Basal Temporal Area Research Articles

Basal temporal language area revisited in Japanese language with a language function density map.

We revisited the anatomo-functional characteristics of the basal temporal language area (BTLA), first described by Lüders et al. (1986), using electrical cortical stimulation (ECS) in the context of Japanese language and semantic networks. We recruited 11 patients with focal epilepsy who underwent chronic subdural electrode implantation and ECS mapping with multiple language tasks for presurgical evaluation. A semiquantitative language function density map delineated the anatomo-functional characteristics of the BTLA (66 electrodes, mean 3.8cm from the temporal tip). The ECS-induced impairment probability was higher in the following tasks, listed in a descending order: spoken-word picture matching, picture naming, Kanji word reading, paragraph reading, spoken-verbal command, and Kana word reading. The anterior fusiform gyrus (FG), adjacent anterior inferior temporal gyrus (ITG), and the anterior end where FG and ITG fuse, were characterized by stimulation-induced impairment during visual and auditory tasks requiring verbal output or not, whereas the middle FG was characterized mainly by visual input. The parahippocampal gyrus was the least impaired of the three gyri in the basal temporal area. We propose that the BTLA has a functional gradient, with the anterior part involved in amodal semantic processing and the posterior part, especially the middle FG in unimodal semantic processing.

Cortical regions and networks of hyperkinetic seizures: Electrocorticography and diffusion tensor imaging study

ObjectiveThe present study investigated the cortical areas and networks responsible for hyperkinetic seizures by analyzing invasive recordings and diffusion tensor imaging (DTI) tractography. MethodsSeven patients with intractable focal epilepsy in whom hyperkinetic seizures were recorded during an invasive evaluation at Sapporo Medical University between January 2012 and March 2020 were enrolled in the present study. Intracranial recordings were analyzed to localize seizure-onset zones (SOZs) and symptomatogenic zones (spread areas at clinical onset). DTI was used to identify the subcortical fibers originating from SOZs. ResultsTen SOZs were located in four areas: (1) the inferior parietal lobule (two SOZs in two patients), (2) temporo-occipital junction (three SOZs in two patients), (3) medial temporal area (three SOZs in three patients) and (4) medial/lateral frontal lobe (two SOZs in two patients). Symptomatogenic zones appeared to be the premotor area, basal temporal area, temporo-occipital junction, and the postcentral gyrus/supramarginal gyrus. The tractographic analysis revealed that the inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), middle longitudinal fasciculus (MLF), arcuate fasciculus (AF)/superior longitudinal fasciculus (SLF) II, III, and cingulum bundle may be associated with hyperkinetic seizures. ConclusionThe present results suggest the cortical areas (the inferior parietal lobule, temporo-occipital junction, medial temporal area, and medial/lateral frontal lobe) and subcortical fibers (IFOF, ILF, MLF, AF/SLFII, III, and the cingulum bundle) responsible for generating hyperkinetic seizures.

WS1.9. Advances in EEG Analysis – Wide-Band EEG, Dense-Array EEG and Quantitative EEG

