Bulk and grain boundary Li-diffusion in dense LiMn2O4 pellets by means of isotope exchange and ToF-SIMS analysis

Lithium diffusion in LiMn₂O₄ pellets is studied by means of isotope exchange and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). A ⁶Li-enriched film deposited by Pulsed Laser Deposition (PLD) on a dense LiMn₂O₄ pellet with natural abundance of lithium isotopes is used to study the tracer diffusion of lithium. The measured profiles are analyzed by numerical models describing the ⁶Li tracer diffusion from the film into the pellet. Experiments in the Harrison type B regime of diffusion kinetics allow for the distinction and simultaneous determination of bulk and grain boundary diffusion coefficients. Changing the experimental conditions to reach Harrison type A behavior yields effective diffusion coefficients for lithium tracer diffusion in LiMn₂O₄. Activation energies for bulk and grain boundary diffusion were obtained from experiments at different temperatures. Our values are critically compared to previous studies.

Unravelling the mechanism of lithium insertion into and extraction from trirutile-type LiNiFeF6 cathode material for Li-ion batteries

For possible future application as cathode material in lithium ion batteries, the lithium insertion mechanism of trirutile-type LiNiFeF₆ was investigated.

Characterization of non-stoichiometric co-sputtered Ba0.6Sr0.4(Ti (1-x)Fe(x))(1+x)O(3-δ) thin films for tunable passive microwave applications

The fabrication of novel iron-doped barium strontium titanate thin films by means of radio frequency (RF) magnetron co-sputtering is shown. Investigations of the elemental composition and the dopant distribution in the thin films obtained by X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and time-of-flight secondary ion mass spectroscopy reveal a homogeneous dopant concentration throughout the thin film. The incorporation of the iron dopant and the temperature-dependent evolution of the crystal structure and morphology are analyzed by electron paramagnetic resonance spectroscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, and scanning electron microscopy. In summary, these results emphasize the RF magnetron co-sputter process as a versatile way to fabricate doped thin films.

Material characteristics of a novel shrinkage-free ZrSiO4 ceramic for the fabrication of posterior crowns

OBJECTIVE

To confirm the clinical applicability of a novel ZrSiO(4) (zircon) based shrinkage-free ceramic material, the flexural strength, fracture toughness and chemical solubility were tested. In addition, the fracture load of full crowns made from this material was tested after cyclic thermomechanical loading.

METHODS

Flexural strength of 12 specimens was measured using a biaxial bending test. Fracture toughness was measured using 10 slotted box shaped specimens. The specimens were fractured using a universal testing machine; fracture loads were recorded. A chemical solubility test was performed in accordance with ISO norm 6872. Additionally, 32 ZrSiO(4) all-ceramic crowns were fabricated on extracted caries-free human molars. Sixteen Empress 2 and 16 PFM crowns served as a reference control. After artificial aging of 1.2 million cycles in the chewing simulator, the survival rate of the crowns was determined. The fracture load of all surviving specimens was obtained by loading the crowns until fracture in a universal testing machine.

RESULTS

A flexural strength of 328MPa was found. The fracture toughness of the ZrSiO(4) ceramic was 5.16MPam(0.5). The chemical solubility amounted to 7.2microg/cm(2). All specimens survived the chewing simulation (survival rate: 100%); no crowns had to be re-cemented. A mean fracture strength of 1790N was found for Everest HPC for Empress 2 crowns, 1715N for Empress 2 crowns and 2416N for PFM crowns. Fracture loads of PFM crowns were significantly higher than for Empress 2 crowns (P=0.032) as well as ZrSiO(4)-crowns (P=0.007). There was no significant difference between ZrSiO(4)-crowns and Empress 2 crowns (P=0.743).

SIGNIFICANCE

At the present stage, Everest HPC can be recommended for the fabrication of single crowns as an alternative to conventional PFM and other all-ceramic crowns, because its fracture strength exceeds average masticatory forces in the posterior region.

Attentional modulation in the detection of irrelevant deviance: a simultaneous ERP/fMRI study

Little is known about the neural mechanisms that control attentional modulation of deviance detection in the auditory modality. In this study, we manipulated the difficulty of a primary task to test the relation between task difficulty and the detection of infrequent, task-irrelevant deviant (D) tones (1,300 Hz) presented among repetitive standard (S) tones (1,000 Hz). Simultaneous functional magnetic resonance imaging (fMRI)/event-related potentials (ERPs) were recorded from 21 subjects performing a two-alternative forced-choice duration discrimination task (short and long tones of equal probability). The duration of the short tone was always 50 msec. The duration of the long tone was 100 msec in the easy task and 60 msec in the difficult task. As expected, response accuracy decreased and response time (RT) increased in the difficult compared with the easy task. Performance was also poorer for D than for S tones, indicating distraction by task-irrelevant frequency information on trials involving D tones. In the difficult task, an amplitude increase was observed in the difference waves for N1 and P3a, ERP components associated with increased attention to deviant sounds. The mismatch negativity (MMN) response, associated with passive deviant detection, was larger in the easy task, demonstrating the susceptibility of this component to attentional manipulations. The fMRI contrast D > S in the difficult task revealed activation on the right superior temporal gyrus (STG) and extending ventrally into the superior temporal sulcus, suggesting this region's involvement in involuntary attention shifting toward unattended, infrequent sounds. Conversely, passive deviance detection, as reflected by the MMN, was associated with more dorsal activation on the STG. These results are consistent with the view that the dorsal STG region is responsive to mismatches between the memory trace of the standard and the incoming deviant sound, whereas the ventral STG region is activated by involuntary shifts of attention to task-irrelevant auditory features.

