The role of inferior frontal gyrus and inferior parietal lobule in semantic processing of Chinese characters

Functional magnetic resonance imaging was used to explore the neural correlates of semantic judgments to Chinese characters. Adult participants were asked to indicate if character pairs were related in meaning that were arranged in a continuous variable according to association strength. This parametric manipulation allowed for a more precise determination of the role of the left inferior parietal lobule in processing meaning, which has not been reported in previous Chinese studies. Consistent with previous findings in English, participants showed activation in left inferior frontal gyrus (BA 47, 45) and left posterior middle temporal gyrus (BA 21). Characters with stronger semantic association elicited greater activation in left inferior parietal lobule (BA 39), suggesting stronger integration of highly related semantic features. By contrast, characters with weaker semantic association elicited greater activation in both an anterior ventral region (BA 47) and a mid-ventral region of left inferior frontal gyrus (BA 45), suggesting a controlled retrieval process and a selection process. Our findings of association strength are discussed in a proposed neuro-anatomical model of semantic processing.     

Motor areas beyond motor performance: deficits in serial prediction following ventrolateral premotor lesions

Previous functional MRI findings have indicated that a premotor-parietal network is involved in the perceptual processing of sequential information. Given that premotor functions have traditionally been restricted to behaviors requiring motor or sensorimotor computations, the goal of the present patient study was to further investigate whether the lateral premotor cortex is critical in purely perceptual sequencing. Patients with either ventral premotor or inferior parietal lesions, in addition to patients with prefrontal lesions and age- and gender-matched healthy controls, were tested during the processing of temporal, object-specific, and spatial sequences. Results revealed that premotor patients as well as parietal patients showed significantly higher error rates than did healthy controls on all sequence tasks. In contrast, prefrontal patients showed no behavioral deficits. These findings support the significance of the ventrolateral premotor cortex, in addition to parietal areas, in nonmotor (attentional) functions.     

Involvement of the Motor System in Comprehension of Non-Literal Action Language: A Meta-Analysis Study

Although numerous studies have shown that the sensory-motor system is involved in semantic processing of language stimuli, it is still unclear whether comprehension of abstract concepts is embodied, and whether the involvement of the sensory-motor system is context-dependent. Investigation of how the motor system is activated during comprehension of non-literal action languages can help address these issues. So far several studies have reported brain activations during non-literal action language comprehension, but the findings are highly inconsistent because of different types of non-literal action language stimuli. To clarify how the motor system is involved in comprehension of different types of non-literal languages, the current study conducted quantitative meta-analyses on fMRI findings about comprehension of sentences describing fictive motions, metaphoric actions, and idiomatic actions. Results showed that fictive motion sentences elicited activation in the right parahippocampal gyrus, an area important for spatial processing. For metaphoric actions, the left precentral gyrus (BA 6) was strongly activated, suggesting a link between metaphoric and literal meanings. For idiomatic actions, activity was found in the left inferior frontal gyrus (BA 44/45), highlighting semantic selection and inhibition. No premotor or motor activity was found in idiom condition. These results together suggest that the involvement of the sensory-motor system in abstract concepts processing is flexible, depending on semantic features of the language stimuli and links between abstract and literal meanings.     

Virtual needle pain stimuli activates cortical representation of emotions in normal volunteers

Psychological factors are known to play an extremely important role in the maintenance and development of chronic pain conditions. However, it is unclear how such factors relate to the central neural processing of nociceptive transmission in healthy individuals. To investigate this issue, the activation of the brain was studied in 30 healthy volunteers responding to virtual pain stimuli by fMRI. In the first series of the study (non-preconditioned study), 15 participants were shown a digital video demonstrating an injection needle puncturing the right palm. In the second series of the study (pre-conditioned study), same-task paradigms were used for another 15 participants. Prior to the fMRI session, real needle punctuate stimuli were applied to the right palm of participants for pre-conditioning. fMRI analysis revealed that bilateral activations in anterior insula (BA45), parietal operculum (S2: BA40), premotor area, medial globus pallidus, inferior occipital gyrus (BA18), left temporal association cortex, right fusiform gyrus, right parietal association cortex and cerebellum occurred due to the task in the preconditioned group. On the other hand, right parietal operculum (S2: BA40), premotor area, parietal association cortex, left inferior frontal gyrus and bilateral temporal association cortex were activated in the non-preconditioned group. In addition, activation of anterior insula, inferior frontal gyrus, precentral gyrus and cerebellum significantly increased in the preconditioned group compared with the non-preconditioned group. These results suggest that the virtual needle puncture task caused memory retrieval of unpleasant experiences which is possibly related to empathy for pain, resulting in the activation of specific brain areas.     

