Benjamin Glaubitz

Impact of frequency drift on gamma-aminobutyric acid-edited MR spectroscopy

To investigate the quantitative impact of frequency drift on Gamma‐Aminobutyric acid (GABA+)‐edited MRS of the human brain at 3 Tesla (T).

Feeling safe in the plane: Neural mechanisms underlying superior action control in airplane pilot trainees—A combined EEG/MRS study

In day‐to‐day life, we need to apply strategies to cascade different actions for efficient unfolding of behavior. While deficits in action cascading are examined extensively, almost nothing is known about the neuronal mechanisms mediating superior performance above the normal level. To examine this question, we investigate action control in airplane pilot trainees. We use a stop‐change paradigm that is able to estimate the efficiency of action cascading on the basis of mathematical constraints. Behavioral and EEG data is analyzed along these constraints and integrated with neurochemical data obtained using Magnetic Resonance Spectroscopy (MRS) from the striatal gamma‐aminobutyric acid (GABA) ‐ergic system. We show that high performance in action cascading, as exemplified in airplane pilot trainees, can be driven by intensified attentional processes, circumventing response selection processes. The results indicate that the efficiency of action cascading and hence the speed of responding as well as attentional gating functions are modulated by striatal GABA and Glutamate + Glutamine concentrations. In superior performance in action cascading similar increases in the concentrations of GABA and Glutamate + Glutamine lead to stronger neurophysiological and behavioral effects as compared to subjects with normal performance in action cascading. Hum Brain Mapp 35:5040–5051, 2014.

Striatal GABA-MRS predicts response inhibition performance and its cortical electrophysiological correlates

AbstractResponse inhibition processes are important for performance monitoring and are mediated via a network constituted by different cortical areas and basal ganglia nuclei. At the basal ganglia level, striatal GABAergic medium spiny neurons are known to be important for response selection, but the importance of the striatal GABAergic system for response inhibition processes remains elusive. Using a novel combination of behavior al, EEG and magnetic resonance spectroscopy (MRS) data, we examine the relevance of the striatal GABAergic system for response inhibition processes. The study shows that striatal GABA levels modulate the efficacy of response inhibition processes. Higher striatal GABA levels were related to better response inhibition performance. We show that striatal GABA modulate specific subprocesses of response inhibition related to pre-motor inhibitory processes through the modulation of neuronal synchronization processes. To our knowledge, this is the first study providing direct evidence for the relevance of the striatal GABAergic system for response inhibition functions and their cortical electrophysiological correlates in humans.

Hippocampal activation during extinction learning predicts occurrence of the renewal effect in extinction recall.

The renewal effect describes the reoccurrence of a previously extinguished response in situations where the context of extinction differs from that of acquisition, thus illustrating the context-dependency of extinction learning. A number of studies on contextual fear extinction have implicated hippocampus and vmPFC in processing and retrieval of context both during extinction learning and recall of extinction. In this functional magnetic resonance imaging (fMRI) study we explored the neural correlates of the renewal effect in associative learning, using a predictive learning task that required participants to learn relations between cues and outcomes presented in particular contexts. During extinction in a novel context, compared to extinction in a context identical to the acquisition context, participants who exhibited the renewal effect (REN) showed increased activation in brain regions including bilateral posterior hippocampus and left parahippocampal gyrus. This activation pattern was absent in participants that did not show the renewal effect (NOREN). In direct comparisons between the groups, the REN group exhibited higher activation in bilateral hippocampus, while the NOREN group showed higher activation in left dlPFC (BA 46) and right anterior cingulate (BA 32). During extinction recall, stimuli that had been extinguished in a different context were again presented in the context of acquisition. Here both groups exhibited predominantly prefrontal activation, with the REN groups focus upon bilateral OFC (BA 47) and bilateral vmPFC (BA 10), while the NOREN group showed generally more widespread activation, predominantly in large clusters of dlPFC (BA 8,9,45). In a direct comparison, the REN group showed higher activation than the NOREN group in left vmPFC (BA 10), while NOREN participants exhibited more activation in dlPFC (BA 9, 46). Activation in left vmPFC during extinction recall correlated with the number of renewal effect responses, while the dlPFC activation showed a negative correlation with renewal effect responses. These results highlight the differential activation patterns of processes that will eventually produce or not produce a renewal effect, indicating that during extinction learning hippocampus encodes the relation between context and cue-outcome, while in extinction recall vmPFC is active to retrieve this association.

