Biomedical subjects

D Timmann

Publications and source records attributed to D Timmann.

34 records · Page 2Linked to original sources

PubMed1997

A reliable method for sustaining a pre-defined pre-innervation level.

Numerous experimental approaches are based on evaluating electromyographically recorded muscle activity. Some experiments require a certain level of pre-innervation in a muscle or muscle group whereas others must avoid this. Measured parameters, such as the time to onset of the muscle response to an electrical stimulus, etc., depend critically on the level of pre-innervation. The pre-innervation level is most commonly estimated from parameters such as the force generated by this muscle or the upright posture of a human subject. These methods, however, are indirect and may yield erroneous results. This paper describes an inexpensive method developed for a wide range of applications in muscle-tonus-based experiments, in which the tonus is precisely controlled. A simple electronic circuit is presented by which the level of muscle pre-innervation is directly recorded, monitored and - depending on the experimental approach - also fed back to the subject. Physiological experiments on the flexion reflex in healthy human subjects document the reliability of our electronic device.

Electromyography↗

PubMed1997

Side effects from increased doses of carbamazepine on neuropsychological and posturographic parameters of humans.

Patients taking anticonvulsant drugs display a broad spectrum of side-effects. Particularly, in the beginning of treatment and with increasing doses of carbamazepine, side effects such as dizziness, ataxia, drowsiness and reduction of alertness occur, which improve some days after the dose has reached a stable level. Our aim was to find objective parameters for grading these side effects and to differentiate between neurophysiological and neuropsychological side effects of carbamazepine in a clinical situation. Twenty-two patients with trigeminal neuralgia were included for a follow-up study with increasing carbamazepine doses (0 mg to 600 mg). The effect of carbamazepine on postural stability was quantified by posturography. Different neuropsychological tests to study cognitive effects of carbamazepine were performed. The composite equilibrium score showed a significant reduction of postural stability with increasing doses of carbamazepine. In sensory analysis the somatosensory ratio was significantly influenced by increased doses of carbamazepine during the study. Mean reaction time of tonic alertness and physical alertness varied significantly with different doses of carbamazepine. There was a significant influence in patients attention during trail making tests and divided attention tests with increase in carbamazepine. In conclusion our observations show that the rate of change of carbamazepine doses is an important determinant of cognitive and motor functions in the phase of increasing doses.

Adult↗

PubMed1997

Prediction and set-dependent scaling of early postural responses in cerebellar patients.

We reported previously that patients with cerebellar deficits were unable to scale the magnitude of their early automatic postural responses to the predicted amplitudes of surface translations based on central set from prior experience. The present study investigated whether this deficit in set-dependent amplitude scaling was based predominantly on the cerebellar patient's disability (i) to predict perturbation amplitudes on the basis of prior experience, (ii) to scale the gain or magnitude of upcoming postural responses or (iii) to habituate postural responses. The increase in size of the early postural response when a larger than actual platform amplitude was expected and decrease when a smaller one was expected was defined as a measure of set-dependent amplitude prediction. The suppression of the postural response when the same platform velocity was repeated was used as a measure of habituation. The correlation between the size of early postural responses and platform amplitudes when presented serially, but not randomly, tested the ability to scale the gain of postural responses based on prior experience. Results show that although cerebellar patients could predict perturbation amplitudes based on prior experience, they could not use this prediction to modify precisely the gain of responses. The ability to habituate the magnitude of postural responses was not affected by cerebellar lesions. Thus, the cerebellum might not be critical for predicting upcoming events or for habituating to repeated postural stimuli, although it is important for accurate tuning of response gain based on prediction.

Adult↗

PubMed1996

Cerebellar activation during classical conditioning of the human flexion reflex: a PET study.

The present study investigated the involvement of the cerebellum in classical conditioning of the cutaneomuscular flexion reflex in four normal volunteers using positron emission tomography (PET). The flexion reflex was elicited by electrical pulses applied to the medial plantar nerve (unconditioned stimulus, US). A tone was presented as the conditioning stimulus, which co-terminated with the US. The incidence of conditioned responses was correlated with changes in rCBI during the acquisition process of flexion reflex conditioning. Blood flow was significantly increased in an area extending from the ipsilateral cerebellum and hippocampus to bilateral frontal regions (p = 0.009). These data provide support for an involvement of the cerebellum as well as hippocampus among other neural systems in classical flexion reflex conditioning.

