FMRI and PET of self-paced finger movement: comparison of intersubject stereotaxic averaged data

A Critical Review of Alien Limb-Related Phenomena and Implications for Functional Magnetic Resonance Imaging Studies

Consensus criteria on corticobasal degeneration (CBD) include alien limb (AL) phenomena. However, the gist of the behavioral features of AL is still “a matter of debate.” CBD-related AL has so far included the description of involuntary movements, frontal release phenomena (frontal AL), or asomatognosia (posterior or “real” AL). In this context, the most frequent symptoms are language and praxis deficits and cortical sensory misperception. However, asomatognosia requires, by definition, intact perception and cognition. Thus, to make a proper diagnosis of AL in the context of CBD, cognitive and language dysfunctions must be carefully verified and objectively assessed. We reviewed the current literature on AL in CBD and now propose that the generic use of the term AL should be avoided. This catchall AL term should instead be deconstructed. We propose that the term AL is appropriate to describe clinical features associated with specific brain lesions. More discrete sets of regionally bound clinical signs that depend on dysfunctions of specific brain areas need to be assessed and presented when posing the diagnosis. Thus, in our opinion, the AL term should be employed in association with precise descriptions of the accompanying involuntary movements, sensory misperceptions, agnosia-asomatognosia contents, and the presence of utilization behavior. The review also offers an overview of functional magnetic resonance imaging-based studies evaluating AL-related phenomena. In addition, we provide a complementary set of video clips depicting CBD-related involuntary movements that should not mistakenly be interpreted as signs of AL.

Effects of the Brain-Derived Neurotrophic Factor Val66Met polymorphism and resting brain functional connectivity on individual differences in tactile cognitive performance in healthy young adults

Cognitive processes involve input from multiple sensory modalities and obvious differences in the level of cognitive function can be observed between individuals. Evidence to date understanding the biological basis of tactile cognitive variability, however, is limited compared with other forms of sensory cognition. Data from auditory and visual cognition research suggest that variations in both genetics and intrinsic brain function might contribute to individual differences in tactile cognitive performance. In the present study, by using the tactual performance test (TPT), a widely used neuropsychological assessment tool, we investigated the effects of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism and resting-state brain functional connectivity (FC) on interindividual variability in TPT performance in healthy, young Chinese adults. Our results showed that the BDNF genotypes and resting-state FC had significant effects on the variability in TPT performance, together accounting for 32.5% and 19.1% of the variance on TPT total score and Memory subitem score respectively. Having fewer Met alleles, stronger anticorrelations between left posterior superior temporal gyrus and somatosensory areas (right postcentral gyrus and right parietal operculum cortex), and greater positive correlation between left parietal operculum cortex and left central opercular cortex, all correspond with better performance of TPT task. And FC between left parietal operculum cortex and left central opercular cortex might be a mediator of the relationship between BDNF genotypes and Memory subitem score. These data demonstrate a novel contribution of intrinsic brain function to tactile cognitive capacity, and further confirm the genetic basis of tactile cognition. Our findings might also explain the interindividual differences in cognitive ability observed in those who are blind and/or deaf from a new perspective.

Lateralization of cervical spinal cord activity during an isometric upper extremity motor task with functional magnetic resonance imaging

The purpose of this study was to use an isometric upper extremity motor task to detect activity induced blood oxygen level dependent signal changes in the cervical spinal cord with functional magnetic resonance imaging. Eleven healthy volunteers performed six 5minute runs of an alternating left- and right-sided isometric wrist flexion task, during which images of the cervical spinal cord were acquired with a reduced field-of-view T2*-weighted gradient-echo echo-planar-imaging sequence. Spatial normalization to a standard spinal cord template was performed, and group average activation maps were generated in a mixed-effects analysis. The task activity significantly exceeded that of the control analyses. The activity was lateralized to the hemicord ipsilateral to the task and reliable across the runs at the group and subject level. Finally, a multi-voxel pattern analysis was able to successfully decode the left and right tasks at the C6 and C7 vertebral levels.

Mirror observation of finger action enhances activity in anterior intraparietal sulcus: a functional magnetic resonance imaging study

