Biomedical subjects

Gisela E Hagberg

Publications and source records attributed to Gisela E Hagberg.

12 recordsLinked to original sources

PubMed2007

Multimodal fMRI tractography in normal subjects and in clinically recovered traumatic brain injury patients.

In this study, we defined an operator-independent protocol for reconstructing the anatomical connections originating from fMRI activations in order to demonstrate that results obtained with this protocol are affected by alterations of functional activations. Seven healthy volunteers and two patients who sustained traumatic brain injury underwent an fMRI with a finger tapping task and a DTI scan. Cortical fMRI activations were used directly as seed mask for tractography for the reconstruction of individual motor pathways. On patients we observed a different motor network if compared to healthy subjects. However, when the activations of healthy subjects were used as seed masks for the tractography in patients, we observed for the patients a pattern of connectivity more similar to what was observed for healthy subjects. At the same time, when the activations of patients were used for the tractography on healthy subjects, we obtained patterns of connectivity similar to those obtained for patients. These results show the potential of the integration of fMRI and tractography for clarifying the mechanisms of cortical plasticity in the recovery of motor functions.

Adult↗

PubMed2006

Implicit learning deficits in dyslexic adults: an fMRI study.

It is assumed that several neuropsychological impairments characterize the cognitive profile of individuals with developmental dyslexia (DD). Phonological and visual processing are often impaired as well as auditory processing, attention, and information processing speed. Although reports in the literature on implicit learning abilities are contradictory, recent neurological and physiological data suggest that these abilities are deficient in individuals with DD. To evaluate implicit learning we administered a classical version of the serial reaction time task (SRTT) related to sequence learning. Using functional magnetic resonance imaging we investigated brain activation patterns associated with implicit learning deficits in 14 adults with DD matched with 14 normal readers. SRTT results indicated the absence of implicit learning in the DD group and different activations between groups mainly in SMA, inferior parietal areas and cerebellar lobule 6. These results can be interpreted in the light of the different capacities for the two groups to build an internal model to guide movements. Further, they explain DD individuals' difficulty in domains not directly related to reading ability.

Adult↗

PubMed2006

Functional changes in the activity of cerebellum and frontostriatal regions during externally and internally timed movement in Parkinson's disease.

We used fMRI to investigate the neurofunctional basis of externally and internally timed movements in Parkinson's disease (PD) patients. Ten PD patients whose medication had been withheld for at least 18h and 11 age- and sex-matched healthy controls were scanned while performing continuation paradigm with a visual metronome. Compared with the controls, PD patients displayed an intact capability to store and reproduce movement frequencies but with a significantly increased movement latencies. No differences in BOLD response were found in both groups when comparing the continuation with the preceding synchronization phase and viceversa, except for activity in visually related regions. Relative to healthy controls during the synchronization phase, PD patients exhibited an overall signal increase in the cerebellum and frontostriatal circuit (putamen, SMA and thalamus) activity together with specific brain areas (right inferior frontal gyrus and insula cortex) that are also implicated in primary timekeeper processes. By contrast, in the continuation phase the only neural network involved to a greater extent by the PD group was the cerebello-thalamic pathway. The lack of neurofunctional differences between the two timing phases suggests that rhythmic externally and internally guided movements engage similar neural networks in PD and matched healthy controls. Moreover, between-group comparison indicates that PD patients OFF medication may compensate for their basal ganglia-cortical loop's dysfunction using different motor pathways involving cerebellum and basal ganglia relays during the two phases of rhythmic movement.

Adult↗

PubMed2006

Validation studies on the 5-hydroxy-L-[beta-11C]-tryptophan/PET method for probing the decarboxylase step in serotonin synthesis.

The two-tissue compartment model, including irreversible trapping in the second compartment (2TCM) is used to describe the kinetics of 5-Hydroxy-L-[beta-(11)C]-tryptophan ([(11)C]HTP), a radioligand used in positron emission tomography (PET) for probing the second enzymatic step in the biosynthesis of serotonin. In this study, we examined the capacity of the model to track pharmacological changes in this biological process. We also investigated the potential loss of [(11)C]HTP-derived radioactivity during a PET study, since loss should be negligible not to alter quantification. Six rhesus monkeys were investigated using bolus [(11)C]HTP/PET methodology before and after pharmacological intervention. The second enzymatic step in serotonin synthesis was inhibited using the aromatic L-amino acid decarboxylase inhibitor NSD1015 (10 mg/kg). The extent of [(11)C]-derived radioactivity loss from the brain was studied by inhibition of the enzyme responsible for formation of the tissue metabolite, monoamine oxidase A, using clorgyline (2 mg/kg). After NSD1015, the uptake of [(11)C]HTP-derived radioactivity was increased in all the investigated brain regions, while the parameter used to reflect decarboxylase activity, the net accumulation rate constant (K(acc)), was decreased by 37% in the striatum, compared with baseline. Pretreatment with clorgyline did not change the brain uptake of [(11)C]HTP-derived radioactivity or K(acc). This study demonstrates that the 2TCM for [(11)C]HTP/PET is able to detect changes occurring during alteration of the biological process (i.e., the conversion of HTP to serotonin). Elimination of the radiotracer metabolite [(11)C]HIAA from the brain may be considered negligible if the PET study is limited to 60 min.

