Magnetoencephalographic correlates of audiotactile interaction

To seek for correlates of an interaction between auditory and somatosensory processing, the brain's magnetic field in response to simultaneously presented auditory (A) and tactile (T) stimuli was compared with the sum of the respective unimodal responses (A+T). The stimuli were binaural 1047-Hz tone bursts of 60 dB sensation level and tactile pressure pulses to the right thumb. The mean interval between two stimuli of the same modality was 1.95 s. The magnetic field was recorded using a 306-channel whole-scalp neuromagnetometer. A clear audiotactile interaction was revealed in the hemisphere contralateral to the side of tactile stimulation in six of eight subjects, whereas in the ipsilateral hemisphere an interaction was noticed in only three subjects. The time courses of these audiotactile interaction fields typically showed major deflections of opposite polarities around 140 and 220 ms. The first deflection appeared to arise in the region of the secondary somatosensory cortex (SII). The polarity of this interaction was consistent with the view that the auditory stimulus resulted in a partial inhibition in SII. In two subjects, strong indications of auditory contributions to the interaction were available, although in different hemispheres. The relatively high interindividual variability of the observed interaction, which represents potential neural substrates for multisensory integration, could indicate that the way subjects perceive the simultaneous presentation of auditory and tactile stimuli differs.     

Dissociable contributions of prefrontal and parietal cortices to response selection

The ability to select between possible responses to a given situation is central to human cognition. The goal of this study was to distinguish between brain areas representing candidate responses and areas selecting between competing response alternatives. Event-related fMRI data were acquired while 10 healthy adults performed a task used to examine response competition: the Eriksen flanker task. Left parietal cortex was activated by either of two manipulations that increased the need to maintain a representation of possible responses. In contrast, lateral prefrontal and rostral anterior cingulate cortices were specifically engaged by the need to select among competing response alternatives. These findings support the idea that parietal cortex is involved in activating possible responses on the basis of learned stimulus-response associations, and that prefrontal cortex is recruited when there is a need to select between competing responses.     

Maintaining coherence of dynamic objects requires coordination of neural systems extended from anterior frontal to posterior parietal brain cortices

Object representation in visual working memory enables humans to perceive a consistent visual world and must satisfy two attributes: coherence and dynamic updating. The present study measured brain activity using functional magnetic resonance imaging (fMRI) during the multiple object permanence tracking (MOPT) task, which requires observers to process simultaneously both coherence maintenance and dynamic updating of objects. Whole brain analysis revealed anterior and ventral parts of frontal area and dorsal frontoparietal activation during both object-moving and object-stationary conditions. Subsequent region-of-interest analyses in the anterior/ventral frontal and the dorsal frontoparietal regions revealed that these two systems engage the two different cognitive processes involved in the MOPT task, with coherency maintenance processed in the anterior/ventral frontal areas and spatial processing in the dorsal frontoparietal network. These results suggest that cooperation between these two systems underpins object representations in visual working memory.     

Working memory maintenance of grasp-target information in the human posterior parietal cortex

Event-related functional magnetic resonance imaging was applied to identify cortical areas involved in maintaining target information in working memory used for an upcoming grasping action. Participants had to grasp with their thumb and index finger of the dominant right hand three-dimensional objects of different size and orientation. Reaching-to-grasp movements were performed without visual feedback either immediately after object presentation or after a variable delay of 2-12 s. The right inferior parietal cortex demonstrated sustained neural activity throughout the delay, which overlapped with activity observed during encoding of the grasp target. Immediate and delayed grasping activated similar motor-related brain areas and showed no differential activity. The results suggest that the right inferior parietal cortex plays an important functional role in working memory maintenance of grasp-related information. Moreover, our findings confirm the assumption that brain areas engaged in maintaining information are also involved in encoding the same information, and thus extend previous findings on working memory function of the posterior parietal cortex in saccadic behavior to reach-to-grasp movements.     

