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PubMed2004

Improved ballistocardiac artifact removal from the electroencephalogram recorded in fMRI.

The simultaneous recording of electroencephalogram (EEG) and functional magnetic resonance image (fMRI) is a promising tool that is capable of providing high spatiotemporal brain mapping, with each modality supplying complementary information. One of the major barriers to obtain high-quality simultaneous EEG/fMRI data is that pulsatile activity due to the heartbeat induces significant artifacts in the EEG. The purpose of this study was to develop a novel algorithm for removing heartbeat artifact, thus overcoming problems associated with previous methods. Our method consists of a mean artifact wave form subtraction, the selective removal of wavelet coefficients, and a recursive least-square adaptive filtering. The recursive least-square adaptive filtering operates without dedicated sensor for the reference signal, and only when the mean subtraction and wavelet-based noise removal is not satisfactory. The performance of our system has been assessed using simulated data based on experimental data of various spectral characteristics, and actual experimental data of alpha-wave-dominant normal EEG and epileptic EEG.

Adult↗

PubMed2004

Abnormalities of thalamic volume and shape in schizophrenia.

OBJECTIVE: Postmortem and neuroimaging studies of schizophrenia have reported deficits in the volume of the thalamus and its component nuclei. However, the pattern of shape change associated with such volume loss has not been investigated. In this study, alterations in thalamic volume, shape, and symmetry were compared in subjects with and without schizophrenia. METHOD: T(1)-weighted magnetic resonance scans were collected in 52 schizophrenia and 65 comparison subjects matched for age, gender, race, and parental socioeconomic status. High-dimensional (large-deformation) brain mapping was used to assess thalamic morphology. RESULTS: Significant differences in thalamic volume, deformities of thalamic shape at the anterior and posterior extremes of the structure, and a significant exaggeration of thalamic asymmetry (i.e., left smaller than right) were found in the schizophrenia subjects. After covarying for total cerebral volume, the difference in thalamic volume became insignificant. When information about thalamic shape was combined with previously collected information about hippocampal shape, the discrimination between schizophrenia patients and comparison subjects was improved. CONCLUSIONS: Thalamic volume was smaller than normal in schizophrenia patients, but only proportionate to reductions in reduced total cerebral volume. The presence of changes in thalamic shape and asymmetry suggest greater pathologic involvement of individual nuclei at its anterior and posterior extremes of the thalamic complex.

Adult↗

PubMed1999

A review of database management systems suitable for neuroimaging.

This study comprises a technical assessment of Database Management Systems (DBMS), which may be of use in the analysis of data obtained from human brain mapping procedures. Due to the large expansion of the neuroimaging field, the use of specialized database software to store and process neuroimages and their attached components is inevitable. The advent of multiple software products, a wealth of technical terms and a wide variety of other applications make the choice of a suitable program sometimes difficult. Through the inclusion of some basic and pertinent criteria (e.g., performance, ease of opening, standardization and portability), we present a descriptive comparison of 12 DBMSs currently available in the commercial and public domain. We have compared and tested three main architecture models which are currently available and assessed their potential applications for imaging purposes: relational, object-oriented, and hybrid. The findings of our study demonstrated that the Illustra software was the best suited for a neuroimaging environment because of its intrinsic ability to handle complex and large objects, such as 3D volumes or geometric structures.

Brain Mapping↗

PubMed2006

Detrimental effects of BOLD signal in arterial spin labeling fMRI at high field strength.

