Biomedical subjects

Michael Erb

Publications and source records attributed to Michael Erb.

51 records · Page 3Linked to original sources

PubMed2003

Comparison of longitudinal metabolite relaxation times in different regions of the human brain at 1.5 and 3 Tesla.

In vivo longitudinal relaxation times of N-acetyl compounds (NA), choline-containing substances (Cho), creatine (Cr), myo-inositol (mI), and tissue water were measured at 1.5 and 3 T using a point-resolved spectroscopy (PRESS) sequence with short echo time (TE). T(1) values were determined in six different brain regions: the occipital gray matter (GM), occipital white matter (WM), motor cortex, frontoparietal WM, thalamus, and cerebellum. The T(1) relaxation times of water protons were 26-38% longer at 3 T than at 1.5 T. Significantly longer metabolite T(1) values at 3 T (11-36%) were found for NA, Cho, and Cr in the motor cortex, frontoparietal WM, and thalamus. The amounts of GM, WM, and cerebrospinal fluid (CSF) within the voxel were determined by segmentation of a 3D image data set. No influence of tissue composition on metabolite T(1) values was found, while the longitudinal relaxation times of water protons were strongly correlated with the relative GM content.

Adult↗

PubMed2003

Successful episodic memory retrieval of newly learned faces activates a left fronto-parietal network.

It is easier to recognize a familiar face than a newly learned face. The neural basis of familiar face recognition has been elucidated in functional imaging and lesion studies. Behavioural and neuropsychological data indicate, however, that brain systems involved in episodic retrieval of familiar and newly learned faces are distinct. In our study, 12 subjects viewed 30 novel faces in an encoding session. In the study condition, event-related functional magnetic resonance imaging (fMRI) was used to compare brain activation during correct recognition of the recently learned faces to that observed during correct rejection of unknown control faces. Differences were present in the left inferior parietal (BA 40) and left medial frontal/anterior cingulate (BA 32/9) cortex. These two regions may be part of a pathway in the dorsal visual stream, responsible for a "feeling of familiarity" in contrast to the ventral pathway in the temporal lobes, which is mainly involved in the recognition of personal identity.

Adult↗

PubMed2003

The neural correlates of perceiving one's own movements.

Feedforward mechanisms are important for movement control. They may also contribute to the identification of self-produced actions by attenuating the sensory consequences of self-produced movements. In our study, subjects opened and closed their hand slowly and continuously (0.5 Hz). This movement was filmed with an MRI compatible video camera and projected online onto a screen, viewed by the subject while BOLD contrast was measured with fMRI. The temporal delay between movement and feedback was parametrically varied (0-200 ms). In each trial, subjects judged whether there was a delay or not. There was a positive correlation between the extent of the temporal delay and activation in the right posterior superior temporal cortex (pSTS) and a negative correlation in the left putamen. A second analysis addressed the neural correlates of subjective judgement under conditions of uncertainty. This contrast showed a differential activation in the cerebellum. These results support the assumption of a forward model implying that predictions generated in motor areas attenuate sensory areas. They also suggest that efference copy mechanisms are not located within specific brain areas but are implemented as a specific form of interaction between perceptual and motor areas depending on the modalities and the type of actions involved. Further, conscious detection of small temporal deviations might be based on signals generated in the cerebellum which provide fine-grained temporal information. These results might be useful to refine theories about the role of forward mechanisms in the emergence of disorders of the self, such as in schizophrenia.

Adult↗

PubMed2003

Observing one's hand become anarchic: an fMRI study of action identification.

The self seems to be a unitary entity remaining stable across time. Nevertheless, current theorizing conceptualizes the self as a number of interacting sub-systems involving perception, intention and action (self-model). One important function of such a self-model is to distinguish between events occurring as a result of one's own actions and events occurring as the result of somebody else's actions. We conducted an fMRI experiment that compared brain activation after an abrupt mismatch between one's own movement and its visual consequences with an abrupt mismatch between one's own movement and somebody else's visually perceived hand movement. A right fronto-parietal network was selectively active during a sudden mismatch between one's own observed and performed hand action.

Awareness↗

PubMed2003

Physiological self-regulation of regional brain activity using real-time functional magnetic resonance imaging (fMRI): methodology and exemplary data.

