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C Dettmers

Publications and source records attributed to C Dettmers.

At least 19 recordsLinked to original sources
PubMed2001

Increased excitability in the primary motor cortex and supplementary motor area in patients with phantom limb pain after upper limb amputation.

Using functional magnetic resonance imaging and single slice FLASH technique, we investigated reorganization of the hand representation of the primary sensorimotor cortex (SMC) in 16 patients with upper extremity amputation. Patients were asked to perform finger tapping with the intact hand, repetitive eye closing and anteflexion of the amputation stump or intact shoulder. Six normal volunteers served as control. In the normal volunteers activations during shoulder anteflexion, finger tapping and eye closure were located within the central sulcus in a medio-lateral fashion. Patients demonstrated invasion of the face or shoulder representation into the hand representation of the amputated limb. Eight phantom limb pain patients showed significantly greater activation in SMC and supplementary motor area (SMA) in contrast to eight patients without phantom limb pain. We conclude, that different parts of the motor system are affected in patients with phantom limb pain--possibly in the sense of an up-regulation of excitability.

Adolescent↗
PubMed2001

Structural and functional cortical abnormalities after upper limb amputation during childhood.

Functional reorganization has been well documented in the human adult brain after amputation of the arm. To assess the effects of amputation on the developing brain, we investigated six patients with upper limb amputation in early childhood and one with right dysmelia. Transcranial magnetic stimulation indicated contralateral cortical disinhibition and enlargement of the excitable area of the stump. FMRI data corroborated these plastic changes and also showed an ipsilateral functional reorganization. In the T1-weighted MRI, we found structural deformities of the contralateral and ipsilateral central sulcus in three patients and a contralateral atrophic parietal lobule in two patients. Therefore, arm amputation in childhood affects functional organization as well as anatomical structure in both hemispheres.

Adolescent↗
PubMed2001

[Is brain blood supply affected by changes in cardiac volume? Measurements of brain blood supply in healthy subjects during volume overload and in patients with artificial pacemaker by changing the pacing rate].

A constant cerebral blood flow (CBF) in the presence of systemic blood pressure changes and cardiac output (CO) alterations during physiological conditions are postulated by the mechanism of cerebral autoregulation. The aim of the present study is the analysis of CBF in pacemaker (PM) patients with unspecific neurological symptoms. CBF was measured in 9 controls and 23 pacemaker patients with 133xenon, CO using Doppler echocardiography or impedance cardiography. Mean and individual CBF in controls remained unchanged when a CO increase of 28% induced by volume overload was observed. In PM patients a mean CO increase of 38% induced by an increase of basic pacing rate caused different effects of CBF. CBF increased or decreased by about 10% or remained constant. In summary, the data suggest an impairment of cerebrovascular function in those patients with concomittant CBF changes due to CO alterations (15/23 approximately equal to 65%). Thus, the analysis of brain perfusion in PM patients with unspecific neurological symptoms is possibly a new diagnostic feature in the future. It can be discussed whether or not indication and optimizing of pacemaker therapy has to be additionally analyzed by determination of endorgan perfusion.

Adult↗
PubMed2001

Inhibition of ipsilateral motor cortex during phasic generation of low force.

OBJECTIVE: To study the effect of different types of unilateral pinch grips on excitability of the ipsilateral motor cortex. METHODS: In 9 healthy volunteers, transcranial magnetic stimuli (TMS) were applied over one motor cortex while the subjects performed either phasic or tonic ipsilateral pinch grips with different force levels (range 1-40% maximum voluntary contraction, MVC). Motor evoked potentials (MEP) were recorded from the relaxed contralateral first dorsal interosseous muscle (FDI) and were compared to MEPs obtained during muscle relaxation of both hands. In additional experiments, transcranial electrical stimuli (TES) were administered and F waves were recorded after electrical stimulation of the ulnar nerve. RESULTS: Phasic pinch grips with low force (1 and 2% MVC) induced a significant decrease of TMS-induced MEP amplitudes. The effect lasted for about 100 ms after reaching the force level and was similar for both right and left-handed pinch grips. TES-induced MEPs and F waves remained unchanged. In contrast, tonic contractions (20 and 40% MVC) enhanced MEPs in the homologous FDI. CONCLUSIONS: Phasic pinch grips with low force inhibit the motor cortex responsible for the contralateral homologous hand muscle. This effect, which is probably mediated transcallosally, might act at the level of the motor cortex.