Arterial spin labeling (ASL) MRI is a useful technique for noninvasive measurement of cerebral blood flow (CBF) in humans. High field strength provides a unique advantage for ASL because of longer blood T(1) relaxation times, making this technique a promising quantitative approach for functional brain mapping. However, higher magnetic field also introduces new challenges. Here it is shown that the CBF response determined using ASL functional MRI (fMRI) at 3.0 T contains significant contamination from blood-oxygenation-level-dependent (BOLD) effects. Due to interleaved acquisitions of label and control images, difference in blood oxygenation status between these two scans can cause incomplete cancellation of the static signal upon image subtraction, resulting in a BOLD-related artifact in the estimated CBF hemodynamics. If not accounted for, such an effect can complicate the interpretation of the ASL results, e.g., causing a delayed onset and offset of the response, or inducing an artifactual poststimulus undershoot. The BOLD contribution also decreases the sensitivity of ASL-based fMRI. Correction methods are proposed to reduce the artifact, giving increased number of activated voxels (18+/-5%, P=0.006) and more accurate estimation of CBF temporal characteristics.

Algorithms↗

PubMed2004

Reduced plasticity of cortical whisker representation in adult tenascin-C-deficient mice after vibrissectomy.

The effect of the extracellular matrix recognition molecule tenascin-C on cerebral plasticity induced by vibrissectomy was investigated with 2-deoxyglucose (2DG) brain mapping in tenascin-C-deficient mice. Unilateral vibrissectomy sparing row C of vibrissae was performed in young adult mice. Two months later, cortical representations of spared row C vibrissae and control row C on the other side of the snout were visualized by [(14)C]2DG autoradiography. In both wild-type and tenascin-C-deficient mice, cortical representation of the spared row was expanded in all layers of the barrel cortex. However, the effect was significantly more extensive in wild-type animals than in the mutant. Elimination of tenascin-C by genetic manipulation thus reduces the effect of vibrissectomy observed in the somatosensory cortex. No increase in number of fibres in the vibrissal nerve of spared vibrissae was seen, and occurrence of additional nerve to the spared follicle was very rare. Thus, in tenascin-C-deficient mice functional plasticity seems to be impaired within the CNS.

Animals↗

PubMed2005

Side effects of transcranial magnetic stimulation biased task performance in a cognitive neuroscience study.

Transcranial magnetic stimulation (TMS) is increasingly used as a research tool for functional brain mapping in cognitive neuroscience. Despite being mostly tolerable, side effects of TMS could influence task performance in behavioural TMS studies. In order to test this issue, healthy subjects assessed the discomfort caused by the stimulation during a verbal working memory task. We investigated the relation between subjective disturbance and task performance. Subjects were stimulated during the delay period of a delayed-match-to-sample task above cortical areas that had been identified before to be involved in working memory. Task performance and subjective disturbance due to side effects were monitored. The subjects' grade of discomfort correlated with the error rates: the higher the discomfort, the more errors were made. Conclusively, TMS side effects may bias task performance in cognitive neuroscience studies and may thereby lead to misinterpretation of results. We emphasize the importance of controlling side effects of the stimulation as a source of biasing effects in TMS studies.

Adult↗

PubMed2004

Brain mechanisms for the formation of new movements during learning: the evolution of classical concepts.

Current concepts hold that the role of the motor cortex is limited to the control of the appropriate motoneurons on the "point-to-point" principle during the performance of specialized movements of the distal parts of the limbs. However, the last decade has seen the appearance of many data on the plasticity of the motor cortex and its active participation in the process of motor learning. Expression of fos genes has been observed in the motor cortex during the formation of specialized movements. Increases in intracortical horizontal connections in layers II-III during learning fine movements has been seen. The cholinergic input to layers II-III of the motor cortex plays a significant role in this. At the same time, data obtained by functional brain mapping have provided evidence that the activity of the motor cortex also increases during the practice of previously learned movements. This raises the question of the specific function of the motor cortex in the process of motor learning. During the formation of new movements during motor training, a number of previously used synergies interfere with the performance of newly formed coordinations and must be inhibited. The central mechanisms of interference of coordinations in humans have only just started to receive study. At the same time, there is an experimental model for the reorganization and inhibition of interfering synergies in animals. Reorganization of coordinations and inhibition of synergies interfering with the performance of a new movement have been shown to be a specific function of the motor area of the cortex. Cortical control persists during the automation of these synergies, which is not the case in other types of learned movements, though this in itself does not mean that conscious control of their performance also persists.