Mirror therapy can be used to promote recovery from paralysis in patients with post-stroke hemiplegia, There are a lot of reports that mirror-image observation of the unilateral moving hand enhanced the excitability of the primary motor area (M1) ipsilateral to the moving hand in healthy subjects. but the neural mechanisms underlying its therapeutic effects are currently unclear. To investigate this issue, we used functional magnetic resonance imaging to measure activity in brain regions related to visual information processing during mirror image movement observation. Thirteen healthy subjects performed a finger-thumb opposition task with the left and right hands separately, with or without access to mirror observation. In the mirror condition, one hand was reflected in a mirror placed above the abdomen in the MRI scanner. In the masked mirror condition, subjects performed the same task but with the mirror obscured. In both conditions, the other hand was held at rest behind the mirror. A between-task comparison (mirror versus masked mirror) revealed significant activation in the ipsilateral hemisphere in the anterior intraparietal sulcus (aIP) while performing all tasks, regardless of which hand was used. The right aIP was significantly activated while moving the right hand. In contrast, in the left aIP, a small number of voxels showed a tendency toward activation during both left and right hand movement. The enhancement of ipsilateral aIP activity by the mirror image observation of finger action suggests that bimodal aIP neurons can be activated by visual information. We propose that activation in the M1 ipsilateral to the moving hand can be induced by information passing through the ventral premotor area from the aIP.

The neural basis of audiomotor entrainment: an ALE meta-analysis

Synchronization of body movement to an acoustic rhythm is a major form of entrainment, such as occurs in dance. This is exemplified in experimental studies of finger tapping. Entrainment to a beat is contrasted with movement that is internally driven and is therefore self-paced. In order to examine brain areas important for entrainment to an acoustic beat, we meta-analyzed the functional neuroimaging literature on finger tapping (43 studies) using activation likelihood estimation (ALE) meta-analysis with a focus on the contrast between externally-paced and self-paced tapping. The results demonstrated a dissociation between two subcortical systems involved in timing, namely the cerebellum and the basal ganglia. Externally-paced tapping highlighted the importance of the spinocerebellum, most especially the vermis, which was not activated at all by self-paced tapping. In contrast, the basal ganglia, including the putamen and globus pallidus, were active during both types of tapping, but preferentially during self-paced tapping. These results suggest a central role for the spinocerebellum in audiomotor entrainment. We conclude with a theoretical discussion about the various forms of entrainment in humans and other animals.

Using in vivo probabilistic tractography to reveal two segregated dorsal 'language-cognitive' pathways in the human brain

Primate studies have recently identified the dorsal stream as constituting multiple dissociable pathways associated with a range of specialized cognitive functions. To elucidate the nature and number of dorsal pathways in the human brain, the current study utilized in vivo probabilistic tractography to map the structural connectivity associated with subdivisions of the left supramarginal gyrus (SMG). The left SMG is a prominent region within the dorsal stream, which has recently been parcellated into five structurally-distinct regions which possess a dorsal-ventral (and rostral-caudal) organisation, postulated to reflect areas of functional specialisation. The connectivity patterns reveal a dissociation of the arcuate fasciculus into at least two segregated pathways connecting frontal-parietal-temporal regions. Specifically, the connectivity of the inferior SMG, implicated as an acoustic-motor speech interface, is carried by an inner/ventro-dorsal arc of fibres, whilst the pathways of the posterior superior SMG, implicated in object use and cognitive control, forms a parallel outer/dorso-dorsal crescent.

Sulcal depth-position profile is a genetically mediated neuroscientific trait: description and characterization in the central sulcus

Genetic and environmental influences on brain morphology were assessed in an extended-pedigree design by extracting depth-position profiles (DPP) of the central sulcus (CS). T1-weighted magnetic resonance images were used to measure CS length and depth in 467 human subjects from 35 extended families. Three primary forms of DPPs were observed. The most prevalent form, present in 70% of subjects, was bimodal, with peaks near hand and mouth regions. Trimodal and unimodal configurations accounted for 15 and 8%, respectively. Genetic control accounted for 56 and 66% of between-subject variance in average CS depth and length, respectively, and was not significantly influenced by environmental factors. Genetic control over CS depth ranged from 1 to 50% across the DPP. Areas of peak heritability occurred at locations corresponding to hand and mouth areas. Left and right analogous CS depth measurements were strongly pleiotropic. Shared genetic influence lessened as the distance between depth measurements was increased. We argue that DPPs are powerful phenotypes that should inform genetic influence of more complex brain regions and contribute to gene discovery efforts.

Altered intra- and inter-regional synchronization of superior temporal cortex in deaf people

Functional organization of the brain can be fundamentally altered by auditory deprivation. Previous studies found that the superior temporal cortex in deaf people is reorganized to process non-auditory stimuli, as revealed by the extrinsic task-induced brain activities. However, it is unknown how the intrinsic activities of this region are impacted by deafness. This study explored this issue using resting-state functional magnetic resonance imaging. We examined 60 congenitally deaf (CD) individuals, 39 acquired deaf (AD) individuals, and 38 hearing controls (HC), and focused on the effect of deafness on the intra- and inter-regional synchronization of different parts of superior temporal sulcus (STS). We found that intra-regional synchronization or regional homogeneity (ReHo) of the middle STS (mSTS) was decreased in AD compared with HC or CD, while the CD had preserved ReHo in mSTS. Greater connectivity was observed between mSTS and posterior STS in CD and HC than in AD, while both CD and AD had weaker connectivity of mSTS with the anterior STS (aSTS) compared with HC. Moreover, the connectivity of mSTS-aSTS in CD and AD was associated with their language skills. These findings confirmed our hypothesis that the intrinsic function of different parts of STS is distinctly impacted by deafness.

