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ObjectiveCognitive and motor impairments are the key clinical manifestations of cerebral small vessel disease (SVD), but their interrelations and combined effects on functional outcome have not been elucidated. We investigated the associations between cognitive and motor functions and their interactions and mediating effects on instrumental activities of daily living (IADL) and quality of life in older individuals with various degrees of white matter hyperintensities (WMH).MethodsParticipants of the Helsinki Small Vessel Disease Study (n=152) were assessed according to an extensive clinical, neuropsychological and MRI protocol. Cognitive composite scores for global cognition, processing speed, executive functions and memory were constructed from multiple tests within each domain. Physical examination included measures of gait speed, balance (single-leg-stance) and functional mobility (timed-up-and-go test). IADL was evaluated with a proxy-based Amsterdam IADL questionnaire and quality of life with a self-report EUROHIS-Qol index. Volumes of WMH and gray matter (GM) were obtained with automated segmentation. Sets of linear regression analyses were used to model the associations between motor and cognitive performances, WMH and GM volumes, and IADL and quality of life.ResultsDomain-specific cognitive and motor functions had strong interrelations with each other, and they were significantly associated with IADL, quality of life as well as WMH and GM volumes. A consistent pattern on significant interactions between cognitive and motor functions was found on IADL, but not on quality of life. In particular, low cognitive scores together with decline in the timed-up-and-go test and gait speed were strongly related to impaired IADL. The association of WMH volume with IADL was mediated by global cognition, whereas the association of GM volume with IADL was mediated by global cognition and timed up-and-go performance.ConclusionThe results highlight the complex interplay and synergism between motor and cognitive abilities on functional outcome in SVD. The combined effect of motor and cognitive disturbances on IADL is likely to be greater than the individual effects of each of the two impairments. WMH and brain atrophy contribute to disability through cognitive and motor impairment.

Alpha-pyrrolidinovalerophenone (alpha-PVP) is a designer drug, the mechanism of action of which resembles that of cocaine and amphetamine. New data about the side effects of alpha-PVP are emerging. We present a case report of an acute ischemic stroke following the recreational use of alpha-PVP. The ischemic lesions were located in the middle cerebral artery and deep watershed areas of the left cerebral hemisphere. Occupational therapy and physiotherapy were initiated, and the patient was discharged with only a mild right hemiparesis.

Purpose Severity of white matter lesion (WML) is typically evaluated on magnetic resonance images (MRI), yet the more accessible, faster, and less expensive method is computed tomography (CT). Our objective was to study whether WML can be automatically segmented from CT images using a convolutional neural network (CNN). The second aim was to compare CT segmentation with MRI segmentation. Methods The brain images from the Helsinki University Hospital clinical image archive were systematically screened to make CT-MRI image pairs. Selection criteria for the study were that both CT and MRI images were acquired within 6 weeks. In total, 147 image pairs were included. We used CNN to segment WML from CT images. Training and testing of CNN for CT was performed using 10-fold cross-validation, and the segmentation results were compared with the corresponding segmentations from MRI. Results A Pearson correlation of 0.94 was obtained between the automatic WML volumes of MRI and CT segmentations. The average Dice similarity index validating the overlap between CT and FLAIR segmentations was 0.68 for the Fazekas 3 group. Conclusion CNN-based segmentation of CT images may provide a means to evaluate the severity of WML and establish a link between CT WML patterns and the current standard MRI-based visual rating scale.

The main objective of this prospective cohort study was to evaluate whether traumatic microbleeds (TMBs) are a significant prognostic factor of return to work (RTW), post-traumatic symptoms, and overall recovery in patients with mild traumatic brain injury (mTBI). One hundred and thirteen patients with mTBI were recruited from the Helsinki University Hospital emergency units. All patients underwent multi-contrast 3T magnetic resonance imaging (MRI) 3-17 days after mTBI. Patients were evaluated in the Traumatic Brain Injury Outpatient Clinic of Helsinki University Hospital 1 month after injury. Post-concussion symptoms were assessed with the Post-Concussion Symptom Questionnaire (RPQ) and overall recovery was assessed with the Glasgow Outcome Scale Extended (GOS-E). Their time to RTW was continuously measured up to 1 year after TBI. Median RTW was 9 days (interquartile range [IQR] 4-30) after mTBI and full RTW rate after 1 year was 98%. Patients with TMBs (n = 22) did not have more post-concussion symptoms (median RPQ 10.0 vs. 7.0, p = 0.217) or worse overall recovery (58% vs. 56% with GOS-E = 8, p = 0.853) than patients without TMBs (n = 91). There was no significant difference in time to RTW (13.5 vs. 7.0 days, p = 0.063). In this study, patients with TMBs did not have delayed RTW or more post-concussion symptoms than other patients with mTBI. TMBs in mTBI do not seem to be a significant prognostic factor of RTW.

