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H Boecker

Publications and source records attributed to H Boecker.

At least 19 recordsLinked to original sources
PubMed2003

Differential modulation of subcortical target and cortex during deep brain stimulation.

The combination of electrical deep brain stimulation (DBS) with functional imaging offers a unique model for tracing brain circuitry and for testing the modulatory potential of electrical stimulation on a neuronal network in vivo. We therefore applied parametric positron emission tomography (PET) analyses that allow characterization of rCBF responses as linear and nonlinear functions of the experimentally modulated stimulus (variable stimulator setting). In patients with electrodes in the thalamic ventrointermediate nucleus (VIM) for the treatment of essential tremor (ET) here we show that variations in voltage and frequency of thalamic stimulation have differential effects in a thalamo-cortical circuitry. Increasing stimulation amplitude was associated with a linear raise in rCBF at the thalamic stimulation site, but with a nonlinear rCBF response in the primary sensorimotor cortex (M1/S1). The reverse pattern in rCBF changes was observed with increasing stimulation frequency. These results indicate close connectivity between the stimulated nucleus (VIM) and primary sensorimotor cortex. Likewise, stimulation parameter-specific modulation occurs at this simple interface between an electrical and a cerebral system and suggests that the scope of DBS extends beyond an ablation-like on-off effect: DBS could rather allow a gradual tuning of activity within a neuronal circuit.

Aged↗
PubMed2002

Subthalamic nucleus stimulation affects striato-anterior cingulate cortex circuit in a response conflict task: a PET study.

The subthalamic nucleus (STN) has generally been considered as a relay station within frontal-subcortical motor control circuitry. Little is known about the influence of the STN on cognitive networks. Clinical observations and studies in animals suggest that the STN participates in non-motor functions which can now be probed in Parkinson's disease patients with deep brain stimulation of the STN, allowing selective and reversible modulation of this nucleus. Using PET, we studied changes in regional cerebral blood flow (rCBF) associated with a response conflict task (Stroop task) in Parkinson's disease patients ON and OFF bilateral STN stimulation. The Stroop task requires subjects to name the font colour of colour words (e.g. "blue") printed in an incongruent colour ink (e.g. yellow). During STN stimulation, impaired task performance (prolonged reaction times) was associated with decreased activation in both right anterior cingulate cortex (ACC) and right ventral striatum. Concomitant increased activation in left angular gyrus indicative of ongoing word processing during stimulation is consistent with an impairment to inhibit habitual responses. ACC and ventral striatum are part of the ACC circuit associated with response conflict tasks. The decreased activation during STN stimulation in the ACC circuit, while response conflict processing worsened, provides direct evidence of STN modulating non-motor basal ganglia-thalamocortical circuitry. Impairment in ACC circuit function could account for the subtle negative effects on cognition induced by STN stimulation.

Adult↗
PubMed2002

A H(2)(15)O positron emission tomography study on mental imagery of movement sequences--the effect of modulating sequence length and direction.

Motor imagery is a state of mental rehearsal of single movements or movement patterns and has been shown to recruit motor networks overlapping with those activated during movement execution. We wished to examine whether the brain areas subserving control of sequential processes could be delineated by pure mental imagery, their activation levels reflecting the processing demands of a sequential task. We studied six right-handed volunteers (39.0 +/- 14 years) with H(2)(15)O positron emission tomography (PET) while they continuously mentally pursued with their right hand one of five sequences differing in complexity (i.e., increases in sequence length, single-finger repetitions, and reversals). Conditions were repeated twice, alternating with two rest scans. Each imagined single motor element was paced at a frequency of 1 Hz. Significant activation increases (P < 0.05, corrected) associated with imagination of right finger movement sequences (conditions I to V combined)--compared to the rest condition--were observed in left sensorimotor cortex (M1/S1) and the adjacent inferior parietal cortex. Further activation increases (P < 0.001, uncorrected) occurred in bilateral dorsal premotor (PMd) cortex, left caudal supplementary motor area, bilateral ventral premotor cortex, right M1, left superior parietal cortex, left putamen, and right cerebellum. Activation decreases occurred in bilateral prefrontal and right temporo-occipital cortex. Activation increases that correlated with sequence complexity were observed only in specific areas of the activated network, notably in left PMd, right superior parietal cortex, and right cerebellar vermis (P < 0.05, corrected). In conclusion, our study, by varying the sequence structure of imagined finger movements, identified task-related activity changes in parietopremotor-cerebellar structures, reflecting their role in mediating sequence control.

