (AED) exposure. METHODS: The NEAD Study is an ongoing prospective observational multicenter study, which enrolled pregnant women with epilepsy on AED monotherapy (1999-2004) to determine if differential long-term neurodevelopmental effects exist across 4 commonly used AEDs (carbamazepine, lamotrigine, phenytoin, or valproate). The primary outcome is IQ at 6 years of age. Planned analyses were conducted using Bayley Scales of Infant Development (BSID at age 2) and Differential Ability Scale (IQ at ages 3 and 4.5). RESULTS: Multivariate intent-to-treat (n = 310) and completer (n = 209) analyses of age 4.5 IQ revealed significant effects for AED group. IQ for children exposed to valproate was lower than each other AED. Adjusted means (95% confidence intervals) were carbamazepine 106 (102-109), lamotrigine 106 (102-109), phenytoin 105 (102-109), valproate 96 (91-100). IQ was negatively associated with valproate dose, but not other AEDs. Maternal IQ correlated with child IQ for children exposed to the other AEDs, but not valproate. Age 4.5 IQ correlated with age 2 BSID and age 3 IQ. Frequency of marked intellectual impairment diminished with age except for valproate (10% with IQ <70 at 4.5 years). Verbal abilities were impaired for all 4 AED groups compared to nonverbal skills. CONCLUSIONS: Adverse cognitive effects of fetal valproate exposure persist to 4.5 years and are related to performances at earlier ages. Verbal abilities may be impaired by commonly used AEDs. Additional research is needed.

Topiramate dose effects on cognition: a randomized double-blind study.

BACKGROUND: Topiramate (TPM), a broad-spectrum antiepileptic drug, has been associated with neuropsychological impairment in patients with epilepsy and in healthy volunteers. OBJECTIVE: To establish whether TPM-induced neuropsychological impairment emerges in a dose-dependent fashion and whether early cognitive response (6-week) predicts later performance (24-week). METHODS: Computerized neuropsychological assessment was performed on 188 cognitively normal adults who completed a double-blind, placebo-controlled, parallel-group, 24-week, dose-ranging study which was designed primarily to assess TPM effects on weight. Target doses were 64, 96, 192, or 384 mg per day. The Computerized Neuropsychological Test Battery was administered at baseline and 6, 12, and 24 weeks. Individual cognitive change was established using reliable change index (RCI) analysis. RESULTS: Neuropsychological effects emerged in a dose-dependent fashion in group analyses (p < 0.0001). RCI analyses showed a dose-related effect that emerged only at the higher dosing, with 12% (64 mg), 8% (96 mg), 15% (192 mg), and 35% (384 mg) of subjects demonstrating neuropsychological decline relative to 5% declining in the placebo group. Neuropsychological change assessed at 6 weeks significantly predicted individual RCI outcome at 24 weeks. CONCLUSIONS: Neuropsychological impairment associated with TPM emerges in a dose-dependent fashion. Subjects more likely to demonstrate cognitive impairment after 24 weeks of treatment can be identified early on during treatment (i.e., within 6 weeks). RCI analysis provides a valuable approach to quantify individual neuropsychological risk.

Effects of breastfeeding in children of women taking antiepileptic drugs.

BACKGROUND: Breastfeeding is known to have beneficial effects, but there is concern that breastfeeding during antiepileptic drug (AED) therapy may be harmful to cognitive development. Animal and human studies have demonstrated that some AEDs can adversely affect the immature brain. However, no investigation has examined effects of breastfeeding during AED therapy on subsequent cognitive abilities in children. METHODS: The Neurodevelopmental Effects of Antiepileptic Drugs Study is an ongoing prospective multicenter observational investigation of long-term effects of in utero AED exposure on cognition. Between 1999 and 2004, we enrolled pregnant women with epilepsy who were taking a single AED (carbamazepine, lamotrigine, phenytoin, or valproate). We recently reported on differential AED effects on age 3 year cognitive outcomes. In this report, we focus on the effects of breastfeeding during AED therapy on age 3 cognitive outcomes in 199 children. RESULTS: A total of 42% of children were breastfed. IQs for breastfed children did not differ from nonbreastfed children for all AEDs combined and for each of the 4 individual AED groups. Mean adjusted IQ scores (95% confidence intervals) across all AEDs were breastfed = 99 (96-103) and nonbreastfed = 98 (95-101). Power was 95% to detect a half SD IQ effect in the combined AED analysis, but was inadequate within groups. CONCLUSIONS: This preliminary analysis fails to demonstrate deleterious effects of breastfeeding during AED therapy on cognitive outcomes in children previously exposed in utero. However, caution is advised due to study limitations. Additional research is needed to confirm this observation and extend investigations to other AEDs and polytherapy.