5-Hydroxytryptophan↗

PubMed2006

Challenges for detection of neuronal currents by MRI.

Neuronal current MRI (nc-MRI) is an imaging method that directly maps magnetic field changes caused by neuronal currents with, at the same time, a high spatial and temporal resolution. A viable nc-MRI method would be of great benefit, both for the study of human brain function and for clinical applications in the field of epilepsy, especially for the noninvasive presurgical mapping of epileptogenic foci. A survey of fundamental issues in nc-MRI is reviewed, and challenges for future developments of the method are described within this context. Particularly, an overview of the models for signal generation is given, and the origin and physiology of different sources of neuronal currents are described. Prospects for predicting neuronal currents by electromagnetic field mapping and using this information, both a priori and a posteriori, for nc-MRI are considered. Ways of increasing specificity in nc-MRI by minimizing secondary hemodynamic and metabolic effects are described as well as means of optimizing the nc-MRI method for pushing the detection limit. Previously published works are described within these categories and future directions for nc-MRI are proposed.

Action Potentials↗

PubMed2005

The appreciation of wine by sommeliers: a functional magnetic resonance study of sensory integration.

We set out to investigate how the expertise of a sommelier is embodied in neural circuitry by comparing brain activity elicited by wine tasting with that found in naive drinkers of wine. We used fMRI to study 7 sommeliers and 7 age- and sex-matched control subjects to test the hypothesis that any difference in brain activity would reflect a learned ability to integrate information from gustatory and olfactory senses with past experience. A group analysis showed activation of a cerebral network involving the left insula and adjoining orbito-frontal cortex in sommeliers. Both these areas have been implicated in gustatory/olfactory integration in primates. In addition, activation was found bilaterally in the dorsolateral prefrontal cortex, which is implicated in high-level cognitive processes such as working memory and selection of behavioral strategies. Naive individuals activated the primary gustatory cortex and brain areas, including the amygdala, implicated in emotional processing.

Adult↗

PubMed2005

Visually cued motor synchronization: modulation of fMRI activation patterns by baseline condition.

A well-known issue in functional neuroimaging studies, regarding motor synchronization, is to design suitable control tasks able to discriminate between the brain structures involved in primary time-keeper functions and those related to other processes such as attentional effort. The aim of this work was to investigate how the predictability of stimulus onsets in the baseline condition modulates the activity in brain structures related to processes involved in time-keeper functions during the performance of a visually cued motor synchronization task (VM). The rational behind this choice derives from the notion that using different stimulus predictability can vary the subject's attention and the consequently neural activity. For this purpose, baseline levels of BOLD activity were obtained from 12 subjects during a conventional-baseline condition: maintained fixation of the visual rhythmic stimuli presented in the VM task, and a random-baseline condition: maintained fixation of visual stimuli occurring randomly. fMRI analysis demonstrated that while brain areas with a documented role in basic time processing are detected independent of the baseline condition (right cerebellum, bilateral putamen, left thalamus, left superior temporal gyrus, left sensorimotor cortex, left dorsal premotor cortex and supplementary motor area), the ventral premotor cortex, caudate nucleus, insula and inferior frontal gyrus exhibited a baseline-dependent activation. We conclude that maintained fixation of unpredictable visual stimuli can be employed in order to reduce or eliminate neural activity related to attentional components present in the synchronization task.

Adult↗

PubMed2005

Fast detection of diffuse axonal damage in severe traumatic brain injury: comparison of gradient-recalled echo and turbo proton echo-planar spectroscopic imaging MRI sequences.

BACKGROUND AND PURPOSE: Diffuse axonal injury (DAI) is a common type of primary neuronal injury in patients with severe traumatic brain injury (TBI), and is frequently accompanied by tissue tear hemorrhage. T2-weighted gradient-recalled echo (GRE) sequences are more sensitive than T2-weighted spin-echo images for detection of hemorrhage. The purpose of this study is to compare turbo Proton Echo Planar Spectroscopic Imaging (t-PEPSI), an extremely fast sequence, with GRE sequence in the detection of DAI. METHODS: Twenty-one patients (mean age 26.8 years) with severe TBI occurred at least 3 months earlier, underwent a brain MR Imaging study on a 1.5-T scanner. A qualitative evaluation of the t-PEPSI sequences was performed by identifying the optimal echo time and in-plane resolution. The number and size of DAI lesions, as well as the signal intensity contrast ratio (SI CR), were computed for each set of GRE and t-PEPSI images, and divided according to their anatomic location as lobar and/or deep brain. RESULTS: There was no significant difference between GRE and t-PEPSI sequences in the detection of the total number of DAI lesions (291 vs. 230, respectively). GRE sequence delineated a higher number of DAI in the temporal lobe compared to the t-PEPSI sequence (74 vs. 37, P < .004), while no differences were found for the other regions. The SI CR was significantly lower with the t-PEPSI than the GRE sequence (P < .00001). CONCLUSION: Owing to its very short scan time and high sensitivity to the hemorrhage foci, the t-PEPSI sequence may be used as an alternative to the GRE to assess brain DAI in severe TBI patients, especially if uncooperative and medically unstable.

