Power spectral density changes and language lateralization during covert object naming tasks measured with high-density EEG recordings

Our objective was to study changes in EEG time-domain power spectral density (PSDt) and localization of language areas during covert object naming tasks in human subjects with epilepsy. EEG data for subjects with epilepsy were acquired during the covert object naming tasks using a net of 256 electrodes. The trials required each subject to provide the names of common objects presented every 4 seconds on slides. Each trial comprised the 1.0 second before and 3.0 seconds after initial object presentation. PSDt values at baseline and during tasks were calculated in the theta, alpha, beta, low gamma, and high gamma bands. The spatial contour plots reveal that PSDt values during object naming were 10-20% higher than the baseline values for different bands. Language was lateralized to left frontal or temporal areas. In all cases, the Wada test disclosed language lateralization to the left hemisphere as well.     

Parametric fMRI analysis of visual encoding in the human medial temporal lobe

A number of functional brain imaging studies indicate that the medial temporal lobe system is crucially involved in encoding new information into memory. However, most studies were based on differences in brain activity between encoding of familiar vs. novel stimuli. To further study the underlying cognitive processes, we applied a parametric design of encoding. Seven healthy subjects were instructed to encode complex color pictures into memory. Stimuli were presented in a parametric fashion at different rates, thus representing different loads of encoding. Functional magnetic resonance imaging (fMRI) was used to assess changes in brain activation. To determine the number of pictures successfully stored into memory, recognition scores were determined afterwards. During encoding, brain activation occurred in the medial temporal lobe, comparable to the results obtained by others. Increasing the encoding load resulted in an increase in the number of successfully stored items. This was reflected in a significant increase in brain activation in the left lingual gyrus, in the left and right parahippocampal gyrus, and in the right inferior frontal gyrus. This study shows that fMRI can detect changes in brain activation during variation of one aspect of higher cognitive tasks. Further, it strongly supports the notion that the human medial temporal lobe is involved in encoding novel visual information into memory.     

A comparison of brain activation patterns during covert and overt paced auditory serial addition test tasks

The Paced Auditory Serial Addition test (PASAT) is a sensitive task for evaluating cognitive impairment in patients with diffuse brain disorders, such as multiple sclerosis patients. Brain areas involved in this task have been investigated in diverse fMRI studies using different methodologies to control the subjects' responses during scanning. Here, we examined the possible differences between overt and covert responses during the PASAT task in 13 volunteers. Results showed similar activations in parietal and frontal brain areas during both versions of the task. The contrast between the two conditions (overt and covert) indicated that differences in these two methodologies were minimal. Unlike the covert condition, the overt version of the task obtained significant activations in the left superior and inferior frontal gyrus, bilateral occipital cortex, caudate nucleus and cerebellum. As expected, no significant overactivations were observed in the covert when compared with the overt condition. Discussion focuses on the lower cost of using verbal responses to monitor performance during the PASAT task, which might be generalisable to other frontal lobe tasks requiring discrete responses.     

Functional MR evaluation of temporal and frontal language dominance compared with the Wada test

OBJECTIVE: To evaluate the reliability of temporal and frontal functional MRI (fMRI) activation for the assessment of language dominance, as compared with the Wada test. PATIENTS AND METHODS: Ten patients with temporal lobe epilepsy were studied using blood oxygen level dependent fMRI and echoplanar imaging (1.5-T). Three tasks were used: semantic verbal fluency, covert sentence repetition, and story listening. Data were analyzed using pixel by pixel autocorrelation and cross-correlation. fMRI laterality indices were defined for several regions of interest as the ratio (L - R)/(L + R), L being the number of activated voxels in the left hemisphere and R in the right hemisphere. Wada laterality indices were defined as the difference in the percentages of errors in language tests between left and right carotid injections. RESULTS: Semantic verbal fluency: The asymmetry of frontal activation was correlated with Wada laterality indices. The strongest correlation was observed in the precentral/middle frontal gyrus/inferior frontal sulcus area. Story listening: The asymmetry of frontal, but not temporal, activation was correlated with Wada laterality indices. Covert sentence repetition: No correlation was observed. CONCLUSIONS: There was a good congruence between hemispheric dominance for language as assessed with the Wada test and fMRI laterality indices in the frontal but not in the temporal lobes. The story listening and the covert sentence repetition tasks increased the sensitivity of detection of posterior language sites that may be useful for brain lesion surgery.     