Is antiepileptic drug use related to depression and suicidal ideation among patients with epilepsy?

Depression and suicide are increased in patients with epilepsy. The U.S. Food and Drug Administration warns that antiepileptic drugs (AEDs) are associated with increased risk of suicidality. This study examines the relationship among depression, suicidal ideation, and AEDs in a prospective cohort of 163 patients with epilepsy from a registry at the University of Florida (January 2006 to August 2008). The Neurological Disorders Depression Inventory for Epilepsy (NDDI-E) was used to measure mood and suicidal ideation across two time points (median = 154 days). Groups included: (1) No AED Change, (2) New AED Added, (3) AED Dose Increased, (4) AED Reduced/Stopped, (5) Multiple AED Changes, and (6) Combined Any AED Change (groups 2-5 combined). No group had worsening mood or suicidal ideation. Significant improvements in proportions of depression and suicidal ideation were seen only for the No AED Change group, which differed only with the AED Dose Increased group with respect to suicidal ideation.

Subjective perception of cognition is related to mood and not performance.

OBJECTIVE: Clinicians monitor cognitive effects of drugs primarily by asking patients to describe their side effects. We examined the relationship of subjective perception of cognition to mood and objective cognitive performance in healthy volunteers and neurological patients. METHODS: Three separate experiments used healthy adults treated with lamotrigine (LTG) and topiramate (TPM), adults with epilepsy on LTG or TPM, and patients with idiopathic Parkinson's disease. Correlations were calculated for change scores on and off drugs in the first two experiments and for the single assessment in Experiment 3. RESULTS: Across all three experiments, significant correlations were more frequent (chi(2)=259, P < or = 0.000) for mood versus subjective cognitive perception (59%) compared with subjective versus objective cognition (2%) and mood versus objective cognitive performance (2%). CONCLUSIONS: Subjective perception of cognitive effects is related more to mood than objective performance. Clinicians should be aware of this relationship when assessing patients' cognitive complaints.

Neuropsychological and neurophysiologic effects of carbamazepine and levetiracetam.

BACKGROUND: The relative effects of levetiracetam (LEV) and carbamazepine (CBZ) on cognitive and neurophysiologic measures are uncertain. METHODS: The effects of LEV and CBZ were compared in healthy adults using a randomized, double-blind, two-period crossover design. Outcome measures included 11 standard neuropsychological tests and the score from a cognitive-neurophysiologic test of attention and memory. Evaluations were conducted at screening, baseline pre-drug treatment, end of each maintenance phase (4 weeks), and end of each washout period after drug treatment. RESULTS: A total of 28 adults (17 women) with mean age of 33 years (range 18 to 51) completed the study. Mean maintenance doses (+/-SD) were CBZ = 564 mg/day (110) and LEV = 2,000 mg/day (0). CBZ was adjusted to mid-range therapeutic level. Mean serum levels (+/-SD) were CBZ = 7.5 mcg/mL (1.5) and LEV = 32.2 mcg/mL (11.2). An overall composite score including all measures revealed worse effects for CBZ compared to LEV (p

In utero antiepileptic drug exposure: fetal death and malformations.

BACKGROUND: Pregnancy outcomes following in utero exposure to antiepileptic drugs (AEDs) are uncertain, limiting an evidenced-based approach. OBJECTIVE: To determine if fetal outcomes vary as a function of different in utero AED exposures. METHODS: This ongoing prospective observational study across 25 epilepsy centers in the USA and UK enrolled pregnant women with epilepsy from October 1999 to February 2004 to determine if differential long-term cognitive and behavioral neurodevelopmental effects exist across the four most commonly used AEDs. This initial report focuses on the incidence of serious adverse outcomes including major congenital malformations (which could be attributable to AEDs) or fetal death. A total of 333 mother/child pairs were analyzed for monotherapy exposures: carbamazepine (n = 110), lamotrigine (n = 98), phenytoin (n = 56), and valproate (n = 69). RESULTS: Response frequencies of pregnancies resulting in serious adverse outcomes for each AED were as follows: carbamazepine 8.2%, lamotrigine 1.0%, phenytoin 10.7%, and valproate 20.3%. Distribution of serious adverse outcomes differed significantly across AEDs and was not explained by factors other than in utero AED exposure. Valproate exhibited a dose-dependent effect. CONCLUSIONS: More adverse outcomes were observed in pregnancies with in utero valproate exposure vs the other antiepileptic drugs (AEDs). These results combined with several recent studies provide strong evidence that valproate poses the highest risk to the fetus. For women who fail other AEDs and require valproate, the dose should be limited if possible.