The left parietal and premotor cortices: motor attention and selection

It is well established that the premotor cortex has a central role in the selection of movements. The role of parts of the parietal cortex in movement control has proved more difficult to describe but appears to be related to the preparation and the redirection of movements and movement intentions. We have referred to some of these processes as motor attention. It has been known since the time of William James that covert motor attention can be directed to an upcoming movement just as visuospatial attention can be directed to a location in space. While some parietal regions, particularly in the right hemisphere, are concerned with covert orienting and the redirecting of covert orienting it may be useful to consider other parietal regions, in the anterior inferior parietal lobule and in the posterior superior parietal lobule, particularly in the left hemisphere, as contributing to motor attention. Such parts of the parietal lobe are activated in neuroimaging experiments when subjects covertly prepare movements or switch intended movements. Lesions or transcranial magnetic stimulation (TMS) affect the redirecting of motor attention. The difficulties apraxic patients experience when sequencing movements may partly be due to an inability to redirect motor attention from one movement to another. The role of the premotor cortex in selecting movements is also lateralized to the left hemisphere. Damage to left hemisphere movement selection mechanisms may also contribute to apraxia. If, however, it remains intact after a stroke then the premotor cortex may contribute to the recovery of arm movements. A group of patients with unilateral left hemisphere lesions and impaired movements in the contralateral right hand was studied. Functional magnetic resonance imaging showed that in some cases the premotor cortex in the intact hemisphere was more active when the stroke-affected hand was used. TMS in the same area in the same patients had the most disruptive effect on movements. In summary, patterns of motor impairment and recovery seen after strokes can partly be explained with reference to the roles of the parietal and premotor cortices in motor attention and selection.     

The encoding of saccadic eye movements within human posterior parietal cortex

Over the last few years, several functionally distinct subregions of the posterior parietal cortex (PPC) have been shown to subserve oculomotor control. Since these areas seem to overlap with regions whose activation is related to attention, we used functional magnetic resonance imaging to compare the cerebral activation pattern evoked by eye movements with different attentional loads, i.e., oscillatory saccades with different frequencies, as well as predictable, and unpredictable saccades. Our results show activation in largely overlapping networks with differing strength of activity and symmetry of involved areas. Predictable saccades having the shortest saccadic latency led to the most pronounced cerebral activity both in terms of cortical areas involved and signal intensity. Predictable and unpredictable saccades were dominated by activation within the right hemisphere, whereas oscillatory saccades showing the longest saccadic latency were dominated by activation within the left hemisphere. In all tasks, the centers of gravity of activation occurred within the posterior part of the intraparietal sulcus (IPS), while the predictable saccades additionally activated its anterior part. The enhanced activity during the execution of predictable saccades was probably related to top-down processing and/or the preparation of the upcoming eye movement. The hemispheric difference could arise from a predominant role of the right PPC for shifting spatial attention and the left PPC for shifting temporal attention. The differential encoding of saccadic eye movements within IPS indicates that the PPC splits up into different functional modules related to the particular demands of a saccade.     

The human prefrontal and parietal association cortices are involved in NO-GO performances: an event-related fMRI study

One of the important roles of the prefrontal cortex is inhibition of movement. We applied an event-related functional magnetic resonance imaging (fMRI) technique to observe changes in fMRI signals of the entire brain during a GO/NO-GO task to identify the functional fields activated in relation to the NO-GO decision. Eleven normal subjects participated in the study, which consisted of a random series of 30 GO and 30 NO-GO trials. The subjects were instructed to press a mouse button immediately after the GO signal was presented. However, they were instructed not to move when the NO-GO signal was presented. We detected significant changes in MR signals in relation to the preparation phases, GO responses, and NO-GO responses. The activation fields related to the NO-GO responses were located in the bilateral middle frontal cortices, left dorsal premotor area, left posterior intraparietal cortices, and right occipitotemporal area. The fields of activation in relation to the GO responses were found in the left primary sensorimotor, right cerebellar anterior lobule, bilateral thalamus, and the area from the anterior cingulate to the supplementary motor area (SMA). Brain activations related to the preparation phases were identified in the left dorsal premotor, left lateral occipital, right ventral premotor, right fusiform, and the area from the anterior cingulate to the SMA. The results indicate that brain networks consisting of the bilateral prefrontal, intraparietal, and occipitotemporal cortices may play an important role in executing a NO-GO response.     