Use of functional MRI in epilepsy]

For the purpose of examining pathophysiological mechanisms of a memory function in epileptic patients or an utility of fMRI for a presurgical assessment in neurosurgical treatment of epilepsy, activated areas in fMRI during verbal or visual memory task were investigated in patient group of temporal lobe epilepsy and normal subject group. Patient group of temporal lobe epilepsy consisted of 7 cases, of which 3 and 3 cases had left and right temporal foci, respectively, except 1 case having undetermined laterality of temporal foci. Normal subjects were 16 cases. All the epileptic and normal subjects were right-handed except for 1 lefty normal subject. Verbal memory tasks were composed of covert and overt recall tasks of 10 words given auditorily, while visual ones were recall tasks of 6 figures given visually. Eventually, in normal subjects, the left side-dominant medial frontal lobes including the superior frontal and anterior cingulate gyri were mainly activated in fMRI during the covert recall tasks of verbal memory, while the left side-dominant inferior frontal and precentral gyri as the motor language areas were chiefly activated in addition to the medial frontal lobe during the overt recall tasks. Further, the bilateral occipital lobes were activated in fMRI during the recall tasks of visual memory. Also in patient groups of temporal lobe epilepsy, the activated areas in fMRI during these tasks were the same as in normal subject group, regardless of the laterality of epileptic temporal foci. These results suggest that fMRI is useful for the determination of the lateralization of the cerebral hemisphere contributing to verbal memory function and therefore for the presurgical assessment of memory function in neurosurgical treatment of epilepsy.     

Attenuated frontal activation in schizophrenia may be task dependent

Functional magnetic resonance imaging was used to examine the neural correlates of two linguistic tasks in schizophrenia. METHOD: Five dextral male schizophrenic patients and five volunteers matched for demographic variables and task performance participated. Echoplanar images were acquired over 5 min at 1.5 T while subjects performed two paced, covert tasks; (1) verbal fluency: silent generation of words beginning with an aurally presented cue letter, contrasted with silent repetition of the aurally presented word 'rest'; (2) semantic decision: deciding whether a visually presented cue word was 'living or non-living' and silently articulating the response, contrasted with rest. Both tasks entailed language processing; only verbal fluency requires the intrinsic generation of verbal material. Between-group differences in the mean power of experimental response to the semantic decision task were identified by a one-way analysis of covariance (ANCOVA), with a measure of stimulus-correlated motion as a covariate. Voxels demonstrating a significant interaction between task and group were identified using a two-way ANCOVA. RESULTS: In controls, both tasks were associated with activation of prefrontal cortex. In patients with schizophrenia there was a significantly reduced power of response in several prefrontal regions during verbal fluency relative to controls, a difference that was not evident for the semantic decision task. There was a significant group x task interaction in the left inferior frontal gyrus, left dorsolateral prefrontal cortex and the supplementary motor area at voxel and regional levels of analysis. CONCLUSIONS: Attenuation of frontal activation during cognitive task performance in schizophrenia does not represent a fixed deficit in frontal function, but may depend on the specific cognitive demands of the experimental task employed.     