Background and purpose: Cerebral small vessel disease is characterized by progressive white matter hyperintensities (WMH) and cognitive decline. However, variability exists in how individuals maintain cognitive capabilities despite significant neuropathology. The relationships between individual cognitive reserve, psychological resilience and cognitive functioning were examined in subjects with varying degrees of WMH. Methods: In the Helsinki Small Vessel Disease Study, 152 subjects (aged 65–75 years) underwent a comprehensive neuropsychological assessment, evaluation of subjective cognitive complaints and brain magnetic resonance imaging with volumetric WMH evaluation. Cognitive reserve was determined by education (years) and the modified Cognitive Reserve Scale (mCRS). Psychological resilience was evaluated with the Resilience Scale 14. Results: The mCRS total score correlated significantly with years of education (r = 0.23, p

Background: We evaluated the prevalence of psychiatric disorders in mild traumatic brain injury (MTBI) patients and investigated psychiatric comorbidity in relation to subjective symptoms and return to work (RTW). Methods: We recruited 103 MTBI patients (mean age 40.8 years, SD 3.1) prospectively from University Hospital. The patients were followed up for one year. The Rivermead Post-Concussion Symptom Questionnaire (RPQ) and Extended Glasgow Outcome Scale (GOSE) were administered one month after MTBI. Three months after MTBI, any psychiatric disorders were assessed using the Structured Clinical Interview for DSM-IV Axis I Disorders. Results: Psychiatric disorders were diagnosed in 26 patients (25.2%). The most common disorders were previous/current depression. At three months, there was no difference between patients with psychiatric disorders versus those without them in RTW (95.7% vs. 87.3%, p = 0.260) or at least in part-time work (100% vs. 94.4%, p = 0.245). In Kaplan–Meier analysis, the median time to RTW was 10 days for both groups. The median RPQ score was 13.0 (Interquartile range (IQR) 6.5–19.0) in patients with a psychiatric disorder compared to 8.5 (IQR 2.3–14.0) in those without one (p = 0.021); respectively, the median GOSE was 7.0 (IQR 7.0–8.0) compared to 8.0 (IQR 7.0–8.0, p = 0.003). Conclusions: Approximately every fourth patient with MTBI had a psychiatric disorder. These patients reported more symptoms, and their functional outcome measured with GOSE at one month after MTBI was worse. However, presence of any psychiatric disorder did not affect RTW. Early contact and adequate follow-up are important when supporting the patient’s return to work.

Supplemental Digital Content is available in the text., Background and Purpose— Cerebral small vessel disease is characterized by a wide range of focal and global brain changes. We used a magnetic resonance imaging segmentation tool to quantify multiple types of small vessel disease–related brain changes and examined their individual and combined predictive value on cognitive and functional abilities. Methods— Magnetic resonance imaging scans of 560 older individuals from LADIS (Leukoaraiosis and Disability Study) were analyzed using automated atlas- and convolutional neural network–based segmentation methods yielding volumetric measures of white matter hyperintensities, lacunes, enlarged perivascular spaces, chronic cortical infarcts, and global and regional brain atrophy. The subjects were followed up with annual neuropsychological examinations for 3 years and evaluation of instrumental activities of daily living for 7 years. Results— The strongest predictors of cognitive performance and functional outcome over time were the total volumes of white matter hyperintensities, gray matter, and hippocampi (P