A brain-computer interface (BCI) based on real-time functional magnetic resonance imaging (fMRI) is presented which allows human subjects to observe and control changes of their own blood oxygen level-dependent (BOLD) response. This BCI performs data preprocessing (including linear trend removal, 3D motion correction) and statistical analysis on-line. Local BOLD signals are continuously fed back to the subject in the magnetic resonance scanner with a delay of less than 2 s from image acquisition. The mean signal of a region of interest is plotted as a time-series superimposed on color-coded stripes which indicate the task, i.e., to increase or decrease the BOLD signal. We exemplify the presented BCI with one volunteer intending to control the signal of the rostral-ventral and dorsal part of the anterior cingulate cortex (ACC). The subject achieved significant changes of local BOLD responses as revealed by region of interest analysis and statistical parametric maps. The percent signal change increased across fMRI-feedback sessions suggesting a learning effect with training. This methodology of fMRI-feedback can assess voluntary control of circumscribed brain areas. As a further extension, behavioral effects of local self-regulation become accessible as a new field of research.

Adult↗

PubMed2003

From will to action: sequential cerebellar contributions to voluntary movement.

The cerebellum is known to be involved in numerous motor related functions, but recent observations suggest that it also performs fundamental operations on nonmotor functions such as perception and cognition. Assuming that the cerebellum has to be consulted in a limited window of time, cerebellar activation should occur in a time-dependent manner in respect to the corresponding telencephalic areas. This hypothesis was tested by combining a simple motor task with the demand of a self-paced delay using event-related functional magnetic resonance imaging. Evaluation with a time-shifted canonical hemodynamic response function revealed spatially and temporally separated cerebral and cerebellar activation accompanying the entire process--from conscious planning to final motor output--within a time frame of 6 s. The cerebral activations spread from the anterior cingulate cortex through the supplementary motor and premotor area to the primary motor and sensory cortices. This cascade was temporally in parallel with cerebellar activations propagating from the neo- to the spinocerebellum. An early lateral cerebellar recruitment 3 s prior movement onset confirms its involvement in cognitive processing. A later medial activation occurring close to movement onset most probably reflects spinocerebellar kinesthetic feedback. Between these two points a striking lateromedial succession was found, which is in line with the hypothesis of the existence of multiple internal models residing in the cerebellum, each communicating with its own corresponding telencephalic region.

Adult↗

PubMed2003

Representation of the perceived 3-D object shape in the human lateral occipital complex.

We used human functional magnetic resonance imaging (fMRI) to test whether the human lateral occipital complex (LOC), an area known to be involved in the analysis of visual shape, represents the perceived 3-D shape of objects or simply their 2-D contours. We employed an fMRI adaptation paradigm, in which repeated presentation of a stimulus results in decreased responses compared to responses to different stimuli. We found adaptation in the LOC for images of objects with the same perceived 3-D shape structure but different 2-D contours that resulted from small rotations of the objects in the frontal plane or in depth. However, no adaptation was observed in the LOC for images of objects that had the same 2-D contours but differed in their perceived 3-D shape; namely, 2-D silhouettes versus 3-D shaded images of objects, or convex versus concave objects. Differences in the fMRI adaptation responses across subregions in the LOC suggest that different neural populations in the LOC may mediate different mechanisms for the processing of object features.

Depth Perception↗

PubMed2003

Relation between regional functional MRI activation and vascular reactivity to carbon dioxide during normal aging.

Recent blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging studies have shown a reduction of cerebral activation during aging, which may be associated with age-related changes of the cerebral vascular system. The authors used a global hypercapnic breath-holding challenge to define nonneuronal contributions to a significantly reduced activation in the primary sensorimotor cortex during finger tapping in a group of old (n = 6; mean age 65 years) compared with a group of young (n = 6; mean age 27 years) subjects. Within significantly activated voxels in both groups during finger tapping, the mean BOLD signal amplitudes were significantly smaller in the group of older subjects for both tasks. In those voxels showing significant activation only in young subjects during finger tapping, the response to hypercapnia was also greatly diminished in older subjects. The attenuated hypercapnic BOLD signal response in older subjects within this region suggests that age-dependent changes of the cerebral vasculature may alter the neuronal-vascular coupling. In older subjects, cerebral vessels may not react as effectively in response to a vasodilating stimulus, which will lead to differences in the number of voxels that pass a criterion threshold despite similar neuronal activation.