Activation reduction in anterior temporal cortices during repeated recognition of faces of personal acquaintances

Repeated recognition of the face of a familiar individual is known to show semantic repetition priming effect. In this study, normal subjects were repeatedly presented faces of their colleagues, and the effect of repetition on the regional cerebral blood flow change was measured using positron emission tomography. They repeated a set of three tasks: the familiar-face detection (F) task, the facial direction discrimination (D) task, and the perceptual control (C) task. During five repetitions of the F task, familiar faces were presented six times from different views in a pseudorandom order. Activation reduction through the repetition of the F tasks was observed in the bilateral anterior (anterolateral to the polar region) temporal cortices which are suggested to be involved in the access to the long-term memory concerning people. The bilateral amygdala, the hypothalamus, and the medial frontal cortices, were constantly activated during the F tasks, and considered to be associated with the behavioral significance of the presented familiar faces. Constant activation was also observed in the bilateral occipitotemporal regions and fusiform gyri and the right medial temporal regions during perception of the faces, and in the left medial temporal regions during the facial familiarity detection task, which are consistent with the results of previous functional brain imaging studies. The results have provided further information about the functional segregation of the anterior temporal regions in face recognition and long-term memory.     

Modulated activation of the human SI and SII cortices during observation of hand actions

Neurons in area F5 of the monkey premotor cortex are activated during both execution and observation of hand actions. A similar "mirror-neuron system" seems to exist also in the human brain, including at least the superior temporal sulcus region, Broca's area, and the primary motor cortex. We recorded somatosensory evoked fields in response to median nerve stimulation from nine healthy subjects during (i) rest, (ii) manipulation of a small object, and (iii) observation of the same action to find out to what extent the somatosensory cortices display behavior similar to the human mirror-neuron system. SI signals were enhanced and SII signals suppressed during both manipulation and observation, except when the right manipulating hand was stimulated. Our results suggest that the SI and SII cortices contribute to the human mirror-neuron system, possibly providing information necessary for preserving the sense of self during action observation.     

Expertise-related deactivation of the right temporoparietal junction during musical improvisation

Musical training has been associated with structural changes in the brain as well as functional differences in brain activity when musicians are compared to nonmusicians on both perceptual and motor tasks. Previous neuroimaging comparisons of musicians and nonmusicians in the motor domain have used tasks involving prelearned motor sequences or synchronization with an auditorily presented sequence during the experiment. Here we use functional magnetic resonance imaging (fMRI) to examine expertise-related differences in brain activity between musicians and nonmusicians during improvisation – the generation of novel musical–motor sequences – using a paradigm that we previously used in musicians alone. Despite behaviorally matched performance, the two groups showed significant differences in functional brain activity during improvisation. Specifically, musicians deactivated the right temporoparietal junction (rTPJ) during melodic improvisation, while nonmusicians showed no change in activity in this region. The rTPJ is thought to be part of a ventral attentional network for bottom-up stimulus-driven processing, and it has been postulated that deactivation of this region occurs in order to inhibit attentional shifts toward task-irrelevant stimuli during top-down, goal-driven behavior. We propose that the musicians' deactivation of the rTPJ during melodic improvisation may represent a training-induced shift toward inhibition of stimulus-driven attention, allowing for a more goal-directed performance state that aids in creative thought.     