Adult↗
PubMed2001

Thalamic stimulation for essential tremor activates motor and deactivates vestibular cortex.

BACKGROUND: The functional effects of deep brain stimulation in the nucleus ventralis intermedius (VIM) of the thalamus on brain circuitry are not well understood. The connectivity of the VIM has so far not been studied functionally. It was hypothesized that VIM stimulation would exert an effect primarily on VIM projection areas, namely motor and parietoinsular vestibular cortex. METHODS: Six patients with essential tremor who had electrodes implanted in the VIM were studied with PET. Regional cerebral blood flow was measured during three experimental conditions: with 130 Hz (effective) and 50 Hz (ineffective) stimulation, and without stimulation. RESULTS: Effective stimulation was associated with regional cerebral blood flow increases in motor cortex ipsilateral to the side of stimulation. Right retroinsular (parietoinsular vestibular) cortex showed regional cerebral blood flow decreases with stimulation. CONCLUSIONS: Beneficial effects of VIM stimulation in essential tremor are associated with increased synaptic activity in motor cortex, possibly due to nonphysiologic activation of thalamofrontal projections or frequency-dependent neuroinhibition. Retroinsular regional cerebral blood flow decreases suggest an interaction of VIM stimulation on vestibular-thalamic-cortical projections that may explain dysequilibrium, a common and reversible stimulation-associated side effect.

Adult↗
PubMed2001

Motor imagery in normal subjects and Parkinson's disease patients: an H215O PET study.

Motor imagery paradigms can be used to investigate motor preparation. We used positron emission tomography to compare regional cerebral blood flow (rCBF) in patients with Parkinson's disease and normal controls under three conditions: rest, motor imagery and motor execution. In controls, imagery activated bilateral dorsolateral and mesial frontal cortex, inferior parietal cortex and precuneus. Motor execution additionally activated primary motor cortex (p < 0.001). Between-group, for imagery there was relative reduction in dorsolateral and mesial frontal activation in the patient group (p<0.01). For execution, there was impaired activation of right dorsolateral frontal cortex and basal ganglia (p<0.01). Our results support the notion that underfunctioning of mesial frontal and dorsolateral prefrontal cortex may underlie motor preparation in Parkinson's disease but also suggest that akinesia may occur in the absence of impaired mesial frontal cortex activation.

Aged↗
PubMed2001

Right lateralized motor cortex activation during volitional blinking.

Using H2 15O positron emission tomography in 6 healthy volunteers, we found that self-initiated and externally cued blinking activated the right primary motor cortex and supplementary motor area (SMA). The left dorsolateral prefrontal cortex (DLPFC) and the rostral SMA showed greater activation during the self-initiated task compared to the externally cued task. This study confirms the hypothesis of right hemispheric lateralization of volitional blinking derived from observations in stroke patients. Furthermore, it underscores the role of DLPFC and rostral SMA in self-initiated movements, which has been found in similar experiments with hand movements.

Aged↗
PubMed2001

Cortical correlates of gesture processing: clues to the cerebral mechanisms underlying apraxia during the imitation of meaningless gestures.