Animals↗

PubMed2006

The role of the supramammillary commissure in MR localization of the subthalamic nucleus.

PURPOSE: We have discovered a method for localization of the subthalamic nucleus (STN) utilizing the supramammillary commissure (SMC) as reference point. It is our purpose to present our experience and compare our methods with others. MATERIALS AND METHODS: Sixteen patients targeted for bilateral DBS for 32 total STN targets were studied by 1 mm MP-RAGE images with coronal T2W images. A modified red nucleus and mustache method was applied. The predicted target points were then confirmed with electronic calipers measuring the differences in methods. RESULTS: Modified red nucleus method using Surgiplan, and EBAL and BAGM electronic brain map atlas matched the target loci of 12 mm, -3 mm, -4 mm on an X-, Y-, and Z-coordinate system with zero at the mid-commissural point. From the coronal view Y is fixed at -3 mm. The mustache method was in error with values of X-axis at 14.25 (+/- 1.41 SD) (p = 0.69), and of Z-axis at -5.0 (+/- 1.60 SD) (p = 0.55). Three-fourths had moderate to marked ventricular enlargement of the III, but only 3 had enlargement of the frontal horns. CONCLUSION: The mustache method erred in the X-axis because the thalamocaudate groove was located lateral to the target point of the STN, and in the Z-axis because of varying thicknesses of the SMC. The top of the SMC is directly lateral from the STN target by 12 mm from the anterior and posterior commissures line. The SMC being a recognizable structure with constant relation to the STN should be the target structure.

Brain Mapping↗

PubMed1989

The topography of the P1 component of the flash visual evoked response.

The scalp topography of the P1 component of the human flash visual evoked response was investigated by means of the biologic brain mapping system. Thirty subjects, ranging in age from 21 to 84 years, had flash visual evoked responses recorded using the standard 10-20 electrode positions referred to a balanced noncephalic reference. The subjects were divided by age into three groups: young, middle and old. A P2 component was recorded over the occipital region for all three groups and a frontal negative component was found to occur concurrently with the P2 occipital component. Neither the young or the middle age groups showed an identifiable P1 component. However this component was clearly present in the older group at 76 msec. The distribution of this component was more widespread anteriorly than the P2 component. In both the middle and the older age groups an earlier frontal negative component was present at around 75 msec; no such component was recordable in the young. This work suggests that the development of the P1 component during middle age is preceded by the development of a frontal negative component of around the same latency.

Adult↗

PubMed2001

Statistical analysis of hippocampal asymmetry in schizophrenia.

The asymmetry of brain structures has been studied in schizophrenia to better understand its underlying neurobiology. Brain regions of interest have previously been characterized by volumes, cross-sectional and surface areas, and lengths. Using high-dimensional brain mapping, we have developed a statistical method for analyzing patterns of left-right asymmetry of the human hippocampus taken from high-resolution MR scans. We introduce asymmetry measures that capture differences in the patterns of high-dimensional vector fields between the left and right hippocampus surfaces. In 15 pairs of subjects previously studied (J. G. Csernansky et al., 1998, Proc. Natl. Acad. Sci. USA 95, 11406-11411). we define the difference in hippocampal asymmetry patterns between the groups. Volume analysis indicated a large normative asymmetry between left and right hippocampus (R > L), and shape analysis allowed us to visualize the normative asymmetry pattern of the hippocampal surfaces. We observed that the right hippocampus was wider along its lateral side in both schizophrenia and control subjects. Also, while patterns of hippocampal asymmetry were generally similar in the schizophrenia and control groups, a principal component analysis based on left-right asymmetry vector fields detected a statistically significant difference between the two groups, specifically related to the subiculum.

