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Biomedical subjects

Dennis A Nowak

Publications and source records attributed to Dennis A Nowak.

At least 19 recordsLinked to original sources
PubMed2006

Dexterity in cerebellar agenesis.

Given the well established role of the cerebellum in motor control, deficient motor performance during life time appears to be common in cerebellar agenesis. However, behavioural data on motor performance in living subjects with cerebellar agenesis are scarce. Dexterity during object manipulation was comparatively investigated in a 63-year old female with cerebellar agenesis and three healthy age- and gender-matched control subjects. Participants performed a transport task with an instrumented object and caught a weight that was dropped into a hand-held receptacle either expectedly from the opposite hand or unexpectedly from the experimenter's hand. Compared to healthy subjects, the subject with cerebellar agenesis generated greater grasping forces. For the transport task the patient showed a clear impairment of the predictive adjustment of grasping forces to the differential loading requirements of movement direction. For the weight-catching task, the patient established an accurate reactive mode of control when the weight was dropped unexpectedly. In case the weight was dropped expectedly from the opposite hand, predictive control mechanisms were severely disturbed in the subject with cerebellar agenesis. These data highlight the role of the cerebellum for predictive force control and are interpreted within the concept of internal models reflecting the causal relationship between actions and their consequences.

Aged↗
PubMed2006

Acute myelopathy of unknown aetiology: a follow-up investigation.

Acute myelopathy refers to acute or subacute spinal cord dysfunction secondary to various causes. Recent studies suggest a number of distinct clinical, laboratory, MRI and outcome profiles for the various aetiologies. Nevertheless, the aetiology of acute myelopathy remains unknown in up to 60% of the patients. The probability of establishing the correct diagnosis increases with the duration of clinical and MRI follow-up. This paper presents the results of a follow-up of nine cases of acute myelopathy of unknown aetiology. One patient was lost during follow-up. Mean age of patients at the time of the follow-up interview was 48 years (+/-12). Average time from discharge to follow-up interview was 3.6 (+/-0.5) years. In four patients (mean age 45+/-13 years) the origin of acute myelopathy remained unclear after an average follow-up of 3.3 years. In one patient the diagnosis of multiple sclerosis was established during follow-up. In another patient the clinical course was suggestive for multiple sclerosis. One patient was diagnosed with systemic collagen vascular disease and in one patient a diagnosis of non-Hodgkin's lymphoma was established. It is unclear whether the patients in whom the aetiology of acute myelopathy remained unknown, even after several years of follow-up, are at a higher risk of developing progressive disease. Larger studies with longer follow-up periods and clear clinical, laboratory and MRI criteria should help to shed some light on this issue.

Adult↗
PubMed2006

Predictive and reactive control of grasping forces: on the role of the basal ganglia and sensory feedback.

We comparatively investigated predictive and reactive grip force behaviour in 12 subjects with basal ganglia dysfunction (six subjects with Parkinson's disease, six subjects with writer's cramp), two subjects chronically lacking all tactile and proprioceptive sensory feedback and 16 sex- and age-matched control subjects. Subjects held an instrumented receptacle between the index finger and thumb. A weight was dropped into the receptacle either unexpectedly from the experimenter's hand with the subject being blindfolded or expectedly from the subject's opposite hand. This paradigm allowed us to study predictive and reactive modes of grip force control. All patients generated an overshoot in grip force, irrespective of whether the weight was dropped expectedly or unexpectedly. When the weight was dropped from the experimenter's hand, a reactive grip force response lagged behind the load perturbation at impact in patients with basal ganglia dysfunction and healthy controls. When the weight was dropped expectedly from the subject's opposite hand, patients with basal ganglia dysfunction and healthy subjects started to increase grip force prior to the release of the weight, indicating a predictive mode of control. We interpret these data to support the notion that the motor dysfunction in basal ganglia disorders is associated with deficits of sensorimotor integration. Both deafferented subjects did not show a reactive mode of force control when the weight was dropped unexpectedly, underlining the importance of sensory feedback to initiate reactive force responses. Also in the predictive mode, grip force processing was severely impaired in deafferented subjects. Thus, at least intermittent sensory information is necessary to establish and update predictive modes of grasping force control.

Adult↗
PubMed2006

CSF drainage ameliorates the motor deficit in normal pressure hydrocephalus: evidence from the analysis of grasping movements.

