Basal Temporal Regions Research Articles

F152. Localization of the epileptogenic zone using direct cortical stimulation during stereo-EEG investigation

Introduction Direct cortical stimulation (CS) is commonly used to outline eloquent cortex where induced seizures are an undesirable side effect. Direct CS can also be used to induce habitual aura and seizures to confirm epileptogenic network (EZ) that is mapped to stereo EEG investigation. Evoked seizures can induce seizures that may or may not be similar to patient’s habitual seizure. The accuracy of CS-induced seizures in localizing EZ has not been studied systematically. Here we compare the CS-induced seizures with spontaneous seizures recorded during a stereo-EEG investigation at a level-IV epilepsy center. Methods We performed a retrospective review of all patients who underwent direct CS at our center during the years 2016–2017. Among these we identified and collected data on 13 patients who underwent direct CS for mapping EZ. Results 9 (69%) patients of the 13 were male, 4 (31%) were female, with a mean age of 33 years. Anatomical targets included mesial temporal lobe (hippocampus, amygdala, temporal pole), lateral and basal temporal regions, insula, anterior cingulate, and orbitofrontal regions. 54% (N = 7) had abnormal brain MRI. Spontaneous seizures were localized to - hippocampus, amygdala hippocampus, hippocampus-temporal pole, ant. Cingulum, superior temporal gyrus, and frontal operculum. With direct CS, 7 (54%) had typical seizures (aura followed by seizures with impaired awareness), 4 (31%) had atypical seizures (aura and clonic activity), and 2 (15%) had both types. Localization of CS-induced seizures overlapped with spontaneous seizures in 9/13 (70%) patients. Overlapping was 100% with mesial temporal structures. 7 (54%) patients underwent surgery, and 3 had RNS placement. Conclusion Direct CS induced seizures complemented localization of spontaneous seizures in two-thirds of the patients who underwent stereo EEG investigation. The accuracy of direct CS in the localization of EZ is higher with infrasylvian structures.

Mapping lexical-semantic networks and determining hemispheric language dominance: Do task design, sex, age, and language performance make a difference?

Blocked and event-related fMRI designs are both commonly used to localize language networks and determine hemispheric dominance in research and clinical settings. We compared activation profiles on a semantic monitoring task using one of the two designs in a total of 43 healthy individual to determine whether task design or subject-specific factors (i.e., age, sex, or language performance) influence activation patterns. We found high concordance between the two designs within core language regions, including the inferior frontal, posterior temporal, and basal temporal region. However, differences emerged within inferior parietal cortex. Subject-specific factors did not influence activation patterns, nor did they interact with task design. These results suggest that despite high concordance within perisylvian regions that are robust to subject-specific factors, methodological differences between blocked and event-related designs may contribute to parietal activations. These findings provide important information for researchers incorporating fMRI results into meta-analytic studies, as well as for clinicians using fMRI to guide pre-surgical planning.

Conscious control of breathing: A key to prevention of sudden unexpected death in epilepsy?

Conscious control of breathing: A key to prevention of sudden unexpected death in epilepsy?

Spatiotemporal Accuracy of Gradient Magnetic-Field Topography (GMFT) Confirmed by Simultaneous Magnetoencephalography and Intracranial Electroencephalography Recordings in Patients with Intractable Epilepsy.

Gradient magnetic-field topography (GMFT) is one method for analyzing magnetoencephalography (MEG) and representing the spatiotemporal dynamics of activity on the brain surface. In contrast to spatial filters, GMFT does not include a process reconstructing sources by mixing sensor signals with adequate weighting. Consequently, noisy sensors have localized and limited effects on the results, and GMFT can handle MEG recordings with low signal-to-noise ratio. This property is derived from the principle of the planar-type gradiometer, which obtains maximum gradient magnetic-field signals just above the electrical current source. We assumed that this characteristic allows GMFT to represent even faint changes in brain activities that cannot be achieved with conventional equivalent current dipole analysis or spatial filters. GMFT is thus hypothesized to represent brain surface activities from onset to propagation of epileptic discharges. This study aimed to validate the spatiotemporal accuracy of GMFT by analyzing epileptic activities using simultaneous MEG and intracranial electroencephalography (iEEG) recordings. Participants in this study comprised 12 patients with intractable epilepsy. Epileptic spikes simultaneously detected on both MEG and iEEG were analyzed by GMFT and voltage topography (VT), respectively. Discrepancies in spatial distribution between GMFT and VT were evaluated for each epileptic spike. On the lateral cortices, areas of GMFT activity onset were almost concordant with VT activities arising at the gyral unit level (concordance rate, 66.7–100%). Median time lag between GMFT and VT at onset in each patient was 11.0–42.0 ms. On the temporal base, VT represented basal activities, whereas GMFT failed but instead represented propagated activities of the lateral temporal cortices. Activities limited to within the basal temporal or deep brain region were not reflected on GMFT. In conclusion, GMFT appears to accurately represent brain activities of the lateral cortices at the gyral unit level. The slight time lag between GMFT and VT is likely attributable to differences in the detection principles underlying MEG and iEEG. GMFT has great potential for investigating the spatiotemporal dynamics of lateral brain surface activities.