Choline acetyltransferase activity and cognitive domain scores of Alzheimer's patients

Choline acetyltransferase activity and cognitive domain scores of Alzheimer's patients. Item scores from the Mattis Dementia Rating Scale (MDRS) and the Mini-Mental State Examination (MMSE) from 389 patients with probable Alzheimer's disease were submitted to principal component analysis with orthogonal rotation. The optimal solution identified four factors that reflected the cognitive domains of attention/registration, verbal fluency/reasoning, graphomotor/praxis and recent memory. A subgroup of patients was identified for whom both the MDRS and the MMSE had been administered within the 12 months before death. Scores were assigned to these patients for the four factors. These cognitive-domain scores were then correlated with postmortem choline acetyltransferase (ChAT) activity in the medial frontal cortex, inferior parietal cortex, and hippocampus. ChAT activity in both the medial frontal and the inferior parietal cortex significantly correlated with scores on the graphomotor/praxis factor. Medial frontal ChAT also correlated significantly with the attention/registration scores. Hippocampal ChAT correlated significantly only with recent memory scores. These results are consistent with current animal research regarding the effect of selective cholinergic lesions on behavior.     

Primary visual cortex and memory

The purpose of this study was to identify the functional fields activated in relation to gestural movements. Using functional magnetic resonance imaging (fMRI), we mapped brain activity in ten right-handed, normal volunteers during activation and control tasks. The activation condition consisted of pantomiming tool-use gestures with either the left hand or right hand, whereas the control condition comprised repetitive, oppositional movements between thumb and index finger. Activated cortical regions were highly lateralized to the left hemisphere during pantomiming of tool use regardless of hand used. Praxis with either hand commonly activated the superior parietal lobule, supplementary motor area, premotor area of the left hemisphere, and cerebellar vermis. However, minimal activation occurred in the inferior parietal lobule, which has been known to be a critical area for praxis generation. Compared with left-hand praxis, right-hand praxis exhibited additional activation in the left putamen and posterior part of the left inferior temporal region. Our findings concur with neuropsychological observations that the left hemisphere in right-handers mediates programming and executing skilled movements and that, within the left hemisphere, praxis is predominantly subserved by the parietal lobe, supplementary motor area, and premotor area. However, unlike previous lesion studies, the results of our fMRI study suggested that the superior parietal lobule more likely than the inferior parietal lobule play an important role in gesture production. Electronic Publication     

Does the left superior longitudinal fascicle subserve language semantics? A brain electrostimulation study

Recent diffusion tensor imaging (DTI) tractography studies indicate that the supramarginal gyrus (SMG) represents a relay between frontal and temporal language sites. Some authors postulate that pathways connecting SMG to the posterior temporal lobe, i.e., the posterior part of the superior longitudinal fascicle (SLF) subserve semantic aspects of language. However, DTI provides only anatomic but not functional data. Therefore, it is impossible to conclude. Interestingly, intra-operative electrical mapping of cortical and subcortical language structures during tumor surgery is recognized as a reliable technique in functional neuroanatomy research. We mapped the underlying white matter of the SMG, especially the SLF, in 11 patients who underwent awake surgery for a glioma involving the left inferior parietal lobule. Using direct electrostimulation, we investigated the exact role of the SLF in language. Our findings indicate that the white matter under the inferior parietal lobule is highly involved in the dorsal phonological system. First, the SMG, connected to the ventral premotor cortex by horizontal fibers of the SLF, subserves articulatory processing, as demonstrated by dysarthria elicited by stimulation. Second, long arcuate fibers, found deeper in the white matter, subserve phonological processing, as supported by phonemic paraphasia induced by electrostimulation. Third, the most important result is that no semantic disturbances were elicited by stimulating the SLF, including its posterior part. Furthermore, no semantic disorders occurred postoperatively. Subcortical brain mapping by direct electrical stimulation does not provide arguments for a possible role of the left SLF in language semantic processing.     

