Usefulness of language and memory testing during intracarotid amobarbital testing: observations from an fMRI study

Mapping of Language-and-Memory Networks in Patients With Temporal Lobe Epilepsy by Using the GE2REC Protocol

Preoperative mapping of language and declarative memory functions in temporal lobe epilepsy (TLE) patients is essential since they frequently encounter deterioration of these functions and show variable degrees of cerebral reorganization. Due to growing evidence on language and declarative memory interdependence at a neural and neuropsychological level, we propose the GE2REC protocol for interactive language-and-memory network (LMN) mapping. GE2REC consists of three inter-related tasks, sentence generation with implicit encoding (GE) and two recollection (2REC) memory tasks: recognition and recall. This protocol has previously been validated in healthy participants, and in this study, we showed that it also maps the LMN in the left TLE (N = 18). Compared to healthy controls (N = 19), left TLE (LTLE) showed widespread inter- and intra-hemispheric reorganization of the LMN through reduced activity of regions engaged in the integration and the coordination of this meta-network. We also illustrated how this protocol could be implemented in clinical practice individually by presenting two case studies of LTLE patients who underwent efficient surgery and became seizure-free but showed different cognitive outcomes. This protocol can be advantageous for clinical practice because it (a) is short and easy to perform; (b) allows brain mapping of essential cognitive functions, even at an individual level; (c) engages language-and-memory interaction allowing to evaluate the integrative processes within the LMN; (d) provides a more comprehensive assessment by including both verbal and visual modalities, as well as various language and memory processes. Based on the available postsurgical data, we presented preliminary results obtained with this protocol in LTLE patients that could potentially inform the clinical practice. This implies the necessity to further validate the potential of GE2REC for neurosurgical planning, along with two directions, guiding resection and describing LMN neuroplasticity at an individual level.

Interactive mapping of language and memory with the GE2REC protocol

Previous studies have highlighted the importance of considering cognitive functions from a dynamic and interactive perspective and multiple evidence was brought for a language and memory interaction. In this study performed with healthy participants, we present a new protocol entitled GE2REC that interactively accesses the neural representation of language-and-memory network. This protocol consists of three runs related to each other, providing a link between tasks, in order to assure an interactive measure of linguistic and episodic memory processes. GE2REC consists of a sentence generation (GE) in the auditory modality and two recollecting (2REC) memory tasks, one recognition performed in the visual modality, and another one recall performed in the auditory modality. Its efficiency was evaluated in 20 healthy volunteers using a 3T MR imager. Our results corroborate the ability of GE2REC to robustly activate fronto-temporo-parietal language network as well as temporal mesial, prefrontal and parietal cortices in encoding during sentence generation and recognition. GE2REC is useful because it: (a) requires simultaneous and interactive language-and-memory processes and jointly maps their neural basis; (b) explores encoding and retrieval, managing to elicit activation of mesial temporal structures; (c) is easy to perform, hence being suitable for more restrictive settings, and (d) has an ecological dimension of tasks and stimuli. GE2REC may be useful for studying neuroplasticity of cognitive functions, especially in patients with temporal lobe epilepsy who show reorganization of both language and memory networks. Overall, GE2REC can provide valuable information in terms of the practical foundation of exploration language and memory interconnection.

Concordance between fMRI and Wada test for memory lateralization in temporal lobe epilepsy: A meta-analysis and systematic review

OBJECTIVE

The Wada test (WT) is increasingly being replaced by functional magnetic resonance imaging (fMRI) to evaluate memory lateralization before temporal lobe epilepsy (TLE) surgery. We aimed to determine, via meta-analysis, agreement between the two tests and identify predictors of disagreement.

METHODS

We performed a systematic search for studies comparing WT and fMRI for memory lateralization with individual-patient data. If results were provided as laterality indexes instead of hemispheric lateralization, the cutoff point for memory lateralization was set to the usual ±2 for WT and ±0.20 for fMRI. We also evaluated results at our Epilepsy Center.