Sustained activation of the human SII cortices by stimulus trains

To compare the functional properties of neurons in the human primary (SI) and secondary (SII) cortices, we recorded somatosensory-evoked fields (SEFs) from seven healthy subjects to single electric stimuli and stimulus trains delivered to the median nerve at 8--12 Hz. The SI and SII cortices responded strikingly differently to stimulus trains: whereas SI followed each stimulus with a sharp transient response up to at least 12 Hz, the transient responses were much less prominent at SII, which mainly responded with a sustained field that returned to base level at 800--1000 ms. The different response patterns of SI and SII suggest that the inhibition, following the early excitatory responses, is weaker at SII than SI, or that inhibitory responses of these two areas differ in their relative timing.     

Activation of the human primary motor cortex during observation of tool use

Tool use is a characteristic human trait, requiring motor skills that are largely learned by imitation. A neural system that supports imitation and action understanding by directly matching observed actions and their motor counterparts has been found in the human premotor and motor cortices. To test whether this "mirror-neuron system" (MNS) would be activated by observation of tool use, we recorded neuromagnetic oscillatory activity from the primary motor cortex of 10 healthy subjects while they observed the experimenter to use chopsticks in a goal-directed and non-goal-directed manner. The left and right median nerves were stimulated alternatingly, and the poststimulus rebounds of the approximately 20-Hz motor-cortex rhythms were quantified. Compared with the rest condition, the level of the approximately 20-Hz rhythm was suppressed during observation of both types of tool use, indicating activation of the primary motor cortex. The suppression was on average 15-17% stronger during observation of goal-directed than non-goal-directed tool use, and this difference correlated positively with the frequency of subjects' chopstick use during the last year. These results support the view that the motor-cortex activation is related to the observer's ability to understand and imitate motor acts.     

Tool responsive regions in the posterior parietal cortex: Effect of differences in motor goal and target object during imagined transitive movements

Neuroanatomical and functional studies have proposed a functional segregation of the human dorsal stream into a dorso-dorsal pathway, believed to serve as an object-independent stream involved with on-line control of action, and a ventro-dorsal pathway that provides conceptual input guiding the functional manipulation of objects. We aim to evaluate whether the inferior parietal cortex deals specifically with action reliant on stored knowledge. Fifteen right-handed, normal volunteers varied the intention of their transitive movements by imagining their dominant arm and hand pointing to, grasping to move, grasping to use, or grasping and using three-dimensional representations of target objects depicting graspable neutral shapes, unfamiliar tools, and familiar tools. Imagined movements intended to make functional use of familiar objects revealed increased activation in the left inferior parietal lobule. Compared to gestures aimed at displacing an object, functional (use) intentions elicited activation in the anterior and middle portions of the lateral bank of the intraparietal sulcus, suggesting involvement in the higher order control of action. Compared to functionally unfamiliar objects, grasping movements aimed at familiar tools activated the convex portion of the inferior parietal lobule, suggesting a role for the ventro-dorsal stream in object-selectivity. These data confirm that stored knowledge for the skillful manipulation of familiar tools of right-handed volunteers is predominantly located in the left inferior parietal lobule, and further suggest that tool use-responsive regions and tool object-responsive regions are not identical, but may form a local network in which different nodes contribute differently to the representation of functional tool use in humans.     

Left posterior parietal cortex participates in both task preparation and episodic retrieval

Optimal memory retrieval depends not only on the fidelity of stored information, but also on the attentional state of the subject. Factors such as mental preparedness to engage in stimulus processing can facilitate or hinder memory retrieval. The current study used functional magnetic resonance imaging (fMRI) to distinguish preparatory brain activity before episodic and semantic retrieval tasks from activity associated with retrieval itself. A catch-trial imaging paradigm permitted separation of neural responses to preparatory task cues and memory probes. Episodic and semantic task preparation engaged a common set of brain regions, including the bilateral intraparietal sulcus (IPS), left fusiform gyrus (FG), and the pre-supplementary motor area (pre-SMA). In the subsequent retrieval phase, the left IPS was among a set of frontoparietal regions that responded differently to old and new stimuli. In contrast, the right IPS responded to preparatory cues with little modulation during memory retrieval. The findings support a strong left-lateralization of retrieval success effects in left parietal cortex, and further indicate that left IPS performs operations that are common to both task preparation and memory retrieval. Such operations may be related to attentional control, monitoring of stimulus relevance, or retrieval.     