1) Wide-band EEG As the faster frequency extreme of wide-band EEG, high frequency oscillation (HFO) was originally described by means of 1) micro-electrode recording in animal model, and ictal HFO occurred before clinical onset. Recently, 2 more types of HFO were well described; 2) invasive electrodes recording in epilepsy surgery (macro-invasive electrodes such as depth-, subdural ones), and 3) scalp electrodes or MEG in epilepsy patients. The multiple mechanisms of HFO generation are considered such as synchronized post-synaptic potentials with sparse pyramidal cell firing, or principal cell action potentials. As the lower frequency of extreme of baseline shifts in the chronic epilepsy focus on epilepsy patients, ictal DC shifts occurred earlier than or as early as ictal HFO significantly (Imamura et al., 2011; Kanazawa et al., 2015). It was newly endorsed by the pathological abnormality, i.e., decreased Kir4.1, selectively seen in the cortices generating ictal DC shifts (Kobayashi et al., 2017). It could suggest more active role of glia before seizure generation, and thus called as active DC shifts. These both findings could represent activity of both epileptic neurons and astrocytes, respectively, mainly as the local field potentials. 2) Quantitative EEG Once digital EEG era has started since 1989, first generation EEG (1989-1996/2000) could provide us with data acquisition of ordinary sampling rate (i.e., 500 Hz) and band pass filter (i.e., 0.5 Hz - 200 Hz). Data display has been much flexible by means of reformat of montage, filter change, sensitivity change, voltage mapping, power spectrum analysis, and 3D source analysis, and so on. It is user friendly, and regarded as the established tool or method. Second generation EEG (1996/2000-present) has been much advanced and complicated tool such as data acquisition such as wide-band EEG, i.e., 0.016 Hz - 600 Hz. It contains DC shifts, infraslow, HFO. Increased sampling rate, i.e., 2000 Hz could widen the extremely faster activitty. Data display such as wide-band display, i.e., 100 ms/page to 5 min/page, time frequency analysis, DSA (Density Modulated Spectral Array), and Ganger causality further led us to the interactive sophisticated circumstances in the clinical and scientific field. 3) Dense-array EEG The more electrodes are placed on the scalp, the better spatial resolution is expected. Once it also could cover the so-called “south hemispheres” of the head, it could delineate the any activity arising from the basal temporal and mesial temporal areas. However, since scalp EEG is attenuated in amplitude and is blurred with wider distribution by means of cortical bone and different soft tissues, the degree of localization map may not be proportionally precise in spite of involvement of many electrodes. In this regard, whole MEG data may overcome of the 2 important factors.

Misleading non-epileptic epileptiform activities on intracranial recordings

Numerous non-epileptic physiological electroencephalographic (EEG) patterns morphologically mimic epileptiform activity. However, misleading non-epileptic findings of electrocorticography (ECoG) have not yet been examined in detail. The aim of the present study was to identify non-epileptic epileptiform ECoG findings. We retrospectively reviewed the intracranial recordings of 21 patients with intractable focal epilepsy who became seizure-free after a presurgical evaluation with subdural electrodes following resective surgeries at Sapporo Medical University between January 2014 and December 2018. Morphological epileptiform findings outside epileptogenic areas were judged as non-epileptic and analyzed. Seventeen areas in nine patients exhibited non-epileptic epileptiform activities. These areas were identified in the lateral temporal cortices, basal temporal areas, rolandic areas, and frontal lobe. Morphological patterns were classified into three types: 1) spiky oscillations, 2) isolated spiky activity, and 3) isolated fast activity. The normal cortex may exhibit non-epileptic epileptiform activities. These activities need to be carefully differentiated from real epileptic abnormalities to prevent the mislocalization of epileptogenic areas.

Threshold and distribution of afterdischarges with electrical cortical stimulation

ObjectiveThe present study aimed to investigate the threshold and distribution of afterdischarges (ADs) with cortical electrical stimulation for functional brain mapping. MethodWe retrospectively analyzed data from 11 patients with medically intractable epilepsy who underwent 50-Hz cortical electrical stimulation for functional mapping followed by resection. These patients became seizure free for more than six months. The threshold and distribution of ADs induced by the stimulation were evaluated. ResultsThe median threshold was 6 mA (range: 2–15 mA) for the frontal lobe, 8 mA (3–15 mA) for the temporal lobe, 6 mA (2–15 mA) for the parietal lobe, and 6 mA (4–12 mA) for the occipital lobe. No significant interlobar differences were observed in AD thresholds. No significant differences were noted between within and outside epileptogenic zones. The distribution of ADs, remote spread was observed in all patients, reflecting fronto-parieto-temporal connections, as well as contiguous spread. The stimulation of premotor areas, the inferior parietal lobule, supplementary motor area, and basal temporal areas appeared to induce ADs in remote cortices. ConclusionWhile no locational differences were observed in AD thresholds, each brain region showed a characteristic pattern for AD spread. Remote AD spread needs to be considered for safe functional mapping.