Development of magnetic moments in Fe1 − xNix-alloys

We have investigated the magnetic properties of Fe1−x Nix -alloys for 13 different compositions ranging from pure Fe to pure Ni. The alloy series was prepared as thin films by co-deposition of Fe and Ni via ultra-high vacuum magnetron sputtering and the concentrations were determined by energy dispersive x-ray fluorescence analysis (EDX). The averaged magnetization and magnetic moment were measured at room temperature using a superconducting quantum interference device (SQUID) magnetometer and a vibrating sample magnetometer (VSM). Making use of x-ray magnetic circular dichroism (XMCD), the individual magnetic moments of Fe and Ni across the alloy concentration range were analyzed; thus their spin and orbital contributions were extracted. The weighted sum of the individual moments agrees very well with the average moments determined via SQUID and VSM. The Ni moment steadily increases from the pure Ni towards to the pure Fe range, while the Fe moment scatters around a value of about 2.4 μB. Close to the invar composition of x = 0.35 we do not observe an anomaly of the magnetic moments, either of the individual moments or of the average moment. We also discuss different assumptions for the analysis of the XMCD spectra and assess the results in the light of recent theoretical predictions and literature values. (Some figures in this article are in colour only in the electronic version)

Resting BOLD fluctuations in the primary somatosensory cortex correlate with tactile acuity

Sensory perception, including 2-point discrimination (2 ptD), is tightly linked to cortical processing of tactile stimuli in primary somatosensory cortices. While the role of cortical activity in response to a tactile stimulus has been widely investigated, the role of baseline cortical activity is largely unknown. Using resting state fMRI we investigated the relationship between local BOLD fluctuations in the primary somatosensory cortex (the representational field of the hand) and 2 ptD of the corresponding index finger (right and left). Cortical activity was measured using fractional amplitudes of the low frequency BOLD fluctuations (fALFF) and synchronicity using regional homogeneity (ReHo) of the S1 hand region during rest. 2 ptD correlated with higher ReHo values in the representational areas of the contralateral S1 cortex (left hand: p = .028; right hand: p = .049). 2 ptD additionally correlated with higher fALFF in the representational area of the left hand (p = .007) and showed a trend for a significant correlation in the representational area of the right hand (p = .051). Thus, higher BOLD amplitudes and synchronicity at rest, as measures of cortical activity and synchronicity, respectively, are related to better tactile discrimination abilities of the contralateral hand. Our findings extend the relationship seen between spontaneous BOLD fluctuations and sensory perception.

Local GABA Concentration Predicts Perceptual Improvements After Repetitive Sensory Stimulation in Humans

Learning mechanisms are based on synaptic plasticity processes. Numerous studies on synaptic plasticity suggest that the regulation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) plays a central role maintaining the delicate balance of inhibition and excitation. However, in humans, a link between learning outcome and GABA levels has not been shown so far. Using magnetic resonance spectroscopy of GABA prior to and after repetitive tactile stimulation, we show here that baseline GABA+ levels predict changes in perceptual outcome. Although no net changes in GABA+ are observed, the GABA+ concentration prior to intervention explains almost 60% of the variance in learning outcome. Our data suggest that behavioral effects can be predicted by baseline GABA+ levels, which provide new insights into the role of inhibitory mechanisms during perceptual learning.

Noradrenergic stimulation modulates activation of extinction-related brain regions and enhances contextual extinction learning without affecting renewal

