Biomedical subjects

D Timmann

Publications and source records attributed to D Timmann.

At least 55 records · Page 3Linked to original sources

PubMed2000

Predictive control of muscle responses to arm perturbations in cerebellar patients.

OBJECTIVES: To examine changes in predictive control of early antagonist responses to limb perturbations in patients with defined lesions of the cerebellum. METHODS: Eight cerebellar patients and eight sex and age matched control subjects participated. Subjects held a handle that was rotated around the elbow joint. They were instructed to hold the forearm at 90 degrees flexion against a mechanical perturbation. Extensor torque (5 Nm) was applied for 140 ms (pulse), or for 1400 ms (step) through an external motor. Motor responses were tested under two different conditions of anticipatory information. In the expected condition, subjects anticipated and received a pulse. Under the unexpected condition, subjects expected steps, but received unexpected pulses. Biceps and triceps EMG as well as angular kinematics were compared between expected and unexpected pulse perturbations to quantify possible effects of prediction. RESULTS: In all healthy subjects, the degree of overshoot in the return flexion movement was significantly less in expected pulse perturbations compared with unexpected trials. The degree of amplitude reduction was significantly smaller in the patient group than in the control group (22.8% v 40.0%). During the expected trials, latency of peak triceps activity was on average 20% shorter in the control group, but 4% larger in the cerebellar patients. CONCLUSIONS: In the expected condition, controls achieved a significant reduction in angular amplitude by generating triceps activity earlier, whereas the ability to use prediction for adjusting early antagonist responses after limb perturbation was impaired in cerebellar patients.

Adolescent↗

PubMed1999

A kinematic study of progressive apraxia with and without dementia.

BACKGROUND: Prehension is an ideationally simple, cued movement requiring proximal (transport) and distal (manipulation) limb control. Patients with this syndrome of progressive apraxia are unable to perform many activities of daily living that require prehension. There is little known about how this syndrome kinematically disrupts such movements or whether concurrent dementia might play a critical role. OBJECTIVES: Using prehension as a paradigm for an ideationally simple, cued functional movement, we sought to (1) characterize the kinematic features of progressive apraxia in general, and (2) contrast the kinematic differences between apraxic patients with and without dementia. METHODS: Eight patients with the syndrome of progressive apraxia (including five without dementia, one of whom had autopsy-confirmed corticobasal ganglionic degeneration, and three with dementia, one of whom had autopsy-confirmed Alzheimer's disease) were compared with eight age-matched normal control subjects on a prehension task using an Optotrak camera system. RESULTS: Compared with control subjects, apraxic subjects had slowed reaction time, slowed transport and manipulation kinematics, greater lateral deviation from the linear prehension trajectory, greater intermanual asymmetry, motor programming disturbances, and mild transport-manipulation uncoupling. There were minor differences between the apraxia subgroups such as greater intermanual differences and impaired grip aperture velocity in the nondemented group, and overall slower movement in the demented group. CONCLUSIONS: There are major kinematic differences between apraxic and control subjects on a prehension task. The differences between clinical-pathologic subgroups are more subtle, and the movement disorder itself rather than concurrent dementia is the greatest determinant of motor disability.

Aged↗

PubMed1999

Non-motor associative learning in patients with isolated degenerative cerebellar disease.

In recent decades it has become clear that the cerebellum is involved in associative motor learning, but its exact role in motor learning as such is still controversial. Recently, a contribution of the cerebellum to different cognitive abilities has also been considered, but it remains unclear whether the cerebellum contributes to cognitive associative learning. We compared nine patients with an isolated cerebellar degenerative disease in a cognitive associative learning task with 10 controls. Patients and controls were matched for age, sex, handedness, level of education, intelligence and capabilities of visual memory. The subjects were asked to learn the association between six pairs of colours and numerals by trial and error. Additionally, a simple reaction time and a visual scanning test were conducted in order to control for the influence of motor performance deficits in cerebellar patients. In comparison with the controls, it took the patients significantly longer to learn the correct associations between colours and numerals, and they were impaired in recognizing them later on. Two patients showed no associative learning effect at all. Neither the simple reaction time nor the visual scanning time correlated substantially with the results of associative learning. Therefore, motor-associated disabilities are unlikely to be the reason for the learning deficit in cerebellar patients. Our results suggest that the cerebellum might contribute to motor-independent processes that are generally involved in associative learning.

Aged↗

PubMed1999

Failure of cerebellar patients to time finger opening precisely causes ball high-low inaccuracy in overarm throws.