The effect of medial frontal and posterior parietal demyelinating lesions on stroop interference

Functional imaging has consistently shown that attention-related areas of medial frontal and posterior parietal cortices are active during the attentional conflict induced by color naming in the presence of distracting words (Stroop task). Such studies, however, have provided few details of the correlational nature between observed regional brain activations and reaction time delay occurring in this situation. We analyzed the effect of medial frontal and posterior parietal lesions on the Stroop response in a group of patients with multiple sclerosis, a neurological disorder in which Stroop response speed is affected to varying degrees. Forty-five patients were assessed using a computer-presented verbal version of the Stroop task and specific MRI protocol. Demyelination areas were measured on five anatomical divisions of the medial frontal white matter and on white matter of the posterior parietal lobe. We found that a combination of frontal and parietal lesion measurements accounted for 45% of the Stroop interference time variance. Patients with more right frontal than left parietal demyelination showed slowed Stroop responses, whereas the predominance of lesions in the left posterior parietal region was associated with a reduced Stroop interference. These results may contribute to defining the specific participation of these attention-related brain areas in the conflict of attention represented by the Stroop paradigm. They also help to explain the variability of the Stroop effect in multiple sclerosis patients and suggest that the Stroop test does not assess just a single cognitive operation, but rather the combined effect of anatomically segregated neural processes.     

单侧后顶叶皮质过度活动对空间定向功能的影响

摘要 目的：探讨单侧后顶叶皮质的过度活动是否会造成对侧同源脑区的功能抑制并影响空间定向功能。 方法：按照一定的入选标准选取健康受试者30人,采用兴奋性间歇性短阵快速脉冲刺激,随机对左/右侧后顶叶皮质进行真/假刺激,结合注意网络测试系统评定受试者视空间注意功能的变化。 结果：间歇性短阵快速脉冲刺激右侧后顶叶皮质,可以提高警觉及定向功能（P＜0.05）;刺激左侧后顶叶皮质,定向功能受损（P＜0.05）。 结论：右侧后顶叶是空间定向活动的关键脑区,左侧后顶叶过度活动可以导致右侧后顶叶功能抑制。建立双侧半球间新的竞争性平衡,对实现单侧后顶叶损害空间定向功能的康复具有重要意义。     

Tractography-based parcellation of the human left inferior parietal lobule

The inferior parietal lobule (IPL) is a functionally and anatomically heterogeneous region. Much of the information about the anatomical connectivity and parcellation of this region was obtained from histological studies on non-human primates. However, whether these findings from non-human primates can be applied to the human inferior parietal lobule, especially the left inferior parietal lobule, which shows evidence of considerable evolution from primates to humans, remains unclear. In this study, diffusion MRI was employed to investigate the anatomical connectivities of the human left inferior parietal lobule. Using a new algorithm, spectral clustering with edge-weighted centroidal voronoi tessellations, to search for regional variations in the probabilistic connectivity profiles of all left inferior parietal lobule voxels with all the rest of the brain identified six subregions with distinctive connectivity properties in the left inferior parietal lobule. Consistent with cytoarchitectonic findings, four subregions were found in the left supramarginal gyrus and two subregions in the left angular gyrus. The specific connectivity patterns of each subregion of the left inferior parietal lobule were supported by both the anatomical and functional connectivity properties for each subregion, as calculated by a meta-analysis-based target method and by voxel-based whole brain anatomical and functional connectivity analyses. The proposed parcellation scheme for the human left inferior parietal lobule and the maximum probability map for each subregion may facilitate more detailed future studies of this brain area.     