Background and purposeCerebral small vessel disease (SVD) is characterized by a wide range of focal and global brain changes. We used automated MRI segmentation to quantify multiple types of SVD brain changes and examined their individual and combined predictive value on cognitive and functional abilities.MethodsMRI scans of 560 subjects of the Leukoaraiosis and Disability Study (LADIS) were analyzed using automated atlas- and convolutional neural network-based segmentation methods yielding volumetric measures of white matter hyperintensities (WMH), lacunes, cortical infarcts, enlarged perivascular spaces and regional brain atrophy. The subjects were followed up with annual neuropsychological examinations for 3 years and evaluation of instrumental activities of daily living for 7 years.ResultsThe strongest predictors of cognitive performance and functional outcome over time were total volumes of WMH, grey matter (GM) and hippocampi (pConclusionsGlobal burden of SVD-related brain changes as quantified by automated image segmentation is a powerful predictor of long-term cognitive decline and functional disability. A combined measure of WMH, lacunar, GM and hippocampal volumes could be used as an imaging identification model of vascular cognitive impairment.

Ischemic stroke is the most common cerebrovascular disease, and its diagnosis, treatment, and study relies on non-invasive imaging. Algorithms for stroke lesion segmentation from magnetic resonance imaging (MRI) volumes are intensely researched, but the reported results are largely incomparable due to different datasets and evaluation schemes. We approached this urgent problem of comparability with the Ischemic Stroke Lesion Segmentation (ISLES) challenge organized in conjunction with the MICCAI 2015 conference. In this paper we propose a common evaluation framework, describe the publicly available datasets, and present the results of the two sub-challenges: Sub-Acute Stroke Lesion Segmentation (SISS) and Stroke Perfusion Estimation (SPES). A total of 16 research groups participated with a wide range of state-of-the-art automatic segmentation algorithms. A thorough analysis of the obtained data enables a critical evaluation of the current state-of-the-art, recommendations for further developments, and the identification of remaining challenges. The segmentation of acute perfusion lesions addressed in SPES was found to be feasible. However, algorithms applied to sub-acute lesion segmentation in SISS still lack accuracy. Overall, no algorithmic characteristic of any method was found to perform superior to the others. Instead, the characteristics of stroke lesion appearances, their evolution, and the observed challenges should be studied in detail. The annotated ISLES image datasets continue to be publicly available through an online evaluation system to serve as an ongoing benchmarking resource (www.isles-challenge.org).

We applied fMRI and diffusion-weighted MRI to study the segregation of cognitive and motor functions in the human cerebro-cerebellar system. Our fMRI results show that a load increase in a nonverbal auditory working memory task is associated with enhanced brain activity in the parietal, dorsal premotor, and lateral prefrontal cortices and in lobules VII–VIII of the posterior cerebellum, whereas a sensory-motor control task activated the motor/somatosensory, medial prefrontal, and posterior cingulate cortices and lobules V/VI of the anterior cerebellum. The load-dependent activity in the crus I/II had a specific relationship with cognitive performance: This activity correlated negatively with load-dependent increase in RTs. This correlation between brain activity and RTs was not observed in the sensory-motor task in the activated cerebellar regions. Furthermore, probabilistic tractography analysis of the diffusion-weighted MRI data suggests that the tracts between the cerebral and the cerebellar areas exhibiting cognitive load-dependent and sensory-motor activity are mainly projected via separated pontine (feed-forward tracts) and thalamic (feedback tracts) nuclei. The tractography results also indicate that the crus I/II in the posterior cerebellum is linked with the lateral prefrontal areas activated by cognitive load increase, whereas the anterior cerebellar lobe is not. The current results support the view that cognitive and motor functions are segregated in the cerebellum. On the basis of these results and theories of the function of the cerebellum, we suggest that the posterior cerebellar activity during a demanding cognitive task is involved with optimization of the response speed.

Automated methods for segmentation of ischemic stroke lesions could significantly reduce the workload of radiologists and speed up the beginning of patient treatment. In this paper, we present a method for subacute ischemic stroke lesion segmentation from multispectral magnetic resonance images (MRI). The method involves classification of voxels with a Random Forest algorithm and subsequent classification refinement with contextual clustering. In addition, we utilize the training data to build statistical group-specific templates and use them for calculation of individual voxel-wise differences from the global mean. Our method achieved a Dice coefficient of 0.61 for the leave-one-out cross-validated training data and 0.47 for the testing data of the ISLES challenge 2015.