RESULTS

Seven published series plus our own were included, comprising 124 patients. Wada test was performed by recognizing objects in half of the studies, and scenes, drawings, and words in the rest. All used scenes or pictures encoding for fMRI. Wada test-fMRI agreement across the studies ranged from 21.1 to 100%, averaging 46.8% (95% confidence interval [CI]: 37.6-56.0%). When cases with bilateral memory in either test were excluded, agreement reached 78.7% (95% CI: 67.6-89.8%), and concordance with contralateral TLE foci 86.4% for the WT and 83.0% for fMRI. Higher agreement was associated with using multiple items during WT (p = 0.001) and higher disagreement with presence of a lesion on MRI (p = 0.024). Binary logistic regression confirmed use of multiple items on WT as the strongest predictor of agreement (odds ratio [OR]: 6.95, 95% CI: 1.84-26.22; p = 0.004) and a bilateral result on the WT or fMRI of disagreement (OR: 0.24, 95% CI: 0.07-0.89 and OR: 0.12, 95% CI: 0.03-0.45; p < 0.05).

CONCLUSION

Concordance between WT and fMRI for memory lateralization is low in patients with TLE and bilateral memoryl memory distribution or a structural etiology, and it improves with encoding of a varied set of items. Both tests can help to lateralize the TLE foci.

NEREC, an effective brain mapping protocol for combined language and long-term memory functions

Temporal lobe epilepsy can induce functional plasticity in temporoparietal networks involved in language and long-term memory processing. Previous studies in healthy subjects have revealed the relative difficulty for this network to respond effectively across different experimental designs, as compared to more reactive regions such as frontal lobes. For a protocol to be optimal for clinical use, it has to first show robust effects in a healthy cohort. In this study, we developed a novel experimental paradigm entitled NEREC, which is able to reveal the robust participation of temporoparietal networks in a uniquely combined language and memory task, validated in an fMRI study with healthy subjects. Concretely, NEREC is composed of two runs: (a) an intermixed language-memory task (confrontation naming associated with encoding in nonverbal items, NE) to map language (i.e., word retrieval and lexico-semantic processes) combined with simultaneous long-term verbal memory encoding (NE items named but also explicitly memorized) and (b) a memory retrieval task of items encoded during NE (word recognition, REC) intermixed with new items. Word recognition is based on both perceptual-semantic familiarity (feeling of 'know') and accessing stored memory representations (remembering). In order to maximize the remembering and recruitment of medial temporal lobe structures, we increased REC difficulty by changing the modality of stimulus presentation (from nonverbal during NE to verbal during REC). We report that (a) temporoparietal activation during NE was attributable to both lexico-semantic (language) and memory (episodic encoding and semantic retrieval) processes; that (b) encoding activated the left hippocampus, bilateral fusiform, and bilateral inferior temporal gyri; and that (c) task recognition (recollection) activated the right hippocampus and bilateral but predominant left fusiform gyrus. The novelty of this protocol consists of (a) combining two tasks in one (language and long-term memory encoding/recall) instead of applying isolated tasks to map temporoparietal regions, (b) analyzing NE data based on performances recorded during REC, (c) double-mapping networks involved in naming and in long-term memory encoding and retrieval, (d) focusing on remembering with hippocampal activation and familiarity judgment with lateral temporal cortices activation, and (e) short duration of examination and feasibility. These aspects are of particular interest in patients with TLE, who frequently show impairment of these cognitive functions. Here, we show that the novel protocol is suited for this clinical evaluation.

Functional MRI applications in epilepsy surgery

Functional magnetic resonance imaging (fMRI) is a non-invasive neuroimaging technique that has grown rapidly in popularity over the past decade. It is already prevalent in psychology, cognitive and basic neuroscience research and is being used increasingly as a tool for clinical decision-making in epilepsy. It has been used to determine language location and laterality in patients, sometimes eliminating the need for invasive tests. fMRI can been used pre-surgically to guide resection margins, preserving eloquent cortex. Other fMRI paradigms assessing memory, visual and somatosensory systems have limited clinical applications currently, but show great promise. Simultaneous recording of electroencephalogram (EEG) and fMRI has also provided insights into the networks underlying seizure generation and is increasingly being used in epilepsy centres. In this review, we present some of the current clinical applications for fMRI in the pre-surgical assessment of epilepsy patients, and examine a number of new techniques that may soon become clinically relevant.