S128. Oscillatory responses evoked by single-pulse electrical stimulation in human cerebral cortex – A Cortico-Cortical Evoked Potential (CCEP) study

Introduction Human brain operates with oscillatory activity in different frequency bands. For example, mu rhythm is well known as an idling rhythm observed in the central area related to motor function. We observed some rhythmic pattern in the averaged waveforms in the CCEP investigation (called “oscillatory response” here), which is originally a method to trace connectivity by single electrical pulse stimulation. We report on the frequency and distribution of the oscillatory responses in CCEP. Methods Subjects are 5 intractable epilepsy patients who underwent chronic implantation of subdural electrodes for presurgical evaluation. Written informed consents were obtained from all subjects. Single-pulse stimuli (0.3 ms, 8–10 mA, alternating polarity, 30 × 2 trials) were applied through two adjacent electrodes (52.8 ± 15.3 stimulus sites per patient). CCEP was recorded from subdural electrodes (105.2 ± 31.8 electrodes per patient) placed on the lateral and medial aspect of the cerebral hemisphere. Lateral fronto-parietal area was covered in all subjects. An oscillatory response in CCEP was detected by visual inspection on the averaged waveform according to the following criteria; (1) it has at least two pairs of peak and trough spaced equally, (2) it can be overlapped with other evoked responses (typical N1/ N2 response). If more than one rhythms with different frequencies were observed in the same electrode, we counted the largest one in amplitude. Results Totally, 2362 oscillatory responses (7.9%) were detected in 29891 observations in 5 subjects, including 443 alpha-band responses (7.5–13.5 Hz), 312 beta-band responses (13.5–30 Hz) and 1505 theta-band responses (3.5–7.5 Hz). Theta rhythm was observed predominantly in the temporal lobe including the basal temporal area (the occurrence rate was 12.45%). Alpha rhythm was observed more often in the parietal lobe including the postcentral gyrus (the occurrence rate was 4.57%), while beta rhythm was often observed around precentral gyrus (the occurrence rate was 1.98%). The frequency of the resting rhythmic activity was equal to that of oscillatory CCEP response in the alpha band in the postcentral gyrus in all subjects. This alpha activity was considered as mu rhythm in all the 3 subjects who performed a hand grasping task. Conclusion Single pulse electrical stimulation evoked oscillatory CCEP responses preferentially in the temporal lobe and the perirolandic area. The correspondence of frequency between the oscillatory response and mu rhythm implies the phase resetting of the physiological oscillation by exogenous input. This unique oscillatory CCEP may help to map these functionally important cortical regions.

Basal temporal languish area in native Chinese: direct evidence from electrocortical stimulation

Objective To map the basal temporal language area (BTLA) in native Chinese and investigate the functional characteristics of BLTA.Methods Three patients with refractory mesial temporal lobe epilepsy were studied.Due to controversial results from non-invasive methods,the chronic subdural electrodes were implanted.The language function on the basal temporal lobe was investigated by means of electrocortical stimulation.Patients were asked to read sentences aloud and perform specific language task during the test.Any responses to electrocortical stimulation with gradual increased current intensity were recorded.Results Left dominant hemispheres of all patients were revealed by Wada test.With low current intensity (7,5,7 mA),slowing speech was observed when stimulating anterior to middle of fusiform gyrus on the left basal temporal lobe.Meanwhile,stimulation with high intensity (11,11,13 mA)produced global aphasia.Furthermore,semantic errors occurred when stimulating electrode 3 cm from temporal pole,while the impairment of naming and face recognition was elicited by stimulating electrode 4 cm from temporal pole with 9 mA current intensity in all three patients.Conclusions The preliminary study confirmed the BTLA in native Chinese,which localized on anterior to middle basal temporal lobe in the dominant hemisphere and involved in the semantic and naming function.The identification of BTLA would be helpful for the clarification of language mechanism and protection of the language function in the surgical treatment of epilepsy. Key words: Epilepsy; Electrocortical stimulation; Cortical mapping; Basal temporal language area

Network hyperexcitability in a patient with partial reading epilepsy: Converging evidence from magnetoencephalography, diffusion tractography, and functional magnetic resonance imaging