Neural correlates of superior intelligence: stronger recruitment of posterior parietal cortex

General intelligence (g) is a common factor in diverse cognitive abilities and a major influence on life outcomes. Neuroimaging studies in adults suggest that the lateral prefrontal and parietal cortices play a crucial role in related cognitive activities including fluid reasoning, the control of attention, and working memory. Here, we investigated the neural bases for intellectual giftedness (superior-g) in adolescents, using fMRI. The participants consisted of a superior-g group (n = 18, mean RAPM = 33.9 +/- 0.8, >99%) from the national academy for gifted adolescents and the control group (n = 18, mean RAPM = 22.8 +/- 1.6, 60%) from local high schools in Korea (mean age = 16.5 +/- 0.8). fMRI data were acquired while they performed two reasoning tasks with high and low g-loadings. In both groups, the high g-loaded tasks specifically increased regional activity in the bilateral fronto-parietal network including the lateral prefrontal, anterior cingulate, and posterior parietal cortices. However, the regional activations of the superior-g group were significantly stronger than those of the control group, especially in the posterior parietal cortex. Moreover, regression analysis revealed that activity of the superior and intraparietal cortices (BA 7/40) strongly covaried with individual differences in g (r = 0.71 to 0.81). A correlated vectors analysis implicated bilateral posterior parietal areas in g. These results suggest that superior-g may not be due to the recruitment of additional brain regions but to the functional facilitation of the fronto-parietal network particularly driven by the posterior parietal activation.     

Multiple components of lateral posterior parietal activation associated with cognitive set shifting

Posterior parietal activation has commonly been observed in previous neuroimaging studies in association with flexible shifting of cognitive set. However, it is not clear whether the parietal activation reflects cognitive processes intrinsic to the shifting itself or other confounding factors such as spatial attention. To address this issue, the Wisconsin Card Sorting Task (WCST) was modified such that spatial components were eliminated from the sensory and motor aspects of the task. Moreover, a visual instruction of a next dimension was introduced to eliminate cognitive processes related to trial and error identification of a next rule, and a control null-instruction was also introduced to eliminate perceptual/oddball effects of the instruction cue. Localizer scans using a visually guided saccade task were also conducted to identify eye movement/spatial attention-related areas. Activity related to set shifting with trial and error was revealed in the lateral parts of the intraparietal regions, while activity related to eye movements/spatial attention was revealed in the medial parts of the intraparietal regions, confirming little spatial contribution to the modified WCST as indexed by the double dissociation. The lateral intraparietal activity was bilateral, but when the instructed shifting was contrasted with the null-instructed shifting to purify the shift-related activity further, the left intraparietal activation was significantly greater than that in the right hemisphere. These results reveal the left hemisphere dominance of purified shifting-related activity in the lateral posterior parietal cortex that may cooperate with the lateral prefrontal cortex whose left hemisphere dominance has already been reported.     

Dissociating prefrontal and parietal cortex activation during arithmetic processing

Lesion and brain-imaging studies have implicated the prefrontal and parietal cortices in arithmetic processing, but do not exclude the possibility that these brain areas are also involved in nonarithmetic operations. In the present study, we used functional magnetic resonance imaging to explore which brain areas contribute uniquely to numeric computation. Task difficulty was manipulated in a factorial design by varying the number of operands and the rate of stimulus presentation. Both manipulations increased the number of operations to be performed in unit time. Manipulating the number of operands allowed us to investigate the specific effect of calculation, while manipulating the rate of presentation allowed us to increase task difficulty independent of calculation. We found quantitative changes in activation patterns in the prefrontal and parietal cortices as well as the recruitment of additional brain regions, including the caudate and midcerebellar cortex, with increasing task difficulty. More importantly, the main effect of arithmetic complexity was observed in the left and right angular gyrus, while the main effect of rate of stimulus presentation was observed in the left insular/orbitofrontal cortex. Our findings indicate a dissociation in prefrontal and parietal cortex function during arithmetic processing and further provide the first evidence for a specific role for the angular gyrus in arithmetic computation independent of other processing demands.