Biomedical subjects

Henning Boecker

Publications and source records attributed to Henning Boecker.

9 recordsLinked to original sources

PubMed2006

Vowel sound extraction in anterior superior temporal cortex.

We investigated the functional neuroanatomy of vowel processing. We compared attentive auditory perception of natural German vowels to perception of nonspeech band-passed noise stimuli using functional magnetic resonance imaging (fMRI). More specifically, the mapping in auditory cortex of first and second formants was considered, which spectrally characterize vowels and are linked closely to phonological features. Multiple exemplars of natural German vowels were presented in sequences alternating either mainly along the first formant (e.g., [u]-[o], [i]-[e]) or along the second formant (e.g., [u]-[i], [o]-[e]). In fixed-effects and random-effects analyses, vowel sequences elicited more activation than did nonspeech noise in the anterior superior temporal cortex (aST) bilaterally. Partial segregation of different vowel categories was observed within the activated regions, suggestive of a speech sound mapping across the cortical surface. Our results add to the growing evidence that speech sounds, as one of the behaviorally most relevant classes of auditory objects, are analyzed and categorized in aST. These findings also support the notion of an auditory "what" stream, with highly object-specialized areas anterior to primary auditory cortex.

Acoustic Stimulation↗

PubMed2005

Frequency-correlated decreases of motor cortex activity associated with subthalamic nucleus stimulation in Parkinson's disease.

According to the classical model of basal ganglia organization, deep brain stimulation (DBS) in the subthalamic nucleus (STN) for the treatment of Parkinson's disease (PD) blocks overactive excitatory projections to inhibitory basal ganglia output structures. This would release the break on thalamofrontal neurons alleviating the poverty of movement, the hallmark of PD. Such parallels to a functional lesion certainly simplify the mechanism of STN DBS. Here, we applied parametric analyses of H2(15)O positron emission tomography (PET) scans at rest while systematically varying stimulation frequency in 6 patients with STN DBS for akinetic PD. A strong positive correlation of rCBF to increasing stimulation frequency was detected around the STN bilaterally. More importantly, we show that gradual increases in STN stimulation frequency are tightly correlated with decreases in motor cortex activity. This demonstrates an active modulation of resting activity within the subcortical stimulation target and within motor cortex by STN DBS. Rather than a possible downstream effect, we propose to consider the tight correlations between DBS frequency and motor cortex activity in the context of an upstream modulation of direct efferents to the STN from primary motor and premotor cortices.

Aged↗

PubMed2005

COMT Val108/158Met genotype affects the mu-opioid receptor system in the human brain: evidence from ligand-binding, G-protein activation and preproenkephalin mRNA expression.

Recent data from [(11)C]carfentanil ligand-PET indicate that in the human brain, the availability of mu-opioid (MOP) receptor binding sites is affected by the Val(108/158)Met polymorphism of the catechol-O-methyltransferase (COMT) gene. This prompted us to validate the impact of COMT Val(108/158)Met on MOP receptors in human post-mortem brain. [(3)H]DAMGO receptor autoradiography was performed in frontal cortex, basal ganglia, thalamus and cerebellum (8 Met/Met, 6 Met/Val, 3 Val/Val). With respect to genotype, numbers of MOP binding sites in COMT Met(108/158) homozygous and Val(108/158)Met heterozygous cases were higher than in Val(108/158) homozygous. Differences were significant in the caudate nucleus (Val/Met vs. Val/Val), nucleus accumbens (Val/Met vs. Val/Val) and the mediodorsal nucleus of the thalamus (Met/Met vs. Val/Val). In the thalamus, this was corroborated by DAMGO-stimulated [(35)S]GTPgammaS autoradiography. Moreover, stepwise multiple regression taking into account various covariables allowed to confirm the COMT genotype as the most predictive factor in this structure. As a mechanism how COMT might exert its action on MOP receptors, it has been suggested that at least in striatopallidal circuits COMT Val(108/158)Met impacts on enkephalin, which is capable of reciprocally regulating MOP receptor expression. Thus, we assessed preproenkephalin mRNA by in situ hybridization. In the striatum, mRNA levels were significantly higher in COMT Met(108/158) homozygous cases indicating that MOP binding sites and enkephalin are regulated in parallel. Moreover, the transcript was not detectable in the thalamus. Thus, mechanisms other than an enkephalin-dependent receptor turnover must be responsible for COMT-related differences in MOP binding site availability in the human brain.