ObjectiveThe pathophysiological mechanisms of partial reading epilepsy are still unclear. We delineated the spatial–temporal characteristics of reading-induced epileptic spikes and hemodynamic activation in a patient with partial reading epilepsy. MethodsMagnetoencephalography (MEG) was recorded during silent letter-by-letter reading, and the source of reading-induced spikes was estimated using equivalent current dipole (ECD) analysis. Diffusion tractography was employed to determine if the white matter pathway connected spike initiation and termination sites. Functional magnetic resonance imaging (fMRI) was employed to determine the spatial pattern of hemodynamic activation elicited by reading. ResultsIn 91 spike events, ECDs were clustered in the left posterior basal temporal area (pBTA) during Katakana reading. In 8 of these 91 events, when the patient continued to read >30min, another ECD cluster appeared in the left ventral precentral gyrus/frontal operculum with a time-difference of ∼24ms. Probabilistic diffusion tractography revealed that the long segment of the arcuate fasciculus connected these two regions. fMRI conjunction analysis indicated that both Katakana and Kanji reading activated the left pBTA, but Katakana activated the left lateral frontal areas more extensively than Kanji. ConclusionsProlonged reading of Katakana induced hyper-activation of the cortical network involved in normal language function, concurrently serving as the seizure onset and symptomatogenic zones. SignificanceReflex epilepsy is believed to result from intrinsic hyper-excitability in the cortical regions recruited during behavioral states that trigger seizures. Our case shows that reading epilepsy can arise from a hyperexcitable network of cortical regions. Physiological activation of this network can have cumulative effects, resulting in greater reciprocal network propagation and electroclinical seizures. These effects, in turn, may give insights into the brain networks recruited by reading.

Cortical Mapping Of Language In The Basal Temporal Area In Pediatric Patients Undergoing Epilepsy Surgery Evaluation. (P3.287)

Cortical Mapping Of Language In The Basal Temporal Area In Pediatric Patients Undergoing Epilepsy Surgery Evaluation. (P3.287)

Go with the flow: Use of a directed phase lag index (dPLI) to characterize patterns of phase relations in a large-scale model of brain dynamics

We introduce a directed phase lag index to investigate the spatial and temporal pattern of phase relations of oscillatory activity in a model of macroscopic structural and functional brain networks. Direction of information flow was determined with the directed phase lag index (dPLI) defined as the probability that the instantaneous phase of X was smaller than the phase of Y (modulo π). X was said to phase-lead Y if 0.5<dPLI(XY)<=1. The dPLI was used to characterize the phase relations between simulated EEG time series. The model consisted of 78 brain regions, coupled according to DTI findings in human subjects (Gong et al., 2009). Activity of each brain region was simulated with a neural mass model. Phase patterns were investigated as a function of coupling strength without stimulation, and with stimulation of the primary visual areas. At rest a clear spatial pattern of phase relations emerged with regions belonging to the anterior part of the default mode network leading in phase and regions belonging to the posterior part of the default mode network and surrounding visual areas lagging in phase. Patterns of phase leading and lagging displayed characteristic patterns with time scales from a few hundred milliseconds to 1-2 s. Stimulation of the primary visual areas induced a reversal of the global phase pattern with the visual and basal temporal areas leading and the anterior and superior frontal areas lagging in phase. This study shows that the directed phase lag index (dPLI) is an effective measure to characterize spatial temporal patterns of phase relations at rest and during stimulation. Coupling strength and node degree were found to be critical determinants of the direction of information flow. At a timescale of milliseconds to seconds the phase dynamics revealed spontaneous structure that might correspond to previously described "microstates". Stimulation of two visual areas reversed the global pattern of phase relations.

Rostral brain axonal injury in congenital central hypoventilation syndrome

Brain injury underlying the state-related loss of ventilatory drive, autonomic, cognitive, and affective deficits in congenital central hypoventilation syndrome (CCHS) patients appears throughout the brain, as demonstrated by magnetic resonance (MR) T2 relaxometry and mean diffusivity studies. However, neither MR measure is optimal to describe types of axonal injury essential for assessing neural interactions responsible for CCHS characteristics. To evaluate axonal integrity and partition the nature of tissue damage (axonal vs. myelin injury) in CCHS, we measured water diffusion parallel (axial diffusivity) and perpendicular (radial diffusivity) to rostral brain fibers, indicative of axonal and myelin changes, respectively, with diffusion tensor imaging (DTI). We performed DTI in 12 CCHS (age 18.5 + or - 4.9 years, 7 male) and 30 control (17.7 + or - 4.6 years, 18 male) subjects, using a 3.0-Tesla MR imaging scanner. Axial and radial diffusivity maps were calculated, spatially normalized, smoothed, and compared between groups (analysis of covariance; covariates, age and gender). Significantly increased radial diffusivity, primarily indicative of myelin injury, emerged in fibers of the corona radiata, internal capsule, corpus callosum, hippocampus through the fornix, cingulum bundle, and temporal and parietal lobes. Increased axial diffusivity, suggestive of axonal injury, appeared in fibers of the internal capsule, thalamus, corona radiata, and occipital and temporal lobes. Multiple brain regions showed both higher axial and radial diffusivity, indicative of loss of tissue integrity with a combination of myelin and axonal injury, including basal ganglia, bed nucleus, and limbic, occipital, and temporal areas. The processes underlying injury are unclear, but likely stem from both hypoxic and developmental processes.