Apart from the classic triad of hypokinetic gait disorder, cognitive dysfunction and urinary incontinence, the clinical spectrum of normal pressure hydrocephalus has been found to affect the upper limbs. It is unclear if the motor deficit of hand and arm movements improves with CSF evacuation. The present study was designed to quantitatively assess the effect of CSF evacuation on the hypokinesia of grasping movements in normal pressure hydrocephalus. Eight subjects with normal pressure hydrocephalus grasped to lift an instrumented object prior to and following evacuation of 40 ml CSF. The build-up of fingertip forces and the kinematics of the lifting movement were slower for patients compared with healthy controls. Patients also generated excessive grasping forces when lifting and holding the object stationary prior to and following CSF evacuation. CSF evacuation significantly improved the gait disorder, the cognitive impairment and the urinary incontinence in normal pressure hydrocephalus. CSF evacuation accelerated the lifting movement and reduced the grip force overshoot. These data suggest that the measurement of grasping forces may provide an additional test to quantify the clinical response to CSF tapping in normal pressure hydrocephalus.

Aged↗
PubMed2006

Sensory timing cues improve akinesia of grasping movements in Parkinson's disease: a comparison to the effects of subthalamic nucleus stimulation.

Five parkinsonian subjects with chronic bilateral stimulation of the subthalamic nucleus and five sex- and age-matched healthy controls grasped, lifted, and held an instrumented object. The grip-lift task was either performed at self-determined speed or in response to an auditory cuing signal. Parkinsonian subjects performed the task with subthalamic nucleus stimulation switched ON and OFF. In Parkinson's disease, stimulation of the subthalamic nucleus and the presentation of auditory timing cues improved akinesia of both the grasp and lift components of the task. The finding that auditory timing cues improve akinesia in the absence of subthalamic nucleus stimulation suggests that the basal ganglia are less involved in the control of movements made in response to environmental cues. However, subthalamic nucleus stimulation caused parkinsonian subjects to apply excessive grip forces, regardless of whether the movement was made under self-determined or externally guided speed conditions. This implies that subthalamic nucleus stimulation produces a generalized upregulation in the gain of all components of a movement without the subtlety of focused control that is required to normalize performance.

Acceleration↗
PubMed2005

Broadening a classic clinical triad: The hypokinetic motor disorder of normal pressure hydrocephalus also affects the hand.

The clinical spectrum of normal pressure hydrocephalus is thought to comprise the triad of hypokinetic gait disorder, dementia and urinary incontinence. In contrast, motor abnormalities involving the upper limbs in normal pressure hydrocephalus have not yet received a great deal of attention. The present study was designed to quantitatively assess grasping movements in normal pressure hydrocephalus and to compare the performance with that in Parkinson's disease. Eight subjects with normal pressure hydrocephalus, eight subjects with Parkinson's disease and eight healthy control subjects grasped to lift an instrumented object. The built-up of fingertip forces during the early phase and the kinematics of the lifting movement during the late phase of the grip-lift synergy were slower for patients compared to healthy controls. Patients generated abnormally high fingertip forces when lifting and holding the object stationary. The slowness of the grip-lift synergy and the force overshoot was similar for both patient groups. Our data demonstrate that the hypokinetic motor deficit in normal pressure hydrocephalus also involves the hand, and that the pattern of deficits shares several features of those found in Parkinson's disease.

Aged↗
PubMed2005

Objective evaluation of manual performance deficits in neurological movement disorders.

Impaired hand function is a frequent finding in movement disorders. The skilled control of prehensile finger forces is an essential feature of tool use in daily life. In healthy subjects, grip force is precisely adjusted to the mechanical object properties, such as weight and surface friction. Grip force is accurately scaled to be only a small amount higher than the minimum necessary to prevent a hand-held object from slipping. When an object is lifted and moved around in space, grip force is modulated in parallel with the movement-induced fluctuations in load. The absence of a temporal delay between grip and load force profiles implies that the central nervous system is able to predict the load variations before the intended manipulation. Sensory information is used to adjust the level of applied finger forces efficiently to the requirements of the mechanical object properties and the task at hand. The characteristics of impaired finger force control include inefficient grip force scaling and imprecision of the temporal coupling between grip and load force profiles. Here, we review the characteristics of deficient grip force behavior in movement disorders, e.g. Parkinson's disease, task-specific dystonia, Gille de la Tourette's syndrome and cerebellar disease. Grip force analysis is a highly sensitive method to document even subtle impairments of finger force control and may be used both as a diagnostic tool and for the objective evaluation of treatment in neurological movement disorders.

Fingers↗
PubMed2005

The clinical variability of Wallenberg's syndrome. The anatomical correlate of ipsilateral axial lateropulsion.

The dorso-lateral medullary syndrome (Wallenberg's syndrome) is produced by infarction of a wedge of lateral medulla posterior to the inferior olivary nucleus and is usually caused by vertebral artery occlusion. Ipsilateral axial lateropulsion as an initial symptom of vertebral artery occlusion is rather rare and the anatomical structure responsible is still uncertain. Here we describe two patients presenting with ipsilateral axial lateropulsion as an initial symptom of vertebral artery occlusion. In one the stroke affected the dorso-lateral aspect of the medulla, in the other more lateral aspects of the medulla were involved. Our data suggest that ipsilateral axial lateropulsion may be caused by lesions of different topography involving either the vestibular nuclei, the cerebellar peduncle or the spinocerebellar tracts.