Renewal in extinction learning describes the recovery of an extinguished response if the extinction context differs from the context present during acquisition and recall. Attention may have a role in contextual modulation of behavior and contribute to the renewal effect, while noradrenaline (NA) is involved in attentional processing. In this functional magnetic resonance imaging (fMRI) study we investigated the role of the noradrenergic system for behavioral and brain activation correlates of contextual extinction and renewal, with a particular focus upon hippocampus and ventromedial prefrontal cortex (PFC), which have crucial roles in processing of renewal. Healthy human volunteers received a single dose of the NA reuptake inhibitor atomoxetine prior to extinction learning. During extinction of previously acquired cue-outcome associations, cues were presented in a novel context (ABA) or in the acquisition context (AAA). In recall, all cues were again presented in the acquisition context. Atomoxetine participants (ATO) showed significantly faster extinction compared to placebo (PLAC). However, atomoxetine did not affect renewal. Hippocampal activation was higher in ATO during extinction and recall, as was ventromedial PFC activation, except for ABA recall. Moreover, ATO showed stronger recruitment of insula, anterior cingulate, and dorsolateral/orbitofrontal PFC. Across groups, cingulate, hippocampus and vmPFC activity during ABA extinction correlated with recall performance, suggesting high relevance of these regions for processing the renewal effect. In summary, the noradrenergic system appears to be involved in the modification of established associations during extinction learning and thus has a role in behavioral flexibility. The assignment of an association to a context and the subsequent decision on an adequate response, however, presumably operate largely independently of noradrenergic mechanisms.

The DA antagonist tiapride impairs context-related extinction learning in a novel context without affecting renewal.

Renewal describes the recovery of an extinguished response if recall is tested in a context different from the extinction context. Behavioral studies demonstrated that attention to relevant context strengthens renewal. Neurotransmitters mediating attention and learning such as the dopaminergic (DA) system presumably modulate extinction learning and renewal. However, the role of DA for non-fear-based extinction learning and renewal in humans has not yet been investigated. This fMRI study investigated effects of DA-antagonism upon context-related extinction in a predictive learning task in which extinction occurred either in a novel (ABA) or an unchanged (AAA) context. The tiapride-treated group (TIA) showed significantly impaired ABA extinction learning and a significant within-group difference between ABA and AAA extinction, compared to placebo (PLAC). Groups did not differ in their level of ABA renewal. In ABA extinction, TIA showed reduced activation in dlPFC and OFC, hippocampus, and temporal regions. Across groups, activation in PFC and hippocampus correlated negatively with ABA extinction errors. Results suggest that in context-related extinction learning DA in PFC and hippocampus is involved in readjusting the cue-outcome relationship in the presence of a novel context. However, relating context to the appropriate association during recall does not appear to rely exclusively on DA signaling.

Structural changes in brain morphology induced by brief periods of repetitive sensory stimulation

ABSTRACT There is a growing interest in identifying the neural mechanisms by which the human brain allows for improving performance. Tactile perceptual measurements, e.g. two‐point discrimination (2ptD), can be used to investigate neural mechanisms of perception as well as perceptual improvement. Improvement can be induced in a practice‐independent manner, e.g. in the tactile domain through repetitive somatosensory stimulation (rSS). With respect to tactile perception, the role of cortical excitability and activation within the somatosensory cortex has been investigated extensively. However, the role of structural properties, such as regional gray matter (GM) volume, is unknown. Using high resolution imaging and voxel‐based morphometry (VBM), we sought to investigate how regional GM volume relates to individual 2ptD performance. Furthermore, we wanted to determine if electrical rSS has an influence on regional GM volume. 2ptD thresholds of the index fingers were assessed bilaterally. High‐resolution (1 mm3), T1‐weighted images were obtained using a 3T scanner pre‐and post‐stimulation. RSS was applied for 45 min to the dominant right hand, specifically to the fingertips of all fingers. At baseline, performance in the 2ptD task was associated with regional GM volume in the thalamus, primary somatosensory cortex, and primary visual cortex (negative association). After 45 min of rSS, we observed an improvement in 2ptD of the stimulated hand, whereas no improvement in tactile performance was seen on the non‐stimulated side. These perceptual changes were accompanied by an increase in GM volume in the left somatosensory cortex and the degree of improvement correlated with GM volume changes in the insular cortex. Our results show that structural changes in the brain, specifically in regions receiving afferent input from the stimulated body site can be induced via a short‐term intervention lasting only 45 min. However, the neurobiological correlates of these changes and the dynamics need to be further elucidated. HighlightsPerformance in a two‐point discrimination task was associated with regional gray matter volume in the primary somatosensory cortex.After 45 min of repetitive sensory stimulation two‐point discrimination thresholds of the stimulated hand decreased, whereas no improvement of tactile performance was seen on the non‐stimulated side.Perceptual changes were accompanied by an increase in gray matter volume in the left secondary, and to a lesser degree, in the primary somatosensory cortex.