Alzheimer's pathology in primary progressive aphasia

Primary progressive aphasia (PPA) is a neurodegenerative disorder with language impairment as the primary feature. Different subtypes have been described and the 3 best characterized are progressive nonfluent aphasia (PNFA), semantic dementia (SD) and logopenic/phonological aphasia (LPA). Of these subtypes, LPA is most commonly associated with Alzheimer's disease (AD) pathology. However, the features of PPA associated with AD have not been fully defined. Here we retrospectively identified 14 patients with PPA and either pathologically confirmed AD or cerebrospinal fluid (CSF) biomarkers consistent with AD. Analysis of neurological and neuropsychological features revealed that all patients had a syndrome of LPA with relatively nonfluent spontaneous speech, phonemic errors, and reduced digit span; most patients also had impaired verbal episodic memory. Analysis of the pattern of cortical thinning in these patients revealed left posterior superior temporal, inferior parietal, medial temporal, and posterior cingulate involvement and in patients with more severe disease, increasing involvement of left anterior temporal and frontal cortices and right hemisphere areas in the temporo-parietal junction, posterior cingulate, and medial temporal lobe. We propose that LPA may be a “unihemispheric” presentation of AD, and discuss this concept in relation to accumulating evidence concerning language dysfunction in AD.     

Differentiated parietal connectivity of frontal regions for “what” and “where” memory

In a previous meta-analysis across almost 200 neuroimaging experiments, working memory for object location showed significantly stronger convergence on the posterior superior frontal gyrus, whereas working memory for identity showed stronger convergence on the posterior inferior frontal gyrus (dorsal to, but overlapping with Brodmann’s area BA 44). As similar locations have been discussed as part of a dorsal frontal—superior parietal reach system and an inferior frontal grasp system, the aim of the present study was to test whether the regions of working-memory related “what” and “where” processing show a similar distinction in parietal connectivity. The regions that were found in the previous meta-analysis were used as seeds for functional connectivity analyses using task-based meta-analytic connectivity modelling and task-independent resting state correlations. While the ventral seed showed significantly stronger connectivity with the bilateral intraparietal sulcus (IPS), the dorsal seed showed stronger connectivity with the bilateral posterior inferior parietal and the medial superior parietal lobule. The observed connections of regions involved in memory for object location and identity thus clearly demonstrate a distinction into separate pathways that resemble the parietal connectivity patterns of the dorsal and ventral premotor cortex in non-human primates and humans. It may hence be speculated that memory for a particular location and reaching towards it as well as object memory and finger positioning for manipulation may rely on shared neural systems. Moreover, the ensuing regions, in turn, featured differential connectivity with the bilateral ventral and dorsal extrastriate cortex, suggesting largely segregated bilateral connectivity pathways from the dorsal visual cortex via the superior and inferior parietal lobules to the dorsal posterior frontal cortex and from the ventral visual cortex via the IPS to the ventral posterior frontal cortex that may underlie action and cognition.     

The Effect of Individual Differences in Working Memory Capacity on Sentence Comprehension: An fMRI Study

This study explores the interaction between working memory systems and language processing by examining how differences in working memory capacity (WMC) modulates neural activation levels and functional connectivity during sentence comprehension. The results indicate that two working memory systems may be involved in sentence comprehension, the verbal working memory system and the episodic buffer, but during different phases of the task. A sub-region of the left inferior frontal gyrus (BA 45) was correlated with WMC during the probe and not during sentence reading while the only region to reveal a correlation with WMC during sentence reading was the posterior cingulate/precuneus area, a region linked to event representation. In addition, functional connectivity analysis suggests that there were two distinct networks affected by WMC. The first was a semantic network that included the middle temporal cortex, an anterior region of the inferior frontal gyrus and the inferior parietal region. The second included the posterior cingulate and BA 45 of the inferior frontal gyrus. We propose here that high capacity readers may generate an event representation of the sentence during reading that aids in comprehension and that this event representation involves the processing of the posterior cingulate cortex.     