Functional magnetic resonance imaging has been widely used to study brain activation induced either by specific sensory stimulation or motor or cognitive task performance. We demonstrate that functional magnetic resonance imaging can provide information of brain regions involved in opioid-induced central nervous system effects. The reproducibility of the responses in the predefined regions of interest was confirmed by repeated boluses of ultra-short acting mu-opioid receptor agonist remifentanil and saline. We report spatially and temporally detailed information after remifentanil administration. Areas rich in mu-opioid receptors showed strong activations, whereas primary somatosensory cortex that has the lowest density of mu-opioid receptors showed negligible activation. The cingulate, orbitofrontal, posterior parietal and insular cortices, and amygdala showed activation, which was temporally closely related to most subjective sensations that were strongest at 80 to 90 s after drug administration. These areas belong to a circuitry that modulates the affective experience of sensory stimuli.

Results from several recent studies suggest that neuronal processing of sound content and its spatial location may be dissociated. The use of modern neuroimaging techniques has allowed for the determination that different brain structures may be specifically activated during working memory processing of pitch and location of sound. The time course of these task-related differences, however, remains uncertain. In the present study, we performed simultaneous whole-head electroencephalogram and magnetoencephalogram recordings, using a new behavioral paradigm, to investigate the dynamics of differences between "what" and "where" evoked responses in the auditory system as a function of memory load. In the location task the latency of the N1m was shorter and its generator was situated more inferiorly than in the pitch task. Working memory processing of the tonal frequency enhanced the amplitude of the N2 component, as well as the negative-going deflection at a latency around 400 ms. A memory-load-dependent task-related difference was found in the positive slow wave which was higher during the location than pitch task at the low load. Late slow waves were affected by memory load but not type of task. These results suggest that separate neuronal networks are involved in the attribute-specific analysis of auditory stimuli and their encoding into working memory, whereas the maintenance of auditory information is accomplished by a common, nonspecific neuronal network.

A sudden change in the direction of motion is a particularly salient and relevant feature of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to different features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophysiological data from animals and functional imaging data from humans suggest a number of brain areas responsive to motion, presumably working as a network. Temporal patterns of activity allow the same network to process information in different ways. The present study in humans sought to determine which motion-sensitive areas are involved in processing changes in the direction of motion and to characterize the temporal patterns of processing within this network of brain regions. To accomplish this, we used both magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). The fMRI data were used as supplementary information in the localization of MEG sources. The change in the direction of visual motion was found to activate a number of areas, each displaying a different temporal behavior. The fMRI revealed motion-related activity in areas MT+ (the human homologue of monkey middle temporal area and possibly also other motion sensitive areas next to MT), a region near the posterior end of the superior temporal sulcus (pSTS), V3A, and V1/V2. The MEG data suggested additional frontal sources. An equivalent dipole model for the generators of MEG signals indicated activity in MT+, starting at 130 ms and peaking at 170 ms after the reversal of the direction of motion, and then again at approximately 260 ms. Frontal activity began 0-20 ms later than in MT+, and peaked approximately 180 ms. Both pSTS and FEF+ showed long-duration activity continuing over the latency range of 200-400 ms. MEG responses in the region of V3A and V1/V2 were relatively small, and peaked at longer latencies than the initial peak in MT+. These data revealed characteristic patterns of activity in this cortical network for processing sudden changes in the direction of visual motion.

Cerebral responses evoked by peripheral stimuli are known to depend critically on the interstimulus interval (ISI). Here we report on the effects of ISI on somatosensory evoked magnetic fields (SEFs) to right median nerve stimulation, obtained in 9 healthy adults with ISIs of 0.15, 0.3, 1, 3 and 5 s. At the contralateral (left) primary sensorimotor cortex (SMI), the first cortical response, N20m, was stable between the ISIs 0.3 and 5 s, but slightly attenuated at the shortest ISI of 0.15 s. In contrast, the P35m and P60m deflections were very sensitive to changes of the ISI, declining steadily with shortening of the ISI throughout the entire range. These deflections were frequently undetectable at the shortest ISI of 0.15 s. Concomitant with the reductions of P35m and P60m, an N45m deflection was enhanced toward the short ISIs. Responses from second somatosensory cortex (SII) and posterior parietal cortex (PPC) were seen only with ISIs of 1 s or greater, being strongest at the 5 s ISI. Based on known effects of the ISI on intracellular evoked potentials, we present the following tentative model for the generation mechanism of the SMI response: N20m represents early excitatory postsynaptic potentials (EPSPs), P35m early inhibitory postsynaptic potentials (IPSPs), N45m secondary EPSPs and P60m late IPSPs in pyramidal neurones of area 3b. For practical purposes, SEFs from SMI can be obtained with short ISIs, while responses from SII and PPC require an ISI of at least 1 s.