Some neurophysiological constraints on models of word naming

The pronunciation of irregular words in deep orthographies like English cannot be specified by simple rules. On the other hand, the fact that novel letter strings can be pronounced seems to imply the existence of such rules. These facts motivate dual-route models of word naming, which postulate separate lexical (whole-word) and non-lexical (rule-based) mechanisms for accessing phonology. We used fMRI during oral naming of irregular words, regular words, and nonwords, to test this theory against a competing single-mechanism account known as the triangle model, which proposes that all words are handled by a single system containing distributed orthographic, phonological, and semantic codes rather than word codes. Two versions of the dual-route model were distinguished: an 'exclusive' version in which activation of one processing route predominates over the other, and a 'parallel' version in which both routes are equally activated by all words. The fMRI results provide no support for the exclusive dual-route model. Several frontal, insular, anterior cingulate, and parietal regions showed responses that increased with naming difficulty (nonword > irregular word > regular word) and were correlated with response time, but there was no activation consistent with the predicted response of a non-lexical, rule-based mechanism (i.e., nonword > regular word > irregular word). Several regions, including the angular gyrus and dorsal prefrontal cortex bilaterally, left ventromedial temporal lobe, and posterior cingulate gyrus, were activated more by words than nonwords, but these 'lexical route' regions were equally active for irregular and regular words. The results are compatible with both the parallel dual-route model and the triangle model. 'Lexical route' regions also showed effects of word imageability. Together with previous imaging studies using semantic task contrasts, the imageability effects are consistent with semantic processing in these brain regions, suggesting that word naming is partly semantically-mediated.

Modulation of the semantic system by word imageability

A prevailing neurobiological theory of semantic memory proposes that part of our knowledge about concrete, highly imageable concepts is stored in the form of sensory-motor representations. While this theory predicts differential activation of the semantic system by concrete and abstract words, previous functional imaging studies employing this contrast have provided relatively little supporting evidence. We acquired event-related functional magnetic resonance imaging (fMRI) data while participants performed a semantic similarity judgment task on a large number of concrete and abstract noun triads. Task difficulty was manipulated by varying the degree to which the words in the triad were similar in meaning. Concrete nouns, relative to abstract nouns, produced greater activation in a bilateral network of multimodal and heteromodal association areas, including ventral and medial temporal, posterior-inferior parietal, dorsal prefrontal, and posterior cingulate cortex. In contrast, abstract nouns produced greater activation almost exclusively in the left hemisphere in superior temporal and inferior frontal cortex. Increasing task difficulty modulated activation mainly in attention, working memory, and response monitoring systems, with almost no effect on areas that were modulated by imageability. These data provide critical support for the hypothesis that concrete, imageable concepts activate perceptually based representations not available to abstract concepts. In contrast, processing abstract concepts makes greater demands on left perisylvian phonological and lexical retrieval systems. The findings are compatible with dual coding theory and less consistent with single-code models of conceptual representation. The lack of overlap between imageability and task difficulty effects suggests that once the neural representation of a concept is activated, further maintenance and manipulation of that information in working memory does not further increase neural activation in the conceptual store.

Distinct Brain Systems for Processing Concrete and Abstract Concepts

Behavioral and neurophysiological effects of word imageability and concreteness remain a topic of central interest in cognitive neuroscience and could provide essential clues for understanding how the brain processes conceptual knowledge. We examined these effects using event-related functional magnetic resonance imaging while participants identified concrete and abstract words. Relative to nonwords, concrete and abstract words both activated a left-lateralized network of multimodal association areas previously linked with verbal semantic processing. Areas in the left lateral temporal lobe were equally activated by both word types, whereas bilateral regions including the angular gyrus and the dorsal prefrontal cortex were more strongly engaged by concrete words. Relative to concrete words, abstract words activated left inferior frontal regions previously linked with phonological and verbal working memory processes. The results show overlapping but partly distinct neural systems for processing concrete and abstract concepts, with greater involvement of bilateral association areas during concrete word processing, and processing of abstract concepts almost exclusively by the left hemisphere.

Ballistocardiogram artifact reduction in the simultaneous acquisition of auditory ERPS and fMRI

Electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) are now being combined to analyze brain function. Confounding the EEG signal acquired in the MR environment is a ballistocardiogram artifact (BA), which is predominantly caused by cardiac-related body movement. The objective of this study was to develop and evaluate a method for reducing these MR-induced artifacts to retrieve small auditory event-related potentials (ERPs) from EEG recorded during fMRI. An algorithm for BA reduction was developed that relies on timing information obtained from simultaneous electrocardiogram (ECG) recordings and subsequent creation of an adaptive BA template. The BA template is formed by median-filtering 10 consecutive BA events in the EEG signal. The continuously updated template is then subtracted from each BA in the EEG. The auditory ERPs are obtained through signal averaging of the remaining EEG signal. Experimental and simulated ERP data were estimated to assess effectiveness of the BA reduction. Simulation showed that the algorithm reduced BA without significantly altering the morphology of a signal periodically inserted in the EEG. Auditory ERP data, obtained in a 1.5-T scanner during a passive auditory oddball paradigm and processed with the BA reduction algorithm, were comparable to data recorded in a mock scanner outside the magnetic field with the same experimental paradigm. It is concluded that through adequate reduction of the BA, relatively small auditory ERPs can be acquired in the MR environment.

Use of preoperative functional neuroimaging to predict language deficits from epilepsy surgery

BACKGROUND

Left anterior temporal lobectomy (L-ATL) may be complicated by confrontation naming deficits.

OBJECTIVE

To determine whether preoperative fMRI predicts such deficits in patients with epilepsy undergoing L-ATL.

METHODS

Twenty-four patients with L-ATL underwent preoperative language mapping with fMRI, preoperative intracarotid amobarbital (Wada) testing for language dominance, and pre- and postoperative neuropsychological testing. fMRI laterality indexes (LIs), reflecting the interhemispheric difference between activated volumes in left and right homologous regions of interest, were calculated for each patient. Relationships between the fMRI LI, Wada language dominance, and naming outcome were examined.