The clinical test of imitation of meaningless gestures is highly sensitive in revealing limb apraxia after dominant left brain damage. To relate lesion locations in apraxic patients to functional brain activation and to reveal the neuronal network subserving gesture representation, repeated H2(15O)-PET measurements were made in seven healthy subjects during a gesture discrimination task. Observing paired images of either meaningless hand or meaningless finger gestures, subjects had to indicate whether they were identical or different. As a control condition subjects simply had to indicate whether two portrayed persons were identical or not. Brain activity during the discrimination of hand gestures was strongly lateralized to the left hemisphere, a prominent peak activation being localized within the inferior parietal cortex (BA40). The discrimination of finger gestures induced a more symmetrical activation and rCBF peaks in the right intraparietal sulcus and in medial visual association areas (BA18/19). Two additional foci of prominent rCBF increase were found. One focus was located at the left lateral occipitotemporal junction (BA 19/37) and was related to both tasks; the other in the pre-SMA was particularly related to hand gestures. The pattern of task-dependent activation corresponds closely to the predictions made from the clinical findings, and underlines the left brain dominance for meaningless hand gestures and the critical involvement of the parietal cortex. The lateral visual association areas appear to support first stages of gesture representation, and the parietal cortex is part of the dorsal action stream. Finger gestures may require in addition precise visual analysis and spatial attention enabled by occipital and right intraparietal activity. Pre-SMA activity during the perception of hand gestures may reflect engagement of a network that is intimately related to gesture execution.

Adult↗
PubMed2001

Event-related functional magnetic resonance imaging in Parkinson's disease before and after levodopa.

Event-related functional MRI (fMRI) was used to study blood oxygen level dependent cortical signal changes associated with volitional limb movements off and on levodopa in Parkinson's disease. Eight patients with early stage akinetic Parkinson's disease and eight healthy volunteers underwent three functional imaging runs (high speed echo planar imaging with 600 scans/run) while performing paced single joystick movements in a freely chosen direction every 7-15 s. The non-magnetic joystick was linked to a monitoring system for on-line registration of performance parameters along with timing of the pacing tones and fMRI-scan acquisition parameters. This allowed correlation of movement onset, i.e. event-onset, to scanning time. We repeated the scanning procedure in the Parkinson's disease patients when akinesia improved 30 min after oral levodopa. Compared with the control group, patients both off and on levodopa showed movement-related impaired activation in the rostral supplementary motor area and increased activation in primary motor cortex (M1) and the lateral premotor cortex bilaterally. Levodopa led to a relative normalization of the impaired activation in the mesial premotor cortex and decreased signal levels in M1, lateral premotor and superior parietal cortex. We conclude that levodopa improves impaired motor initiation in the supplementary motor area and decreases hyperfunction of lateral premotor and M1 associated with Parkinson's disease during simple volitional movements.

Aged↗
PubMed2001

The role of the striatum and hippocampus in planning: a PET activation study in Parkinson's disease.

Previous work has identified the prefrontal cortex (PFC) and striatum as participating in the planning and selection of movements. We compared the brain activation patterns during planning in Parkinson's disease patients and age-matched controls using H(2)(15)O-PET and the Tower of London (TOL) task. In this study, our mildly affected Parkinson's disease group performed as well as the control group but showed a different pattern of neuronal activation. In the two groups, overlapping areas of the PFC were activated but, whereas the right caudate nucleus was activated in the control group, this was not evident in the Parkinson's disease patients. This suggests that normal normal frontal lobe activation can occur in Parkinson's disease despite abnormal processing within the basal ganglia. Moreover, right hippocampus activity was suppressed in the controls and enhanced in the Parkinson's disease patients. This could represent a shift to the declarative memory system in Parkinson's disease during performance of the TOL task, possibly resulting from insufficient working memory capacity within the frontostriatal system.

Aged↗
PubMed2001

Time-resolved fMRI of activation patterns in M1 and SMA during complex voluntary movement.