Associations between brain white matter integrity and disease severity in obstructive sleep apnea.

Obstructive sleep apnea (OSA) is characterized by recurrent upper airway blockage, with continued diaphragmatic efforts to breathe during sleep. Brain structural changes in OSA appear in various regions, including white matter sites that mediate autonomic, mood, cognitive, and respiratory control. However, the relationships between brain white matter changes and disease severity in OSA are unclear. This study examines associations between an index of tissue integrity, magnetization transfer (MT) ratio values (which show MT between free and proton pools associated with tissue membranes and macromolecules), and disease severity (apnea-hypopnea index [AHI]) in OSA subjects. We collected whole-brain MT imaging data from 19 newly diagnosed, treatment-naïve OSA subjects (50.4 ± 8.6 years of age, 13 males, AHI 39.7 ± 24.3 events/hr], using a 3.0-Tesla MRI scanner. With these data, whole-brain MT ratio maps were calculated, normalized to common space, smoothed, and correlated with AHI scores by using partial correlation analyses (covariates, age and gender; P < 0.005). Multiple brain sites in OSA subjects, including superior and inferior frontal regions, ventral medial prefrontal cortex and nearby white matter, midfrontal white matter, insula, cingulate and cingulum bundle, internal and external capsules, caudate nuclei and putamen, basal forebrain, hypothalamus, corpus callosum, and temporal regions, showed principally lateralized negative correlations (P < 0.005). These regions showed significant correlations even with correction for multiple comparisons (cluster-level, family-wise error, P < 0.05), except for a few superior frontal areas. Predominantly negative correlations emerged between local MT values and OSA disease severity, indicating potential usefulness of MT imaging for examining the OSA condition. These findings indicate that OSA severity plays a significant role in white matter injury. © 2016 Wiley Periodicals, Inc.

The relative importance of imaging markers for the prediction of Alzheimer's disease dementia in mild cognitive impairment - Beyond classical regression.

Selecting a set of relevant markers to predict conversion from mild cognitive impairment (MCI) to Alzheimer's disease (AD) has become a challenging task given the wealth of regional pathologic information that can be extracted from multimodal imaging data.Here, we used regularized regression approaches with an elastic net penalty for best subset selection of multiregional information from AV45-PET, FDG-PET and volumetric MRI data to predict conversion from MCI to AD. The study sample consisted of 127 MCI subjects from ADNI-2 who had a clinical follow-up between 6 and 31 months. Additional analyses assessed the effect of partial volume correction on predictive performance of AV45- and FDG-PET data.Predictor variables were highly collinear within and across imaging modalities. Penalized Cox regression yielded more parsimonious prediction models compared to unpenalized Cox regression. Within single modalities, time to conversion was best predicted by increased AV45-PET signal in posterior medial and lateral cortical regions, decreased FDG-PET signal in medial temporal and temporobasal regions, and reduced gray matter volume in medial, basal, and lateral temporal regions. Logistic regression models reached up to 72% cross-validated accuracy for prediction of conversion status, which was comparable to cross-validated accuracy of non-linear support vector machine classification. Regularized regression outperformed unpenalized stepwise regression when number of parameters approached or exceeded the number of training cases. Partial volume correction had a negative effect on the predictive performance of AV45-PET, but slightly improved the predictive value of FDG-PET data.Penalized regression yielded more parsimonious models than unpenalized stepwise regression for the integration of multiregional and multimodal imaging information. The advantage of penalized regression was particularly strong with a high number of collinear predictors.