Adult↗
PubMed2001

Case report: regional cerebral hypoperfusion induced by ventricular tachycardia - short-term hippocampal hypoperfusion and its potential relationship to selective neuronal damage.

BACKGROUND: Focussing on regional cerebral hypoperfusion during hemodynamically stable, but borderline hypotensive, sustained ventricular tachycardia (VT) experimental studies show (1) a reduction of cerebral blood flow (CBF) during tachyarrhythmias in contrast to the concept of CBF autoregulation, (2) a mediation of hypoperfusion by neuronal and humoral mechanisms, and (3) an involvment of microcirculation due to an ischemic stress response of the cerebral tissue. The clinical relevance of these observations remains still unclear. CASE REPORTS: Two patients with coronary artery disease, left ventricular dysfunction and sustained monomorphic VT underwent electrophysiological study. VT was induced and the tracer (99m)Tc-HMPAO was injected after 3 minutes of ongoing VT. Regional CBF during this life threatening arrhythmia was determined with brain SPECT. A scanning protocol was performed after termination of VT. The measurements were repeated at baseline during normofrequent sinus rhythm (SR) one week later. CBF during SR was significantly reduced in the temporal lobe in comparison to the conditions during stable VT, particularly in the left hippocampus. CONCLUSION: The reduction of hippocampal CBF due to cerebrovascular vasoconstriction and neuronal reflex mechanism previously observed in experiments during stable, sustained VT can be confirmed in a clinical scenario by high resolution (99m)Tc-HMPAO brain SPECT. This supports the hypothesis that repetitive stable VT can play a role in the pathophysiology of cerebrovascular insufficiency. Further clinical studies are needed to analyze the impact of tachyarrhythmias on cognitive and mnemic function.

Aged↗
PubMed2001

Surface orientation discrimination activates caudal and anterior intraparietal sulcus in humans: an event-related fMRI study.

Perception of surface orientation is an essential step for the reconstruction of the three-dimensional (3D) structure of an object. Human lesion and functional neuroimaging studies have demonstrated the importance of the parietal lobe in this task. In primate single-unit studies, neurons in the caudal part of the intraparietal sulcus (CIP) were found to be active during the extraction of surface orientation through monocular (two-dimensional) cues such as texture gradients and linear perspective as well as binocular (3D) cues such as disparity gradient and orientation disparity. We used event-related fMRI to study the functional neuroanatomy of surface orientation discrimination using stimuli with monocular depth cues in six volunteers. Both posterior (CIP) and anterior (AIP) areas within the intraparietal sulcus showed a stronger activation during surface orientation as compared with a control (color discrimination) task using identical stimuli. Furthermore, the signal changes in CIP showed a greater performance effect than those in AIP, suggesting that CIP is tightly linked to the discrimination task.

Adult↗
PubMed2000

[Cardiac pacemaker therapy for optimizing brain circulation. A possible prevention for cerebrovascular diseases?].

HISTORY AND CLINICAL FINDINGS: A 78-year-old patient experienced dizziness, impairment of mnemic and cognitive function, chronic fatigue and recurrent syncope. INVESTIGATIONS: Hypertensive heart disease, reduced left ventricular function, and ventricular ectopia classification Lown IVb was documented. Computed tomography showed minimal brain atrophia. Stenoses of the brain supplying arteries and of other intracranial diseases were excluded. A distinct correlation between cardiac output and cerebral blood flow in correspondence to changes of heart rate were found (cardiac output 4.2 l/min during sinus rhythm, 7.4 l/min during temporary atrial pacing--AAI-Mode with a pacing rate of 90/min; 4.8 l/min--AAI-Mode with a pacing rate of 120/min; cerebral blood flow: 70, 74 and 62 ml/100 g per minute, respectively). Thus, impairment of cerebral blood flow autoregulation can be assumed. TREATMENT AND COURSE: After implantation of a permanent pacemaker the patient was without any complaints. The mnemic and cognitive function improved, dizziness and fatigue disappeared. Synopsis did not occur. 14 months later a sudden onset of complaints occurred caused by atrial fibrillation (heart rate 120/min). Cardiac output and cerebral blood flow were now 4.0 l/min and 35 ml/100 g per minute. After antiarrhythmic drug therapy and restoration of sinus rhythm cardiac output and cerebral blood flow increased and the complaints disappeared again. CONCLUSION: In patients with impaired capacity of cerebral autoregulation a reduced cardiac function and output can induce a reduction of cerebral blood flow. Thus, impairment of mnemic and cognitive function as well as other unspecific neurological deficits can be caused. In these cases pacemaker therapy has to be discussed as an effective therapeutical concept.