Adolescent↗

PubMed2004

Combination of BOLD-fMRI and VEP recordings for spin-echo MRI detection of primary magnetic effects caused by neuronal currents.

In the present paper, for the first time, the feasibility to detect primary magnetic field changes caused by neuronal activity in vivo by spin-echo (SE) magnetic resonance imaging (MRI) is investigated. The detection of effects more directly linked to brain activity than secondary hemodynamic-metabolic changes would enable the study of brain function with improved specificity. However, the detection of neuronal currents by MRI is hampered by such accompanying hemodynamic changes. Therefore, SE image acquisition, rather than gradient-echo (GE) image acquisition, was preferred in the present work since the detection of primary neuronal and not blood oxygenation level-dependent (BOLD)-related effects may be facilitated by this approach. First of all, a precise spatiotemporal synchronization of image acquisition with the neuronal event had to be performed to avoid refocusing of the dephasing phenomenon during the course of the SE sequence. At this aim, we propose the combined use of visual evoked potential (VEP) recordings and BOLD-fMRI measurements prior to SE MRI scanning. Moreover, we exemplify by theory and experimentation how the control of artefactual signal changes due to BOLD and movement effects may be further improved by the experimental design. Finally, results from a pilot study using the proposed combination of VEP recordings and MRI techniques are reported, suggesting the feasibility of this method.

Adult↗

PubMed2004

Simultaneous EEG-fMRI acquisition: how far is it from being a standardized technique?

Simultaneous EEG-fMRI is a powerful tool to study spontaneous and evoked brain activity because of the complementary advantages of the two techniques in terms of temporal and spatial resolution. In recent years, a significant number of scientific works have been published on this subject. However, many technical problems related to the intrinsic incompatibility of EEG and MRI methods are still not fully solved. Furthermore, simultaneous acquisition of EEG and event-related fMRI requires precise synchronization of all devices involved in the experimental setup. Thus, timing issue must be carefully considered in order to avoid significant methodological errors. The aim of the present work is to highlight and discuss some of technical and methodological open issues associated with the combined use of EEG and fMRI. These issues are presented in the context of preliminary data regarding simultaneous acquisition of event-related evoked potentials and BOLD images during a visual odd-ball paradigm.

Adult↗

PubMed2003

Quantitative NumART2* mapping in functional MRI studies at 1.5 T.

Quantitative mapping of the effective transverse relaxation time, T2* and proton density was performed in a motor activation functional MRI (fMRI) study using multi-echo, echo planar imaging (EPI) and NumART2* (Numerical Algorithm for Real time T2*). Comparisons between NumART2* and conventional single echo EPI with an echo time of 64 ms were performed for five healthy participants examined twice. Simulations were also performed to address specific issues associated with the two techniques, such as echo time-dependent signal variation. While the single echo contrast varied with the baseline T2* value, relative changes in T2* remained unaffected. Statistical analysis of the T2* maps yielded fMRI activation patterns with an improved statistical detection relative to conventional EPI but with less activated voxels, suggesting that NumART2* has superior spatial specificity. Two effects, inflow and dephasing, that may explain this finding were investigated. Particularly, a statistically significant increase in proton density was found in a brain area that was detected as activated by conventional EPI but not by NumART2* while no such changes were observed in brain areas that showed stimulus correlated signal changes on T2* maps.

Algorithms↗

PubMed2002

Kinetic compartment modeling of [11C]-5-hydroxy-L-tryptophan for positron emission tomography assessment of serotonin synthesis in human brain.

The substrate for the second enzymatic step in serotonin synthesis, 5-hydroxy-L-tryptophan, labeled in the beta-position ([11C]-HTP), was used for positron emission tomography (PET) measurements in six healthy human participants, examined on two occasions. One- and two-tissue kinetic compartment modeling of time-radioactivity curves was performed, using arterial, metabolite-corrected [11C]-HTP values as input function. The availability of unchanged tracer in arterial blood plasma was > or = 80% up to 60 minutes after injection, while [11C]-hydroxyindole acetic acid and [11C]-serotonin accounted for the remaining radioactivity, amounting to < or = 16% and < or = 4%, respectively. Compartment modeling was performed for brain stem, putamen, caudate nucleus, anterior cingulate, white matter, and superior occipital, occipitotemporal, and temporal cortices. The average biologic half-life for plasma-to-tissue equilibrium was 7 to 12 minutes, and the volume of distribution was 0.2 to 0.5 microL.mL(-1). In all regions except white matter, the kinetic compartment model that included irreversible [11C]-HTP trapping showed significantly improved model fits with respect to a one-tissue compartment model. The [11C]-HTP trapping rate constant depended on the estimated tissue availability of the serotonin precursor tryptophan, known to reflect serotonin synthesis in healthy individuals, and correlated with serotonin tissue concentration and synthesis rates reported previously in literature. These findings suggest the use of [11C]-HTP PET measurements to investigate serotonin synthesis.

5-Hydroxytryptophan↗