Electrophysiological and functional connectivity of the human supplementary motor area

Neuro-imaging methods for detecting functional and structural inter-regional connectivity are in a rapid phase of development. While reports of regional connectivity patterns based on individual methods are becoming common, studies comparing the results of two or more connectivity-mapping methods remain rare. In this study, we applied transcranial magnetic stimulation during PET imaging (TMS/PET), a stimulation-based method, and meta-analytic connectivity modeling (MACM), a task-based method to map the connectivity patterns of the supplementary motor area (SMA). Further, we drew upon the behavioral domain meta-data of the BrainMap® database to characterize the behavioral domain specificity of two maps. Both MACM and TMS/PET detected multi-synaptic connectivity patterns, with the MACM-detected connections being more extensive. Both MACM and TMS/PET detected connections belonging to multiple behavioral domains, including action, cognition and perception. Finally, we show that the two connectivity-mapping methods are complementary in that, the MACM informed on the functional nature of SMA connections, while TMS/PET identified brain areas electrophysiologically connected with the SMA. Thus, we demonstrate that integrating multimodal database and imaging techniques can derive comprehensive connectivity maps of brain areas.

Coordinate-based activation likelihood estimation meta-analysis of neuroimaging data: a random-effects approach based on empirical estimates of spatial uncertainty

A widely used technique for coordinate-based meta-analyses of neuroimaging data is activation likelihood estimation (ALE). ALE assesses the overlap between foci based on modeling them as probability distributions centered at the respective coordinates. In this Human Brain Project/Neuroinformatics research, the authors present a revised ALE algorithm addressing drawbacks associated with former implementations. The first change pertains to the size of the probability distributions, which had to be specified by the used. To provide a more principled solution, the authors analyzed fMRI data of 21 subjects, each normalized into MNI space using nine different approaches. This analysis provided quantitative estimates of between-subject and between-template variability for 16 functionally defined regions, which were then used to explicitly model the spatial uncertainty associated with each reported coordinate. Secondly, instead of testing for an above-chance clustering between foci, the revised algorithm assesses above-chance clustering between experiments. The spatial relationship between foci in a given experiment is now assumed to be fixed and ALE results are assessed against a null-distribution of random spatial association between experiments. Critically, this modification entails a change from fixed- to random-effects inference in ALE analysis allowing generalization of the results to the entire population of studies analyzed. By comparative analysis of real and simulated data, the authors showed that the revised ALE-algorithm overcomes conceptual problems of former meta-analyses and increases the specificity of the ensuing results without loosing the sensitivity of the original approach. It may thus provide a methodologically improved tool for coordinate-based meta-analyses on functional imaging data.

Functional neuroimaging correlates of finger-tapping task variations: an ALE meta-analysis

Finger-tapping tasks are one of the most common paradigms used to study the human motor system in functional neuroimaging studies. These tasks can vary both in the presence or absence of a pacing stimulus as well as in the complexity of the tapping task. A voxel-wise, coordinate-based meta-analysis was performed on 685 sets of activation foci in Talairach space gathered from 38 published studies employing finger-tapping tasks. Clusters of concordance were identified within the primary sensorimotor cortices, supplementary motor area, premotor cortex, inferior parietal cortices, basal ganglia, and anterior cerebellum. Subsequent analyses performed on subsets of the primary set of foci demonstrated that the use of a pacing stimulus resulted in a larger, more diverse network of concordance clusters, in comparison to varying the complexity of the tapping task. The majority of the additional concordance clusters occurred in regions involved in the temporal aspects of the tapping task, rather than its execution. Tapping tasks employing a visual pacing stimulus recruited a set of nodes distinct from the results observed in those tasks employing either an auditory or no pacing stimulus, suggesting differing cognitive networks when integrating visual or auditory pacing stimuli into simple motor tasks. The relatively uniform network of concordance clusters observed across the more complex finger-tapping tasks suggests that further complexity, beyond the use of multi-finger sequences or bimanual tasks, may be required to fully reveal those brain regions necessary to execute truly complex movements.