Aged↗
PubMed1999

A blueprint for movement: functional and anatomical representations in the human motor system.

Despite a clear somatotopic organization of the motor cortex, a movement can be learned with one extremity and performed with another. This suggests that there exists a limb-independent coding for movements. To dissociate brain regions coding for movement parameters from those relevant to the chosen effector, subjects wrote their signature with their dominant index finger and ipsilateral big toe, and we determined those areas activated by both conditions using functional magnetic resonance imaging. The results show that movement parameters for this highly trained movement are stored in secondary sensorimotor cortices of the extremity with which it is usually performed, i.e., the dominant hand, including dorsal and ventral lateral premotor cortices. These areas can be accessed by the foot and are therefore functionally independent from the primary representation of the effector. Thus, somatotopy in secondary structures in the human motor system seems to be defined functionally, and not on the basis of anatomical representations.

Adult↗
PubMed1999

Abnormal motor cortex organization contralateral to early upper limb amputation in humans.

We performed both a functional magnetic resonance imaging (fMRI) study using single slice FLASH technique and an investigation with transcranial magnetic stimulation (TMS) in a 21-year-old patient. He had suffered a left upper extremity amputation at age 7. Anteflexion of the amputation stump produced an unusual, broad activation contralateral to the movement. TMS revealed an enlarged cortical motor output area of the deltoid muscle at the amputation stump. Application of paired magnetic stimulation demonstrated decreased intracortical inhibition (ICI). A T1-weighted image indicated a lack of the characteristic shape of the central sulcus contralateral to the amputation. In addition to previous functional studies, these new structural data suggest that maturation of the central sulcus develops in response to daily practice of the contralateral hand, possibly until adolescence.

Adult↗
PubMed1999

Effects of constraint-induced movement therapy on patients with chronic motor deficits after stroke: a replication.

BACKGROUND AND PURPOSE: Constraint-induced movement therapy (CI therapy) has previously been shown to produce large improvements in actual amount of use of a more affected upper extremity in the "real-world" environment in patients with chronic stroke (ie, >1 year after the event). This work was carried out in an American laboratory. Our aim was to determine whether these results could be replicated in another laboratory located in Germany, operating within the context of a healthcare system in which administration of conventional types of physical therapy is generally more extensive than in the United States. METHODS: Fifteen chronic stroke patients were given CI therapy, involving restriction of movement of the intact upper extremity by placing it in a sling for 90% of waking hours for 12 days and training (by shaping) of the more affected extremity for 7 hours on the 8 weekdays during that period. RESULTS: Patients showed a significant and very large degree of improvement from before to after treatment on a laboratory motor test and on a test assessing amount of use of the affected extremity in activities of daily living in the life setting (effect sizes, 0.9 and 2.2, respectively), with no decrement in performance at 6-month follow-up. During a pretreatment control test-retest interval, there were no significant changes on these tests. CONCLUSIONS: Results replicate in Germany the findings with CI therapy in an American laboratory, suggesting that the intervention has general applicability.

Adult↗
PubMed1998

Motor cortex plasticity during constraint-induced movement therapy in stroke patients.

Stroke patients in the chronic phase received constraint-induced (CI) movement therapy. The motor cortex was spatially mapped using focal transcranial magnetic stimulation (TMS) before and after 2 weeks of treatment. Motor-output areas of the abductor pollicis brevis muscle, motor evoked potential (MEP) amplitudes and location of centre of gravity (CoG) of motor cortex output were studied. After CI therapy, motor performance improved substantially in all patients. There was also an increase of motor output area size and MEP amplitudes, indicating enhanced neuronal excitability in the damaged hemisphere for the target muscles. The mean centre of gravity of the motor output maps was shifted considerably after the rehabilitation, indicating the recruitment of motor areas adjacent to the original location. Thus, even in chronic stroke patients, reduced motor cortex representations of an affected body part can be enlarged and increased in level of excitability by an effective rehabilitation procedure. The data therefore demonstrate a CNS correlate of therapy-induced recovery of function after nervous system damage in humans.