Aged↗
PubMed2005

Preserved and impaired aspects of predictive grip force control in cerebellar patients.

OBJECTIVE: To analyze preserved and impaired aspects of feedforward grip force control during cyclic arm movements with a hand-held object after cerebellar damage. METHODS: We tested eight subjects with unilateral or bilateral cerebellar pathologies and eight healthy control subjects. Participants performed cyclic vertical arm movements with a hand held instrumented object at three different speeds. RESULTS: Compared to controls, patients excerted increased grip forces. The minimum force ratio between grip force and load force was constant across all movement frequencies, suggesting that patients anticipated speed-related changes in load magnitudes by adjusting the grip force. Thus the scaling of grip force level to self-generated load magnitudes was preserved. The coupling between grip and load profiles was assessed by cross correlation analysis. Patients exhibited significantly decreased maximum coefficients of cross correlation implicating impaired anticipation of inertial load fluctuations. However feedforward control could be preserved, as obvious from zero time lags of the maximum cross correlation coefficient. CONCLUSIONS: Our findings suggest that cerebellar lesions affect the processing of predictive grip force modulation in anticipation of inertial loads. Our results add further evidence to the theoretical concept that the cerebellum implements internal feedforward models. However, preserved functions may indicate compensatory mechanisms or extra-cerebellar aspects of grip and load force regulation. SIGNIFICANCE: The observed dissociation of performance deficits may have direct clinical implication and may guide the development of individual therapeutic strategies for patients with cerebellar disorders.

Adult↗
PubMed2005

Grip force behavior during object manipulation in neurological disorders: toward an objective evaluation of manual performance deficits.

The control of prehensile finger forces is an essential feature of skilled manual performance. The basic aspects of healthy grip force behavior have been well documented. In healthy subjects, grip force is precisely adjusted to the mechanical object properties. Grip force is always slightly higher than the minimum necessary to prevent the object from slipping. When we move a hand-held object, grip force is modulated in parallel with movements-induced load fluctuations without an obvious delay. The absence of a temporal delay between grip and load force profiles suggests that the central nervous system is able to predict the load variations before the intended manipulation and consequently regulates grip force in anticipation. Feedback from the grasping fingertips is used to adjust the level of applied fingertip force efficiently to the actual loading requirements. Pathologic grip force control affects the efficiency of produced force and the precision of the temporal coupling between grip and load force profiles. Here, we review the characteristics of pathologic grip force behavior in various neurological disorders. Detailed examination of grip force control is simple and well suited for the objective evaluation of impaired motor function of the hand and its rehabilitation.

Biomechanical Phenomena↗
PubMed2005

Grip force behavior in Gilles de la Tourette syndrome.

We analyzed predictive and reactive grip force behavior in 15 patients with Gilles de la Tourette syndrome (GTS) and 15 sex- and age-matched healthy control subjects. Nine patients were without medication; six patients were on medication. In a first experiment, participants lifted and held instrumented objects of different weight. In a second experiment, participants performed vertical point-to-point and continuous arm movements at different frequencies with a hand-held object. In a third experiment, preparatory and reactive grip force responses to sudden load perturbations were analyzed when a weight was dropped into a hand-held cup either by the subject or unexpectedly by the experimenter. Compared to the healthy subjects, GTS patients had increased grip forces relative to the load force in all tasks. Despite this finding, they adjusted the grip force to changes in load force (due to either a change in the mass lifted or accelerating the mass during continuous movements) in the same way as healthy subjects. The temporal coupling between grip and load force profiles was also similar in patients and healthy controls, and they displayed normal anticipation of impact forces when they dropped a weight into a hand-held cup. We found no significant effect of medication on the performance of GTS patients, regardless of the task performed. These results are consistent with deficient sensory-motor processing in Gilles de la Tourette syndrome.

Acceleration↗
PubMed2005

Diagnostic relevance of transcranial magnetic and electric stimulation of the facial nerve in the management of facial palsy.