Modeling motor connectivity using TMS/PET and structural equation modeling

Structural equation modeling (SEM) was applied to positron emission tomographic (PET) images acquired during transcranial magnetic stimulation (TMS) of the primary motor cortex (M1(hand)). TMS was applied across a range of intensities, and responses both at the stimulation site and remotely connected brain regions covaried with stimulus intensity. Regions of interest (ROIs) were identified through an activation likelihood estimation (ALE) meta-analysis of TMS studies. That these ROIs represented the network engaged by motor planning and execution was confirmed by an ALE meta-analysis of finger movement studies. Rather than postulate connections in the form of an a priori model (confirmatory approach), effective connectivity models were developed using a model-generating strategy based on improving tentatively specified models. This strategy exploited the experimentally imposed causal relations: (1) that response variations were caused by stimulation variations, (2) that stimulation was unidirectionally applied to the M1(hand) region, and (3) that remote effects must be caused, either directly or indirectly, by the M1(hand) excitation. The path model thus derived exhibited an exceptional level of goodness (chi(2)=22.150, df=38, P=0.981, TLI=1.0). The regions and connections derived were in good agreement with the known anatomy of the human and primate motor system. The model-generating SEM strategy thus proved highly effective and successfully identified a complex set of causal relationships of motor connectivity.

Three-dimensional locations and boundaries of motor and premotor cortices as defined by functional brain imaging: a meta-analysis

The mesial premotor cortex (pre-supplementary motor area and supplementary motor area proper), lateral premotor cortex (dorsal premotor cortex and ventral premotor cortex), and primary sensorimotor cortex (primary motor cortex and primary somatosensory cortex) have been identified as key cortical areas for sensorimotor function. However, the three-dimensional (3-D) anatomic boundaries between these regions remain unclear. In order to clarify the locations and boundaries for these six sensorimotor regions, we surveyed 126 articles describing pre-supplementary motor area, supplementary motor area proper, dorsal premotor cortex, ventral premotor cortex, primary motor cortex, and primary somatosensory cortex. Using strict inclusion criteria, we recorded the reported normalized stereotaxic coordinates (Talairach and Tournoux or MNI) from each experiment. We then computed the probability distributions describing the likelihood of activation, and characterized the shape, extent, and area of each sensorimotor region in 3-D. Additionally, we evaluated the nature of the overlap between the six sensorimotor regions. Using the findings from this meta-analysis, along with suggestions and guidelines of previous researchers, we developed the Human Motor Area Template (HMAT) that can be used for ROI analysis. HMAT is available through e-mail from the corresponding author.

Spatiotemporal mapping of cortical activity accompanying voluntary movements using an event-related beamforming approach

We describe a novel spatial filtering approach to the localization of cortical activity accompanying voluntary movements. The synthetic aperture magnetometry (SAM) minimum-variance beamformer algorithm was used to compute spatial filters three-dimensionally over the entire brain from single trial neuromagnetic recordings of subjects performing self-paced index finger movements. Images of instantaneous source power ("event-related SAM") computed at selected latencies revealed activation of multiple cortical motor areas prior to and following left and right index finger movements in individual subjects, even in the presence of low-frequency noise (e.g., eye movements). A slow premovement motor field (MF) reaching maximal amplitude approximately 50 ms prior to movement onset was localized to the hand area of contralateral precentral gyrus, followed by activity in the contralateral postcentral gyrus at 40 ms, corresponding to the first movement-evoked field (MEFI). A novel finding was a second activation of the precentral gyrus at a latency of approximately 150 ms, corresponding to the second movement-evoked field (MEFII). Group averaging of spatially normalized images indicated additional premovement activity in the ipsilateral precentral gyrus and the left inferior parietal cortex for both left and right finger movements. Weaker activations were also observed in bilateral premotor areas and the supplementary motor area. These results show that event-related beamforming provides a robust method for studying complex patterns of time-locked cortical activity accompanying voluntary movements, and offers a new approach for the localization of multiple cortical sources derived from neuromagnetic recordings in single subject and group data.

The human parietal operculum. II. Stereotaxic maps and correlation with functional imaging results

In this study we describe the localization of the cytoarchitectonic subdivisions of the human parietal operculum in stereotaxic space and relate these anatomically defined cortical areas to the location of the functionally defined secondary somatosensory cortex (SII cortex) using a meta-analysis of functional imaging results. The human parietal operculum consists of four distinct cytoarchitectonic areas (OP 1-4) as shown in the preceding publication. The 10 cytoarchitectonically examined brains were 3-D-reconstructed and spatially normalized to the T1-weighted single-subject template of the Montreal Neurological Institute (MNI). A probabilistic map was calculated for each area in this standard stereotaxic space. A cytoarchitectonic summary map of the four cortical areas on the human parietal operculum which combines these probabilistic maps was subsequently computed for the comparison with a meta-analysis of functional locations of SII. The meta-analysis used the results from 57 fMRI and PET studies and allowed the comparison of the functionally defined SII region to the cytoarchitectonic map of the parietal operculum. The functional localization of SII showed a good match to the cytoarchitectonically defined region. Therefore the cytoarchitectonic maps of OP 1-4 of the human parietal operculum can be interpreted as an anatomical correlate of the (functionally defined) human SII region. Our results also suggest that the SII foci reported in functional imaging studies may actually reflect activations in either of its architectonic subregions.