RESULTS

Both the fMRI LI (p < 0.001) and the Wada test (p < 0.05) were predictive of naming outcome. fMRI showed 100% sensitivity and 73% specificity in predicting significant naming decline. Both fMRI and the Wada test were more predictive than age at seizure onset or preoperative naming performance.

CONCLUSIONS

Preoperative fMRI predicted naming decline in patients undergoing left anterior temporal lobectomy surgery.

Neural correlates of lexical access during visual word recognition

People can discriminate real words from nonwords even when the latter are orthographically and phonologically word-like, presumably because words activate specific lexical and/or semantic information. We investigated the neural correlates of this identification process using event-related functional magnetic resonance imaging (fMRI). Participants performed a visual lexical decision task under conditions that encouraged specific word identification: Nonwords were matched to words on orthographic and phonologic characteristics, and accuracy was emphasized over speed. To identify neural responses associated with activation of nonsemantic lexical information, processing of words and nonwords with many lexical neighbors was contrasted with processing of items with no neighbors. The fMRI data showed robust differences in activation by words and word-like nonwords, with stronger word activation occurring in a distributed, left hemisphere network previously associated with semantic processing, and stronger nonword activation occurring in a posterior inferior frontal area previously associated with grapheme-to-phoneme mapping. Contrary to lexicon-based models of word recognition, there were no brain areas in which activation increased with neighborhood size. For words, activation in the left prefrontal, angular gyrus, and ventrolateral temporal areas was stronger for items without neighbors, probably because accurate responses to these items were more dependent on activation of semantic information. The results show neural correlates of access to specific word information. The absence of facilitatory lexical neighborhood effects on activation in these brain regions argues for an interpretation in terms of semantic access. Because subjects performed the same task throughout, the results are unlikely to be due to task-specific attentional, strategic, or expectancy effects.

Language lateralization in left-handed and ambidextrous people: fMRI data

BACKGROUND

It is generally accepted that most people have left-hemispheric language dominance, though the actual incidence of atypical language distribution in non-right-handed subjects has not been extensively studied. The authors examined language distribution in these subjects and evaluated the relationships between personal handedness, family history of sinistrality, and a language laterality index (LI) measured with fMRI.

METHODS

The authors used whole-brain fMRI to examine 50 healthy, non-right-handed subjects (Edinburgh Handedness Inventory quotient between -100 and 52) while they performed language activation and nonlinguistic control tasks. Counts of active voxels (p < 0.001) were computed in 22 regions of interest (ROI) covering both hemispheres and the cerebellum. LI were calculated for each ROI and each entire hemisphere using the formula [L - R]/[L + R].

RESULTS

Activation was predominantly right hemispheric in 8% (4/50), symmetric in 14% (7/50), and predominantly left hemispheric in 78% (39/50) of the subjects. Lateralization patterns were similar for all hemispheric ROI. Associations were observed between personal handedness and LI (r = 0.28, p = 0.046), family history of sinistrality and LI (p = 0.031), and age and LI (r = -0.49, p < 0.001).

CONCLUSIONS

The incidence of atypical language lateralization in normal left-handed and ambidextrous subjects is higher than in normal right-handed subjects (22% vs 4-6%). These whole-brain results confirm previous findings in a left-handed cohort studied with fMRI of the lateral frontal lobe. Associations observed between personal handedness and LI and family history of handedness and LI may indicate a common genetic factor underlying the inheritance of handedness and language lateralization.

Pure topographic disorientation: A distinctive syndrome with varied localization

Pure topographic disorientation (TD), defined as impaired recall of routes in familiar surroundings, has been attributed to lesions of the right parahippocampus. The authors present three patients encountered consecutively with TD and compare them to previously published cases. Lesions causing TD included a right splenial/cuneus infarct, a right > left medial temporo-occipital infarct, and a left splenial infarct. TD as an isolated symptom may occur from lesion in a variety of posterior medial locations, including the parahippocampus, splenium, and retrosplenial cortex.

Human temporal lobe activation by speech and nonspeech sounds

Functional organization of the lateral temporal cortex in humans is not well understood. We recorded blood oxygenation signals from the temporal lobes of normal volunteers using functional magnetic resonance imaging during stimulation with unstructured noise, frequency-modulated (FM) tones, reversed speech, pseudowords and words. For all conditions, subjects performed a material-nonspecific detection response when a train of stimuli began or ceased. Dorsal areas surrounding Heschl's gyrus bilaterally, particularly the planum temporale and dorsolateral superior temporal gyrus, were more strongly activated by FM tones than by noise, suggesting a role in processing simple temporally encoded auditory information. Distinct from these dorsolateral areas, regions centered in the superior temporal sulcus bilaterally were more activated by speech stimuli than by FM tones. Identical results were obtained in this region using words, pseudowords and reversed speech, suggesting that the speech-tones activation difference is due to acoustic rather than linguistic factors. In contrast, previous comparisons between word and nonword speech sounds showed left-lateralized activation differences in more ventral temporal and temporoparietal regions that are likely involved in processing lexical-semantic or syntactic information associated with words. The results indicate functional subdivision of the human lateral temporal cortex and provide a preliminary framework for understanding the cortical processing of speech sounds.

Intravenous tissue plasminogen activator for acute ischemic stroke in patients aged 80 years and older : the tPA stroke survey experience

BACKGROUND AND PURPOSE

Intravenous tissue plasminogen activator (tPA) administered within 3 hours of symptom onset is the first available effective therapy for acute ischemic stroke (AIS). Few data exist, however, on its use in very elderly patients. We examined the characteristics, complications, and short-term outcome of AIS patients aged >/=80 years treated with tPA.