Unfolding the mystery: Rare presentation of Japanese encephalitis as catatonia

Catatonia is a syndrome of specific motor abnormalities, closely associated with disorders of mood, thought, and cognition. The principal symptoms of catatonia are mutism, immobility, negativism, posturing, stereotypy, and echo phenomena. Catatonia occurs in various psychiatric illnesses as well as medical disorders like infections of the central nervous system such as encephalitis, autoimmune disorders, cerebrovascular events, systemic metabolic disturbances, and toxic drug states. Catatonia may often mislead the clinician and the patient may be misdiagnosed as primarily suffering from a psychiatric disorder and be treated accordingly. Encephalitis may present with various psychiatric symptoms including catatonic features as its sequel that may sometimes be misunderstood as a primary psychiatric disorder. We highlight a case of a young female in her postpartum period, who presented with initial aggressive behavior and sleep deprivation followed by features of catatonia accompanied with fever. She initially responded well to benzodiazepines; however, her subsequent response was poor. When she was subjected to neuroimaging, it revealed signal intensity alteration in the bilateral basal ganglia and temporal regions suggestive of encephalitis; cerebrospinal fluid (CSF) viral markers examination revealed immunoglobulin M (IgM) positivity for Japanese encephalitis (JE). This case report highlights the diagnostic dilemma and management issues of a case of JE with catatonic symptoms.

Cortical thickness and hippocampal shape in pure vascular mild cognitive impairment and dementia of subcortical type

The progression pattern of brain structural changes in patients with isolated cerebrovascular disease (CVD) remains unclear. To investigate the role of isolated CVD in cognitive impairment patients, patterns of cortical thinning and hippocampal atrophy in pure subcortical vascular mild cognitive impairment (svMCI) and pure subcortical vascular dementia (SVaD) patients were characterized. Forty-five patients with svMCI and 46 patients with SVaD who were negative on Pittsburgh compound B (PiB) positron emission tomography imaging and 75 individuals with normal cognition (NC) were recruited. Compared with NC, patients with PiB(-) svMCI exhibited frontal, language and retrieval type memory dysfunctions, which in patients with PiB(-) SVaD were further impaired and accompanied by visuospatial and recognition memory dysfunctions. Compared with NC, patients with PiB(-) svMCI exhibited cortical thinning in the frontal, perisylvian, basal temporal and posterior cingulate regions. This atrophy was more prominent and extended further toward the lateral parietal and medial temporal regions in patients with PiB(-) SVaD. Compared with NC subjects, patients with PiB(-) svMCI exhibited hippocampal shape deformities in the lateral body, whilst patients with PiB(-) SVaD exhibited additional deformities within the lateral head and inferior body. Our findings suggest that patients with CVD in the absence of Alzheimer's disease pathology can be demented, showing cognitive impairment in multiple domains, which is consistent with the topography of cortical thinning and hippocampal shape deformity.

The extended supracerebellar transtentorial approach for resection of medial tentorial meningiomas.

Background:The supracerebellar transtentorial (SCTT) approach has been established as a safe corridor to access the posteriomedial basal temporal region. Previous reports have demonstrated the efficacy of this route in the resection of intrinsic tumors and small arteriovenous malformations. Only one report in the English literature has described its use to resect a medial tentorial meningioma.Methods:The authors discuss the relevant surgical anatomy of this approach and its advantages compared with more traditional routes, and illustrate its application to remove medial tentorial meningiomas through two operative cases with accompanying videos.Results:In illustrative case one, the patient recovered from surgery with no deficits. All his preoperative symptoms had resolved at 3-month follow-up. At the 4-year follow-up, MRI did not demonstrate any growth of the residual tumor. In case two, gross total resection was achieved and the patient did not suffer any postoperative language or visual deficit. At 2-year follow-up, no tumor recurrence was present.Conclusion:The SCTT approach has a potential to safely access extra-axial lesions located around the medial tentorial incisura. As demonstrated in these two cases, the approach merits consideration in patients with tentorial meningiomas as an alternative to more widely utilized skull base approaches and subtemporal routes.