Cognitive and behavioral effects of lamotrigine and topiramate in healthy volunteers.

BACKGROUND: The relative cognitive and behavioral effects of lamotrigine (LTG) and topiramate (TPM) are unclear. METHODS: The authors directly compared the cognitive and behavioral effects of LTG and TPM in 47 healthy adults using a double-blind, randomized crossover design with two 12-week treatment periods. During each treatment condition, subjects were titrated to receive either LTG or TPM at a target dose of 300 mg/day for each. Neuropsychological evaluation included 17 measures yielding 41 variables of cognitive function and subjective behavioral effects. Subjects were tested at the end of each antiepileptic drug (AED) treatment period and during two drug-free conditions (pretreatment baseline and 1 month following final AED withdrawal). RESULTS: Direct comparison of the two AEDs revealed significantly better performance on 33 (80%) variables for LTG, but none for TPM. Even after adjustment for blood levels, performance was better on 19 (46%) variables for LTG, but none for TPM. Differences spanned both objective cognitive and subjective behavioral measures. Comparison of TPM to the non-drug average revealed significantly better performance for non-drug average on 36 (88%) variables, but none for TPM. Comparison of LTG to non-drug average revealed better performance on 7 (17%) variables for non-drug average and 4 (10%) variables for LTG. CONCLUSIONS: Lamotrigine produces significantly fewer untoward cognitive and behavioral effects compared to topiramate (TPM) at the dosages, titrations, and timeframes employed in this study. The dosages employed may not have been equivalent in efficacy. Future studies are needed to delineate the cognitive and behavioral effects of TPM at lower dosages.

Differential cognitive and behavioral effects of topiramate and valproate.

OBJECTIVE: Cognitive effects have been reported during topiramate (TPM) treatment, but effects relative to standard antiepileptic drugs are unclear. METHODS: The authors compared TPM and valproate (VPA) added to carbamazepine (CBZ) in adults with partial seizures. A comprehensive neuropsychological test battery including cognitive, mood, and quality of life measures was used in this multicenter, randomized, double-blind study. After a 4-week baseline, study drug was titrated over 8 weeks to target dosages of 400 mg/d TPM, 2,250 mg/d VPA, or placebo and then maintained for an additional 12 weeks. The neuropsychological test battery was administered at baseline and at the end of titration and maintenance periods. RESULTS: Slightly more patients on TPM dropped out. Neuropsychological data at all three test periods were available for 62 patients. At the end of maintenance, effects of TPM and VPA were comparable, except for two variables (Symbol Digit Modalities Test and Controlled Oral Word Association Test), in which TPM had greater negative effects relative to VPA. The statistical differences appeared to be due in large part to a small subset of patients who were more negatively affected by TPM. Cognitive effects of TPM relative to VPA were greater at the end of titration than at the end of maintenance. CONCLUSIONS: With adjunctive therapy at moderate dose escalation rate, the cognitive effects of TPM are slightly worse overall than VPA in patients who tolerate therapy over several months.

Gamma coherence and conscious perception.

BACKGROUND: High-frequency (e.g., gamma 30 to 50 Hz) coherent neural activity has been postulated to underlie binding of independent neural assemblies and thus integrate processing across distributed neuronal networks to achieve a unified conscious experience. Prior studies suggest that gamma activity may play a role in perceptual mechanisms, but design limitations raise concerns. Thus, controversy exists as to the hypothesis that gamma activity is necessary for perceptual awareness. In addition, controversy exists as to whether the primary sensory cortices are involved directly in the mechanisms of conscious perception or just in processes prior to conscious awareness. OBJECTIVE: To investigate the relation of gamma coherence and perception. METHODS: Digital intracranial electrocorticographic recordings from implanted electrodes were obtained in six patients with intractable epilepsy during a simple somatosensory detection task for near-threshold stimuli applied to the contralateral hand. Signal analyses were then conducted using a quantitative approach that employed two-way Hanning digital bandpass filters to compute running correlations across pairs of channels at various time epochs for each patient and each perception state across multiple bandwidths. RESULTS: Gamma coherence occurs in the primary somatosensory cortex approximately 150 to 300 milliseconds after contralateral hand stimuli that are perceived, but not for nonperceived stimuli, which did not differ in character/intensity or early somatosensory evoked potentials. CONCLUSION: The results are consistent with the possible direct involvement of primary sensory cortex in elemental awareness and with a role for gamma coherence in conscious perception.