Adult↗

PubMed2002

Brain circuits involved in emotional learning in antisocial behavior and social phobia in humans.

While psychopaths (PP) lack anticipatory fear, social phobics (SP) are characterized by excessive fear. Criminal PP, SP and healthy controls (HC) participated in differential aversive delay conditioning with neutral faces as conditioned (CS) and painful pressure as unconditioned stimuli. Functional magnetic resonance imaging revealed differential activation in the limbic-prefrontal circuit (orbitofrontal cortex, insula, anterior cingulate, amygdala) in the HC. By contrast, the PP displayed brief amygdala, but no further brain activation. The SP showed increased activity to the faces in the amygdala and orbitofrontal cortex already during habituation. Thus, a hypoactive frontolimbic circuit may represent the neural correlate of psychopathic behavior, whereas an overactive frontolimbic system may underly social fear.

Adult↗

PubMed2002

Intracranial oscillations of cerebrospinal fluid and blood flows: analysis with magnetic resonance imaging.

PURPOSE: To detect oscillations of the cerebrospinal fluid (CSF) flow related to the heartbeat and frequencies lower than 0.6 Hz and to compare these oscillations of CSF and blood flow in cerebral vessels by using echo planar imaging in real time mode. The existence of such waves has been well known but has not yet been shown by MRI. MATERIALS AND METHODS: In a slice perpendicular to the aqueduct, CSF flow as well as CBF, could be determined in sagittal sinus, basilar artery, and capillary vessels. After Fourier analysis, four frequency bands were assigned. RESULTS: In the very high-frequency (heart rate) range, the integrals under the CSF curves were more closely related to arterial CBF than to changes in the sinus. Also, in the high-frequency (respiration rate), low-frequency (0.05-0.15 Hz), and very-low-frequency (0.008-0.05 Hz) ranges, the integrals under the CSF curves corresponded with arterial and capillary CBF. CONCLUSION: Slow and fast oscillations in CSF flow are detectable in healthy persons with a proportional allotment to arterial and capillary CBF.

Adolescent↗

PubMed2002

Proton magnetic resonance spectroscopy with metabolite nulling reveals regional differences of macromolecules in normal human brain.

PURPOSE: To quantify the macromolecular content in different anatomic brain regions and to evaluate an age dependency of the macromolecular concentrations. MATERIAL AND METHODS: A short echo time Stimulated Echo Acquisition Mode (STEAM) sequence was used without and with inversion recovery metabolite nulling in 8-12 healthy volunteers. Quantitation was achieved by an extended LCModel, and macromolecular resonances at 0.9, 1.4, 2.1, and 3.0 ppm were evaluated. RESULTS: In the cerebellum, the 1.4, 2.1, and 3.0 ppm resonances were highest compared to all other regions (P < 0.02); the 0.9 ppm resonance was significantly higher than that of pons (P < 0.01). In the motor cortex, the 0.9, 1.4, and 2.1 ppm resonances were higher than those of white matter and pons (P < 0.02). Pons and white matter did not differ significantly from each other. A significant correlation of the macromolecular concentrations with the age could not be found. CONCLUSION: There were higher macromolecular concentrations in the cerebellum and motor cortex than in pons or white matter. These were probably due to the higher portions of gray matter in these volumes of interest (VOIs) than in the other regions.

Adult↗

PubMed2002

Right-hemispheric organization of language following early left-sided brain lesions: functional MRI topography.

Left-hemispheric (LH) brain lesions acquired early in life can induce language organization in the undamaged right hemisphere (RH). This study addresses the anatomical correlates of language processing in the RH of such individuals. Five hemiparetic patients with left periventricular brain lesions of pre- and perinatal origin were included, in whom fMRI during a word generation task had yielded predominantly RH activation; five age- and sex-matched healthy right-handers served as controls. The patterns of activation in the RH of patients showed a striking similarity with the LH patterns of the normal controls, and voxel-wise comparison failed to detect significant differences. This demonstrates that in patients with early LH damage, RH recruitment for language occurs in brain areas homotopic to the LH regions involved in language processing under normal circumstances.

Adult↗

PubMed2002

Object-selective responses in the human motion area MT/MST.