Brain plasticity for verbal and visual memories in patients with mesial temporal lobe epilepsy and hippocampal sclerosis: an fMRI study

We aimed to identify the brain areas involved in verbal and visual memory processing in normal controls and patients with unilateral mesial temporal lobe epilepsy (MTLE) associated with unilateral hippocampal sclerosis (HS) by means of functional magnetic resonance imaging (fMRI). The sample comprised nine normal controls, eight patients with right MTLE, and nine patients with left MTLE. All subjects underwent fMRI with verbal and visual memory paradigms, consisting of encoding and immediate recall of 17 abstract words and 17 abstract drawings. A complex network including parietal, temporal, and frontal cortices seems to be involved in verbal memory encoding and retrieval in normal controls. Although similar areas of activation were identified in both patient groups, the extension of such activations was larger in the left-HS group. Patients with left HS also tended to exhibit more bilateral or right lateralized encoding related activations. This finding suggests a functional reorganization of verbal memory processing areas in these patients due to the failure of left MTL system. As regards visual memory encoding and retrieval, our findings support the hypothesis of a more diffuse and bilateral representation of this cognitive function in the brain. Compared to normal controls, encoding in the left-HS group recruited more widespread cortical areas, which were even more widespread in the right-HS group probably to compensate for their right mesial temporal dysfunction. In contrast, the right-HS group exhibited fewer activated areas during immediate recall than the other two groups, probably related to their greater difficulty in dealing with visual memory content.

[Imaging in epilepsy: functional studies]

Neuroimaging studies play a fundamental role in the diagnosis and evaluation of epilepsy. Technological advances in neuroimaging techniques have made it possible to obtain functional as well as structural information. The pathophysiology of epilepsy consists of an abnormal increase in cerebral activity that can be appreciated on neuroimaging techniques like functional magnetic resonance imaging (fMRI), PET, and SPECT. In patients with epilepsy that is refractory to drug therapy, the main aim of surgery is to control seizures and thus to improve the quality of life. In the preoperative workup of these patients, fMRI has an increasingly important role, evaluating the location of functional areas that must be safeguarded during surgery.

Improvement of clinical language localization with an overt semantic and syntactic language functional MR imaging paradigm

BACKGROUND AND PURPOSE

Functional MR imaging (fMRI) is a promising but, in some aspects, still debated noninvasive tool for functional language mapping. We developed a clinical fMRI overt language design at the sentential level to optimize sensitivity for language-related areas of the brain. To evaluate applicability and sensitivity, we investigated a consecutive series of presurgical patients with epilepsy with minimal morphologic brain abnormalities.

MATERIALS AND METHODS

Thirty right-handed patients with temporal lobe epilepsy (TLE) and a control group of 23 right-handed healthy subjects participated in the study. The language design included semantic and syntactic error-detection tasks and was constructed to represent the most relevant aspects of everyday language demands. It was applied during block-designed fMRI runs. We performed image preprocessing and statistical analysis with SPM5 at a group level, applying widely used statistical criteria. The study was approved by the local ethics committee, and all participants gave written informed consent.

RESULTS

Given the strict statistical criteria, the sensitivity for inferior frontal and posterior temporal activations (comprising Broca and Wernicke regions) was improved relative to previous findings in the literature. For both language areas, we found 100% sensitivity in healthy subjects (Brodmann areas, BA22 and BA44) and 97% sensitivity in patients (when including BA47). Lateralization results demonstrated the capability to detect atypical language lateralizations in patients, which were more frequent in than those in healthy subjects.