[Intracarotid amytal testing in the evaluation for epilepsy surgery]. / Test del amital intracarotídeo para evaluar la cirugía de la epilepsia.

INTRODUCTION: The Wada test for language and memory still plays an important role in evaluating the surgery performed on epileptic patients. The measures of the functional deficits carried out with the Wada test, associated with known brain lesions, aid in determining the lateralization of the onset of seizures and provide some estimate of the risk to memory after a temporal lobotomy. DEVELOPMENT: A more refined procedure, based on the correlations with the titration from MRI, fMR and MR spectroscopy, will be needed. Moreover, using the Wada test it is possible to make long term forecasts about the cognitive outcome and about the control of seizures. When used together with other neurological, functional and psychometric evaluations, it becomes easier to select the patients with most chances of benefiting from surgical epilepsy treatment. Finally, the non invasive measures of brain functioning include fMR, which provides far more information than that obtained using the Wada test. However, it remains to be determined whether the procedure based on activation provides data of the same quality as those obtained by the Wada test, which can provide a more adequate reversible model of the effects of surgery on cognition. CONCLUSION: . Ideally, as MRI and other imaging techniques progress, they will be able to offer complementary images, which will improve our capacity to forecast and prevent important post operative cognitive deficiencies.

Test del amital intracarotídeo para evaluar la cirugía de la epilepsia / Intracarotid amytal testing in the evaluation for epilepsy surgery

Introducción. El test de Wada del lenguaje y la memoria todavía desempeña un papel importante en la evaluación de la cirugía en pacientes epilépticos. Las medidas de los déficit funcionales realizadas con el test de Wada, asociadas con conocidas lesiones cerebrales, contribuyen a establecer la lateralización del inicio de las crisis y proporcionan alguna estimación del riesgo en la memoria tras la lobotomía temporal. Desarrollo. Habrá que proseguir con un procedimiento más preciso, basado en las correlaciones con la volumetría de RM, RMf y espectroscopía por RM. Y más importante: la predicción a largo plazo del resultado cognitivo y del control de las crisis es posible con el test de Wada, en conjunción con otras valoraciones neurológicas, funcionales y psicométricas que faciliten la selección de pacientes que con mayor probabilidad se pueden beneficiar del tratamiento quirúrgico de la epilepsia. Las medidas no invasivas de la función cerebral incluyen la RMf, que proporcionará mucha más información que la derivada del test de Wada. Sin embargo, todavía se ha de establecer si el procedimiento basado en la activación puede ofrecer datos comparables a los del test de Wada, que puede proporcionar un modelo reversible más adecuado de los efectos quirúrgicos sobre la cognición. Conclusión. Idealmente, los avances en la RMf y otras técnicas de imagen proporcionarán una imagen complementaria que mejorará la capacidad de predecir y evitar los importantes déficit cognitivos postoperatorios (AU)

Topography of somatosensory processing: cerebral lateralization and focused attention.

Healthy dextrals underwent fMRI during a task of graphesthesia requiring detection of any number written consecutively from an otherwise random number sequence. Test conditions included (1) focus on unilateral right hand stimuli, (2) focus on unilateral left hand stimuli, (3) focus on right hand only during bilateral hand stimulation, (4) focus on left hand only during bilateral hand stimulation, and (5) rest. Attention to unilateral hand stimulation produced bihemispheric activation with minimal or no activation of ipsilateral primary sensorimotor region. Attention to unilateral left hand stimuli resulted in more activation than attention to unilateral right hand stimuli. Stimulation of the nonattended hand activated the contralateral somatosensory area, but to a lesser spatial extent than attended stimuli. Comparing focused attention to the left versus right side during identical sensory inputs (i.e., bilateral hand stimulation), focused attention to the right hand increased activation in the left somatosensory region, but focused attention to the left hand increased activation in both cerebral hemispheres. Thus, focused attention to unilateral somatosensory stimuli produces bilateral cerebral activation, but the increase in blood flow is greater in the contralateral hemisphere. Unattended stimuli activate the contralateral primary somatosensory area. Left/right asymmetries were demonstrated consistent with cerebral lateralization.