The perception of moving objects and our successful interaction with them entail that the visual system integrates shape and motion information about objects. However, neuroimaging studies have implicated different human brain regions in the analysis of visual motion (medial temporal cortex; MT/MST) and shape (lateral occipital complex; LOC), consistent with traditional approaches in visual processing that attribute shape and motion processing to anatomically and functionally separable neural mechanisms. Here we demonstrate object-selective fMRI responses (higher responses for intact than for scrambled images of objects) in MT/MST, and especially in a ventral subregion of MT/MST, suggesting that human brain regions involved mainly in the processing of visual motion are also engaged in the analysis of object shape.

Brain Mapping↗

PubMed2002

Two types of ipsilateral reorganization in congenital hemiparesis: a TMS and fMRI study.

Reorganization after early brain injuries is not only determined by the maturational stage of the CNS at the time of the insult (timing), but also by the structural properties, location and extent of the lesion. This study addresses the impact of different lesion extents on the type of reorganization induced in a cohort of patients with lesions of uniform structure and location (unilateral periventricular defects) and similar timing (early third trimester of pregnancy). Twelve young adult patients with congenital hemiparesis and 10 age-matched controls were studied. The severity of structural damage to hand motor projections of the cortico-spinal tract was assessed on semi-coronal MRI reconstructions along anatomical landmarks of cortico-spinal tract somatotopy. The functional integrity of these crossed cortico-spinal projections in the affected hemisphere, as well as the presence of any abnormal ipsilateral projections to the paretic hand, was examined by transcranial magnetic stimulation (TMS). Cortical activation during simple voluntary hand movements was studied by functional MRI (fMRI). Patients with small lesions (SL; n = 4) and only mild hand motor impairment possessed intact crossed cortico-spinal projections to the paretic hand, whereas no motor response could be elicited by TMS of the affected hemisphere in those with large lesions (LL; n = 6) and more severe hand motor impairment. Evidence for compensatory recruitment of the unaffected hemisphere was found in both subgroups. In the SL group, fMRI demonstrated ipsilateral activation of premotor areas, without any abnormal projections to the paretic hand originating from these sites. In the LL group, such abnormal ipsilateral projections to the paretic hand were indeed found, and fMRI confirmed cortical activation of an abnormal ipsilateral hand motor representation in the primary sensorimotor region of the unaffected hemisphere. Two patients with intermediate-sized lesions presented combined features of both groups (SL, LL). In conclusion, this study provides evidence that the type of cortico-spinal reorganization depends on the extent of the brain lesion. We propose that involvement of the ipsilateral hemisphere can be (i) of the premotor type, i.e. without ipsilateral motor projections but with significant activation of ipsilateral premotor areas, or (ii) of the primary motor type, i.e. with abnormal ipsilateral cortico-spinal projections to the paretic hand.

Adolescent↗

PubMedDate not supplied

B-waves in cerebral and spinal cerebrospinal fluid pulsation measurement by magnetic resonance imaging.

OBJECTIVE: Noninvasive measurement of B-waves is possible by magnetic resonance (MR) imaging using echo planar imaging (EPI) sequences. In this study, the proportion of B-waves in the cerebrospinal fluid (CSF) of the spinal canal and in the aqueductus cerebri was evaluated under normal and pathologic conditions, respectively. The proportion of the influence of pulse and respiration on the CSF pulsations was estimated. METHODS: The spinal CSF was evaluated in 7 volunteers at 5 spinal levels (C1, C2/3, C 6/7, T5, and T12). Examination of the CSF frequencies at the aqueduct was performed in 14 volunteers, 10 patients with normal pressure hydrocephalus, and 5 patients with an aqueductal stenosis. An EPI sequence was applied at 1.5 T. During the 8-minute measurement time, pulse and respiration were coregistered. A MATLAB routine analyzed the spectral portion of the B-waves and the pulse- and respiration-dependent frequencies of the CSF. RESULTS: The amount of B-waves was small in cerebral (2.5%) and spinal measurements (3.4%) but significantly higher in the spinal CSF (P < 0.001). There was no statistically different amount of B-waves in the aqueduct for volunteers and hydrocephalic patients and between the different spinal levels in healthy volunteers. Spinal measurements revealed a rising portion of respiration-related frequencies from C1 to T12, whereas the portion of pulse-related frequencies declined. CONCLUSIONS: The data support that B-waves are a physiologic phenomenon. They can be delineated in the spinal and cerebral CSF. A higher amount of spinal B-waves reflects a stronger venous and respiratory influence.

Adult↗