The aim of this study was to use time-resolved functional magnetic resonance imaging (fMRI) to investigate temporal differences in the activation of the supplementary motor area (SMA) and the primary motor cortex (M1). We report data from eight human volunteers who underwent fMRI examinations in a 1.5T Philips Gyroscan ACS-NT MRI scanner. While wearing a contact glove, subjects executed a complex automated sequence of finger movements either spontaneously or in response to external auditory cues. Based on the result of a functional scout scan, a single slice that included the M1 and the SMA was selected for image acquisition (echo planar imaging, repetition time 100 ms, echo time 50 ms, 64 x 64 matrix, 1,000 images). Data were analyzed with a shifting cross-correlation approach using the STIMULATE program and in-house programs written in Interactive Data Language (IDL(TM)). Time-course data were generated for regions of interest in the M1 as well as in the rostral and caudal SMA. Mean time between onset of the finger movement sequence and half-maximum of the signal change in M1 was 3.6 s for the externally cued execution (SD 0.5) and 3.5 s for the spontaneous execution (SD 0.6). Activation in the rostral section of the SMA occurred 0.7 s earlier than it did in the M1 during the externally cued execution and 2.0 s earlier during the spontaneous execution, a difference significant at the P < 0.01 level. Our results indicate that rostral SMA activation precedes M1 activation by varying time intervals in the sub-second range that are determined by the mode of movement initialization. By applying a paradigm that exerts a differential influence on temporal activation, we could ensure that the observed timing differences were not the result of differences in hemodynamic response function.

Acoustic Stimulation↗
PubMed2000

Lasting cortical activation after repetitive TMS of the motor cortex: a glucose metabolic study.

OBJECTIVE: Cerebral [18F]fluorodeoxy-D-glucose PET ([18F]FDG-PET) was used to visualize the lasting neuronal activation after repetitive transcranial magnetic stimulation (rTMS) over the left hand area of the primary motor cortex (M1HAND). BACKGROUND: Applied over M1HAND, rTMS has been shown to produce a modulation of corticomotor excitability beyond the time of stimulation itself. METHODS: Eight right-handed subjects underwent nonquantitative [18F]FDG-PET measurements during two experimental conditions: at rest and after focal subthreshold 5-Hz rTMS over the left M1HAND. In the post-rTMS condition, [18F]FDG was injected immediately after the administration of 1,800 magnetic pulses over the left M1HAND. Relative differences in normalized regional cerebral metabolic rate of glucose (normalized rCMRglc) between conditions were determined using a voxel-by-voxel Student's t-test and volume-of-interest (VOI) analysis. Analysis was a priori restricted to the M1HAND, the supplementary motor area (SMA), and the primary auditory cortex of both hemispheres. RESULTS: A 5-Hz rTMS of the left M1HAND caused a lasting relative increase in normalized rCMRglc within the M1HAND bilaterally and the SMA. The magnitude and the topographic pattern of persisting relative rCMRglc increases within these motor cortical areas demonstrated considerable interindividual variations. CONCLUSIONS: Subthreshold 5-Hz repetitive transcranial magnetic stimulation (rTMS) over the hand area of the primary motor cortex is associated with a persisting neuronal activation in a distinct set of motor cortical areas beyond the time of stimulation. The current findings demonstrate that [18F]FDG-PET can localize and quantify regional net changes in synaptic cortical activity after rTMS and thus might elucidate the mechanisms underlying rTMS-associated therapeutic effects.

Adult↗
PubMed1999

A positron emission tomographic study of subthalamic nucleus stimulation in Parkinson disease: enhanced movement-related activity of motor-association cortex and decreased motor cortex resting activity.

BACKGROUND: Long-term high-frequency stimulation of the subthalamic nucleus (STN) improves akinesia in Parkinson disease. The neural correlates of STN stimulation are not well understood. Positron emission tomography can be applied to the in vivo study of the mechanisms of deep brain stimulation. OBJECTIVE: To study changes in regional cerebral blood flow as an index of synaptic activity in patients with Parkinson disease with effective STN stimulation on and off during rest and movement. METHODS: Eight patients with Parkinson disease who had electrodes implanted in the STN underwent 12 measurements of regional cerebral blood flow with water O 15 positron emission tomography at rest and during performance of paced freely selected joystick movements, both with and without STN stimulation (3 scans per experimental condition). Motor performance and reaction and movement times were monitored. Statistical parametric mapping was used to compare changes in regional cerebral blood flow between conditions and differences in activation. RESULTS: All patients showed improvement in reaction and movement times during scans with the stimulator on. As predicted, increases in activation of rostral supplementary motor area and premotor cortex ipsilateral to stimulation were observed when stimulation was on during contralateral movement (P<.001). Unpredicted observations included decreases in regional cerebral blood flow in primary motor cortex at rest induced by STN stimulation. CONCLUSION: Stimulation of the STN reduces the movement-related impairment of frontal motor association areas and the inappropriate motor cortex resting activity in Parkinson disease.