Reorganization of cortical language areas in patients with aphasia: a functional MRI study

The purpose of this study is to delineate the pattern of reorganization of cortical language areas using functional magnetic resonance imaging (fMRI) after rehabilitation therapy in patients with aphasia. Six right-handed aphasic patients were investigated. Causes of aphasia were intracerebral hemorrhages of the left basal ganglia in 3 patients, cerebral infarction of the left MCA in 2, and surgical resection of the frontotemporal lobes to control intractable epilepsy in 1. An auditory sentence completion task was used to activate brain language areas during the fMRI. Three patients with left frontal lesions showed activation in the right inferior frontal lobes while performing language tasks, whereas the other 3, whose lesions located at subcortical areas, showed activation in the bilateral frontal and temporal lobes. Our results demonstrated the differences in interhemispheric reorganization of the language network depending on the location of the lesion in aphasic patients. While the patients with subcortical lesion showed tendency of bilateral frontal activation, those with cortical lesion showed activation of the right frontal lobe.     

Premotor cortex in man: Evidence for innervation of proximal limb muscles

Summary Fourteen patients with frontal CT-lesions involving premotor cortex showed moderate weakness of contralateral shoulder and hip muscles. This premotor syndrome in man resembles that described for lesions of brainstem pathways in monkeys, except that axial musculature was not disturbed when these lesions were unilateral. Medial extent of the lesion involving the SMA was accompanied by additional slight limb-kinetic apraxia.     

Converging functional magnetic resonance imaging evidence for a role of the left inferior frontal lobe in semantic retention during language comprehension

Increasing evidence supports dissociable short-term memory (STM) capacities for semantic and phonological representations. Cognitive neuropsychological data suggest that damage to the left inferior and middle frontal gyri are associated with deficits of semantic STM, while damage to inferior parietal areas is associated with deficits of phonological STM. Patients identified as having semantic STM deficits are also impaired on a number of language comprehension and production paradigms. We used one such comprehension task derived from cognitive neuropsychological data to test predictions with functional magnetic resonance imaging (fMRI) using healthy participants. Using a task that required participants to make semantic anomaly judgements, we found significantly greater activation in areas of the left inferior frontal and middle frontal gyri for phrases that required maintenance of multiple words for eventual integration with a subsequent noun or verb. These data are consistent with our previous patient studies (Hanten & Martin, 2000; R. C. Martin & He, 2004; R. C. Martin & Romani, 1994 Martin, R. C. and Romani, C. 1994. Verbal working memory and sentence comprehension: A multiple-components view. Neuropsychology, 8: 506–523. [Crossref] , [Google Scholar]) that suggest that semantic STM is associated with the left inferior and middle frontal gyri and that deficits of semantic STM have particular consequences for comprehension tasks that require maintenance of several word meanings in unintegrated form.     

A case for conflict across multiple domains: Memory and language impairments following damage to ventrolateral prefrontal cortex

Patients with focal lesions to the left inferior frontal gyrus (LIFG; BA 44/45) exhibit difficulty with language production and comprehension tasks, although the nature of their impairments has been somewhat difficult to characterize. No reported cases suggest that these patients are Broca's aphasics in the classic agrammatic sense. Recent case studies, however, do reveal a consistent pattern of deficit regarding their general cognitive processes: They are reliably impaired on tasks in which conflicting representations must be resolved by implementing top-down cognitive control (e.g., Stroop; memory tasks involving proactive interference). In the present study, we ask whether the language production and comprehension impairments displayed by a patient with circumscribed LIFG damage can best be understood within a general conflict resolution deficit account. We focus on one patient in particular—patient I.G.—and discuss the implications for language processing abilities as a consequence of a general cognitive control disorder. We compared I.G. and other frontal patients to age-matched control participants across four experiments. Experiment 1 tested participants' general conflict resolution abilities within a modified working memory paradigm in an attempt to replicate prior case study findings. We then tested language production abilities on tasks of picture naming (Experiment 2) and verbal fluency (Experiment 3), tasks that generated conflict at the semantic and/or conceptual levels. Experiment 4 tested participants' sentence processing and comprehension abilities using both online (eye movement) and offline measures. In this task, participants carried out spoken instructions containing a syntactic ambiguity, in which early interpretation commitments had to be overridden in order to recover an alternative, intended analysis of sentence meaning. Comparisons of I.G.'s performance with frontal and healthy control participants supported the following claim: I.G. suffers from a general conflict resolution impairment, which affects his ability to produce and comprehend language under specific conditions—namely, when semantic, conceptual, and/or syntactic representations compete and must be resolved.     