Musical competence may confer cognitive advantages that extend beyond processing of familiar musical sounds. Behavioural evidence indicates a general enhancement of both working memory and attention in musicians. It is possible that musicians, due to their training, are better able to maintain focus on task-relevant stimuli, a skill which is crucial to working memory. We measured the blood oxygenation-level dependent (BOLD) activation signal in musicians and non-musicians during working memory of musical sounds to determine the relation among performance, musical competence and generally enhanced cognition. All participants easily distinguished the stimuli. We tested the hypothesis that musicians nonetheless would perform better, and that differential brain activity would mainly be present in cortical areas involved in cognitive control such as the lateral prefrontal cortex. The musicians performed better as reflected in reaction times and error rates. Musicians also had larger BOLD responses than non-musicians in neuronal networks that sustain attention and cognitive control, including regions of the lateral prefrontal cortex, lateral parietal cortex, insula, and putamen in the right hemisphere, and bilaterally in the posterior dorsal prefrontal cortex and anterior cingulate gyrus. The relationship between the task performance and the magnitude of the BOLD response was more positive in musicians than in non-musicians, particularly during the most difficult working memory task. The results confirm previous findings that neural activity increases during enhanced working memory performance. The results also suggest that superior working memory task performance in musicians rely on an enhanced ability to exert sustained cognitive control. This cognitive benefit in musicians may be a consequence of focused musical training. Public Library of Science

Goal-directed behavior lowers activity in brain areas that include the medial frontal cortex, the medial and lateral parietal cortex, and limbic and paralimbic brain regions, commonly referred to as the “default network.” These activity decreases are believed to reflect the interruption of processes that are ongoing when the mind is in a restful state. Previously, the nature of these processes was probed by varying cognitive task parameters, but the presence of emotional processes, while often assumed, was little investigated. With fMRI, we studied the effect of systematic variations of both cognitive load and emotional stimulus connotation on task-related decreases in the default network by employing an auditory working memory (WM) task with musical sounds. The performance of the WM task, compared to passive listening, lowered the activity in medial and lateral, prefrontal, parietal, temporal, and limbic regions. In a subset of these regions, the magnitude of decrease depended on the memory load; the greater the cognitive load, the larger the magnitude of the observed decrease. Furthermore, in the right amygdala and the left precuneus, areas previously associated with processing of unpleasant dissonant musical sounds, there was an interaction between the experimental condition and the stimulus type. The current results are consistent with the previously reported effect of task difficulty on task-related brain activation decreases. The results also indicate that task-related decreases may be further modulated by the emotional stimulus connotation.

Using functional magnetic resonance imaging (fMRI) and n-back tasks we investigated whether, in 11-13-year-old children, spatial (location) and nonspatial (color) information is differentially processed during visual attention (0-back) and working memory (WM) (2-back) tasks and whether such cognitive task performance, compared to a resting state, results in regional deactivation. The location 0-back task, compared to the color 0-back task, activated segregated areas in the frontal, parietal and occipital cortices whereas no differentially activated voxels were obtained when location and color 2-back tasks were directly contrasted. Several midline cortical areas were less active during 0- and 2-back task performance than resting state. The task-induced deactivation increased with task difficulty as demonstrated by larger deactivation during 2-back than 0-back tasks. The results suggest that, in 11-13-year-old children, the visual attentional network is differently recruited by spatial and nonspatial information processing, but the functional organization of cortical activation in WM in this age group is not based on the type of information processed. Furthermore, 11-13-year-old children exhibited a similar pattern of cortical deactivation that has been reported in adults during cognitive task performance compared to a resting state.