Adult↗

PubMed2005

Left inferior parietal dominance in gesture imitation: an fMRI study.

The inability to imitate gestures is an essential feature of apraxia. However, discrepancies exist between clinical studies in apraxic patients and neuroimaging findings on imitation. We therefore aimed to investigate: (1) which areas are recruited during imitation under conditions similar to clinical tests for apraxic deficits; (2) whether there are common lateralized areas subserving imitation irrespective of the acting limb side; and also (3) whether there are differences between hand and finger gestures. We used fMRI in 12 healthy, right handed subjects to investigate the imitation of four types of variable gestures that were presented by video clips (16 different finger and 16 different hand gestures with either the right or the left arm). The respective control conditions consisted of stereotyped gestures (only two gestures presented in pseudorandom order). Subtraction analysis of each type of gesture imitation (variable>stereotyped) revealed a bilateral activation pattern including the inferior parietal cortex Brodmann Area (BA 40), the superior parietal cortex, the inferior frontal cortex (opercular region), the prefrontal motor cortex, the lateral occipito-temporal junction, and the cerebellum. These results were supported by statistical conjunction of all four subtraction analyses and by the common analysis of all four types of gesture imitation. The direct comparison of the right and left hemispheric activation revealed a lateralization to the left only of the inferior parietal cortex. Comparisons between different types of gesture imitation yielded no significant results. In conclusion, gesture imitation recruits bilateral fronto-parietal regions, with significant lateralization of only one area, namely the left inferior parietal cortex. These in vivo data indicate left inferior parietal dominance for gesture imitation in right handers, confirming lesion-based theories of apraxia.

Adult↗

PubMed2005

What to learn from in vivo opioidergic brain imaging?

Ligand-PET studies are attracting increasing interest in experimental and clinical research. As the most elaborated of PET techniques, ligand-PET allows the demonstration of receptor distributions, and thus, the delineation of neurochemical pathologies in the disease state. Recent developments are promising that ligand-PET will even allow to characterize dynamic and short-term changes in neurotransmission and will tremendously add to the understanding of neurophysiology on the receptor level. In pain studies, mainly the mu-opioidergic agonist [(11)C]-carfentanil and the unspecific opioid receptor antagonist [(11)C]-diprenorphine are applied. Utilizing these ligands the thalamus, prefrontal and cingulate cortex, basal ganglia and midbrain structures have been shown to possess high amounts of opioidergic receptors in vivo and it is well accepted, that the receptor density is higher in projections of the medial than those of the lateral pain system. Changes in receptor availability were observed in patients suffering from chronic pain. Rheumatoid arthritis, trigeminal neuralgia and central poststroke pain (CPSP) all lead to decreased ligand binding in pain processing regions during the painful period in comparison to pain free intervals or healthy subjects. These decreases may either be the consequence of increased endogenous release or indicate receptor internalization/down-regulation or loss of neurons carrying these receptors. Recent studies also evidenced [(11)C]-carfentanil binding changes due to acute experimental pain. One possible interpretation of these changes is that the PET-ligand might be displaced by endogenous opioidergic ligands. One major region, where this "ligand displacement" was observed, was the thalamus. These findings highlight the importance of the opioidergic system in pain processing and the power of ligand-PET to advance the understanding of pain.

Analgesics, Opioid↗

PubMed2004

Quantification of [18F]diprenorphine kinetics in the human brain with compartmental and non-compartmental modeling approaches.