Gender differences in brain activation on a mental rotation task

ABSTRACT Few neuroimaging studies have explored gender differences on mental rotation tasks. Most studies have utilized samples with both genders, samples mainly consisting of men, or samples with six or fewer females. Graduate students in science fields or liberal arts programs (20 males, 20 females) completed a mental rotation task during functional magnetic resonance imaging (fMRI). When a pair of cube figures was shown, the participant made a keypad response based on whether the pair is the same/similar or different. Regardless of gender, the bilateral middle frontal gyrus, bilateral intraparietal sulcus (IPS), and the left precuneus were activated when a subject tried to solve the mental rotation task. Increased activation in the right inferior frontal gyrus/middle frontal gyrus, the left precuneus/posterior cingulate cortex/cuneus region, and the left middle occipital gyrus was found for men as compared to women. Better accuracy and shorter response times were correlated with an increased activation in the bilateral intraparietal sulcus. No significant brain activity differences related to mental rotation were found between academic majors. These findings suggest that networks involved in visual attention appear to be more strongly activated in the mental rotation tasks in men as compared to women. It also suggests that men use a more automatic process when analyzing complex visual reasoning tasks while women use a more top-down process.     

The role of the lateral prefrontal cortex and anterior cingulate in stimulus-response association reversals

Many complex tasks require us to flexibly switch between behavioral rules, associations, and strategies. The prefrontal cerebral cortex is thought to be critical to the performance of such behaviors, although the relative contribution of different components of this structure and associated subcortical regions are not fully understood. We used functional magnetic resonance imaging to measure brain activity during a simple task which required repeated reversals of a rule linking a colored cue and a left/right motor response. Each trial comprised three discrete events separated by variable delay periods. A colored cue instructed which response was to be executed, followed by a go signal which told the subject to execute the response and a feedback instruction which indicated whether to "hold" or "flip" the rule linking the colored cue and response. The design allowed us to determine which brain regions were recruited by the specific demands of preparing a rule contingent motor response, executing such a response, evaluating the significance of the feedback, and reconfiguring stimulus-response (SR) associations. The results indicate that an increase in neural activity occurs within the anterior cingulate gyrus under conditions in which SR associations are labile. In contrast, lateral frontal regions are activated by unlikely/unexpected perceptual events regardless of their significance for behavior. A network of subcortical structures, including the mediodorsal nucleus of the thalamus and striatum were the only regions showing activity that was exclusively correlated with the neurocognitive demands of reversing SR associations. We conclude that lateral frontal regions act to evaluate the behavioral significance of perceptual events, whereas medial frontal-thalamic circuits are involved in monitoring and reconfiguring SR associations when necessary.     

Comparison of rhyming and word generation with FMRI

Functional magnetic resonance imaging (FMRI) has been successfully used to non-invasively map language function, but has several disadvantages. These include severe motion sensitivity, which limits overt verbal responses in behavioral paradigms, such as word generation. The lack of overt responses prevents behavioral validation, making data interpretation difficult. Our objective was to compare the FMRI activation patterns of a novel silent rhyme determination task requiring a non-verbal response, to covert word generation from visually presented letters. Five strongly right-handed subjects performed both tasks during multi-slice coronal echo-planar T2*-weighted FMRI. Single subject activation maps were generated for each task by correlation analysis of single pixel time series to a boxcar reference function. These maps for the two tasks were separately interpolated to 256(3), transformed into Talairach space, summed, and thresholded at t>6. Combined activation maps from both tasks showed similar robust perisylvian language area activation, including inferior frontal gyrus, posterior superior temporal lobe, and fusiform gyrus. Subjects performed well on the rhyming task, which activated left hemisphere cortical regions more selectively than the word generation task. The rhyming task showed less activation than the word generation task in areas typically not considered specifically related to language function, such as the dorsolateral prefrontal cortex and anterior cingulate. The rhyming task is a useful tool for brain mapping and clinical applications, potentially more specific to cortical language areas than verbal fluency.     