Adult↗

PubMed1996

Temporal control of the reach and grip components during a prehension task in humans.

The kinematic changes of the manipulation and transport components during a prehensile movement were examined in an experimental condition that required alterations during the manipulation phase. Subjects started with a normal finger posture but were required to briefly open and close their thumb and index finger while transporting the wrist to grasp the object. The changes in the aperture altered most of the kinematic landmarks of the wrist. There was considerable slowing of most kinematic characteristics for the wrist transport, and the velocity profile of the wrist showed two peaks. The time of occurrence of the first peak was poorly correlated with the time of the first maximal finger aperture (before the brief finger touch). In contrast, the second wrist velocity peak was highly correlated with the time to the second maximal finger aperture (just before the grasp of the object). Thus, as the reach progressed and the object to be grasped was approached, the temporal relationship between the wrist and aperture components of the movement became more temporally related.

Adult↗

PubMed1996

Grasping component alterations and limb transport.

The kinematic changes associated with the manipulation and transport components during a prehensile movement were examined using an experimental paradigm that required alterations in only the manipulation component. Instead of starting with the thumb and index finger naturally together (control condition), subjects began the reach-to-grasp movement with their thumb and fingers fully extended (experimental condition). In contrast to the control condition, in the experimental conditions the thumb and index finger started to close during wrist transport, then opened again prior to object grasp. In addition, there was a brief inflection in the ascending portion of the velocity profile of the wrist in over half the trials. However, all the primary features of the transport component profile remained unaltered. The results suggest that there can be substantial reorganization of the grip aperture during the first part of the reach without altering the temporal and spatial relationships between grip aperture and transport as the object to be grasped is approached.

Adult↗

PubMed1996

Classical conditioning of the human flexion reflex.

The eyeblink conditioning paradigm is a well established model for studying learning processes in humans and animals. In this study a flexion reflex conditioning paradigm was established using the standard delay paradigm. The flexion reflex was elicited in 10 young, healthy subjects by a train of electrical pulses (100 ms, 100 Hz, 0.65 ms) applied to the medial plantar nerve (unconditioned stimulus, US). A tone (1000 Hz, 550 ms) was presented via headphones as the conditioning stimulus and which coterminated with the US. Responses were recorded from the anterior tibial muscles. Subjects were conditioned within one session of 120 trials of paired stimuli. This was established statistically via the continuous change in characteristic parameters of the responses throughout the experiment. Although the process of limb muscle conditioning takes longer than eyeblink conditioning, this type of flexion-reflex conditioning may possibly serve as a further model for the study of plastic changes within the nervous system. Moreover, the considerable versatility of limb movements offers the advantage of greater possibilities for testing the conditioning result.

Adult↗

PubMed1996

Visuomotor learning in cerebellar patients.

The aim of the present study was to demonstrate that patients with pathology affecting substantial regions of the cerebellum can improve their performance in a series of two-dimensional tracing tasks, thus supporting the view that this type of motor behavior can be acquired even when the integrity of this structure is compromised. Eight patients with chronic, isolated cerebellar lesions and eight age- and sex-matched healthy controls were tested. Three patients had mild, five had moderate upper limb ataxia. The experiment was divided into two parts. In the first, subjects traced an irregularly shaped outline over 20 consecutive trials ('Trace 1' task). Next, subjects were asked to redraw the object without any underlying template as a guide ('Memory 1' task). In the second part of the study, subjects were asked to trace a different, irregularly shaped outline over 20 consecutive trials ('Trace 2' task). Next, they were required to redraw it by memory with its axis rotated 90 degrees ('Memory 2' task). In each of the memory tasks the template was placed over the drawn image after each trial and shown to the subjects. The error of performance was determined by calculating three different measurements, each focused on different aspects of the task. Based on these measurements, the cerebellar patients showed improvement in both memory tasks. In the 'Memory 1' task the calculated error decreased significantly for the patients with mild ataxia. In the 'Memory 2' task all cerebellar patients improved their performance substantially enough to reduce significantly the magnitude of all three error measurements. The experiments demonstrate that patients with cerebellar lesions are capable of improving substantially their performance of a complex motor task involving the recall of memorized shapes and the visuomotor control of a tracing movement.