Dishabituation of the BOLD response to speech sounds

Background

Neural systems show habituation responses at multiple levels, including relatively abstract language categories. Dishabituation – responses to non-habituated stimuli – can provide a window into the structure of these categories, without requiring an overt task.

Methods

We used an event-related fMRI design with short interval habituation trials, in which trains of stimuli were presented passively during 1.5 second intervals of relative silence between clustered scans. Trains of four identical stimuli (standard trials) and trains of three identical stimuli followed by a stimulus from a different phonetic category (deviant trials) were presented. This paradigm allowed us to measure and compare the time course of overall responses to speech, and responses to phonetic change.

Results

Comparisons between responses to speech and silence revealed strong responses throughout the extent of superior temporal gyrus (STG) bilaterally. Comparisons between deviant and standard trials revealed dishabituation responses in a restricted region of left posterior STG, near the border with supramarginal gyrus (SMG). Novelty responses to deviant trials were also observed in right frontal regions and hippocampus.

Conclusion

A passive, dishabituation paradigm provides results similar to studies requiring overt responses. This paradigm can readily be extended for the study of pre-attentive processing of speech in populations such as children and second-language learners whose overt behavior is often difficult to interpret because of ancillary task demands.

Preoperative mapping of cortical motor function: prospective comparison of functional magnetic resonance imaging and [15O]-H2O-positron emission tomography in the same co-ordinate system

BACKGROUND

Two of the most widely accepted approaches to map eloquent cortical areas preoperatively are positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). As yet, no study has compared these two modalities within the same frame of reference in tumour patients.

AIM

We employed [15O]-H2O-PET and fMRI in patients undergoing presurgical evaluation and compared the results with those obtained by direct electrical cortical stimulation (DECS).

METHODS

Twenty-five patients with tumours of different aetiology near the central region were investigated. fMRI and PET were processed using the same methods, i.e. statistical parametric mapping (SPM) without anatomical normalization, and transformed into the same frame of reference.

RESULTS

fMRI activity was found in more cranial and lateral sections, i.e. closer to the brain surface, in comparison with PET, which demonstrated parenchymal activation. The mean localization difference between fMRI and PET was 8.1 +/- 4.6 mm (range, 2-18 mm). fMRI and [15O]-H2O-PET could reliably identify the central sulcus, as demonstrated by DECS.

CONCLUSIONS

fMRI and [15O]-H2O-PET demonstrate comparable results and are sensitive and reliable tools to map the central region, especially in cases of infiltrating brain tumours. However, fMRI is more prone to artefacts, such as the visualization of draining veins, which may explain the more cranial and lateral activation visualized by fMRI, whereas PET depicts capillary perfusion changes and therefore shows activation closer to the parenchyma.

Neural correlates of eye blinking; improved by simultaneous fMRI and EOG measurement

Neural correlates of eye blink in healthy human subjects can be investigated using functional magnetic resonance imaging. However, the focus of most previous studies has been on intentional eye blinking. The goal of the present study was to examine the neural correlates of spontaneous eye blinking with the help of EOG measurements during data acquisition of fMRI. After the removal of the pulse artifact in the EOG signal, EOG waveform clearly indicates eye blinking, which was equivalent to those measured outside of the MRI scanner. On the basis of this detection, each blinking event can be used as a temporal cue for the event-related fMRI. In a comparison, we also investigated the neural correlates of blink inhibition. Based on the brain activation pattern, the activation of the bilateral parahippocampal, the visual cortex was commonly observed for both conditions. The additional activation of the precentral gyrus, corresponding to blink inhibition, and the right medial frontal gyrus, corresponding to spontaneous blinking were observed. Based on these results, we conclude that the medial frontal gyrus is responsible for spontaneous eye blinking, whereas precentral activation appears to be related to blink inhibition.