A meta-analytic review of verbal fluency performance following focal cortical lesions

A meta-analysis of 31 studies with 1,791 participants was conducted to investigate the sensitivity of tests of verbal fluency to the presence of focal cortical lesions. Relative to healthy controls, participants with focal frontal injuries had large and comparable deficits on phonemic (r = .52) and semantic (r = .54) fluency. For frontal but not nonfrontal patients, phonemic fluency deficits qualified as differential deficits when compared with IQ and psychomotor speed; phonemic fluency was also more strongly and more specifically related to the presence of frontal lesions than the Wisconsin Card Sorting Test scores. In contrast, temporal damage was associated with a lesser deficit on phonemic fluency (r = .44) but a larger deficit on semantic fluency (r = .61).     

Mirror apraxia affects the peripersonal mirror space. A combined lesion and cerebral activation study

Mirror apraxia is a condition in which patients with lesions of the posterior parietal cortex have deficits in reaching to objects presented through a mirror. The aim of the present study was to investigate possible mechanisms underlying this disorder. First, we addressed the question of whether mirror apraxia is exhibited to the same extent in peripersonal and in body space. Four patients with lesions of the posterior parietal lobe on either side and with marked mirror apraxia were required to reach for objects that were presented to them through a mirror and located either in body space (i.e. on the body surface) or in peripersonal space (i.e. in the reaching distance). Whereas reaching for objects located in body space was flawless in all patients, the performance deteriorated when the same objects were transferred to the peripersonal space. Although the objects were located only a few centimetres above the body surface, the patients reached towards the virtual object in the mirror. Based on these results we suggest that mirror apraxia may originate from a dissociation between the representations of body schema and peripersonal space and that objects located on the body surface become integrated into the body schema. In the second part of the study, using positron emission tomography study (PET), we studied the cerebral activation pattern during reaching to objects presented through a mirror in the peripersonal space in healthy subjects. The results show that increased neural activity in the anterior part of the intraparietal sulcus and in the dorsal premotor cortex was bound to the transformation of the target position from the mirror space to the real space. In contrast, the activity related to object localization in the mirror occurred at the parieto-occipital junction. Both mirror and arm transformation involved the medial posterior part of the superior parietal lobule, putatively area V6a. The results demonstrate that acting through a mirror is processed in a number of cortical areas of the dorsal stream.     

Neural basis of attributional style in schizophrenia

Attributional style means how people typically infer the causes of emotional behaviors. No study has shown neural basis of attributional style in schizophrenia, although it was suggested as a major area of social cognition research of schizophrenia. Fifteen patients with schizophrenia and 16 healthy controls underwent functional magnetic resonance imaging while performing three (happy, angry, and neutral) conditions of attribution task. Each condition included inferring situational causes of an avatar’ (virtual character) emotional or neutral behavior. In the between-groups contrast maps of the happy conditions, the patient group compared to the control group showed decreased activations in the inferior frontal (BA 44) and the ventral premotor cortex (BA 6), in which the % signal changes were associated with negative symptoms. In the angry conditions, the patient group compared to the control group exhibited increased activations in the precuneus/posterior cingulate cortex (Pcu/PCC) (BA 7/31), in which the % signal changes were related to positive symptoms. In conclusion, patients with schizophrenia may have functional deficits in mirror neuron system when attributing positive behaviors, which may be related to a lack of inner simulation and empathy and negative symptoms. In contrast, patients may have increased activation in the Pcu/PCC related to self-representations while attributing negative behaviors, which may be related to failures in self- and source-monitoring and positive symptoms.     