Adolescent↗

PubMed1995

Progressive apraxia in clinically discordant monozygotic twins.

OBJECTIVE: To determine disease concordancy in the first identical twin with corticobasal degeneration. The patients were 63-year-old, erythrocyte antigen-confirmed monozygotic male twins who were clinically discordant for progressive apraxia caused by corticobasal degeneration. INTERVENTIONS: Neuropsychologic and kinesiologic testing, magnetic resonance imaging, and positron emission tomographic measurements of cerebral metabolic rate for glucose. RESULTS: The affected twin had lower neuropsychologic and kinesiologic test scores than did his brother, particularly on tests sensitive to right-compared with left-hemisphere function; widespread cerebral atrophy, worst in right parietotemporal cortices; and reduced whole-brain cerebral metabolic rate for glucose, worst in right posterior cortices. The clinically asymptomatic twin had normal neuropsychologic and kinesiologic test scores but performed more poorly on tests sensitive to left- compared with right-hemisphere function; had no abnormalities on magnetic resonance imaging; and had left temporoparietal as well as mild whole-brain hypometabolism. CONCLUSIONS: Corticobasal degeneration may remain clinically discordant in identical twins after 7 years. Positron emission tomography and neuropsychologic findings suggest the possibility of a preclinical stage of corticobasal degeneration. There is generalized cortical atrophy in patients with corticobasal degeneration in addition to focal atrophy.

Apraxias↗

PubMed1995

Influence of flupirtine on human lower limb reflexes.

The influence of a single oral dose (400 mg) of flupirtine on lower limb reflexes was investigated in normal human subjects using H-reflex testing, flexor reflex testing and dynamic posturography. Flupirtine did not significantly change the latency of the H-reflex or the Hmax/Mmax ratio. Both, the first (F1) and the second (F2) components of the flexor reflex were significantly depressed. Flupirtine significantly decreased the size of the ML response following fast transient platform movements rotating toe-up around the ankle joint. We conclude that flupirtine acts on polysynaptic spinal pathways. In addition to its well known analgesic effect flupirtine might have a muscle relaxant effect.

Adult↗

PubMed1995

Localization of a cerebellar timing process using PET.

We used positron emission tomography (PET) to localize a cerebellar timing function. Six healthy volunteers estimated time differences by comparing a test interval (defined by two tones) with a standard interval. In the timing condition, subjects lifted their right index finger if the test interval was shorter and their right middle finger if it was longer than the standard interval. In the control condition, the two intervals were identical and subjects had to alternate between lifting their index and middle fingers. We examined regional cerebral blood flow (rCBF) using the standard C15O2 inhalation technique. Comparison of control and rest conditions revealed significant increases of rCBF during the control condition in the inferior parts of the ipsilateral cerebellar hemisphere, reflecting finger movements. Comparison of timing and control conditions showed additional activations of the cerebellar vermis and hemispheres bilaterally during the timing condition, reflecting the cerebellar timing process. We conclude that the cerebellum is involved in time-critical perception ("timing"). This nonmotor task can be separated from a motor task (finger movement).

Acoustic Stimulation↗

PubMed1994

Influence of visual and somatosensory input on leg EMG responses in dynamic posturography in normals.