METHODS

Patients aged >/=80 years (n=30) were compared with counterparts aged <80 years (n=159) included in the tPA Stroke Survey, a US retrospective survey of 189 consecutive AIS patients treated with intravenous tPA at 13 hospitals.

RESULTS

Risk of intracerebral hemorrhage (fatal, symptomatic, and total) was 3%, 3%, and 7% in the elderly age group and 2%, 6%, and 9%, respectively, in their younger counterparts (P=NS for all comparisons). Likelihood of favorable outcome, defined as modified Rankin score 0 to 1, National Institutes of Health Stroke Scale score </=5, or marked improvement by hospital discharge, was comparable between groups (37%, 54%, and 43% versus 30%, 54%, and 43%, respectively; P=NS for all comparisons). Elderly patients were more likely to be treated by stroke specialists (87% versus 60%; P=0.005) and less likely to have an identified protocol deviation (13% versus 33%; P=0.03). Elderly patients were discharged more often to nursing care facilities (17% versus 5%; P=0.003). In logistic regression models there were no differences in odds ratio for favorable or poor outcome, other than tendency for higher in-hospital mortality in elderly patients (odds ratio, 2.8; 95% CI, 0.81 to 9.62; P=0.10).

CONCLUSIONS

Among AIS patients treated with intravenous tPA, age-related differences in characteristics and disposition were identified. No evidence for withholding tPA treatment for AIS in appropriately selected patients aged >/=80 years was identified.

Neural systems underlying the recognition of familiar and newly learned faces

Memory for famous faces can be used to examine the neural systems underlying retrieval from long-term memory. To date, there have been a limited number of functional neuroimaging investigations examining famous face recognition. In this study, we compared recognition of famous faces to recognition of newly learned faces. Whole-brain, event-related functional magnetic resonance imaging was used to image regional changes in neural activity in 11 subjects during the encoding of unfamiliar faces and during familiarity judgments for: (1) newly learned faces, (2) unfamiliar face distractors, and (3) famous faces. Image analyses were restricted to correct recognition trials. Recognition accuracy and response time to famous and recently learned faces were equivalent. Recognition of famous faces was associated with a widespread network of bilateral brain activations involving the prefrontal, lateral temporal, and mesial temporal (hippocampal and parahippocampal regions) regions compared to recognition of recently encoded faces or unfamiliar faces seen for the first time. Findings are discussed in relation to current proposals concerning the neural regions thought to participate in long-term memory retrieval and, more specifically, in relation to retrieval of information from the person identity semantic system.

Language dominance in neurologically normal and epilepsy subjects: a functional MRI study

Language dominance and factors that influence language lateralization were investigated in right-handed, neurologically normal subjects (n = 100) and right-handed epilepsy patients (n = 50) using functional MRI. Increases in blood oxygenation-dependent signal during a semantic language activation task relative to a non-linguistic, auditory discrimination task provided an index of language system lateralization. As expected, the majority of both groups showed left hemisphere dominance, although a continuum of activation asymmetry was evident, with nearly all subjects showing some degree of right hemisphere activation. Using a categorical dominance classification, 94% of the normal subjects were considered left hemisphere dominant and 6% had bilateral, roughly symmetric language representation. None of the normal subjects had rightward dominance. There was greater variability of language dominance in the epilepsy group, with 78% showing left hemisphere dominance, 16% showing a symmetric pattern and 6% showing right hemisphere dominance. Atypical language dominance in the epilepsy group was associated with an earlier age of brain injury and with weaker right hand dominance. Language lateralization in the normal group was weakly related to age, but was not significantly related to sex, education, task performance or familial left-handedness.

Initial clinical experience with IV tissue plasminogen activator for acute ischemic stroke: a multicenter survey. The t-PA Stroke Survey Group

We assessed initial clinical experience with IV tissue plasminogen activator (t-PA) treatment of acute ischemic stroke in a standardized retrospective survey of hospitals with experienced acute stroke treatment systems. The incidence of symptomatic intracerebral hemorrhage (ICH) was 6% (11 of 189 patients; 95% CI 3 to 11%), similar to that in the National Institute of Neurological Disorders and Stroke (NINDS) t-PA Stroke Study. Deviations from the NINDS protocol guidelines were identified in 30% of patients (56 of 189). The incidence of symptomatic ICH was 11% among patients with protocol deviations as compared with 4% in patients who were treated according to the NINDS protocol guidelines, suggesting that strict adherence to protocol guidelines is prudent.

Mapping of semantic, phonological, and orthographic verbal working memory in normal adults with functional magnetic resonance imaging

Twelve neurologically normal participants (4 men and 8 women) performed semantic, phonological, and orthographic working memory tasks and a control task during functional magnetic resonance imaging. Divergent regions of the posterior left hemisphere used for decoding and storage of information emerged in each working memory versus control task comparison. These regions were consistent with previous literature on processing mechanisms for semantic, phonological, and orthographic information. Further, working memory versus control task differences extended into the left frontal lobe, including premotor cortex, and even into subcortical structures. Findings were consistent with R. C. Martin and C. Romani's (1994) contention that different forms of verbal working memory exist and further suggest that a reconceptualization of premotor cortex functions is needed.

Mapping of semantic, phonological, and orthographic verbal working memory in normal adults with functional magnetic resonance imaging

Twelve neurologically normal participants (4 men and 8 women) performed semantic, phonological, and orthographic working memory tasks and a control task during functional magnetic resonance imaging. Divergent regions of the posterior left hemisphere used for decoding and storage of information emerged in each working memory versus control task comparison. These regions were consistent with previous literature on processing mechanisms for semantic, phonological, and orthographic information. Further, working memory versus control task differences extended into the left frontal lobe, including premotor cortex, and even into subcortical structures. Findings were consistent with R. C. Martin and C. Romani's (1994) contention that different forms of verbal working memory exist and further suggest that a reconceptualization of premotor cortex functions is needed.