To prospectively evaluate magnetoencephalography (MEG) and functional magnetic resonance (MR) imaging, as compared with intraoperative cortical mapping, for identification of the central sulcus.Fifteen patients (six men, nine women; age range, 25-58 years) with a lesion near the primary sensorimotor cortex (13 gliomas, one cavernous hemangioma, and one meningioma) were examined after institutional review board approval and written informed consent from each patient were obtained. At MEG, evoked magnetic fields to median nerve stimulation were recorded; at functional MR imaging, hemodynamic responses to self-paced palmar flexion of the wrist were imaged. General linear model analysis with contextual clustering (P.01) was used to analyze functional MR imaging data, and dipole modeling was used to analyze MEG data. MEG and functional MR localizations were compared with intraoperative cortical mappings. The distance from the area of functional MR imaging activation to the tumor margin was compared between the patients with discordant and those with concordant intraoperative mapping findings by using unpaired t testing.MEG depicted the central sulcus correctly in all 15 patients, as verified at intraoperative mapping. The functional MR imaging localization results agreed with the intraoperative mappings in 11 patients. In all four patients with a false localization, the primary activation was in the postcentral sulcus region, but it did not differ significantly from the primary activation in the patients with correct localization with respect to proximity to the tumor (P = .38). Furthermore, at functional MR imaging, multiple nonprimary areas were activated, with considerable interindividual variation.Although both MEG and functional MR imaging can provide useful information for neurosurgical planning, in the present study, MEG proved to be superior for locating the central sulcus. Activation of multiple nonprimary cerebral areas may confound the interpretation of functional MR imaging results.

Udgivelsesdato: 2005-Dec Musicians and nonmusicians listened to major, minor, and dissonant musical chords while their BOLD brain responses were registered with functional magnetic resonance imaging. In both groups of listeners, minor and dissonant chords, compared with major chords, elicited enhanced responses in several brain areas, including the amygdala, retrosplenial cortex, brain stem, and cerebellum, during passive listening but not during memorization of the chords. The results indicate that (1) neural processing in emotion-related brain areas is activated even by single chords, (2) emotion processing is enhanced in the absence of cognitive requirements, and (3) musicians and nonmusicians do not differ in their neural responses to single musical chords during passive listening.

Objective Slow evoked responses have been extensively studied using electrophysiological and neuroimaging methods, but there is no consensus regarding their generators. We investigated the generators of the P3 and positive slow wave (PSW) in the evoked responses to probes recorded during auditory working memory tasks to find out whether there is dissociation between functional networks involved in the generation of the P3 and PSW and between spatial and nonspatial auditory processing within this time window. Methods Whole-head magneto-(MEG) and electroencephalography (EEG); analysis of MEG data using minimum-norm current estimates. Results The associative temporal, occipito-temporal and parietal areas contributed to the generation of the slow evoked responses. The temporal source increased while the occipito-temporal source diminished activity during transition from the P3 to PSW. The occipito-temporal generator of the P3 was activated more during the spatial than nonspatial task, and the left temporal generator of the PSW tended to be more strongly activated during the nonspatial task. Conclusions These findings indicate that partially distinct functional networks generate the P3 and PSW and provide evidence for segregation of spatial and nonspatial auditory information processing in associative areas beyond the supratemporal auditory cortex. Significance The present results support the dual-stream model for auditory information processing.

The present study evaluated neurophysiologic function of the primary sensorimotor cortex in juvenile neuronal ceroid lipofuscinosis. A 122-channel magnetometer, which allowed studies of the somatosensory system in millimeter and millisecond precision, was used to record somatosensory evoked magnetic fields to median nerve stimulation from 10 patients and their matched control subjects. In both patients and controls, the somatosensory evoked magnetic fields from primary sensorimotor area typically consisted of N20m, P35m, and P60m deflections. In the patients, N20m was significantly delayed, whereas P35m peaked earlier than in the control subjects. The source strengths for N20m and P35m were greater in the patients than in the controls. Both deflections showed a significant positive correlation with the disease duration: the sources were stronger in the older patients than in the younger ones. P60m deflections were normal or reduced in the patients. The results indicated increased thalamocortical excitability in the sensorimotor cortex in juvenile neuronal ceroid lipofuscinosis. (J Child Neurol 1997;12:355-360).