Adult↗
PubMed1999

Mapping the network for planning: a correlational PET activation study with the Tower of London task.

We used the Tower of London task (TOL) and H(2)(15)O-PET to map the network of brain structures involved in planning. Six healthy right-handed subjects had 12 measurements of relative regional cerebral blood flow (rrCBF) during six conditions, each performed twice. There was one rest condition, and five sets of TOL problems at different complexity levels, performed on a touch-sensitive computer monitor with the right arm. Complexity was defined as the number of moves required to solve each problem. Activation was analysed in two ways: a category analysis comparing levels of rrCBF during rest and task was done to identify all structures involved in performance of the TOL; and a correlation analysis was carried out to delineate a subset of structures where the levels of rrCBF correlated with task complexity. Activated brain areas in which rrCBF increases did not correlate with complexity could be grouped into: (i) regions belonging to the dorsal stream of visual input processing, namely visual cortical areas 17, 18 and 19, and posterior parietal cortical areas 7 and 40; and (ii) regions involved in the execution and sequencing of arm movements (right cerebellum, left primary motor cortex and supplementary motor area). Brain regions where levels of rrCBF correlated with task complexity included lateral premotor cortex (area 6), rostral anterior cingulate cortex (areas 32 and 24), dorsolateral prefrontal cortex (areas 9 and 46) bilaterally, and right dorsal caudate nucleus. We propose that dorsolateral prefrontal, lateral premotor, anterior cingulate and caudate areas form a network for the planning of movement that interacts with brain areas primarily involved in visual processing and movement execution.

Aged↗
PubMed1999

Sensory processing in Parkinson's and Huntington's disease: investigations with 3D H(2)(15)O-PET.

There is conjoining experimental and clinical evidence supporting a fundamental role of the basal ganglia as a sensory analyser engaged in central somatosensory control. This study was aimed at investigating the functional anatomy of sensory processing in two clinical conditions characterized by basal ganglia dysfunction, i.e. Parkinson's and Huntington's disease. Based on previously recorded data of somatosensory evoked potentials, we expected deficient sensory-evoked activation in cortical areas that receive modulatory somatosensory input via the basal ganglia. Eight Parkinson's disease patients, eight Huntington's disease patients and eight healthy controls underwent repetitive H(2)(15)O-PET activation scans during two experimental conditions in random order: (i) continuous unilateral high-frequency vibratory stimulation applied to the immobilized metacarpal joint of the index finger and (ii) rest (no vibratory stimulus). In the control cohort, the activation pattern was lateralized to the side opposite to stimulus presentation, including cortical [primary sensory cortex (S1); secondary sensory cortex (S2)] and subcortical (globus pallidus, ventrolateral thalamus) regional cerebral blood flow (rCBF) increases (P < 0.001). Between-group comparisons (P < 0.01) of vibration-induced rCBF changes between patients and controls revealed differences in central sensory processing: (i) in Parkinson's disease, decreased activation of contralateral sensorimotor (S1/M1) and lateral premotor cortex, contralateral S2, contralateral posterior cingulate, bilateral prefrontal cortex (Brodmann area 10) and contralateral basal ganglia; (ii) in Huntington's disease, decreased activation of contralateral S2, parietal areas 39 and 40, and lingual gyrus, bilateral prefrontal cortex (Brodmann areas 8, 9, 10 and 44), S1 (trend only) and contralateral basal ganglia; (iii) in both clinical conditions relative enhanced activation of ipsilateral sensory cortical areas, notably caudal S1, S2 and insular cortex. Our data show that Parkinson's disease and Huntington's disease, beyond well-established deficits in central motor control, are characterized by abnormal cortical and subcortical activation on passive sensory stimulation. Furthermore, the finding that activation increases in ipsilateral sensory cortical areas may be interpreted as an indication of either altered central focusing and gating of sensory impulses, or enhanced compensatory recruitment of associative sensory areas in the presence of basal ganglia dysfunction. Altered sensory processing is thought to contribute to pertinent motor deficits in both conditions.