Frontal brain activation during the Wisconsin Card Sorting Test assessed with two-channel near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) is a new non-invasive optical technique suitable to assess the concentration changes of oxygenated (O₂HB) and deoxygenated (HHB) hemoglobin in brain tissue. Previous NIRS studies showed distinct patterns of blood oxygenation changes during different cognitive tasks. In particular, bilateral frontal hypo-oxygenation was found during reading, right frontal hyper-oxygenation during the Continuous Performance Test, and left frontal hyper-oxygenation during the Verbal Fluency Test. The Wisconsin Card Sorting Test (WCST) is a neuropsychological test which is presumed to activate prevalently the frontal lobes. This was demonstrated by lesion studies and functional imaging (single photon emission computed tomography and positron emission tomography). In the present study, a two-channel NIRS system was applied to investigate frontal brain areas of ten healthy subjects during performance of the WCST. A significant bilateral increase of O₂HB in frontal brain regions without hemispheric differences was found during the WCST compared with a baseline at rest. This result indicates an enhanced perfusion of the frontal lobes consistent with local activation. The findings add further evidence that the NIRS technique is sensitive enough to detect physiological blood oxygenation changes. Furthermore, a comparison with previous studies revealed an activation pattern distinct from those observed during other cognitive tasks. It is concluded that the results reflect local responses to specific task demands of the WCST. Received: 3 August 1997 / Accepted: 7 July 1998     

Compensatory hyperactivations as markers of latent working memory dysfunctions in patients with obsessive-compulsive disorder: an fMRI study

Objective

Behavioural studies have implicated working memory (WM) deficits in obsessive–compulsive disorder (OCD). However, findings are inconsistent, which could be explained by compensation strategies used by a subgroup of OCD patients. To test this hypothesis, we examined patients without a behavioural deficit in WM during performance of different WM tasks using functional magnetic resonance imaging (fMRI).

Methods

We scaned 11 patients and 11 matched control subjects while they performed 3 verbal and spatial item-recognition tasks.

Results

Patients and healthy subjects engaged the same set of brain regions. However, in direct comparison, the patients exhibited significantly greater task-related activation in several frontal and parietal brain areas known to underlie WM.

Conclusion

Patients without manifest WM deficits exhibit increased activation in frontal and parietal brain areas relative to healthy subjects during WM task performance. These hyperactivations may permit them to compensate for reduced efficiency of their WM systems and may thus serve as markers of latent WM dysfunctions.Medical subject headings: obsessive–compulsive disorder, memory, magnetic resonance imaging, cognition     

Brain activity patterns during phonological verbal fluency performance with varying levels of difficulty: a functional magnetic resonance imaging study in Portuguese-speaking healthy individuals

A large number of functional neuroimaging studies have investigated the brain circuitry which is engaged during performance of phonological verbal fluency tasks, and the vast majority of these have been carried out in English. Although there is evidence that this paradigm varies depending on the language spoken, it is unclear if this difference is associated with differences in brain activation patterns. Also, there is neuroimaging evidence that the patterns of regional cerebral activation during verbal fluency tasks may vary with the level of task demanded. In particular, the engagement of the anterior cingulate cortex seems to be relative to cognitive demand. We compared functional magnetic resonance imaging data in healthy Portuguese-speaking subjects during overt production of words beginning with letters classified as easy or hard for word production in Portuguese. Compared to the baseline condition, the two verbal fluency tasks (with either easy or hard letters) engaged a network including the left inferior and middle frontal cortices, anterior cingulate cortex, putamen, thalamus and cerebellum (p < .001). The direct comparison between the two verbal fluency conditions showed greater cerebellar activation in the easy condition relative to the hard condition. In the anterior cingulate cortex, there was a direct correlation between activity changes and verbal fluency performance during the hard condition only. Despite grammatical differences, the changes in patterns of brain activity during verbal fluency performance observed in our study are in accordance with findings of previous neuroimaging studies of verbal fluency carried out in English and other languages, with recruitment of a set of distributed cerebral areas during word production.     