CONCLUSIONS

We developed a clinical language fMRI design that integrates various relevant aspects of everyday language demands and provides robust localization of core language areas.

Functional MRI and Wada studies in patients with interhemispheric dissociation of language functions

Rare patients with chronic epilepsy show interhemispheric dissociation of language functions on intracarotid amobarbital (Wada) testing. We encountered four patients with interhemispheric dissociation in 490 consecutive Wada language tests. In all cases, performance on overt speech production tasks was supported by the hemisphere contralateral to the seizure focus, whereas performance on comprehension tasks was served by the hemisphere with the seizure focus. These data suggest that speech production capacity is more likely to shift hemispheres than is language comprehension. Wada and fMRI language lateralization scores were discordant in three of the four patients. However, the two methods aligned more closely when Wada measures loading on comprehension were used to calculate lateralization scores. Thus, interhemispheric dissociation of language functions could explain some cases of discordance on Wada/fMRI language comparisons, particularly when the fMRI measure used is not sensitive to speech production processes.

Functional brain mapping and its applications to neurosurgery

Functional brain mapping may be useful for both preoperative planning and intraoperative neurosurgical decision making. "Gold standard" functional studies such as direct electrical stimulation and recording are complemented by newer, less invasive techniques such as functional magnetic resonance imaging. Less invasive techniques allow more areas of the brain to be mapped in more subjects (including healthy subjects) more often (including pre- and postoperatively). Expansion of the armamentarium of tools allows convergent evidence from multiple brain mapping techniques to bear on pre- and intraoperative decision making. Functional imaging techniques are used to map motor, sensory, language, and memory areas in neurosurgical patients with conditions as diverse as brain tumors, vascular lesions, and epilepsy. In the future, coregistration of high resolution anatomic and physiological data from multiple complementary sources will be used to plan more neurosurgical procedures, including minimally invasive procedures. Along the way, new insights on fundamental processes such as the biology of tumors and brain plasticity are likely to be revealed.

Comparison between functional magnetic resonance imaging at 1.5 and 3 Tesla: effect of increased field strength on 4 paradigms used during presurgical work-up

OBJECTIVES

We sought to evaluate the benefit of 3 T compared with 1.5 T during presurgical functional magnetic resonance imaging.

MATERIALS AND METHODS

Six participants performed a motor, a visual, and 2 language paradigms both at 1.5 and 3 T. The number of activated voxels, mean t-value, and assessment of language dominancy were compared between both field strengths. Group analysis was performed to evaluate the influence of field strength on the cortical language activation patterns.

RESULTS

The number of activated voxels and mean t-values were significantly higher at 3 T for all paradigms. Using the same statistical threshold, language activation was significantly less lateralized, and more activation zones were depicted at 3 T compared with 1.5 T.

CONCLUSIONS

Sensitivity associated with visual, motor and language functional magnetic resonance imaging increased significantly at 3 T. Additional cortical areas were depicted during language processing at 3 T. For assessment of language dominancy, usage of more stringent statistical thresholds at 3 T is suggested.

Reliability of language mapping with magnetic source imaging in epilepsy surgery candidates

The external validity of a noninvasive language mapping protocol with magnetoencephalography (MEG) has been established through direct comparisons with invasive functional mapping techniques. This study examines the test-retest and interrater reliability of this protocol under realistic testing conditions in 21 epilepsy surgery candidates. Brain activation maps were obtained in the context of an auditory word recognition task and represented by temporally contiguous dipolar activity sources. Both the duration and strength of the associated magnetic flux were used as measures of the magnitude of regional brain activity. Hemispheric asymmetry indices based on these measures showed good interrater reliability and intraparticipant reproducibility. Similar findings were obtained with respect to the location of the geometric center of receptive language-specific cortex (Wernicke's) area in the dominant hemisphere. The results further support the adequacy of this MEG-based brain mapping protocol as a noninvasive tool for receptive language localization in epilepsy surgery candidates.