6-O-(2-[(18)F]fluoroethyl)-6-O-desmethyldiprenorphine ([(18)F]FDPN) is a nonselective opiate ligand that binds to postsynaptic micro, kappa and delta opiate receptors. Due to the longer half-life of F-18, compared to C-11, labeling DPN with F-18 allows for alternative experimental protocols and potentially the evaluation of endogenous opioid release. The applicability of this compound to assorted experimental protocols motivated the evaluation of [(18)F]FDPN kinetics with compartmental and non-compartmental models. The results indicate that a two-tissue compartmental model best characterizes the data obtained following a bolus injection of [(18)F]FDPN (120-min scanning protocol). Estimates of distribution volume (DV) were robust, being highly correlated for the one-tissue compartmental model as well as the invasive Logan model and the basis function method. Furthermore, the DV estimates were also stable under a shortened protocol of 60 min, showing a significant correlation with the full protocol. The binding potential (BP) values showed more variability between methods and in some cases were more sensitive to protocol length. In conclusion, this evaluation of [(18)F]FDPN kinetics illustrates that DV values can be estimated robustly using compartmental modeling, the basis function method or the invasive Logan modeling approach on a volume of interest level. BP values were also found to correlate with DV values; however, these results should be interpreted with the understanding that specific binding in the reference region (occipital region) may exist.

Adult↗

PubMed2004

Distraction modulates connectivity of the cingulo-frontal cortex and the midbrain during pain--an fMRI analysis.

Neuroimaging studies with positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have delineated a human pain network in vivo. Despite the recognition of cerebral structures engaged in pain transmission, the cerebral mechanisms involved in pain modulation are still not well understood. Here, we investigated healthy volunteers using fMRI during experimental heat pain and distraction induced by a visual incongruent color-word Stroop task. A factorial design permitted categorical and covariation analysis of four conditions, namely innocuous and noxious heat; with and without distraction. Pain without distraction evoked an activation pattern similar to that observed in previous neuroimaging pain studies. Distraction was associated with a significant reduction of the visual analogue scale (VAS) ratings for pain intensity and unpleasantness and a reduction of pain-related activation in multiple brain areas, particularly in the so-called 'medial pain system'. Distraction significantly increased the activation of the cingulo-frontal cortex including the orbitofrontal and perigenual anterior cingulate cortex (ACC), as well as the periaquaeductal gray (PAG) and the posterior thalamus. Covariation analysis revealed functional interaction between these structures during pain stimulation and distraction, but not during pain stimulation per se. According to our results, the cingulo-frontal cortex may exert top-down influences on the PAG and posterior thalamus to gate pain modulation during distraction.

Adult↗

PubMed2003

Subthalamic nucleus stimulation affects a frontotemporal network: a PET study.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an effective strategy in the treatment of motor symptoms in advanced Parkinson's disease. However, clinical studies have shown that DBS can affect verbal fluency. Seven Parkinson's disease patients with bilateral DBS of the STN were studied with positron emission tomography (PET) to investigate the effects of STN stimulation on regional cerebral blood flow during a verbal fluency task. Activation of the right orbitofrontal cortex and verbal fluency-associated activation within a left-sided frontotemporal network were decreased during STN stimulation compared with the OFF state. Our results offer an explanation for the commonest neuropsychological side effect of STN stimulation and show that STN stimulation affects a frontotemporal network during a fluency task.

Aged↗

PubMed2002

The role of lateral premotor-cerebellar-parietal circuits in motor sequence control: a parametric fMRI study.

Functional characterisation of higher order motor systems can be obtained by modulating the processing demands imposed onto relevant motor circuitries. Here we performed whole-brain functional magnetic resonance imaging (fMRI) and parametric statistical analyses in eight healthy volunteers to study task-related recruitment of motor circuits associated with unilateral finger movement sequences of increasing length and complexity, but with equal basic motor parameters. Statistical parametric mapping software was applied for analysis. Categorical analysis of the main effect of motor action showed cerebral activation in the established cortical and subcortical motor network. Parametric analyses of the blood-oxygen-level-dependent (BOLD) contrast revealed significant signal increases correlating to sequence length and complexity in a subset of activated areas, notably contralateral ventral and dorsal premotor cortex, bilateral superior parietal cortex, left inferior frontal gyrus/Broca's area, right dentate nucleus, and left visual association cortex. These data underscore the importance of ventral premotor-cerebellar-parietal circuits in processing length and complexity of sequential finger movements.

Adult↗