Quantitative meta-analysis on state and trait aspects of auditory verbal hallucinations in schizophrenia

Auditory verbal hallucinations (AVHs) have a high prevalence in schizophrenic patients. An array of studies have explored the neural correlates of AVHs by means of functional neuroimaging and have associated AVHs with diverse brain regions, some of which have been shown to be involved in speech generation, speech perception, and auditory stimulus processing. We divided these studies into "state" studies comparing periods of presence and absence of AVHs within-subject and "trait" studies comparing patients experiencing AVHs with patients without AVHs or healthy controls during tasks with verbal material. We set out to test the internal consistency and possible dissociations of the neural correlates of AVHs. We used activation likelihood estimation to perform quantitative meta-analyses on brain regions reported in state and trait studies on AVHs to assess significant concordance across studies. State studies were associated with activation in bilateral inferior frontal gyrus, bilateral postcentral gyrus, and left parietal operculum. Trait studies on the other hand showed convergence of decreases in hallucinating subjects in left superior temporal gyrus, left middle temporal gyrus, anterior cingulate cortex, and left premotor cortex activity. Based on the clear dissociation of brain regions that show convergence across state in comparison to trait studies, we conclude that the state of experiencing AVHs is primarily related brain regions that have been implicated in speech production ie, Broca's area, whereas the general trait that makes humans prone to AVHs seems to be related to brain areas involved in auditory stimuli processing and speech perception, ie, auditory cortex.     

Cognitive processing in Chinese literate and illiterate subjects: an fMRI study

Functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) were used to map brain activation during language tasks. While previous studies have compared performance between alphabetic literate and illiterate subjects, there have been no such data in Chinese-speaking individuals. In this study, we used fMRI to examine the effects of education on neural activation associated with silent word recognition and silent picture-naming tasks in 24 healthy right-handed Chinese subjects (12 illiterates and 12 literates). There were 30 single Chinese characters in the silent word recognition task and 30 meaningful road-signs in the silent picture-naming task. When we compared literate and illiterate subjects, we observed education-related differences in activation patterns in the left inferior/middle frontal gyrus and both sides of the superior temporal gyrus for the silent word recognition task and in the bilateral inferior/middle frontal gyrus and left limbic cingulated gyrus for the silent picture-naming task. These results indicate that the patterns of neural activation associated with language tasks are strongly influenced by education. Education appears to have enhanced cognitive processing efficiency in language tasks.     

Brain activation when hearing one's own and others' names

Using functional magnetic resonance imaging, brain activation patterns were examined in response to hearing one's own first name in contrast to hearing the names of others. There are several regions in the left hemisphere that show greater activation to one's own name, including middle frontal cortex, middle and superior temporal cortex, and cuneus. These findings provide evidence that hearing one's own name has unique brain functioning activation specific to one's own name in relation to the names of others.     

Cortical activation during reading aloud of long sentences: fMRI study

The purpose of this study was to investigate human brain activity during the reading aloud of Japanese sentences using fMRI. Twenty-three right-handed normal Japanese subjects performed three reading tasks: covert reading of meaningful or meaningless sentences, and reading aloud of meaningful sentences. Areas in the bilateral frontal and temporal cortices were activated during the reading-aloud task compared with the covert reading task. In addition, activation of these brain areas showed significant positive correlation with the reading speed during the reading-aloud task. Our results indicate that bilateral frontal-temporal networks are involved in phonological processing during reading aloud.     

Does dichotic listening probe temporal lobe functions?

OBJECTIVE: To explore cortical hemodynamic responses using fMRI in the context of three dichotic listening tasks. BACKGROUND: Dichotic listening is a widely used behavioral technique indicating brain laterality during which subjects are presented with two different auditory signals at the same time, one arriving at each ear. fMRI offers the potential to explore the hemodynamic response during dichotic listening and to relate the behavioral indices with these cortical measures. METHOD: fMRI was performed for 10 right-handed normal subjects listening to consonant-vowel syllable pairs with the task of detecting a "target" syllable by pressing a button. The target stimulus appeared equally often in the left and right ear. The subjects were instructed to either concentrate on the stimuli presented in both ears (DIV) or only in the left ear (FL) or right ear (FR). In addition, a control condition was used during which the syllables were presented binaurally. Hemodynamic responses were measured by applying whole-head echo planar imaging techniques and statistically analyzed by using statistical parametric mapping (SPM99) software. RESULTS: During dichotic listening, there were generally extended activations in frontotemporal networks. For the DIV condition, the authors found strong bilateral activations in the inferior frontal gyrus, Broca's area, the left middle frontal gyrus, and in the left superior temporal gyrus. During the FL condition, there was an additional cluster in the right inferior frontal gyrus. For the FR condition, there were stronger activations in Broca's area and the left superior temporal gyrus. CONCLUSIONS: These findings were taken as evidence that dichotic listening is more demanding, requiring more processing capacity distributed in frontotemporal networks. The behavioral measures of dichotic listening were not simply a function of temporal lobe activation. Rather, the cortical activations support the notion that different processing strategies controlled by different neural structures are applied during dichotic listening.     