The contribution of visual and somatosensory input to stabilization after sudden postural disturbances was investigated. Fast transient platform movements (50 degrees/sec, 4 degrees), rotating toe-up around the ankle-joint, evoke EMG responses in the triceps surae (TS) and anterior tibial (TA) muscles. The short and medium latency responses (SL, ML) in the TS destabilize, the long latency responses (LL) in the TA stabilize the upright posture. The influence of vision was tested in normals comparing the conditions eyes open with eyes closed. The influence of additional somatosensory input was tested with the operator's index finger touching the back of the subject with eyes closed. Absent visual input (eyes closed) resulted in a decrease in latency of the stabilizing LL response and an increase in the integrated EMG (iEMG). With eyes closed the latency of the LL response decreased by 4 msec on average (mean eyes open: 111.6 msec (S.D. = 17.3), eyes closed: 107.6 msec (S.D. = 17.5); P < 0.001 (Wilcoxon test)), the iEMG increased by 10% (mean eyes open: 13.9 microV.sec (S.D. = 7.6), eyes closed: 15.5 microV.sec (S.D. = 8.6); P < 0.001). Additional somatosensory input as an external reference for body orientation in space resulted in an increase in latency and decrease in iEMG: the latency increased by 7 msec on average (mean eyes closed: 107.6 msec (S.D. = 17.5), index finger and eyes closed: 114.7 msec (S.D. = 19.9); P < 0.001), the iEMG decreased by 20% (mean eyes closed 15.5 microV.sec (S.D. = 8.6), index finger and eyes closed: 12.3 microV.sec (S.D. = 7.5); P < 0.001). There was no significant change in latency of SL and ML. We conclude that postural EMG responses in leg muscles after fast transient platform movements change according to different functional demands, modulated via visual and somatosensory input.

Adolescent↗

PubMed1993

The role of vertebral and internal carotid artery disease in the pathogenesis of vertebrobasilar transient ischemic attacks.

Color-coded duplex sonography has improved the evaluation of the hemodynamics of the vertebral arteries (VA). A reliable differentiation between a normal vessel, hypoplasia, stenosis and occlusion of VA can now be made. We studied two groups of patients in a prospective study with isolated carotid artery disease (n = 48), and with a combination of carotid and vertebral artery disease (n = 14), to determine the role of VA in the pathogenesis of transient ischemic attacks (TIAs) in the vertebrobasilar system. Apart from the existing arteriosclerotic changes of the internal carotid arteries, the condition of the VA was of importance for the occurrence of TIAs in the vertebrobasilar territory. We found that 8% of the patients with isolated hemodynamically relevant stenosis or occlusion of one or both internal carotid arteries had a TIA in the vertebrobasilar territory. Patients with combined carotid and vertebral artery disease had an increase of TIAs in the same region in 71%. The high rate of TIAs in this group might be attributed to the combined effect of carotid and vertebral artery disease, as a third group (n = 30) with isolated vertebral artery disease showed TIAs in only 13%.

Blood Flow Velocity↗

PubMed1992

[Doppler and duplex sonography of the vertebral arteries].

In a prospective study 451 patients were examined with extracranial CW-Doppler sonography (mastoidal slope), suboccipital transcranial Doppler sonography and colour-coded duplex sonography to evaluate unusual vertebral arteries (hypoplasia, stenosis and occlusion). Colour duplex sonography was used as reference method. CW-Doppler sonography had a sensitivity of 100% and a specificity of 27% for the detection of an unusual vertebral artery. For transcranial Doppler sonography these values are 38% and 58%. Our study showed that CW-Doppler is a useful screening examination for identifying pathological findings of vertebral arteries. In case of abnormalities in CW-Doppler, duplex sonography, especially colour-coded duplex sonography, should be added.

Adult↗

PubMed1990

Diagnostic significance of tibial nerve somatosensory evoked potentials (spinal and cortical components) with spinal cord lesions.

Forty normal subjects were investigated with the somatosensory evoked potential technique following stimulation of the posterior tibial nerve in order to yield information upon normal values, and especially the origin of the cervical potential. Subsequently an electrophysiologic localization of tumours along the spinal cord was attempted in 18 patients with spinal tumours. In C2 recordings with Fz reference 3 components, N28, N30, and N34, are visible. Simultaneous cortical and cervical recordings with mastoid, knee, and neck references suggest a cranio-cervical origin of N28, a subcortical origin of N30 and a thalamic or thalamo-cortical origin of N34. In patients, the lumbar spinal cord potentials regularly yielded a useful additional information with respect to the tumour site. The cervical potentials added in 5 out of 18 patients additional information localizing the tumour within the spinal cord or brain-stem.

Adult↗

PubMedDate not supplied

Liposarcoma with unusual neurological manifestations.

Central nervous system involvement in liposarcoma is rare, the only symptom reported in the literature being local compression of the spinal cord. An exceptional case with peripheral nerve involvement due to local recurrence, in addition to spinal cord compression and cavernous sinus syndrome due to metastases is reported.

Adult↗