Brain Mapping↗

PubMed2002

The neural basis of the blood-oxygen-level-dependent functional magnetic resonance imaging signal.

Magnetic resonance imaging (MRI) has rapidly become an important tool in clinical medicine and biological research. Its functional variant (functional magnetic resonance imaging; fMRI) is currently the most widely used method for brain mapping and studying the neural basis of human cognition. While the method is widespread, there is insufficient knowledge of the physiological basis of the fMRI signal to interpret the data confidently with respect to neural activity. This paper reviews the basic principles of MRI and fMRI, and subsequently discusses in some detail the relationship between the blood-oxygen-level-dependent (BOLD) fMRI signal and the neural activity elicited during sensory stimulation. To examine this relationship, we conducted the first simultaneous intracortical recordings of neural signals and BOLD responses. Depending on the temporal characteristics of the stimulus, a moderate to strong correlation was found between the neural activity measured with microelectrodes and the BOLD signal averaged over a small area around the microelectrode tips. However, the BOLD signal had significantly higher variability than the neural activity, indicating that human fMRI combined with traditional statistical methods underestimates the reliability of the neuronal activity. To understand the relative contribution of several types of neuronal signals to the haemodynamic response, we compared local field potentials (LFPs), single- and multi-unit activity (MUA) with high spatio-temporal fMRI responses recorded simultaneously in monkey visual cortex. At recording sites characterized by transient responses, only the LFP signal was significantly correlated with the haemodynamic response. Furthermore, the LFPs had the largest magnitude signal and linear systems analysis showed that the LFPs were better than the MUAs at predicting the fMRI responses. These findings, together with an analysis of the neural signals, indicate that the BOLD signal primarily measures the input and processing of neuronal information within a region and not the output signal transmitted to other brain regions.

Animals↗

PubMedDate not supplied

Quantitative analysis of EEG in boys with attention-deficit-hyperactivity disorder: controlled study with clinical implications.

Sixteen-channel topographic brain mapping of electroencephalograms of 25 right-handed males, 9-12 years of age, with attention-deficit-hyperactivity disorder revealed increased theta (4-7.75 Hz) and decreased beta 1 (12.75-21 Hz) when compared with 27 controls matched for age and grade level. The differences were greater when patients were tested for reading and drawing skills, but were decreased when they were at rest during visual fixation. Although the differences in patients with attention-deficit-hyperactivity disorder were generalized, increased theta was more prominent in frontal regions, while beta 1 was significantly decreased in temporal regions. Principal component analysis was used to combine the variables into 2 components which accounted for 82% of the total variance. A discriminant function analysis using these components was able to predict group membership for attention-deficit-hyperactivity disorder patients 80% of the time and 74% for controls. These findings support the use of topographic electroencephalography for further elucidation of the neurophysiology of attention-deficit-hyperactivity disorder.

Arousal↗

PubMed2000

Electrophysiologic signs of auditory distraction in elderly listeners.

Brain mapping was used to investigate the ability of young and elderly female listeners to attend to /ga/ syllabic events at one ear in the presence of speech babble competition at the opposite ear. An oddball stimulus presentation paradigm was used to record the N1 and P2 components of the late auditory evoked potential (LAEP) from 19 scalp locations. With speech competition, elderly listeners exhibited significantly larger reductions in P2 amplitude than did young listeners. The competition produced no changes in N1 amplitude in either group. These findings contrast with those of an earlier study in which age-related reductions in N1 but not P2 amplitude were found when listeners attended to tones rather than speech stimuli in the presence of speech competition. These studies suggest that amplitude reductions in different LAEP components may provide electrophysiologic indices of age-related breakdowns in processing sounds in the presence of competition. Which LAEP components are affected may depend on experimental variables such as task difficulty or the nature of the stimuli (e.g., speech vs nonspeech).

Adult↗

PubMedDate not supplied

[Wilder G. Penfield at the Residencia de Estudiantes (madrid, 1924)].