Neural basis of endogenous and exogenous spatial orienting. A functional MRI study

Whole-brain functional magnetic resonance imaging (MRI) was used to examine the neural substrates of internally (endogenous) and externally (exogenous) induced covert shifts of attention. Thirteen normal subjects performed three orienting conditions: endogenous (location of peripheral target predicted by a central arrow 80% of the time), exogenous (peripheral target preceded by noninformative central cue). Behavioral results indicated faster reaction times (RTs) for valid than for invalid trials for the endogenous condition but slower RTs for valid than for invalid trials for the exogenous condition (inhibition of return). The spatial extent and intensity of activation was greatest for the endogenous condition, consistent with the hypothesis that endogenous orienting is more effortful (less automatic) than exogenous orienting. Overall, we did not observe distinctly separable neural systems associated with the endogenous and exogenous orienting conditions. Both exogenous and endogenous orienting, but not the control condition, activated bilateral parietal and dorsal premotor regions, including the frontal eye fields. These results suggest a specific role for these regions in preparatory responding to peripheral stimuli. The right dorsolateral prefrontal cortex (BA 46) was activated selectively by the endogenous condition. This finding suggests that voluntary, but not reflexive, shifts of attention engage working memory systems.

Language processing is strongly left lateralized in both sexes. Evidence from functional MRI

Functional MRI (fMRI) was used to examine gender effects on brain activation during a language comprehension task. A large number of subjects (50 women and 50 men) was studied to maximize the statistical power to detect subtle differences between the sexes. To estimate the specificity of findings related to sex differences, parallel analyses were performed on two groups of randomly assigned subjects. Men and women showed very similar, strongly left lateralized activation patterns. Voxel-wise tests for group differences in overall activation patterns demonstrated no significant differences between women and men. In further analyses, group differences were examined by region of interest and by hemisphere. No differences were found between the sexes in lateralization of activity in any region of interest or in intrahemispheric cortical activation patterns. These data argue against substantive differences between men and women in the large-scale neural organization of language processes.

Conceptual processing during the conscious resting state. A functional MRI study

Localized, task-induced decreases in cerebral blood flow are a frequent finding in functional brain imaging research but remain poorly understood. One account of these phenomena postulates processes ongoing during conscious, resting states that are interrupted or inhibited by task performance. Psychological evidence suggests that conscious humans are engaged almost continuously in adaptive processes involving semantic knowledge retrieval, representation in awareness, and directed manipulation of represented knowledge for organization, problem-solving, and planning. If interruption of such 'conceptual' processes accounts for task-induced deactivation, tasks that also engage these conceptual processes should not cause deactivation. Furthermore, comparisons between conceptual and nonconceptual tasks should show activation during conceptual tasks of the same brain areas that are 'deactivated' relative to rest. To test this model, functional magnetic resonance imaging data were acquired during a resting state, a perceptual task, and a semantic retrieval task. A network of left-hemisphere polymodal cortical regions showed higher signal values during the resting state than during the perceptual task but equal values during the resting and semantic conditions. This result is consistent with the proposal that perceptual tasks interrupt processes ongoing during rest that involve many of the same brain areas engaged during semantic retrieval. As further evidence for this model, the same network of brain areas was activated in two direct comparisons between semantic and perceptual processing tasks. This same 'conceptual processing' network was also identified in several previous studies that contrasted semantic and perceptual tasks or resting and active states. The model proposed here offers a unified account of these findings and may help to explain several unanticipated results from prior studies of semantic processing.

Is speech arrest during wada testing a valid method for determining hemispheric representation of language?

BACKGROUND AND OBJECTIVE

The intracarotid amobarbital procedure, or Wada test, is the method of choice to determine hemispheric representation of language, and is routinely used in the presurgical evaluation for intractable epilepsy. Some investigators perform comprehensive language assessments, but others base language lateralization solely on speech arrest. This study sought to determine whether speech arrest alone during Wada testing provides valid data regarding language lateralization.

METHODS

The subjects (previously reported) were 21 patients evaluated for intractable epilepsy, who underwent language lateralization by Wada testing and functional MRI (FMRI). For each patient, language representation was determined by calculating: (1) a Wada laterality index based exclusively on speech arrest; (2) a Wada laterality index based on comprehensive language assessment; and (3) an FMRI laterality quotient. Correlation coefficients and categorical classifications were analyzed.

RESULTS

There was no significant correlation between the Wada laterality quotient derived from duration of speech arrest and either the comprehensive Wada language laterality score (r =.35, p =.12) or FMRI language laterality score (r =.32, p =.16). Categorical classification as left, right or bilateral language also showed marked discordance between speech arrest and the other two methods.

CONCLUSION

Duration of speech arrest during Wada testing is not a valid measure of language dominance.

Side of seizure focus predicts left medial temporal lobe activation during verbal encoding

OBJECTIVE

Functional MRI (FMRI) was used to investigate the effect of medial temporal lobe (MTL) pathology on activation of language encoding areas in patients with temporal lobe epilepsy (TLE).

METHODS

Whole-brain FMRI was obtained. Twenty-eight patients with either left TLE (LTLE) or right TLE (RTLE) performed a semantic decision task alternating with an auditory perceptual task.

RESULTS

Activation of language areas in the frontal and parietal lobes was similar in both groups, with no group differences in the total number of active voxels. However, the RTLE group showed much stronger activation of the left MTL, including the hippocampus, parahippocampal gyrus, and collateral sulcus, than did the LTLE group.

CONCLUSIONS

Activation of the left MTL during semantic encoding discriminates patients with RTLE and LTLE. This FMRI technique may potentially be of use in determining memory lateralization and for predicting the side of seizure focus in TLE.