Dissociating cortical regions activated by semantic and phonological tasks: a FMRI study in blind and sighted people

Previous neuroimaging studies of language processing in blind individuals described cortical activation of primary (V1) and higher tier visual areas, irrespective of the age of blindness onset. Specifically, participants were given nouns and asked to generate an associated verb. These results confirmed the presence of adaptations in the visual cortex of blind people and suggested that these responses represented linguistic operations. The present functional magnetic resonance imaging study attempted to further characterize these responses as being preferential for semantic or phonological processing. Three groups of participants (sighted, early onset, and late-onset blind) heard lists of related words and attended to either a common meaning (semantic task) or common rhyme (phonological task) that linked the words. In all three groups, the semantic task elicited stronger activity in the left anterior inferior frontal gyrus and the phonological task evoked stronger activity bilaterally in the inferior parietal cortex and posterior aspects of the left inferior frontal gyrus. Only blind individuals showed activity in occipital, temporal, and parietal components of visual cortex. The spatial extent of visual cortex activity was greatest in early blind, who exhibited activation in all ventral and dorsal visual cortex subdivisions (V1 through MT) for both tasks. Preferential activation appeared for the semantic task. Late blind individuals exhibited responses in ventral and dorsal V1, ventral V2, VP and V8, but only for the semantic task. Our findings support prior evidence of visual cortex activity in blind people engaged in auditory language processing and suggest that this activity may be related to semantic processing.     

Localization of grasp representations in humans by positron emission tomography

Positron emission tomography imaging of cerebral blood flow was used to localize brain areas involved in the representation of hand grasping movements. Seven normal subjects were scanned under three conditions. In the first, they observed precision grasping of common objects performed by the examiner. In the second, they imagined themselves grasping the objects without actually moving the hand. These two tasks were compared with a control task of object viewing. Grasp observation activated the left rostral superior temporal sulcus, left inferior frontal cortex (area 45), left rostral inferior parietal cortex (area 40), the rostral part of left supplementary motor area (SMA-proper), and the right dorsal premotor cortex. Imagined grasping activated the left inferior frontal (area 44) and middle frontal cortex, left caudal inferior parietal cortex (area 40), a more extensive response in left rostral SMA-proper, and left dorsal premotor cortex. The two conditions activated different areas of the right posterior cerebellar cortex. We propose that the areas active during grasping observation may form a circuit for recognition of hand-object interactions, whereas the areas active during imagined grasping may be a putative human homologue of a circuit for hand grasping movements recently defined in nonhuman primates. The location of responses in SMA-proper confirms the rostrocaudal segregation of this area for imagined and real movement. A similar segregation is also present in the cerebellum, with imagined and observed grasping movements activating different parts of the posterior lobe and real movements activating the anterior lobe.     

Superior temporal gyrus thickness correlates with cognitive performance in multiple sclerosis

Decreased cortical thickness that signifies gray matter pathology and its impact on cognitive performance is a research field with growing interest in relapsing–remitting multiple sclerosis (RRMS) and needs to be further elucidated. Using high-field 3.0 T MRI, three-dimensional T1-FSPGR (voxel size 1 × 1 × 1 mm) cortical thickness was measured in 82 regions in the left hemisphere (LH) and right hemisphere (RH) in 20 RRMS patients with low disease activity and in 20 age-matched healthy subjects that in parallel underwent comprehensive cognitive evaluation. The correlation between local cortical atrophy and cognitive performance was examined. We identified seven regions with cortical tissue loss that differed between RRMS and age-matched healthy controls. These regions were mainly located in the frontal and temporal lobes, specifically within the gyrus rectus, inferior frontal sulcus, orbital gyrus, parahippocampal gyrus, and superior temporal gyrus, with preferential left asymmetry. Increased cortical thickness was identified in two visual sensory regions, the LH inferior occipital gyrus, and the RH cuneus, implicating adaptive plasticity. Correlation analysis demonstrated that only the LH superior temporal gyrus thickness was associated with cognitive performance and its thickness correlated with motor skills (r = 0.65, p = 0.003), attention (r = 0.45, p = 0.042), and information processing speed (r = 0.50, p = 0.025). Our findings show that restricted cortical thinning occurs in RRMS patients with mild disease and that LH superior temporal gyrus atrophy is associated with cognitive dysfunction.