Hanja (Ideogram) alexia and agraphia in patients with semantic dementia

Posterior fusiform gyrus (BA 37) is responsible for Hanja (ideogram) alexia in stroke patients. Patients with semantic dementia (SD) have lesions in the basal temporal area. The close proximity in these two lesions and the fact that reading ideograms requires holistic processing as is necessary in recognition of objects, suggests a possibility that ideogram alexia/agraphia may occur in patients with SD. We established and carried out Hanja and Hangul (phonogram) reading/writing tasks on six SD patients and nine Alzheimer's disease (AD) patients as control to see if these two patient groups show dissociation in the two sets of tests. SPM analysis was performed on the SD patients' PET images to look for any dysfunctions in the posterior fusiform gyrus. The SD patients manifested Hanja alexia/agraphia whereas Hangul reading/writing ability was relatively preserved. There were group differences between SD and AD in the Hanja tasks but not in the Hangul tasks. The SPM analysis revealed no hypometabolism in the posterior fusiform gyrus, but only in the middle and the anterior part of the temporal gyrus. Dysfunction in the middle temporal gyrus (BA 21) may have disrupted the temporal lobe connections preventing the function of the posterior fusiform gyrus.

Temporal Dynamics of Japanese Morphogram and Syllabogram Processing in the Left Basal Temporal Area Studied by Event-Related Potentials

Visual language processing in the left basal temporal area (LBTA) was investigated using subdural electrodes in two patients with medically intractable temporal lobe epilepsy. Reading of Japanese syllabogram (kana) and morphogram (kanji) both provoked two types of event-related potentials, one with the peak latency of approximately 200 milliseconds and the other approximately 300 milliseconds, at the anterior and posterior portion of the fusiform, parahippocampal, and inferior temporal gyri within LBTA. By electrical stimulation using the same electrodes, in contrast, kana reading was selectively impaired in one area in the posterior portion of LBTA where a sharp event-related potential was recorded at approximately 200 milliseconds, and kanji reading was selectively impaired in another area also in the posterior portion of LBTA, where a blunt event-related potential was recorded at approximately 300 milliseconds. Because kana reading is functionally fundamental compared with kanji reading, relatively early signals at 200 milliseconds might be related to postperceptual but still fundamental functions such as letter-by-letter language processing and relatively late signals at 300 milliseconds might be associated with postperceptual, relatively higher-order functions such as word-as-a-whole language processing. The results indicate the existence of two distinct functional areas for written-language processing within LBTA. Both kanji and kana signals reach specific area at the same timing.

Posterior cerebral artery infarcts and semantic category dissociations: a study of 28 patients

In this study we analysed the relationship between damage in the territory of the posterior cerebral artery and semantic knowledge, with special reference to category dissociations. Twenty-eight posterior cerebral artery stroke patients (18 left, 8 right and 2 bilateral posterior cerebral artery infarctions) completed a neuropsychological battery aimed at assessing semantic knowledge. The battery included picture naming, word-picture matching, a verbal semantic questionnaire and a picture reality decision task. For each participant, the lesion was reconstructed on the basis of MRI images, and was classified according to the involvement of the areas supplied by posterior cerebral artery. Defective naming scores were observed in 12 of 18 left posterior cerebral artery cases (67%), four of eight right posterior cerebral artery cases (50%), and one of two bilateral posterior cerebral artery cases (50%). Only in the bilateral posterior cerebral artery lesion case did we observe the pattern expected in pure visual agnosia, i.e. poor picture naming, poor picture reality decision, and normal verbal semantic questionnaire. Nine left posterior cerebral artery cases and two right posterior cerebral artery cases presented with poor performance on both the picture naming task and the verbal semantic questionnaire, thus suggesting semantic impairment. For 5 of the 12 left posterior cerebral artery patients who fared poorly on the naming task, biological stimuli (overall) were significantly more impaired than artifacts. In three of these five subjects, performance on plant-life stimuli was significantly less accurate than that on animals. A further left posterior cerebral artery patient presented a disproportionate impairment on plant-life stimuli only on the word-picture matching and on the questionnaire. The patterns of performance in these subjects suggest that the observed dissociations originated at the semantic level. Among left posterior cerebral artery patients, a naming deficit only occurred when damage to the fusiform gyrus extended anterior to Talairach's y-coordinate -50, and a disproportionate impairment of biological categories only when the lesion extended anterior to y = -32.5. Results show that the semantic deficit for the category of plant life is a genuine cognitive pattern, and does not depend on loss of colour knowledge. The contrast of left posterior cerebral artery strokes and herpes simplex encephalitis cases shows that the neural substrates for the semantic representation of plant life and animals are, at least in part, distinct. Middle and posterior portions of the left fusiform are crucial for the representation of plant-life knowledge, whereas left anterior temporal areas are more crucial than left posterior and basal temporal areas for the representation of knowledge about animals.