INTRODUCTION: Wilder Graves Penfield (1891-1976) is considered to be one of the 20th century's most gifted and brilliant neuroscientists. He made crucial contributions in the field of epileptology or in brain mapping. He was the founder and director of the advanced Montreal Neurological Institute, regarded as being one of the most prestigious neurological and neurosurgical centres in the world. DEVELOPMENT: His wish to further basic neuroscientific knowledge as much as possible led him to Europe. In the spring of 1924 he arrived in Madrid with his wife and two children on an 'exciting adventure' to improve his knowledge of the histology of the nervous system. Inside the walls of the Residencia de Estudiantes (1910-1936) could be found an enlightening generation of artists and scientists who represented the beginning of the modernization of the country. The building had some humble but very active laboratories, where the scholars elaborated their scientific projects in order to opt for grants allowing them to travel to foreign centres. The North American scientist spent four and a half months participating enthusiastically in what was at that time an avant-garde subject: the discovery and characterisation of glial cells, which would be developed in a number of publications. He was also 'fascinated' by the 'cultural renaissance' that was taking place in Spain.

Academies and Institutes↗

PubMed1995

A conceptual overview and critique of functional neuroimaging techniques in humans: I. MRI/FMRI and PET.

A critical evaluation of current, noninvasive brain-mapping techniques indicates that no one technique in isolation can adequately address the varied questions of interest to basic researchers and clinicians. Consequently, an integrated analysis of anatomical and functional measurements has become the ultimate goal to better characterize the nature of neuronal and hemodynamic responses to sensory and cognitive stimulation. Such an analysis will optimize both spatial and temporal resolution, thereby enabling patterns of activation to be followed throughout the central nervous system, a prerequisite for examining stages of information processing. This review, written in two parts, provides a conceptual overview of three techniques (MRI/fMRI, PET, and MEG/EEG) and examines current efforts at integrating these measures. Each technique is initially evaluated in isolation by considering a set of primary issues (e.g., spatial resolution, temporal resolution, the nature of the signal, individual variability, repeatability, etc.). The first part compares and contrasts MRI/fMRI techniques with PET. Part II, which examines MEG/EEG techniques and current attempts at integrating techniques, will appear in a subsequent volume. This two-part review focuses on issues, not results per se, and it is assumed that the reader is not proficient in any of the techniques described.

Brain↗

PubMedDate not supplied

Physiological characteristics of capacity constraints in working memory as revealed by functional MRI.

A fundamental characteristic of working memory is that its capacity to handle information is limited. While there have been many brain mapping studies of working memory, the physiological basis of its capacity limitation has not been explained. We identified characteristics of working memory capacity using functional magnetic resonance imaging (fMRI) in healthy subjects. Working memory capacity was studied using a parametric 'n-back' working memory task involving increasing cognitive load and ultimately decreasing task performance. Loci within dorsolateral prefrontal cortex (DLPFC) evinced exclusively an 'inverted-U' shaped neurophysiological response from lowest to highest load, consistent with a capacity-constrained response. Regions outside of DLPFC, in contrast, were more heterogeneous in response and often showed early plateau or continuously increasing responses, which did not reflect capacity constraints. However, sporadic loci, including in the premotor cortex, thalamus and superior parietal lobule, also demonstrated putative capacity-constrained responses, perhaps arising as an upstream effect of DLPFC limitations or as part of a broader network-wide capacity limitation. These results demonstrate that regionally specific nodes within the working memory network are capacity-constrained in the physiological domain, providing a missing link in current explorations of the capacity characteristics of working memory.

Adolescent↗

PubMed1999

The electrical and magnetical cerebral responses evoked by electrical stimulation of the esophagus and the location of their cerebral sources.