Adult↗
PubMed1998

Imaging brain activation induced by long trains of repetitive transcranial magnetic stimulation.

Using positron emission tomography (PET), we measured the relative changes in regional cerebral metabolic rate of glucose (rCMRglc) during 2 Hz repetitive transcranial magnetic stimulation (rTMS) of the left sensorimotor cortex (SM1) and during imitation of rTMS-induced arm movements. Such stimulation caused an rCMRglc increase of about 8% within the SM1. The relative rCMRglc increase within SM1 was significantly greater in magnitude and larger in area during voluntary imitation of rTMS-induced arm movements. Moreover, the rostral part of the SMA was significantly more activated by voluntary movements than during rTMS. Combining rTMS and PET has the potential to visualize rTMS-related net brain activation, and may open up new possibilities for functional network analysis by comparing willed brain activation with electromagnetic brain activation.

Adult↗
PubMed1998

Functional imaging of tremor.

We review the insight that has been obtained from positron emission tomography (PET) and magnetic resonance imaging (MRI) activation studies on the functional anatomy underlying different forms of tremor. The effects of treatment, both pharmacologic and interventional approaches, on the dysfunctional cerebral systems involved in tremor, also are considered. Finally, we speculate on the neuropharmacologic basis of different types of tremor based on available in vivo PET evidence.

Brain↗
PubMed1998

Role of the human rostral supplementary motor area and the basal ganglia in motor sequence control: investigations with H2 15O PET.

The aim of this study was to investigate the functional anatomy of distributed cortical and subcortical motor areas in the human brain that participate in the central control of overlearned complex sequential unimanual finger movements. On the basis of previous research in nonhuman primates, a principal involvement of basal ganglia medial premotor loops [corrected] was predicted for central control of finger sequences performed automatically. In pertinent areas, a correlation of activation levels with the complexity of a motor sequence was hypothesized. H2 15O positron emission tomography (PET) was used in a group of seven healthy male volunteers [mean age 32.0 +/- 10.4 yr] to determine brain regions where levels of regional cerebral blood flow (rCBF) correlated with graded complexity levels of five different key-press sequences. All sequences were overlearned before PET and involved key-presses of fingers II-V of the right hand. Movements of individual fingers were kept constant throughout all five conditions by external pacing at 1-Hz intervals. Positive correlations of rCBF with increasing sequence complexity were identified in the contralateral rostral supplementary motor area (pre-SMA) and the associated pallido-thalamic loop, as well as in right parietal area 7 and ipsilateral primary motor cortex (M1). In contrast, while rCBF in contralateral M1 and [corrected] extensive parts of caudal SMA was increased compared with rest during task performance, significant correlated increases of rCBF with sequence complexity were not observed. Inverse correlations of rCBF with increasing sequence complexity were identified in mesial prefrontal-, medial temporal-, and anterior cingulate areas. The findings provide further evidence in humans supporting the notion of a segregation of SMA into functionally distinct subcomponents: although pre-SMA was differentially activated depending on the complexity of a sequence of learned finger movements, such modulation was not detectable in caudal SMA (except the most antero-superior part), implicating a motor executive role. Our observations of complexity-correlated rCBF increases in anterior globus pallidus suggest a specific role for the basal ganglia in the process of sequence facilitation and control. They may act to filter and focus input from motor cortical areas as patterns of action become increasingly complex.

Adult↗