Ipsilateral facial sensory and motor responses to basal fronto-temporal cortical stimulation: Evidence suggesting direct activation of cranial nerves

To clarify the generator mechanism of sensory and motor facial responses ipsilateral to electrical stimulation of the inferior fronto-temporal cortex in epilepsy patients. Out of 30 patients who have been evaluated with chronically implanted subdural electrodes for medically intractable partial seizure or brain tumor involving the basal frontal or temporal cortex, 4 patients (age ranging 24–57 years) showed sensory and motor responses in the ipsilateral face to high frequency electrical cortical stimulation of the inferior fronto-temporal cortex. We investigated motor evoked potentials (MEPs) in the facial muscle by single pulse stimulation in 2 out of 4 patients. Three patients showed both sensory symptoms and muscle contraction in the ipsilateral lower face when the orbitofrontal or basal temporal cortex was stimulated with 50 Hz electric current. One patient had only sensory symptoms in the lower face when ipsilateral basal temporal area was stimulated. MEPs at the left orbicularis oris muscle were constantly elicited with the onset latency of 7 ms throughout the stimulus rate of 2–30 Hz in 1 patient out of 2 patients was tested. In another patient, MEP onset latency was 3.0 ms with 11 Hz stimulation. With electrical stimulation of the basal fronto-temporal cortex, the ipsilateral facial twitch might occur through either the direct activation of the facial nerve by the current spread in the middle cranial fossa or through the mechanism similar to blink reflex.

EEG Source Imaging in Pediatric Epilepsy Surgery: A New Perspective in Presurgical Workup

Epilepsy is a relatively frequent disease in children, with considerable impact on cognitive and social life. Successful epilepsy surgery depends on unambiguous focus identification and requires a comprehensive presurgical workup, including several neuroimaging techniques [magnetic resonance imaging, positron emission tomography (PET), and single-photon emission computed tomography (SPECT)]. These may be difficult to apply in younger or developmentally delayed children or both, requiring sedation, and hence, a significant workforce. Modern electric source imaging (ESI) provides accurate epileptic source-localization information in most patients, with minimal patient discomfort or need for cooperation. The purpose of the present study was to determine the usefulness of ESI in pediatric EEG recordings performed with routine electrode arrays. Preoperative EEGs recorded from 19 to 29 scalp electrodes were reviewed, and interictal epileptiform activity was analyzed by using a linear source-imaging procedure (depth-weighted minimum norm) in combination with statistical parametric mapping. In 27 (90%) of 30 patients, the ESI correctly localized the epileptogenic region. These numbers compare favorably with the results from other imaging techniques in the same patients (PET, 82%; ictal SPECT, 70%). In extratemporal epilepsy, ESI was correct in all cases, and in temporal lobe epilepsy, in 10 of 13 cases. In two temporal lobe patients showing less-accurate ESI results, 128-electrode data could be analyzed, and in both cases, the 128-electrode ESI was correct. ESI with standard clinical EEG recordings provides excellent localizing information in pediatric patients, in particular in extratemporal lobe epilepsy. The lower yield in temporal lobe epilepsy seems to be due to undersampling of basal temporal areas with routine scalp recordings.