OBJECTIVES: After electrical stimulation of the esophagus cerebral responses are recordable, their cortical source is under discussion. Brain mapping using electroencephalography recordings demonstrated partially controversial results. Sources of evoked responses can be localized more easily using magnetoencephalography than electroencephalography. METHODS: We examined 22 volunteers by recording electrical somatosensory potentials after electrical stimulation of the esophagus. In 9 of these 22 subjects additional recording of magnetic fields was performed and the sources of the evoked magnetic fields were computed. RESULTS: The evoked potentials after electrical stimulation of the esophagus had a similar latency as the previously published data. The source localization done by magnetoencephalography suggest that first a region of the postcentral gyrus is activated which is temporo-lateral to the primary somatosensory cortex of the pharynx. This region is suggested to be the primary somatosensory region of the esophagus. This source was followed by a source in the parietal operculum thought being part of the secondary somatosensory cortex. Simultaneously the insular cortex was activated pointing to a parallel neuronal pathway to the central autonomic nervous system. CONCLUSION: After electrical stimulation of the esophagus somatosensory cortical areas of the temporal postcentral gyrus and the operculum are activated. In parallel activation of the insular cortex as part of the central autonomic network was found.

Adult↗

PubMed1998

Cyclophosphamide cystitis as a model of visceral pain in rats: a c-fos and Krox-24 study at telencephalic levels, with a note on pituitary adenylate cyclase activating polypeptide (PACAP).

This article is the fifth of a series aimed at mapping brain activities as they result from the development of cyclophosphamide (CP) cystitis in behaving rats using c-fos and Krox-24 expression. The inactive hepatic metabolites of CP are metabolized in the kidney to produce acrolein, which generates cystitis. Data come from animals which were injected once i.p. with either 1 ml saline (sham) or 100 mg/kg CP in 1 ml saline under transient volatile anesthesia and which behaved freely for 1-4 h postinjection, 4 h being the minimum time for cystitis to completely develop. Survival times longer than 4 h were not studied owing to ethical considerations. The first 2 h postinjection cover a period of time over which inputs of multifactorial origin (stress and pain due to the intraperitoneal injection process, possible effects due to the presence of hepatic CP metabolites in blood, cystitis onset) interact in an indistinguishable way; the last 2 h are more cystitis specific as the other effects have vanished. Complete screening of telencephalic levels has been performed. These data complete previously published data at both spinal and subtelencephalic levels. Of all the telencephalic structures, only the bed nucleus of the stria terminalis in the dorsal part of its lateral division (BSTLd) and, to a lesser degree, the nucleus centralis of the amygdala, mostly in its caudal portion (cCeA), appeared to be significantly driven over the most specific cystitis period. Both of these structures had related, but not identical patterns of expression. They both reacted shortly after CP injection, but, while cCeA maintained its activity throughout cystitis development, BSTLd showed a rebound, reaching a peak value when cystitis was fully developed. Both of these areas are the only telencephalic areas to contain high PACAP38 immunoreactivity. This is evidence that, (1) both the BSTLd and cCeA could be the most rostral areas that visceronociceptive inflow would reach when cystitis genesis is under way, and (2) PACAP38 could be one of the neurochemical agents involved in telencephalic visceronociceptive processing. From our complete mapping of brain activities under a fully developed cystitis situation (4 h postinjection), it appears that the activities in BSTLd and cCeA are concomitant with those of both the dorsal vagal complex (DVC), paratrigeminal nucleus (PaT), and the ventrocaudal bulbar reticular formation (vcBRF) at brainstem levels, suggesting they all form the main part of the neural network that subserves the central processing of cystitis-related inputs, comprising pain and associated pseudoaffective responses. Both the DVC and BSTLd, which are the most powerfully driven areas, would be particularly important in such a way. The origin of these activities should be found in both vagal (as sensed through PaT activity) and spinal (pelvic) influences. This network profoundly differs from those reported for painful situations, either somatic or visceral, which controversally accompany positive cardiac inotropism.

Animals↗