Executive functions in multiple sclerosis: an analysis of temporal ordering, semantic encoding, and planning abilities

Previous studies have consistently demonstrated impairments in conceptual reasoning and set-shifting abilities in patients with multiple sclerosis (MS). Other executive functions have been less frequently examined. We compared 44 MS patients and 48 demographically matched controls on a temporal-ordering and semantic-encoding task and on a test of planning (Tower of Hanoi). Compared with controls, MS patients experienced deficient semantic encoding and planning but unimpaired temporal-order memory. For both tasks, post hoc analyses indicated that chronic-progressive MS patients contributed most to the group differences. A combination of poor planning and slowed information-processing speed was hypothesized to have contributed to MS patients' impaired Tower of Hanoi performance. Further research is needed to explore the possible relationship between semantic-encoding and planning deficits in MS and social and occupational disabilities.

Executive functions in multiple sclerosis: an analysis of temporal ordering, semantic encoding, and planning abilities

Previous studies have consistently demonstrated impairments in conceptual reasoning and set-shifting abilities in patients with multiple sclerosis (MS). Other executive functions have been less frequently examined. We compared 44 MS patients and 48 demographically matched controls on a temporal-ordering and semantic-encoding task and on a test of planning (Tower of Hanoi). Compared with controls, MS patients experienced deficient semantic encoding and planning but unimpaired temporal-order memory. For both tasks, post hoc analyses indicated that chronic-progressive MS patients contributed most to the group differences. A combination of poor planning and slowed information-processing speed was hypothesized to have contributed to MS patients' impaired Tower of Hanoi performance. Further research is needed to explore the possible relationship between semantic-encoding and planning deficits in MS and social and occupational disabilities.

Distributed neural systems underlying the timing of movements

Timing is essential to the execution of skilled movements, yet our knowledge of the neural systems underlying timekeeping operations is limited. Using whole-brain functional magnetic resonance imaging, subjects were imaged while tapping with their right index finger in synchrony with tones that were separated by constant intervals [Synchronization (S)], followed by tapping without the benefit of an auditory cue [Continuation (C)]. Two control conditions followed in which subjects listened to tones and then made pitch discriminations (D). Both the S and the C conditions produced equivalent activation within the left sensorimotor cortex, the right cerebellum (dorsal dentate nucleus), and the right superior temporal gyrus (STG). Only the C condition produced activation of a medial premotor system, including the caudal supplementary motor area (SMA), the left putamen, and the left ventrolateral thalamus. The C condition also activated a region within the right inferior frontal gyrus (IFG), which is functionally interconnected with auditory cortex. Both control conditions produced bilateral activation of the STG, and the D condition also activated the rostral SMA. These results suggest that the internal generation of precisely timed movements is dependent on three interrelated neural systems, one that is involved in explicit timing (putamen, ventrolateral thalamus, SMA), one that mediates auditory sensory memory (IFG, STG), and another that is involved in sensorimotor processing (dorsal dentate nucleus, sensorimotor cortex).

Functional MRI evidence for subcortical participation in conceptual reasoning skills

Lesions involving the dorsolateral prefrontal lobes may produce deficits on conceptual reasoning (CR) tasks in humans. Such deficits can also occur with subcortical lesions involving the basal ganglia, thalamus, or cerebellum, suggesting a common, yet widespread, neural network supporting this executive function. Here we report the results of a whole brain functional magnetic resonance imaging (fMRI) experiment in healthy volunteers while performing a CR task. Compared to a sensorimotor control condition, the CR task resulted in discrete subcortical activation sites primarily involving the right basal ganglia, right thalamus and left lateral cerebellum. Cortical activation was present in multiple systems, including the dorsolateral prefrontal and inferior frontal/insular areas; posterior parietal, superior extrastriate, and premotor areas; inferior extrastriate and middle temporal regions; and midline pre-supplementary motor and anterior cingulate regions. Our findings provide strong evidence that CR is mediated by interacting neural systems involving the cerebral cortex, basal ganglia, thalamus, and cerebellum.

Human brain language areas identified by functional magnetic resonance imaging

Functional magnetic resonance imaging (FMRI) was used to identify candidate language processing areas in the intact human brain. Language was defined broadly to include both phonological and lexical-semantic functions and to exclude sensory, motor, and general executive functions. The language activation task required phonetic and semantic analysis of aurally presented words and was compared with a control task involving perceptual analysis of nonlinguistic sounds. Functional maps of the entire brain were obtained from 30 right-handed subjects. These maps were averaged in standard stereotaxic space to produce a robust "average activation map" that proved reliable in a split-half analysis. As predicted from classical models of language organization based on lesion data, cortical activation associated with language processing was strongly lateralized to the left cerebral hemisphere and involved a network of regions in the frontal, temporal, and parietal lobes. Less consistent with classical models were (1) the existence of left hemisphere temporoparietal language areas outside the traditional "Wernicke area," namely, in the middle temporal, inferior temporal, fusiform, and angular gyri; (2) extensive left prefrontal language areas outside the classical "Broca area"; and (3) clear participation of these left frontal areas in a task emphasizing "receptive" language functions. Although partly in conflict with the classical model of language localization, these findings are generally compatible with reported lesion data and provide additional support for ongoing efforts to refine and extend the classical model.

Neuroanatomy of language processing studied with functional MRI

This article discusses recent data from functional magnetic resonance imaging (FMRI) studies of language. Although preliminary, these data suggest activation of the left prefrontal cortex across a variety of tasks, with less activation of posterior cortical areas known to play a role in language. Potential sources of error in functional imaging studies related to task subtraction techniques are briefly discussed. The semantic decision task used by the author and colleagues, which produces left lateralized activation of both prefrontal and temporoparietal areas, is presented in detail, and the activation pattern observed in these studies is discussed in the context of converging neuropsychological and positron emission tomography data. It is argued that superior temporal responses evoked by listening to speech represent sensory rather than language processes. The data bring into question the classical disconnection model of transcortical aphasia and confirm the participation of left prefrontal areas in comprehension. FMRI shows promise as an alternative to the intracarotid amobarbital test for language dominance.