Catching what we can’t see: Contribution of epileptic mesial sources to EEG

The possibility to observe electrical potentials from deep brain sources to surface EEG remains unclear and debated among the neuroscience community. This question is particularly crucial in the temporal lobe epilepsies investigations because they involve complex (mesial and/or lateral) epileptogenic networks. Seven patients undergoing pre-surgical evaluation of drug resistant temporal lobe epilepsy were selected from a prospective series of thirty patients in whom simultaneous EEG-SEEG recordings had been performed since 2009. Interictal intracerebral spikes (IIS) were selected on SEEG signals blinded to EEG signals. These IIS were triggered as temporally known (T0) brain sources, and then EEG signals were automatically averaged according to these T0 markers in order to obtain mean interictal surface spikes (ISS). In mean, 9 SEEG electrodes and 16 surface EEG electrodes were simultaneously used where 684Â ± 186 IIS were selected by patient (total number: 4,787). According to the anatomical distribution of the IIS, 21 foci were defined and classified according to three categories: mesial (9 foci), mesial and neocortical (M + NC, 5 foci) and neocortical part of the temporal lobe (NC, 7 foci). Negative mean interictal surface spikes (ISS) were mainly observed in anterior and basal temporal region. In mean, 8.7 mean EEG signals were validated as an ISS for each IIS network. Amplitude, duration and SNR of each IIS class were: 7.2 μV, 72 ms and 16.5 dB for M class; 36.1 μV, 78.1 ms and 22 dB for M + NC class; 10 μV, 87.1 ms and 17.7 dB for NC class. Mesial brain sources contribute to surface EEG. Contrary to several hypothesis, mesial temporal structures cannot be considered as closed electrical field structures or too depth to contribute. The main problem to observe signals from these deep structures concerns the low signal to noise ratio, which for instance required signal processing to see ISS originated from mesial structures.

Real-Time Functional Mapping With Electrocorticography in Pediatric Epilepsy

SIGFRIED (SIGnal modeling For Real-time Identification and Event Detection) software provides real-time functional mapping (RTFM) of eloquent cortex for epilepsy patients preparing to undergo resective surgery. This study presents the first application of paradigms used in functional magnetic resonance (fMRI) and electrical cortical stimulation mapping (ESM) studies for shared functional cortical mapping in the context of RTFM. Results from the 3 modalities are compared. A left-handed 13-year-old male with intractable epilepsy participated in functional mapping for localization of eloquent language cortex with fMRI, ESM, and RTFM. For RTFM, data were acquired over the frontal and temporal cortex. Several paradigms were sequentially presented: passive (listening to stories) and active (picture naming and verb generation). For verb generation and story processing, fMRI showed atypical right lateralizing language activation within temporal lobe regions of interest and bilateral frontal activation with slight right lateralization. Left hemisphere ESM demonstrated no eloquent language areas. RTFM procedures using story processing and picture naming elicited activity in the right lateral and basal temporal regions. Verb generation elicited strong right lateral temporal lobe activation, as well as left frontal lobe activation. RTFM results confirmed atypical language lateralization evident from fMRI and ESM. We demonstrated the feasibility and usefulness of a new RTFM stimulation paradigm during presurgical evaluation. Block design paradigms used in fMRI may be optimal for this purpose. Further development is needed to create age-appropriate RTFM test batteries.

Convergent Connectivity and Graded Specialization in the Rostral Human Temporal Lobe as Revealed by Diffusion-Weighted Imaging Probabilistic Tractography

In recent years, multiple independent neuroscience investigations have implicated critical roles for the rostral temporal lobe in auditory and visual perception, language, and semantic memory. Although arising in the context of different cognitive functions, most of these suggest that there is a gradual convergence of sensory information in the temporal lobe that culminates in modality- and perceptually invariant representations at the most rostral aspect. Currently, however, too little is known regarding connectivity within the human temporal lobe to be sure of exactly how and where convergence occurs; existing hypotheses are primarily derived on the basis of cross-species generalizations from invasive nonhuman primate studies, the validity of which is unclear, especially where language function is concerned. In this study, we map the connectivity of the human rostral temporal lobe in vivo for the first time using diffusion-weighted imaging probabilistic tractography. The results indicate that convergence of sensory information in the temporal lobe is in fact a graded process that occurs along both its longitudinal and lateral axes and culminates in the most rostral limits. We highlight the consistency of our results with those of prior functional neuroimaging, computational modeling, and patient studies. By going beyond simple fasciculus reconstruction, we systematically explored the connectivity of specific temporal lobe areas to frontal and parietal language regions. In contrast to the graded within-temporal lobe connectivity, this intertemporal connectivity was found to dissociate across caudal, mid, and rostral subregions. Furthermore, we identified a basal rostral temporal region with very limited connectivity to areas outside the temporal lobe, which aligns with recent evidence that this subregion underpins the extraction of modality- and context-invariant semantic representations.