Cortical networks for working memory and executive functions sustain the conscious resting state in man

The cortical anatomy of the conscious resting state (REST) was investigated using a meta-analysis of nine positron emission tomography (PET) activation protocols that dealt with different cognitive tasks but shared REST as a common control state. During REST, subjects were in darkness and silence, and were instructed to relax, refrain from moving, and avoid systematic thoughts. Each protocol contrasted REST to a different cognitive task consisting either of language, mental imagery, mental calculation, reasoning, finger movement, or spatial working memory, using either auditory, visual or no stimulus delivery, and requiring either vocal, motor or no output. A total of 63 subjects and 370 spatially normalized PET scans were entered in the meta-analysis. Conjunction analysis revealed a network of brain areas jointly activated during conscious REST as compared to the nine cognitive tasks, including the bilateral angular gyrus, the left anterior precuneus and posterior cingulate cortex, the left medial frontal and anterior cingulate cortex, the left superior and medial frontal sulcus, and the left inferior frontal cortex. These results suggest that brain activity during conscious REST is sustained by a large scale network of heteromodal associative parietal and frontal cortical areas, that can be further hierarchically organized in an episodic working memory parieto-frontal network, driven in part by emotions, working under the supervision of an executive left prefrontal network.     

Exploring the social brain in schizophrenia: left prefrontal underactivation during mental state attribution

OBJECTIVE: Evidence suggests that patients with schizophrenia have a deficit in "theory of mind," i.e., interpretation of the mental state of others. The authors used functional magnetic resonance imaging (MRI) to investigate the hypothesis that patients with schizophrenia have a dysfunction in brain regions responsible for mental state attribution. METHOD: Mean brain activation in five male patients with schizophrenia was compared to that in seven comparison subjects during performance of a task involving attribution of mental state. RESULTS: During performance of the mental state attribution task, the patients made more errors and showed less blood-oxygen-level-dependent signal in the left inferior frontal gyrus. CONCLUSIONS: To the authors' knowledge, this is the first functional MRI study to show a deficit in the left prefrontal cortex in schizophrenia during a socioemotional task.     

Functional magnetic resonance imaging study of frontal lobe activation during word generation in obsessive-compulsive disorder.

BACKGROUND: Functional imaging studies have demonstrated abnormal patterns of brain activity in obsessive-compulsive disorder, which consistently suggest the alteration of frontal lobe functioning. We performed a brain activation study in obsessive-compulsive disorder using a cognitive task involving the frontal lobes. METHODS: Twenty patients and 20 healthy control subjects were assessed with functional magnetic resonance imaging during a phonologically guided word generation task. The study analysis was based on the comparison of group average time-course functional changes occurring at the site of largest frontal cortex activation during alternating rest and task periods. RESULTS: In terms of relative signal changes, patients showed a significantly greater activation during word generation and a defective suppression of this activation during the following rest period. Both abnormal imaging findings significantly correlated with the severity of the clinical process assessed by the Yale-Brown Obsessive-Compulsive Scale. CONCLUSIONS: The results indicate that functional magnetic resonance imaging during cognitive challenge may be useful to reveal distinctive features of latent brain dysfunction in obsessive-compulsive disorder.