Now you see it, now you don't: statistical and methodological considerations in fMRI.

We illustrate the effects of statistical threshold, spatial clustering, voxel size, and two approaches to multiple comparison correction on fMRI results. We first analyzed fMRI images obtained from a single subject during a noun-verb matching task. Data were analyzed with Statistical Parametric Mapping (SPM) using two different voxel sizes, and results were displayed at three different levels of statistical significance. At each statistical threshold, results were first uncorrected for multiple comparisons and spatial extent and then presented using a spatial extent cluster of 20 voxels. We then statistically controlled the Type I error rate associated with multiple comparisons by using the false discovery rate and by the random field adjustment for false-positive rate used by SPM. We also examined group results from language and graphesthesia paradigms at three levels of statistical significance. In all circumstances, apparent random activations decreased as more conservative statistical approaches were employed, but activation in areas considered to be functionally significant was also reduced. These issues are important in the choice of analytic approach and interpretation of fMRI results, with clear implications for the surgical management of individual patients when fMRI results are used to delineate specific areas of eloquent cortex.

Differential cognitive and behavioral effects of carbamazepine and lamotrigine.

BACKGROUND: The relative cognitive and behavioral effects of lamotrigine compared with the older standard antiepileptic drugs (AED) are uncertain. OBJECTIVE: To directly compare the cognitive and behavioral effects of carbamazepine and lamotrigine. METHODS: The cognitive and behavioral effects of carbamazepine and lamotrigine were assessed in 25 healthy adults using a double-blind, randomized crossover design with two 10-week treatment periods. During each treatment condition, subjects received either lamotrigine (150 mg/day) or carbamazepine (mean 696 mg/day) adjusted to a dose to achieve midrange standard therapeutic blood levels (mean 7.6 microg/mL). Subjects were tested at the end of each AED treatment period and in three drug-free conditions (two pretreatment baselines and a final posttreatment period [1 month after last AED]). The neuropsychological test battery included 19 measures yielding 40 total variables. RESULTS: Direct comparison of the two AED revealed significantly better performance on 19 (48%) variables for lamotrigine but none for carbamazepine. Differences spanned both objective cognitive and subjective behavioral measures, including cognitive speed, memory, graphomotor coding, neurotoxic symptoms, mood factors, sedation, perception of cognitive performance, and other quality-of-life perceptions. Comparison of carbamazepine with the nondrug average revealed significantly better performance for nondrug average on 24 (62%) variables but none for carbamazepine. Comparison of lamotrigine with nondrug average revealed better performance on one (2.5%) variable for nondrug average and on one (2.5%) variable for lamotrigine. CONCLUSION: Lamotrigine produces significantly fewer untoward cognitive and behavioral effects than carbamazepine at the dosages used in this study.

Relationship of extinction to perceptual thresholds for single stimuli.

OBJECTIVE: To demonstrate the effects of target stimulus intensity on extinction to double simultaneous stimuli. BACKGROUND: Attentional deficits contribute to extinction in patients with brain lesions, but extinction (i.e., masking) can also be produced in healthy subjects. The relationship of extinction to perceptual thresholds for single stimuli remains uncertain. METHODS: Brief electrical pulses were applied simultaneously to the left and right index fingers of 16 healthy volunteers (8 young and 8 elderly adults) and 4 patients with right brain stroke (RBS). The stimulus to be perceived (i.e., target stimulus) was given at the lowest perceptual threshold to perceive any single stimulus (i.e., Minimal) and at the threshold to perceive 100% of single stimuli. The mask stimulus (i.e., stimulus given to block the target) was applied to the contralateral hand at intensities just below discomfort. RESULTS: Extinction was less for target stimuli at 100% than Minimal threshold for healthy subjects. Extinction of left targets was greater in patients with RBS than elderly control subjects. Left targets were extinguished less than right in healthy subjects. In contrast, the majority of left targets were extinguished in patients with RBS even when right mask intensity was reduced below right 100% threshold for single stimuli. RBS patients had less extinction for right targets despite having greater left mask - threshold difference than control subjects. In patients with RBS, right "targets" at 100% threshold extinguished left "masks" (20%) almost as frequently as left masks extinguished right targets (32%). CONCLUSIONS: Subtle changes in target intensity affect extinction in healthy adults. Asymmetries in mask and target intensities (relative to single-stimulus perceptual thresholds) affect extinction in RBS patients less for left targets but more for right targets as compared with control subjects.