Controlling the false positive rate in fuzzy clustering using randomization: application to fMRI activation detection

Despite its potential advantages for fMRI analysis, fuzzy C-means (FCM) clustering suffers from limitations such as the need for a priori knowledge of the number of clusters, and unknown statistical significance and instability of the results. We propose a randomization-based method to control the false-positive rate and estimate statistical significance of the FCM results. Using this novel approach, we develop an fMRI activation detection method. The ability of the method in controlling the false-positive rate is shown by analysis of false positives in activation maps of resting-state fMRI data. Controlling the false-positive rate in FCM allows comparison of different fuzzy clustering methods, using different feature spaces, to other fMRI detection methods. In this article, using simulation and real fMRI data, we compare a novel feature space that takes the variability of the hemodynamic response function into account (HRF-based feature space) to the conventional cross-correlation analysis and FCM using the cross-correlation feature space. In both cases, the HRF-based feature space provides a greater sensitivity compared to the cross-correlation feature space and conventional cross-correlation analysis. Application of the proposed method to finger-tapping fMRI data, using HRF-based feature space, detected activation in sub-cortical regions, whereas both of the FCM with cross-correlation feature space and the conventional cross-correlation method failed to detect them.

ICA-based spatiotemporal approach for single-trial analysis of postmovement MEG beta synchronization⋆

The extraction of event-related oscillatory neuromagnetic activities from single-trial measurement is challenging due to the non-phase-locked nature and variability from trial to trial. The present study presents a method based on independent component analysis (ICA) and the use of a template-based correlation approach to extract Rolandic beta rhythm from magnetoencephalographic (MEG) measurements of right finger lifting. A single trial recording was decomposed into a set of coupled temporal independent components and corresponding spatial maps using ICA and the reactive beta frequency band for each trial identified using a two-spectrum comparison between the postmovement interval and a reference period. Task-related components survived dual criteria of high correlation with both the temporal and the spatial templates with an acceptance rate of about 80%. Phase and amplitude information for noise-free MEG beta activities were preserved not only for optimal calculation of beta rebound (event-related synchronization) but also for profound penetration into subtle dynamics across trials. Given the high signal-to-noise ratio (SNR) of this method, various methods of source estimation were used on reconstructed single-trial data and the source loci coherently anchored in the vicinity of the primary motor area. This method promises the possibility of a window into the intricate brain dynamics of motor control mechanisms and the cortical pathophysiology of movement disorder on a trial-by-trial basis.

A signal subspace approach for modeling the hemodynamic response function in fMRI

Many fMRI analysis methods use a model for the hemodynamic response function (HRF). Common models of the HRF, such as the Gaussian or Gamma functions, have parameters that are usually selected a priori by the data analyst. A new method is presented that characterizes the HRF over a wide range of parameters via three basis signals derived using principal component analysis (PCA). Covering the HRF variability, these three basis signals together with the stimulation pattern define signal subspaces which are applicable to both linear and nonlinear modeling and identification of the HRF and for various activation detection strategies. Analysis of simulated fMRI data using the proposed signal subspace showed increased detection sensitivity compared to the case of using a previously proposed trigonometric subspace. The methodology was also applied to activation detection in both event-related and block design experimental fMRI data using both linear and nonlinear modeling of the HRF. The activated regions were consistent with previous studies, indicating the ability of the proposed approach in detecting brain activation without a priori assumptions about the shape parameters of the HRF. The utility of the proposed basis functions in identifying the HRF is demonstrated by estimating the HRF in different activated regions.

Activation detection in fMRI using a maximum energy ratio statistic obtained by adaptive spatial filtering

An adaptive spatial filtering method is proposed that takes into account contextual information in fMRI activation detection. This filter replaces the time series of each voxel with a weighted average of time series of a small neighborhood around it. The filter coefficients at each voxel are derived so as to maximize a test statistic designed to indicate the presence of activation. This statistic is the ratio of the energy of the filtered time series in a signal subspace to the energy of the residuals. It is shown that the filter coefficients and the maximum energy ratio can be found through a generalized eigenproblem. This approach equates the filter coefficients to the elements of an eigenvector corresponding to the largest eigenvalue of a specific matrix, while the largest eigenvalue itself becomes the maximum energy ratio that can be used as a statistic for detecting activation. The distribution of this statistic under the null hypothesis is derived by a nonparametric permutation technique in the wavelet domain. Also, in this paper we introduce a new set of basis vectors that define the signal subspace. The space spanned by these basis vectors covers a wide range of possible hemodynamic response functions (HRF) and is applicable to both event related and block design fMRI signal analysis. This approach circumvents the need for a priori assumptions about the exact shape of the HRF. Resting-state experimental fMRI data were used to assess the specificity of the method, showing that the actual false-alarm rate of the proposed method is equal or less than its expected value. Analysis of simulated data and motor task fMRI datasets from six volunteers using the method proposed here showed an improved sensitivity as compared to a conventional test with a similar statistic applied to spatially smoothed data.