Brain Mapping↗
PubMed1998

Cerebral vasoconstriction during sustained ventricular tachycardia induces an ischemic stress response of brain tissue in rats.

Arterial hypotension can cause cerebral ischemia when the autoregulation of the cerebral circulation is exhausted. We hypothesized that sudden cerebral vasoconstriction induced by moderate hypotensive, but hemodynamically stable, sustained ventricular tachycardias (MHT-VT) further compromises cerebral blood flow (CBF) and induces an ischemic stress response of the brain. CBF-measurements and morphological studies were performed without and with blockade of alpha-adrenergic receptors in order to determine the impact of MHT-VF on brain perfusion and brain tissue. Using a model of MHT-VT, CBF was measured with colored microspheres in 71 rats during control conditions. after the onset of MHT-VT, after the onset of moderate hypotensive hypovolemia (MHH), and after additional non- selective (alpha-blockade with phentolamine and selective alpha1-blockade with prazosin, respectively (0.2-0.4 mg/kg body weight). Plasma catecholamine concentrations were measured in 18 additional rats during control conditions. during MHT-VT and during MHH. The occurrence of heat shock protein (hsp) 72 and activated microglia in the brain was analysed in 18 additional rats in controls, after MHT-VT and MHH. After 20 min of the respective induced hypotension, control conditions were restored for a period of 8 h, by stopping VT or by infusion of isotonic saline solution. CBF was 0.98+/-0.16 (mean+/-S.D.) ml/g/min during control conditions at an arterial pressure of 118+/-13 mmHg, 0.50+/-0.05 ml/g/min (P<0.05 v control) during MHT-VT (76+/-4 mm Hg) and 0.75+/-0.14 ml/g/min (P<0.05 v control and v MHT-VT ) during MHH (71 +/- 8 mm Hg). CBF was better preserved with non-selective alpha-blockade during MHT-VT (0.78+/-0.15 ml/g/min, P<0.05 v MHT-VT and control) as well as with selective alpha1-blockade (0.67+/-0.08 ml/g/min, P<0.05 v MHT-VT and control). Plasma catecholamines were elevated during MHT-VT (P<0.05 v control) but not during MHH (P = N.S. v control). hsp 72 and activated microglia were found in hippocampal regions only after MHT-VT (P<0.05 v control and MHH). These morphological changes were prevented by non-selective alpha-blockade. Stable sustained MHT-VT further reduce the already compromised CBF leading to morphological alterations in the brain which are characteristic of an early ischemic stress response. alpha-Blockade prevents alpha1-adrenergic vasoconstriction and attenuates cerebral hypoperfusion.

Adrenergic alpha-Antagonists↗
PubMed1998

Hemodynamic sequelae of ventricular tachyarrhythmias on cerebral blood flow.

The present experiments were designed to compare the behavior of cerebral blood flow (CBF) during acute moderate and severe hypotensive episodes induced by either ventricular tachycardias (VT) or by hemorrhage. Using the microsphere method CBF was determined in 20 Sprague-Dawley rats during sinus rhythm (Group A), in 28 animals during high-rate VT (Group B) and in 10 animals after hemorrhage (Group C). According to the decrease in blood pressure and with respect to the lower threshold of cerebral autoregulation Group B was divided into 2 subgroups (B1: 80-130 mmHg; B2: 50-80 mmHg) retrospectively. While CBF remained constant in Group B1 (0.98 +/- 0.3 ml g-1 min-1 vs. 1.01 +/- 0.32 in controls, NS), CBF decreased markedly during severely hypotensive VT in Group B2 (0.52 +/- 0.2 ml g-1 min-1, p < 0.001 vs. A; p < 0.05 vs. C) and during hypovolemic hypotension in Group C (0.77 +/- 0.22 ml g-1 min-1 vs. A; NS). Cerebrovascular resistance and autoregulation indices indicated a maintenance of CBF regulation during hypovolemic hypotension and a failure during normovolemic hypotension. These findings indicate that the autoregulatory ability of the brain is substantially more stable during hypovolemic hypotension than during normovolemic hypotension. Therefore, the hemodynamic sequelae of acute hypotensive episodes on CBF depend on the underlying cause of hypotension.