We investigated the idea that the cerebellum is required for precise timing of fast skilled arm movements by studying one situation where timing precision is required, namely finger opening in overarm throwing. Specifically, we tested the hypothesis that in overarm throws made by cerebellar patients, ball high-low inaccuracy is due to disordered timing of finger opening. Six cerebellar patients and six matched control subjects were instructed to throw tennis balls at three different speeds from a seated position while angular positions in three dimensions of five arm segments were recorded at 1,000 Hz with the search-coil technique. Cerebellar patients threw more slowly than controls, were markedly less accurate, had more variable hand trajectories, and showed increased variability in the timing, amplitude, and velocity of finger opening. Ball high-low inaccuracy was not related to variability in the height or direction of the hand trajectory or to variability in finger amplitude or velocity. Instead, the cause was variable timing of finger opening and thereby ball release occurring on a flattened arc hand trajectory. The ranges of finger opening times and ball release times (timing windows) for 95% of the throws were on average four to five times longer for cerebellar patients; e.g., across subjects mean ball release timing windows for throws made under the medium-speed instruction were 11 ms for controls and 55 ms for cerebellar patients. This increased timing variability could not be explained by disorder in control of force at the fingers. Because finger opening in throwing is likely controlled by a central command, the results implicate the cerebellum in timing the central command that initiates finger opening in this fast skilled multijoint arm movement.

Adolescent↗

PubMed1998

Perturbed step initiation in cerebellar subjects. 1. Modifications of postural responses.

Recent experiments in healthy subjects have demonstrated that automatic postural responses can be suppressed when subjects are instructed to step instead of maintain stance in response to the surface translation. The aim of the present study was to investigate the role of the cerebellum in coordinating this interaction between the central command to step and peripherally triggered automatic postural responses. Eight subjects with cerebellar degeneration and eight control subjects were instructed to either maintain stance or step forward in response to a backward translation. In order to determine whether prediction of perturbation amplitude assisted suppression of postural responses, three platform translations were presented in both a serial (predictable) and a random (unpredictable) order. Cerebellar subjects were able to suppress their initial postural responses to the same amount as control subjects when instructed to step forward in response to backward translations, despite their hypermetria and inability to scale responses to predictable perturbation amplitudes. Control, but not cerebellar, subjects scaled the size of their postural responses to predictable perturbation amplitudes. The perturbation amplitude, however, had no effect on the size of early automatic responses when they were suppressed by instruction to step. The size of the suppressed postural response was independent of predictability of perturbation amplitudes in both control and cerebellar subjects. The dynamic interaction between automatic postural responses to an external perturbation and anticipatory postural adjustments for step initiation seems independent of prediction of perturbation amplitude and the integrity of the cerebellum. Although cerebellar subjects show larger-than-normal magnitude and variability of postural responses and an inability to scale the size of responses to predictable perturbation amplitudes, the cerebellum does not seem to be critical for suppression of the early postural response with a centrally intended movement.

Adaptation, Physiological↗

PubMed1998

Postural responses to changing task conditions in patients with cerebellar lesions.

OBJECTIVE: To investigate the role of the cerebellum in postural adaptation for changes to the stimulus type of support surface displacements (backward translations v "toes up" rotations). METHODS: A group of 13 patients with chronic, isolated lesions of the cerebellum and 15 control subjects were tested. Automatic postural responses of the medial gastrocnemius and anterior tibial muscles were recorded. The first paradigm consisted of 10 rotational perturbations followed by 10 backward translations of the platform, and 10 backward translations followed by 10 rotations. The second paradigm consisted of 18 rotations and two randomly interposed translational perturbations, and 18 translations with two rotations randomly interposed. RESULTS: When the type of perturbation changed from an expected translation to an unexpected rotation and vice versa both control subjects and cerebellar patients showed an immediate and significant change in the response amplitude of the medial gastrocnemius and at the same time an immediate and significant change in the response amplitude of the anterior tibial muscles. Neither controls nor cerebellar patients showed effects of prediction in surface displacements of unexpected types of perturbation. Both controls and cerebellar patients showed no gradual increase in the gastrocnemius response in subsequent trials of surface translations following a block of 10 surface rotations and no gradual increase in the response amplitude of the anterior tibial muscle in subsequent trials of surface rotations following a block of 10 surface translations. CONCLUSIONS: Despite postural hypermetria, the integrity of the cerebellum does not seem critical for adaptation of postural synergies to changing stimulus types of surface displacements. The present results support previous findings suggesting that the main role of the cerebellum in automatic postural responses may be gain control.

Adult↗

PubMed1998

Involvement of the human cerebellum during habituation of the acoustic startle response: a PET study.

The present study investigated the involvement of the human cerebellum in the habituation of the acoustic startle response using PET. The startle response was elicited in seven young, healthy subjects by a tone presented via headphones. Startle responses were recorded from the right sternocleidomastoid muscle. Regional cerebral blood flow (rCBF) was assessed in nine scans and one startle stimulus was applied during each scan. The reduction of size of the sternocleidomastoid muscle response was correlated with changes in rCBF during the ongoing process of startle response habituation. A significant decrease of rCBF was found in the medial cerebellum. These data are consistent with an involvement of the medial parts of the human cerebellum in non-associative learning as proposed by previous animal studies.

Acoustic Stimulation↗

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↗