Age‐related regional brain T2‐relaxation changes in healthy adults

To determine normal T2-relaxation values from different brain areas in healthy adults, assess age-related T2-relaxation changes in those sites, and evaluate potential gender-related T2-relaxation value differences. We performed proton-density and T2-weighted imaging in 60 healthy adults (male: 38, age range = 31-64 years, mean age ± SD = 46.1 ± 9.3 years; female: 22, age range = 37-66 years, mean age ± SD = 49.5 ± 8.3 years), using a 3.0 Tesla MRI scanner. T2-relaxation values were calculated voxel-by-voxel from proton-density and T2-weighted images, and whole-brain T2-relaxation maps were constructed and normalized to a common space. A set of regions-of-interest were outlined within the basal ganglia, limbic, frontal, parietal, temporal, occipital, thalamic, hypothalamic, cerebellar, and pontine regions using mean background images derived from normalized and averaged T2-weighted images of all individuals, and regional T2-relaxation values were determined from these regions-of-interest and normalized T2-relaxation maps. Pearson's correlations were calculated between T2-relaxation values and age, and male-female differences evaluated with independent-samples t-tests. T2-relaxation values typically increased with age in multiple brain sites; only a few regions showed declines, including the putamen and ventral pons. Sex-related differences in T2-relaxation values appeared in basal ganglia, frontal, temporal, occipital, and cerebellar regions; males showed higher values over females in these sites. Establishment of normative adult T2-relaxation values over different brain areas, with age and sex as co-factors, offers baseline values against which disease-related tissue changes can be assessed.

Safety and utility of supplemental depth electrodes for localizing the ictal onset zone in pediatric neocortical epilepsy

Depth electrodes provide a better sampling of sulci and regions of cortex that lie tangential to the plane of subdural electrodes. The aim of this study was to evaluate the utility of supplemental depth electrodes in the surgical treatment of pediatric patients with neocortical epilepsy. Cases involving 12 consecutive pediatric patients (mean age [SD] 10.9 ± 4.4 years) were reviewed. Focal resective surgery (in 9 cases) or functional hemispherectomy (in 3 cases) was performed after intracranial monitoring. The mean total number of electrodes was 118 ± 29; the mean numbers of grid, strip, and depth electrodes were 95 ± 27, 10 ± 6, and 13 ± 5, respectively The most common pathological condition was focal cortical dysplasia. In 4 cases, depth electrodes demonstrated the ictal onset zone in an area not easily accessible by grids or strips (in the basal temporal region in 3 cases and the upper opercular region in 1 case). In 3 of these 4 cases, the ictal onset zone was defined exclusively by the depth electrodes. In each of these 3 cases, the surface electrodes (on grids or strips) demonstrated early propagation but not ictal onset. In 9 cases, the depth electrodes also demonstrated the early propagation zone. The information about the ictal onset zone and the early propagation zone helped to provide additional information that affected the extent (in 7 cases) or depth (in 3 cases) of the resection. The proportion of the electrodes involved in resection relative to the total number of implanted electrodes was low (mean ± SD, 0.26 ± 0.09). Nine patients (75.0%) became seizure free (Engel class IA outcome) after surgery (mean duration of follow-up 25.7 ± 4.29 months). There were no surgical complications related to intracranial electroencephalography monitoring. Most patients (75.0%) became seizure free after extensive monitoring and more limited resection of seizure-onset regions. Supplemental depth electrodes contribute to improved outcome by providing information about the ictal onset zone that is not accessible by grid or strip electrodes in some cases. The supplemental depth electrodes conferred an extra dimension of depth to the analysis, which allowed for successful outcome with more limited resection.