OBJECTIVE: Earlier investigations have suggested that isolated conduction block of the facial nerve to transcranial magnetic stimulation early in the disorder represents a very sensitive and potentially specific finding in Bell's palsy differentiating the disease from other etiologies. METHODS: Stimulation of the facial nerve was performed electrically at the stylomastoid foramen and magnetically at the labyrinthine segment of the Fallopian channel within 3 days from symptom onset in 65 patients with Bell's palsy, five patients with Zoster oticus, one patient with neuroborreliosis and one patient with nuclear facial nerve palsy due to multiple sclerosis. RESULTS: Absence or decreased amplitudes of muscle responses to early transcranial magnetic stimulation was not specific for Bell's palsy, but also evident in all cases of Zoster oticus and in the case of neuroborreliosis. Amplitudes of electrically evoked muscle responses were more markedly reduced in Zoster oticus as compared to Bell's palsy, most likely due to a more severe degree of axonal degeneration. The degree of amplitude reduction of the muscle response to electrical stimulation reliably correlated with the severity of facial palsy. CONCLUSIONS: Transcranial magnetic stimulation in the early diagnosis of Bell's palsy is less specific than previously thought. While not specific with respect to the etiology of facial palsy, transcranial magnetic stimulation seems capable of localizing the site of lesion within the Fallopian channel. SIGNIFICANCE: Combined with transcranial magnetic stimulation, early electrical stimulation of the facial nerve at the stylomastoid foramen may help to establish correct diagnosis and prognosis.

Adult↗
PubMed2005

The beneficial effects of subthalamic nucleus stimulation on manipulative finger force control in Parkinson's disease.

We investigated the differential effects of levodopa medication and STN stimulation on finger force control in Parkinson subjects grasping to lift an object and performing vertical point-to-point movements of a hand-held object. The experiments were conducted in four treatment conditions: off-drug/off-stimulation, off-drug/on-stimulation, on-drug/off-stimulation and on-drug/on-stimulation. We found that the bradykinesia in Parkinsonian subjects improved by both levodopa medication and STN stimulation. As compared to healthy subjects, excessive grip force was observed in all Parkinson subjects, regardless of the treatment condition. This force excess was most pronounced in the on-drug condition and ameliorated by STN stimulation. We observed reliable correlations between the amount of force overflow and the severity of levodopa-induced dyskinesias in the on-drug condition. Despite some similarities regarding therapeutic effects on bradykinesia, our findings contrast with earlier observations with respect to the differential effects of levodopa and STN stimulation on the scaling of fingertip forces in Parkinson's disease. While levodopa causes an overshoot of fingertip forces, STN stimulation appears to be sufficient to alleviate, but not normalise the force excess. STN stimulation enables Parkinson subjects to scale grip force more accurately to the loads arising from voluntary manipulation of hand-held objects.

Adult↗
PubMed2005

Impaired generalization of weight-related information during grasping in cerebellar degeneration.

When we repetitively lift an object, the balance between grip force normal to the object's surface and load force tangential to the object's surface is accurately programmed to match the physical object properties within a few lifts. Here, we ask if the accuracy of grip force scaling to object weight and the transfer of weight-related information from one hand to the other is impaired in cerebellar degeneration. Subjects with generalized cerebellar degenerative disorders were tested. Subjects first repeatedly lifted a constant weight with the dominant hand, followed by a series of lifts of the same weight with the opposite hand. The experiments were performed with a light and a heavy weight. Patients and controls scaled the grip force output differentially to different weight. The comparison of grip force scaling for the first and last lifts with a constant weight demonstrated that healthy subjects and cerebellar patients adjusted grip forces more accurately to a specific weight with increasing number of lifts performed at each hand. The ability to transfer weight-related information from one hand to the other was analyzed by comparing the last lift with a constant weight of the dominant hand with the first lift of the same weight performed by the opposite hand. Healthy subjects scaled the grip force output precisely to a given weight immediately after a change in hand, suggesting that they succeeded to transfer weight-related information in between both hemispheres. In contrast, cerebellar patients produced an inaccurate grip force overshoot when lifting a given weight with the opposite hand. Our data suggest that the cerebellum plays a major role for the generalization of weight-related information during object manipulation.

Aged↗
PubMed2005

High-frequency repetitive transcranial magnetic stimulation over the hand area of the primary motor cortex disturbs predictive grip force scaling.

When we repetitively lift an object, our grip force is influenced by the mechanical object properties of the preceding lift, irrespective of whether the subsequent lift is performed with the same hand or the hand opposite to the preceding lift. This study investigates if repetitive high-frequency transcranial magnetic stimulation (rTMS) over the dominant primary motor cortex affects this relationship. After completion of 10 lifts of an object using the dominant hand, rTMS was applied over the dominant primary motor cortex for 20 s. On the first lift following rTMS, the peak grip force was significantly higher than on the lift preceding rTMS. Moreover, this measure remained elevated throughout the following set of lifts after rTMS. rTMS did not change the peak lift force generated by more proximal arm muscles. The same effect was observed when the lifts following rTMS over the dominant motor cortex were performed with the ipsilateral hand. These effects were not observed when subjects rested both hands on their lap or when a sham stimulation was applied for the same period of time. These preliminary data suggest that rTMS over the sensorimotor cortex disturbs predictive grip force planning.

Adult↗