OBJECTIVE: To present applications of magnetoencephalography (MEG) in studies of neurosurgical patients. METHODS: MEG maps magnetic fields generated by electric currents in the brain, and allows the localization of brain areas producing evoked sensory responses and spontaneous electromagnetic activity. The identified sources can be integrated with other imaging modalities, e.g., with magnetic resonance imaging scans of individual patients with brain tumors or intractable epilepsy, or with other types of brain imaging data. RESULTS: MEG measurements using modern whole-scalp instruments assist in tailoring individual therapies for neurosurgical patients by producing maps of functionally irretrievable cortical areas and by identifying cortical sources of interictal and ictal epileptiform activity. The excellent time resolution of MEG enables tracking of complex spaciotemporal source patterns, helping, for example, with the separation of the epileptic pacemaker from propagated activity. The combination of noninvasive mapping of subcortical pathways by magnetic resonance imaging diffusion tensor imaging with MEG source localization will, in the near future, provide even more accurate navigational tools for preoperative planning. Other possible future applications of MEG include the noninvasive estimation of language lateralization and the follow-up of brain plasticity elicited by central or peripheral neural lesions or during the treatment of chronic pain. CONCLUSION: MEG is a mature technique suitable for producing preoperative “road maps” of eloquent cortical areas and for localizing epileptiform activity.

Movement in the visual field is an important part of perceptual information. Previous imaging studies have identified a number of cortical areas sensitive to visual motion [1,2], including what is considered to be the human homologue of area MT/V5 [3,4]. Our study sought to reproduce and expand upon a previous functional magnetic resonance imaging (fMRI) investigation [4] and to examine the timing of activity in the network of regions participating in the processing of visual motion information with magnetoencephalography (MEG).

We demonstrate that spatially accurate and selective stimulation is crucial when cortical functions are studied by the creation of temporary lesions with transcranial magnetic stimulation (TMS). Previously, the interpretation of the TMS results has been hampered by inaccurate knowledge of the site and strength of the induced electric current in the brain. With a Navigated Brain Stimulation (NBS) system, which provides real‐time magnetic resonance image (MRI)‐guided targeting of the TMS‐induced electric field, we found that TMS of a spatially restricted cortical S1 thenar area is sufficient to abolish sensation from a weak electric stimulation of the corresponding skin area. We demonstrate that with real‐time navigation, TMS can be repeatably directed at millimeter‐level precision to a target area defined on the MRI. The stimulation effect was temporally and spatially specific: the greatest inhibition of sensation occurred when TMS was applied 20 ms after the cutaneous test stimulus and the TMS effect was sensitive to 8–13 mm displacements of the induced electric field pattern. The results also indicate that TMS selectively to S1 is sufficient to abolish perception of cutaneous stimulation of the corresponding skin area. Hum Brain Mapp, 2005. © 2005 Wiley‐Liss, Inc.

Somatosensory point localization is a clinical test evaluating spatial accuracy of the somatosensory system. Possible effects of the interstimulus interval (ISI) on point localization threshold have not been previously examined. In the present set of experiments the effect of time delay on somatosensory point localization was studied using ISIs of 1, 3, 5, 7, and 9 s, and applying a newly developed computer-controlled application method of a Semmes-Weinstein monofilament. It was found that the point localization threshold was not significantly affected by the ISI length. However, the response time was shorter and response accuracy better at the shorter (1 and 3 s) than at the longer (5, 7, and 9 s) ISIs, suggesting a change in the mechanism underlying point localization decision criteria in ISIs longer than 3 s.

Presents a contextual clustering procedure for statistical parametric maps (SPM) calculated from time varying three-dimensional images. The algorithm can be used for the detection of neural activations from functional magnetic resonance images (fMRI). An important characteristic of SPM is that the intensity distribution of background (nonactive area) is known whereas the distributions of activation areas are not. The developed contextual clustering algorithm divides an SPM into background and activation areas so that the probability of detecting false activations by chance is controlled, i.e., hypothesis testing is performed. Unlike the much used voxel-by-voxel testing, neighborhood information is utilized, an important difference. This is achieved by using a Markov random field prior and iterated conditional modes (ICM) algorithm. However, unlike in the conventional use of ICM algorithm, the classification is based only on the distribution of background. The results from the authors' simulations and human fMRI experiments using visual stimulation demonstrate that a better sensitivity is achieved with a given specificity in comparison to the voxel-by-voxel thresholding technique. The algorithm is computationally efficient and can be used to detect and delineate objects from a noisy background in other applications.