Animals↗
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↗
PubMed1997

[Progressive cerebral parenchyma damage caused by recurrent arterial hypotension].

To date clinical and experimental investigations have focused on acute strokes and complete infarctions. Histological and immunological staining in animal experiments and improved imaging techniques in patients suggest that selective or incomplete infarction is a common pathomechanism. Incomplete infarction can manifest as laminar necrosis at autopsy and as leukoaraiosis in imaging studies. An important mechanism in the genesis of leukoaraiosis is vascular pathology of the long penetrating arteries of the deep white matter combined with episodes of decreased perfusion pressure or hypotension. We demonstrate that the cumulative effect of repetitive, moderate hypotensive episodes on cognitive performance or cerebral tissue has not been adequately studied and appreciated.

Animals↗
PubMed1997

Confirmation of CT criteria to distinguish pathophysiologic subtypes of cerebral infarction.

PURPOSE: To determine whether cerebral infarctions classified as embolic or hemodynamic by their appearance on CT scans reflect distinct pathophysiologic entities. METHODS: Cerebral infarctions were retrospectively classified into two groups according to their morphologic appearance on CT scans: territorial infarctions and watershed, or terminal supply area, infarctions. Specific CO2 reactivity for both groups of patients was determined with the xenon-133 method and 32 stationary detectors. Twenty-one patients with unilateral, supratentorial, ischemic cerebral infarctions were selected. CT findings were highly suggestive of a territorial infarction in 14 patients (mean age, 56 years) and of a watershed infarction in seven patients (mean age, 52 years). RESULTS: The initial slope index of the territorial and watershed infarction groups during CO2 inhalation was 55.1 +/- 2.4 sec-1 and 52.0 +/- 1.9 sec-1, respectively, in the infarcted hemispheres and 58.3 +/- 2.3 sec-1 and 55.1 +/- 1.5 sec-1, respectively, in the noninfarcted hemispheres. CO2 reactivity of the unaffected detectors was 1.75 +/- 0.3 sec-1 mm Hg-1 and 1.51 +/- 0.2 sec-1 mm Hg-1 for the territorial and watershed infarction groups, respectively. CO2 reactivity of the affected detectors was 1.75 +/- 0.3 sec-1 mm Hg-1 and 1.27 +/- 0.2 sec-1 mm Hg-1 for the two groups, respectively. The CO2 reactivity difference between affected detectors of the hemodynamic group and age-matched healthy control subjects was significant. CONCLUSIONS: The difference in CO2 reactivity between the two groups supports the concept that CT criteria can identify two pathophysiologic entities. In addition, we conclude that during the chronic stage, lower CO2 reactivity of the watershed infarction indicates that the global hemodynamic situation in these infarcts is more severely compromised than in territorial infarctions.

Aged↗
PubMed1996

Cerebral activation during the exertion of sustained static force in man.

The aim of our study was to determine alterations of cerebral activity during prolonged static force exertion. Regional cerebral blood flow (rCBF) was measured using H2(15)O positron emission tomography (PET) while six male normal subjects pressed a morse-key with their right index finger with a constant force of 20% of their maximal voluntary contraction (MVC) for different periods of time (1.5-4.5 min). Exertion of static force led to activation which was at least as extensive as that during exertion of repetitive dynamic force pulses. Despite a considerable sense of fatigue and increased effort at the end of a 4.5 min key press, no compensatory changes of activity were detected in motor or sensory related structures. The right dorsolateral prefrontal cortex demonstrated a significant correlation between rCBF and duration of key-press, possibly reflecting processes over-riding fatigue. Prominent basal ganglia activation was demonstrated in this static force task, but not in a previous force task involving repetitive dynamic force pulses. This suggests that sustained exertion of a static force is an active process modulated, at least in part, by the basal ganglia.

Adult↗