Learning robot actions based on self-organising language memory

In the MirrorBot project we examine perceptual processes using models of cortical assemblies and mirror neurons to explore the emergence of semantic representations of actions, percepts and concepts in a neural robot. The hypothesis under investigation is whether a neural model will produce a life-like perception system for actions. In this context we focus in this paper on how instructions for actions can be modeled in a self-organising memory. Current approaches for robot control often do not use language and ignore neural learning. However, our approach uses language instruction and draws from the concepts of regional distributed modularity, self-organisation and neural assemblies. We describe a self-organising model that clusters actions into different locations depending on the body part they are associated with. In particular, we use actual sensor readings from the MIRA robot to represent semantic features of the action verbs. Furthermore, we outline a hierarchical computational model for a self-organising robot action control system using language for instruction.

Activations related to "mirror" and "canonical" neurones in the human brain: an fMRI study

In the macaque monkey ventral premotor cortex (F5), "canonical neurones" are active when the monkey observes an object and when the monkey grasps that object. In the same area, "mirror neurones" fire both when the monkey observes another monkey grasping an object and when the monkey grasps that object. We used event-related fMRI to investigate where in the human brain activation can be found that reflects both canonical and mirror neuronal activity. There was activation in the intraparietal and ventral limbs of the precentral sulcus when subjects observed objects and when they executed movements in response to the objects (canonical neurones). There was activation in the dorsal premotor cortex, the intraparietal cortex, the parietal operculum (SII), and the superior temporal sulcus when subjects observed gestures (mirror neurones). Finally, activations in the ventral premotor cortex and inferior frontal gyrus (area 44) were found when subjects imitated gestures and executed movements in response to objects. We suggest that in the human brain, the ventral limb of the precentral sulcus may form part of the area designated F5 in the macaque monkey. It is possible that area 44 forms an anterior part of F5, though anatomical studies suggest that it may be a transitional area between the premotor and prefrontal cortices.

Functional MRI of brain activation evoked by intentional eye blinking

Eye blinking is not only a reflexive action to protect the ocular surface from injury and desiccation; it can also be done intentionally. However, only a few studies have investigated the brain mechanism controlling intentional blinking, and there are still inconsistencies among the reported activation patterns in the human brain evoked by intentional blinking. In monkeys, some areas where blinking is evoked by electrical microstimulation have been found in the premotor areas and in the posterior parietal cortex. But there have been no reports about neuronal activity related to blinking in the cerebral cortex. In the present study, the brain activation evoked by intentional blinking was examined in humans by using fMRI, and the activations were found in the middle precentral gyrus, but not in the posterior parietal cortex, suggesting that the premotor areas, rather than the posterior parietal cortex, are important for controlling intentional blinking.

Role of the cerebellum in motor cognition

Cerebellar data from five experiments using different groups of subjects performing the same motor learning task are presented. Positron emission tomography (PET) as well as functional magnetic resonance imaging (fMRI) was used to study changes in cerebellar activations as an effect of learning. Cerebellar brain activations obtained during the performance of a new motor task were compared to activations during the performance of the same task after as well as during practice. To account for changes in velocity and somatosensory processing as an effect of practice, two control conditions were included. Behavioral data showed that as an effect of practice performance speed as well as accuracy increased in all five experiments and groups. Neuroimaging data from adults as well as children showed differential changes in brain activations in different cerebellar areas. In all experiments an area in the left lateral cerebellum showed practice-related decreases, which were most likely related to a decrease in errors. In two experiments a highly significant correlation was found between the decrease in errors and the decrease in left cerebellar activation. An area in the right lateral cerebellum and one in the ipsilateral anterior vermis showed activations that seemed related to the level of capacity at which the subjects were performing and might refer to timing-related aspects of the task.

Interhemispheric transmission of visuomotor information in humans: fMRI evidence

Normal human subjects underwent functional magnetic resonance imaging (fMRI) while performing a simple visual manual reaction-time (RT) task with lateralized brief stimuli, the so-called Poffenberger's paradigm. This paradigm was employed to measure interhemispheric transmission (IT) time by subtracting mean RT for the uncrossed hemifield-hand conditions, that is, those conditions not requiring an IT, from the crossed hemifield-hand conditions, that is, those conditions requiring an IT to relay visual information from the hemisphere of entry to the hemisphere subserving the response. The obtained difference is widely believed to reflect callosal conduction time, but so far there is no direct physiological evidence in humans. The aim of our experiment was twofold: first, to test the hypothesis that IT of visuomotor information requires the corpus callosum and to identify the cortical areas specifically activated during IT. Second, we sought to discover whether IT occurs mainly at premotor or perceptual stages of information processing. We found significant activations in a number of frontal, parietal, and temporal cortical areas and in the genu of the corpus callosum. These activations were present only in the crossed conditions and therefore were specifically related to IT. No selective activation was present in the uncrossed conditions. The location of the activated callosal and cortical areas suggests that IT occurs mainly, but not exclusively, at premotor level. These results provide clear cut evidence in favor of the hypothesis that the crossed-uncrossed difference in the Poffenberger paradigm depends on IT rather than on a differential hemispheric activation.