Relationship between finger movement rate and functional magnetic resonance signal change in human primary motor cortex

Functional magnetic resonance imaging (FMRI) is a noninvasive technique for mapping regional brain changes in response to sensory, motor, or cognitive activation tasks. Interpretation of these activation experiments may be confounded by more elementary task parameters, such as stimulus presentation or movement rates. We examined the effect of movement rate on the FMRI response recorded from the contralateral primary motor cortex. Four right-handed healthy subjects performed flexion-extension movements of digits 2-5 of the right hand at rates of 1, 2, 3, 4, or 5 Hz. Results of this study indicated a positive linear relationship between movement rate and FMRI signal change. Additionally, the number of voxels demonstrating functional activity increased significantly with faster movement rates. The magnitude of the signal change at each movement rate remained constant over the course of three 8-min scanning series. These findings are similar to those of previous rate studies of the visual and auditory system performed with positron emission tomography (PET) and FMRI.

Function of the left planum temporale in auditory and linguistic processing

Previous research suggests that the human left planum temporale (PT) plays an important role in language. To test this hypothesis, functional MRI (fMRI) data were collected from 12 normal right-handed subjects during passive and active listening to words and tone sequences. Several left hemisphere areas, including the superior temporal sulcus, middle temporal gyrus, angular gyrus and lateral frontal lobe showed stronger activation during the word conditions. This was not true of the PT, which responded equally to tones and words during passive listening and more strongly to tones during active listening. The PT is likely to be involved in early auditory processing, while specifically linguistic functions are mediated by multimodal association areas distributed elsewhere in the left hemisphere.

Determination of language dominance using functional MRI: a comparison with the Wada test

We performed functional MRI (FMRI) in 22 consecutive epilepsy patients undergoing intracarotid amobarbital (Wada) testing and compared language lateralization measures obtained with the two procedures. FMRI used a single-word semantic decision task previously shown to activate lateralized language areas in normal adults. Correlation between the two tests was highly significant (r = 0.96; 95% CIs 0.90 to 0.98; p < 0.0001). These results validate the FMRI technique and suggest that "active" areas observed with this semantic processing task correspond to those underlying hemispheric dominance for language. This strong correlation observed supports the view that language lateralization is a continuous rather than a dichotomous variable. In addition to lateralization information, FMRI consistently demonstrated focal regions of activity in lateral frontal and temporo-parieto-occipital cortex. These functional maps may be helpful in defining the boundaries of surgical excisions.

Lateralized human brain language systems demonstrated by task subtraction functional magnetic resonance imaging

OBJECTIVE

To develop a procedure for noninvasive measurement of language lateralization with functional magnetic resonance imaging (MRI).

DESIGN

Functional neuroimaging using time-series echo-planar MRI.

SETTING

University medical center research facility.

SUBJECTS

Five healthy, right-handed, young adults.

MAIN OUTCOME MEASURES

Number of MRI voxels in left and right hemispheres showing task-related signal increases during two contrasting auditory processing tasks. The nonlinguistic task involved processing of pure tones, while the linguistic task involved processing of single words based on semantic content.

RESULTS

The pure-tone processing task activated temporal lobe auditory areas and dorsolateral frontal regions bilaterally. Using this task as a control condition, the semantic processing task resulted in lateralized activity in distributed regions of the left hemisphere. A significant effect of task on intrahemispheric activity pattern was demonstrated in every subject. Results were reproduced in preliminary studies of test-retest reliability.

CONCLUSIONS

The results demonstrate the lateralized anatomy of semantic linguistic systems in contrast to non-linguistic auditory sensory processors and introduce a task subtraction technique adapted for functional MRI as a noninvasive measure of language lateralization.

Somatotopic mapping of the human primary motor cortex with functional magnetic resonance imaging

We applied functional magnetic resonance imaging (FMRI) to map the somatotopic organization of the primary motor cortex using voluntary movements of the hand, arm, and foot. Eight right-handed healthy subjects performed self-paced, repetitive, flexion/extension movements of the limbs while undergoing echo-planar imaging. Four subjects performed movements of the right fingers and toes, while the remaining subjects performed movements of the right fingers and elbow joint. There was statistically significant functional activity in the left primary motor cortex in all subjects. The pattern of functional activity followed a topographic representation: finger movements resulted in signal intensity changes over the convexity of the left motor cortex, whereas toe movements produced changes either at the interhemispheric fissure or on the dorsolateral surface adjacent to the interhemispheric fissure. Elbow movements overlapped the more medial signal intensity changes observed with finger movements. Functionally active regions were confined to the cortical ribbon and followed the gyral anatomy closely. These findings indicate that FMRI is capable of generating somatotopic maps of the primary motor cortex in individual subjects.

Functional magnetic resonance imaging of somatosensory stimulation

Functional magnetic resonance imaging (FMRI) has detected changes in regional cerebral blood flow and volume in response to motor movements, visual stimuli, and auditory stimuli in each of their respective primary cortices. This experiment was conducted to determine whether signal changes in the somatosensory cortex secondary to tactile stimulation could be demonstrated. The palm of the right hand was periodically stimulated while the subject was undergoing echo-planar imaging with a 1.5-T magnetic resonance scanner equipped with local gradient and radio frequency coils. Sagittal and coronal images of 10- to 15-mm slice thickness were selected to include the postcentral gyrus and surrounding regions. Temporally correlated signal changes of 1% to 5% occurred in the peri-rolandic region in each of six subjects. The time course of signal changes was comparable to that found in other primary sensory and motor cortices. The results provide preliminary evidence of the sensitivity of FMRI to activation of the somatosensory cortex with tactile stimulation and support FMRI as a promising noninvasive technique for study of the functional organization and integrity of the cerebrum.