Radiation-Induced Mineralizing Microangiopathy in a Case of Recurrent Craniopharyngioma

Mineralizing microangiopathy is a late complication of radiation-induced brain injury that occurs during the treatment of CNS malignancies in children and adults. Early diagnosis of the radiation-induced brain injury helps to tailor the radiation dose and prevent further complications. Here we describe an operated oatient with craniopharyngioma who underwent external beam radiotherapy. The patient developed gradual loss of vision after two years and a review CT scan revealed the local recurrence of tumour with dystrophic calcification of the basal ganglia, frontal and temporal subcortical regions representing recurrent craniopharyngioma with radiation-induced mineralizing microangiopathy.

Relapsing low-grade glioma treated with bevacizumab and irinotecan as third-line therapy.

e12556 Background: A 63-year-old Hispanic patient was diagnosed as right side fronto-temporal grade 2 astrocytoma with gemistocytic changes on 10/2006. He underwent subtotal resection with placement of carmustine wafer, fractionated RT (6,300 cGy) and temozolomide 75 mg/m2 for 42 ds. He received mantainance therapy with temozolomide 150 mg/m2 for 5 days every 28 ds. Following relapse after 10 months he underwent stereotactic radiosurgery but 4 weeks later his condition worsened; an MRI showed progression of tumor size with edema involving the right basal ganglia, frontal and temporal regions. CCNU/procarbazine was started but stopped after 7 ds because of severe vomiting. He presented 4 months later in a stuporous state with left side paralysis and expressive-receptive aphasia. Methods: On 04/2008 therapy was started with bevacizumab (Bv) 10 mg/kg and irinotecan (Iri) 340 mg/m2 every 2 weeks. Results: 24 hrs after treatment he began to open eyes, moved his left fingers and toes and understood words. Furth...

NEURAL CONNECTION BETWEEN BILATERAL BASAL TEMPORAL REGIONS

In patients with temporal lobe epilepsy, invasive electroencephalographic study has shown that epileptic activities arising from the unilateral temporal lobe often propagate to the contralateral temporal lobe. Which commissural pathways are responsible for this spreading remains controversial. Some previous studies, however, have suggested that interhemispheric connections between bilateral basal temporal regions (BTR) might have a significant role in propagation of epileptic activities. We attempted to elucidate the neural connections between bilateral BTRs using the cortico-cortical evoked potential (CCEP) method. Five consecutive patients with temporal lobe epilepsy who underwent intracranial electroencephalographic monitoring were studied. CCEP responses were recorded from a total of 24 electrodes after stimulation of the contralateral BTRs (24 CCEPs/720 recordings; 3.33%). There were 3 types of CCEP waveform: type N-P (16 of 24; 66.7%) consisting of an initial negative peak followed by a positive peak; type N (4 of 24; 16.7%) showing a negative peak only, and type P (4 of 24; 16.7%) showing a positive peak only. The latencies ranged from 48.2 to 102.3 ms (mean, 65.5 ms) for negative peaks and 70.2 to 122.0 ms (mean, 95.2 ms) for positive peaks. In all patients, the basal temporal language area was associated with at least 1 CCEP, either as a stimulated region or a recorded region (11 of 24; 45.8%). These data indicate that there is a neural connection between bilateral BTRs. In consideration of the involvement of the basal temporal language area, we speculate that these responses may reflect some physiological connections between bilateral BTRs.

Brain regions underlying word finding difficulties in temporal lobe epilepsy

Word finding difficulties are often reported by epileptic patients with seizures originating from the language dominant cerebral hemisphere, for example, in temporal lobe epilepsy. Evidence regarding the brain regions underlying this deficit comes from studies of peri-operative electro-cortical stimulation, as well as post-surgical performance. This evidence has highlighted a role for the anterior part of the dominant temporal lobe in oral word production. These conclusions contrast with findings from activation studies involving healthy speakers or acute ischaemic stroke patients, where the region most directly related to word retrieval appears to be the posterior part of the left temporal lobe. To clarify the neural basis of word retrieval in temporal lobe epilepsy, we tested forty-three drug-resistant temporal lobe epilepsy patients (28 left, 15 right). Comprehensive neuropsychological and language assessments were performed. Single spoken word production was elicited with picture or definition stimuli. Detailed analysis allowed the distinction of impaired word retrieval from other possible causes of naming failure. Finally, the neural substrate of the deficit was assessed by correlating word retrieval performance and resting-state brain metabolism in 18 fluoro-2-deoxy-d-glucose-Positron Emission Tomography. Naming difficulties often resulted from genuine word retrieval failures (anomic states), both in picture and in definition tasks. Left temporal lobe epilepsy patients showed considerably worse performance than right temporal lobe epilepsy patients. Performance was poorer in the definition than in the picture task. Across patients and the left temporal lobe epilepsy subgroup, frequency of anomic state was negatively correlated with resting-state brain metabolism in left posterior and basal temporal regions (Brodmann's area 20-37-39). These results show the involvement of posterior temporal regions, within a larger antero-posterior-basal temporal network, in the specific process of word retrieval in temporal lobe epilepsy. A tentative explanation for these findings is that epilepsy induces functional deafferentation between anterior temporal structures devoted to semantic processing and neocortical posterior temporal structures devoted to lexical processing.