Language activation distributions revealed by fMRI in post-operative epilepsy patients: differences between left- and right-sided resections

OBJECTIVE

To reveal differences of cerebral activation related to language functions in post-operative temporal lobe epilepsy (TLE) patients.

METHODS

Right (RTL) and left temporal lobe (LTL) resected patients, and healthy controls were studied using functional magnetic resonance imaging (fMRI). Only patients with complete left-hemispheric language dominance according to the intracarotid amytal procedure (IAP) were included. Language-related activations were evoked by performing word generation and text reading language tasks. Activation lateralization and temporo-frontal distribution effects were analysed.

RESULTS

For word generation, only LTL patients showed reduced left lateralized activation compared to controls, due to a decrease in activation in the left prefrontal cortex and an increase in the right prefrontal cortex. For reading, the left-hemispheric lateralization in RTL patients increased because of enhanced activity in the left prefrontal cortex, whereas for LTL patients the activation became bilaterally distributed over the temporal lobes. Lateralization results between pre-operative IAP and post-operative fMRI were highly discordant. Significant temporo-frontal distribution changes manifested from the reading but not from the word generation task.

CONCLUSION

The cerebral language representation in post-operative LTL epilepsy patients is more bi-hemispherically lateralized than in controls and RTL patients. Post-operative temporo-frontal and interhemispheric redistribution effects, involving contralateral homologous brain areas, are suggested to contribute to the cerebral reorganisation of language function.

Lessons for neuropsychology from functional MRI in patients with epilepsy

This contribution aims to review the major findings of pre- and postsurgical functional magnetic resonance imaging (fMRI) in patients with refractory epilepsy from a neuropsychological perspective. We compared the contribution of fMRI with the intracarotid amytal procedure (IAP) with respect to functional mapping of language and memory in patients with therapy-resistant epilepsy. We conclude that using comprehensive language paradigms, fMRI has been able (1) to provide estimates of the degree of language lateralization including the degree of involvement of the nondominant hemisphere, (2) to provide information on the location of its activated network during expressive and receptive language, and (3) to help delineate eloquent language regions in the vicinity of the surgical target, thus preventing postoperative complications. The contribution of the frequently observed nondominant hemisphere activation to language should be explored and its clinical relevance determined. Evidence from fMRI studies is accumulating that reorganization of cognitive and motor function favors the activation of contralateral homotopic areas, although this process is far from understood. The exact functional contribution of atypical areas of activation should be investigated critically. In the presurgical evaluation process, detailed and reliable localization of language and memory functions of the individual patient is mandatory and should be the ultimate goal in the development of comprehensive clinical fMRI protocols.

Recognition memory of serially or simultaneously presented words or figures, of epilepsy patients with or without mesial temporal sclerosis

Previous studies, examining short-term recognition memory in patients with partial seizures as a consequence of mesial temporal sclerosis (MTS) have reported inconsistent findings. Dependent on the paradigms used for measuring recognition memory, some studies have demonstrated that the mesial temporal structures are not critically involved in short-term recognition memory. In addition, other studies found a lateralization effect that is consistent with the generally accepted association between left temporal lobe lesions and verbal memory deficits, and right temporal lobe lesions and non-verbal memory impairments. In the present study verbal and non-verbal recognition memory was tested in 41 patients with left or right temporal lobe epilepsy with MTS (22 left; 19 right) versus 44 patients with left or right temporal lobe epilepsy but without MTS (28 left; 16 right). Verbal and non-verbal recognition tasks were presented in both a serial and simultaneous condition to test a hypothesized local/global paradigm. Multiple analyses of variance (MANOVA) showed that unilateral MTS has no marked effects on verbal or non-verbal recognition memory of patients with seizures. An interaction effect between MTS and the lateralization of epileptic activity was found on memory performance: MTS only leads to deficits in recognition memory in patients with right-sided epileptiform activity. As hypothesized, patients with left temporal lobe abnormalities, have specific deficits with recognizing serially presented information.