Effects of stimulus rate on signal response during functional magnetic resonance imaging of auditory cortex

Functional magnetic resonance imaging (FMRI) detects focal MRI signal changes in brain tissue that are believed to result from changes in neuronal activity. We describe the dependence of this response in auditory cortex on the rate of presentation of simple speech stimuli. Speech syllables were presented to five normal subjects at rates ranging from 0.17 to 2.5 Hz, while the subjects performed a phoneme discrimination task. Regions studied with FMRI during this task included the lateral aspect of both temporal lobes. All subjects showed bilateral superior temporal lobe MRI signal increases that were coincident with stimulus presentation and performance of the task. The magnitude of this response increased in a monotonic, non-linear manner with increasing stimulus rate. This rate-response relationship was nearly identical in right and left hemispheres. The relationship may reflect metabolic activity integrated over time and subject to non-linear characteristics of neuronal recovery or blood flow regulation. The dependence of response magnitude on stimulation rate supports the hypothesis that the FMRI phenomenon indirectly reflects neuronal metabolic activity. The measures provided here should assist in the design of optimal activation strategies for the human auditory cortex.

Functional magnetic resonance imaging of human auditory cortex

Magnetic resonance imaging methods recently demonstrated regional cerebral signal changes in response to limb movement and visual stimulation, attributed to blood flow enhancement. We studied 5 normal subjects scanned while listening to auditory stimuli including nonspeech noise, meaningless speech sounds, single words, and narrative text. Imaged regions included the lateral aspects of both hemispheres. Signal changes in the superior temporal gyrus and superior temporal sulcus were observed bilaterally in all subjects. Speech stimuli were associated with significantly more widespread signal changes than was the noise stimulus, while no consistent differences were observed between responses to different speech stimuli. Considerable intersubject variability in the topography of signal changes was observed. These observations confirm the utility of magnetic resonance imaging in the study of human brain structure-function relationships and emphasize the role of the superior temporal gyrus in perception of acoustic-phonetic features of speech, rather than processing of semantic features.

Intrahemispheric localization of drawing dysfunction

We evaluated drawing disability in 37 patients with right hemispheric stroke and in eight controls with no brain disease. Blinded evaluations included measures of overall recognizability and hemineglect. By mapping the CT lesions of patients, we found that damage to parieto-occipital cortex in poor drawers correlated with poor performance on a line bisection task whereas frontal, subcortical damage in poor drawers did not. We propose that drawing disability may be produced by visual-spatial dysfunction in patients with posterior lesions and by a disturbance of integrated motor function in those with frontal, subcortical damage.

Functional magnetic resonance imaging of complex human movements

Functional magnetic resonance imaging (FMRI) is a new, noninvasive imaging tool thought to measure changes related to regional cerebral blood flow (rCBF). Previous FMRI studies have demonstrated functional changes within the primary cerebral cortex in response to simple activation tasks, but it is unknown whether FMRI can also detect changes within the nonprimary cortex in response to complex mental activities. We therefore scanned six right-handed healthy subjects while they performed self-paced simple and complex finger movements with the right and left hands. Some subjects also performed the tasks at a fixed rate (2 Hz) or imagined performing the complex task. Functional changes occurred (1) in the contralateral primary motor cortex during simple, self-paced movements; (2) in the contralateral (and occasionally ipsilateral) primary motor cortex, the supplementary motor area (SMA), the premotor cortex of both hemispheres, and the contralateral somatosensory cortex during complex, self-paced movements; (3) with less intensity during paced movements, presumably due to the slower movement rates associated with the paced (relative to self-paced) condition; and (4) in the SMA and, to a lesser degree, the premotor cortex during imagined complex movements. These preliminary results are consistent with hierarchical models of voluntary motor control.

The topography of callosal reading pathways. A case-control analysis

Lesion topography and reading ability were analysed in 17 patients with dominant posterior cerebral artery territory infarction. Patients with dominant posterior cerebral artery infarction in whom reading was unaffected served as an anatomical control group. Normal readers had lesions in the medial and ventral occipital lobe, sparing dorsal white matter pathways and the ventral temporal lobe. Global and permanent alexia occurred only with additional injury to the splenium, forceps major or white matter above the occipital horn of the lateral ventricle. These data suggest that callosal pathways mediating reading lie above the occipital horn and have little connection with the ventromedial occipital region. Patients with 'spelling dyslexia' had large lesions of the ventral temporal lobe involving cortical regions believed to participate in later stages of visual processing. These findings provide a framework for the prediction of dyslexia type and severity based on lesion topography.

Left hemiparalexia

Three patients with left splenial lesions made paralexic errors restricted to the left end of words. Errors appeared more frequently when a correct response was highly dependent on the initial letter of the stimulus. One patient had full visual fields with hemialexia affecting the left visual field. The other two patients had complete right hemianopia. We attribute left-sided reading errors in the hemianopic patients to a retinotopically restricted disconnection pattern that selectively disrupts transfer of information originating from the peripheral left visual field. Functional resistance of the more numerous transcallosal projections representing visual field adjacent to the vertical meridian may account for such a pattern. The emergence of positional reading errors from retinotopically restricted left hemifield disconnection suggests that callosal information transfer during normal reading may primarily involve elemental sensory rather than lexical/semantic information.

Visual hemineglect and hemihallucinations in a patient with a subcortical infarction

An alcoholic patient with a mainly right subcortical infarction developed contralateral left-sided neglect and then, in the context of alcohol withdrawal, unilateral hallucinations in the non-neglected right hemispace. It is hypothesized that an interruption of the striatocortical pathways could prevent the right hemisphere from representing appropriately internally produced stimuli.