Language Processing: The Neural Basis of Nouns and Verbs

A new study of the functional anatomy of noun and verb production suggests an important role for semantic representations in the cortical processing of these two distinct grammatical classes.

High-Frequency γ-Band Activity in the Basal Temporal Cortex during Picture-Naming and Lexical-Decision Tasks

Gamma-band activity (GBA) in electroencephalograms (EEGs) has been shown to reflect various cognitive processes. GBA has typically been recorded in the 30-60 Hz range in scalp EEGs. Recently, task-related "high GBA" (HGBA) with frequencies up to 100 Hz has been observed in studies with invasive electrocorticograms (ECoGs). In the present study, we recorded ECoGs from the bilateral basal temporal cortices in a patient with epilepsy and evaluated the task-related HGBA (most prominently in the 80-120 Hz range) accompanying picture-naming and lexical-decision tasks. We examined picture naming using two categories (line drawings of animals and tools). The lexical-decision task was performed using words and pseudowords of two distinct Japanese writing forms, kanji (morphograms) and kana (syllabograms). Task-related HGBA was observed bilaterally during the naming task. Recordings from some electrodes revealed significant differences in HGBA between animal and tool pictures. In contrast to the naming task, there was apparent left dominance in the lexical-decision task. Furthermore, significant differences in HGBA were observed between the Japanese kanji and kana words and between the kanji words and kanji pseudowords. A number of differences in the HGBA observed in the recordings from the basal temporal area were consistent with previous findings from neuroimaging and patient studies and suggest that HGBA is a good correlate of visual cognitive functions.

Processing of Japanese morphogram and syllabogram in the left basal temporal area: electrical cortical stimulation studies

Language functions in the left basal temporal area (LBTA) were investigated using electrical cortical stimulation during functional mapping in six Japanese patients with refractory epilepsy. This study provides the first direct evidence that kana (Japanese syllabogram) is processed in the LBTA. Electrical stimulation of some areas within LBTA induced disturbance in overt reading of kana words only in the first trials, with no errors in the subsequent trials. By contrast, stimulation of the same area caused obvious disturbance in kana non-word reading in all trials. Since a kana word carries both meaning and sound while a kana non-word carries only sounds of a letter string, the contrasting results of partial and complete disturbance imply a possibility that there are two distinct pathways for kana reading: one dealing with both phonological and semantic aspects of the words and the other dealing only with phonological aspect. Kanji words (Japanese morphogram) and objects/pictures were found to be processed in an area different from the area for the kana non-word processing. Furthermore, the present study also identified the common area for processing kanji reading and object/picture naming. There were no errors in matching pictures with kanji words, indicating that concepts of pictures and meanings of kanji words were not interfered by the electrical stimulation of that area. The new insight provides a clue for partial description of processing pathways for language-related visual information in LBTA. Three types of information (morphological, phonological, and semantic) are conveyed together at some stages and are separated into different routes at some other stages.

Interareal connectivity in the human language system: a cortico-cortical evoked potential study

Objective To investigate functional connectivity in the human language system in vivo by means of a cortico-cortical evoked potential (CCEP) study. Methods Eight epilepsy patients underwent chronic subdural electrode implantation in the language dominant hemisphere for epilepsy surgery. Single pulse electrical stimuli were delivered to the anterior language (eight patients), posterior language (four) or face motor (two) area, and CCEPs were obtained by averaging electrocorticograms recorded from the perisylvian and extrasylvian basal temporal language areas time locked to the stimulus. Results Stimulation at the anterior language area elicited CCEPs (7/8 patients at 3–21 electrodes) in the middle and posterior part of the superior temporal gyrus, the adjacent part of the middle temporal gyrus and the supramarginal gyrus. CCEPs occurred at and/or around the core language area identified by conventional electrical stimulation. Similar early and late CCEPs were obtained from the basal temporal area by stimulating the anterior language area (3/3). In contrast, stimulation of the adjacent face motor area did not elicit CCEPs in language areas but rather in the postcentral gyrus. Stimulation of the posterior language area produced CCEPs in the anterior language (3/4) as well as in the basal temporal area (1/2). Conclusion This study, for the first time, demonstrated that perisylvian and extrasylvian language areas participate in the language system as components of a network by means of feed-forward and feed-back projections. Judging from the CCEP distribution in the posterior language area, a rather broad neuronal network seems to surround the previously recognized core region of this area.