Evidence for a basal temporal visual language center

Dejerine and Benson and Geschwind postulated disconnection of the dominant angular gyrus from both visual association cortices as the basis for pure alexia, emphasizing disruption of white matter tracts in the dominant temporooccipital region. Recently functional imaging studies provide evidence for direct participation of basal temporal and occipital cortices in the cognitive process of reading. The exact location and function of these areas remain a matter of debate. To confirm the participation of the basal temporal region in reading. Extraoperative electrical stimulation of the dominant hemisphere was performed in three subjects using subdural electrodes, as part of presurgical evaluation for refractory epilepsy. Pure alexia was reproduced during cortical stimulation of the dominant posterior fusiform and inferior temporal gyri in all three patients. Stimulation resulted in selective reading difficulty with intact auditory comprehension and writing. Reading difficulty involved sentences and words with intact letter by letter reading. Picture naming difficulties were also noted at some electrodes. This region is located posterior to and contiguous with the basal temporal language area (BTLA) where stimulation resulted in global language dysfunction in visual and auditory realms. The location corresponded with the visual word form area described on functional MRI. These observations support the existence of a visual language area in the dominant fusiform and occipitotemporal gyri, contiguous with basal temporal language area. A portion of visual language area was exclusively involved in lexical processing while the other part of this region processed both lexical and nonlexical symbols.

P2-030: Hemispheric asymmetry of cortical thickness in individuals with no cognitive impairment and Alzheimer's disease

Background: Human brain has hemispheric dominance for cortical functions such as cognition and motor, and some volumetric studies have suggested that there is structural brain asymmetry in healthy individuals. Recent voxel based morphometry (VBM) studies in AD have demonstrated that the left hemisphere is preferentially affected than the right. However, previous studies involved small sample size and their results were inconsistent. In contrast to VBM, cortical surface-based thickness measurement performed at the nodes of a 3-D polygonal mesh has the advantage of providing a direct quantitative index of cortical morphology and enabling more precise measurement in deep sulci. We tried to learn if there is asymmetry of cortical thickness in subjects with no cognitive impairment (NCI) and if AD preferentially affects right versus left hemisphere as the disease progresses and if there is any regional differences in this hemispheric asymmetry. Methods: Participants consisted of 148 NCI subjects and 196 AD patients. AD patients fulfilled the criteria for probable AD proposed by the National Institute of Neurological and Communicative Disorders and Stroke and the AD and Related Disorders Association. All the subjects underwent MRI including 3D volume images for cortical thickness analysis across the entire brain. Results: In NCI left hemisphere, relative to right hemisphere, showed cortical hypertrophy in language areas such Broca’s, Wernicke’s area, and basal temporal region, and motor cortex. In contrast, compared to left hemisphere, right hemisphere cortices were more hypertrophic in precuneus, cingulate gyrus, temoporparietal association cortex, parahippocampal gyrus and occipital lobe. In AD, this trend was generally maintained regardless of disease severity except that left hemisphere, relative to right hemisphere, showed cortical thinning in medial temporal region and anterior cingulate gyrus. Conclusions: Our results suggest that hemispheric dominance of cognitive and motor functions can be demonstrated by surface based cortical thickness measurements in normal cognitive group. The fact that hemispheric asymmetry of cortical thickness was generally maintained as AD progresses is consistent with the cognitive reserve theory. In addition, as the disease severity increases,medial temporal regions and anterior cingulate gyrus may degenerate in the left hemisphere more than the right.