Medium-range oscillatory network and the 20-Hz sensorimotor induced potential

Although synchronously oscillating neuronal assemblies have been the subject of many studies, a clear identification of the spatiotemporal characteristics of a medium-range oscillatory network is still lacking. Herein, we present a method for the extraction of a new waveform, namely the mean induced potential (IP), which allows the identification of the spatiotemporal characteristics of induced EEG responses. The IP calculation was applied to the 20-Hz component of the sensorimotor rhythm in order to obtain a 20-Hz sensorimotor induced potential (20-Hz SIP). The spatiotemporal characteristics of the 20-Hz bursts seen after median nerve stimulation and self-paced finger movements were extracted by means of current source density reconstruction and synchronization analysis. A cortical network including the controlateral primary motor cortex, the supplementary motor area, and the controlateral supramarginalis gyrus was found to generate the 20-Hz bursts, and the various activated areas were found to be highly synchronized. Our results demonstrate for the first time the existence of a medium-range cortical network in the human sensorimotor region whose constituents oscillate synchronously.

Effect of slice orientation on reproducibility of fMRI motor activation at 3 Tesla

The effect of slice orientation on reproducibility and sensitivity of 3T fMRI activation using a motor task has been investigated in six normal volunteers. Four slice orientations were used; axial, oblique axial, coronal and sagittal. We applied analysis of variance (ANOVA) to suprathreshold voxel statistics to quantify variability in activation between orientations and between subjects. We also assessed signal detection accuracy in voxels across the whole brain by using a finite mixture model to fit receiver operating characteristic (ROC) curves to the data. Preliminary findings suggest that suprathreshold cluster characteristics demonstrate high motor reproducibility across subjects and orientations, although a significant difference between slice orientations in number of activated voxels was demonstrated in left motor cortex but not cerebellum. Subtle inter-orientation differences are highlighted in the ROC analyses, which are not obvious by ANOVA; the oblique axial slice orientation offers the highest signal detection accuracy, whereas coronal slices give the lowest.

Identification of multiple nonprimary motor cortical areas with simple movements

The human cortex reportedly contains at least five nonprimary motor areas: in the frontolateral convexity, the dorsal and ventral premotor cortex (PMd and PMv), and in the frontomesial wall, the presupplementary and supplementary motor areas (pre-SMA and SMA), and the rostral, dorsal and ventral cingulate areas (CMAr, CMAd, and CMAv). Activation of these regions in neuroimaging studies has been generally associated either with the performance of complex motor tasks or with reorganization occurring with motor recovery in the presence of pathology. Recent evidence from neuroimaging studies suggests that the same areas are activated with well controlled simple movements in healthy subjects providing support to the observation that their contribution may be more quantitative rather than exclusively specific to a certain aspect of motor behaviour. An important consequence of this observation is that activation of multiple nonprimary motor areas during simple motor tasks should not be considered unique to patients with upper or lower motoneuron lesions but rather as a normal physiological process.

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.

Susceptibility-induced loss of signal: comparing PET and fMRI on a semantic task

Functional magnetic resonance imaging (fMRI) has become a popular tool for investigations into the neural correlates of cognitive activity. One limitation of fMRI, however, is that it has difficulty imaging regions near tissue interfaces due to distortions from macroscopic susceptibility effects which become more severe at higher magnetic field strengths. This difficulty can be particularly problematic for language tasks that engage regions of the temporal lobes near the air-filled sinuses. This paper investigates susceptibility-induced signal loss in the temporal lobes and proposes that by defining a priori regions of interest and using the small-volume statistical correction of K. J. Worsley, S. Marrett, P. Neelin, A. C. Vandal, K. J. Friston, and A. C. Evans (1996, Hum. Brain Mapp. 4: 58-83), activations in these areas can sometimes be detected by increasing the statistical power of the analysis. We conducted two experiments, one with PET and the other with fMRI, using almost identical semantic categorization paradigms and comparable methods of analysis. There were areas of overlap as well as differences between the PET and fMRI results. One anticipated difference was a lack of activation in two regions in the temporal lobe on initial analyses in the fMRI data set. With a specific region of interest, however, activation in one of the regions was detected. These experiments demonstrate three points: first, even for almost identical cognitive tasks such as those in this study, PET and fMRI may not produce identical results; second, differences between the two methods due to macroscopic susceptibility artifacts in fMRI can be overcome with appropriate statistical corrections, but only partially; and third, new data acquisition paradigms are necessary to fully deal with susceptibility-induced signal loss if the sensitivity of the fMRI experiment to temporal lobe activations is to be enhanced.