A. Häußler

Circadian Variations in the Kinematics of Handwriting and Grip Strength

The present study determined whether the motor process of handwriting is influenced by a circadian rhythm during writing tasks of high everyday relevance and analyzed the relationship to the circadian rhythm of grip strength. Ten healthy young male subjects underwent a 40 h sleep‐deprivation protocol under constant routine conditions. Starting at 09:00 h, subjects performed three handwriting tasks of increasing perceptual‐motor complexity (writing a sentence, writing ones signature, and copying a text for 3 min) and assessed grip strength of both hands every 3 h. Handwriting performance was analyzed by writing speed, writing fluency, script size, break times, and pen pressure. The handwriting tasks revealed a coincident circadian rhythm for the frequency of handwriting as a measure of movement speed, with slowest writing speed at 03:16 h. A weak effect of task complexity was evident for the non‐writing episodes: while copying a text, break times were influenced by a circadian rhythm, whereas during sentence writing, the non‐writing episodes remained constant. The circadian rhythm of grip strength paralleled the time course of motivation ratings, with least motivation and weakest grip strength around 06:00 h concurrently for both hands. The rate of force production also displayed circadian rhythmicity and sharply decreased with the onset of melatonin secretion. Neither grip strength nor the kinematics of handwriting was influenced by sleep deprivation; only the level of the force rate was decreased the second day. The results show a clear circadian rhythm in the speed of handwriting and grip strength.

Circadian rhythm in handwriting.

The aim of the present study was to determine whether the motor process of handwriting is influenced by a circadian rhythm. Nine healthy young male subjects underwent a 40‐h sleep deprivation protocol under constant routine conditions. Starting at 09:00u2003hours, subjects performed every 3u2003h two handwriting tasks of different complexity. Handwriting performance was evaluated by writing speed, writing fluency and script size. The frequency of handwriting, as a measure of movement speed, revealed a circadian rhythm, validated by harmonic regression, with a slowing at the time of the onset of melatonin secretion (22:17u2003hours) and a trough in the very early morning at around 03:30u2003hours. In the temporal variability of handwriting an effect of task complexity was suggested in the direction of circadian variations in parallel with speed only for the sentence. Despite deficits of speed and temporal variability, writing fluency did not change significantly across sessions indicating that the basic automation of handwriting was preserved at any time. On the second day, daytime levels of the kinematics of handwriting did not reflect impaired performance after sleep deprivation. Our results show for the first time a clear circadian rhythm for the production of handwriting.

Influences of Load Characteristics on Impaired Control of Grip Forces in Patients With Cerebellar Damage

Various studies showed a clear impairment of cerebellar patients to modulate grip force in anticipation of the loads resulting from movements with a grasped object. This failure corroborated the theory of internal feedforward models in the cerebellum. Cerebellar damage also impairs the coordination of multiple-joint movements and this has been related to deficient prediction and compensation of movement-induced torques. To study the effects of disturbed torque control on feedforward grip-force control, two self-generated load conditions with different demands on torque control-one with movement-induced and the other with isometrically generated load changes-were directly compared in patients with cerebellar degeneration. Furthermore the cerebellum is thought to be more involved in grip-force adjustment to self-generated loads than to externally generated loads. Consequently, an additional condition with externally generated loads was introduced to further test this hypothesis. Analysis of 23 patients with degenerative cerebellar damage revealed clear impairments in predictive feedforward mechanisms in the control of both self-generated load types. Besides feedforward control, the cerebellar damage also affected more reactive responses when the externally generated load destabilized the grip, although this impairment may vary with the type of load as suggested by control experiments. The present findings provide further support that the cerebellum plays a major role in predictive control mechanisms. However, this impact of the cerebellum does not strongly depend on the nature of the load and the specific internal forward model. Contributions to reactive (grip force) control are not negligible, but seem to be dependent on the physical characteristics of an externally generated load.

CIRCADIAN RHYTHM IN FORCE TRACKING AND IN DUAL TASK COSTS

The present study determined a circadian rhythm in force control during a visually guided tracking task under single task conditions (i.e., tracking task presented alone) and dual task conditions (i.e., tracking task together with a memory task). Nine healthy young male subjects participated in a Constant Routine protocol involving a week of regular bedtimes, a baseline night of 8 h sleep, and subsequent wakefulness of 40 h. Subjects performed an eye-hand coordination task that required tracking an unpredictable target (presented on a computer screen) by using grip force to adjust a visual feedback to the changing target. Tracking performance (both in precision and delay) were time-of-day-specific with worst performance at around 04:00 h. The dual task costs, as an index of interference of two tasks performed simultaneously, only showed a significant effect of the memory task on tracking precision during the circadian minimum. In contrast, dual task costs were close to zero during midday and absent in tracking delay. Tracking precision descriptively revealed inter-individual differences: half of the subjects maintained fairly stable performance during the 40 h of wakefulness, whereas the other half showed a clear circadian rhythmicity in tracking precision. Thus, tracking precision seems to be a sensitive parameter for conditions of divided attention and inter-individual variability during the circadian minimum, whereas tracking delay revealed neither a dichotomy of task conditions nor inter-individual differences in performance-amplitude over sessions. Nonetheless, both tracking precision and delay showed a comparable circadian rhythmicity. (Author correspondence: Isabelle.Jasper@extern.lrz-muenchen.de)

A system for the study of visuomotor coordination during reaching for moving targets.

Prehensile behavior is a popular task in current research on human motor control. Most studies on reaching used stationary target objects and, therefore, most models do not address the challenges the motor system must respond to when reaching for moving objects. The machines used in earlier studies to produce object motion offered a limited range of trajectories and restricted control over various movement parameters. We have developed a device that allows a great variety of object trajectories along a flat-table surface and gives the experimenter full control over all movement parameters. A linear positioning system is used to move a sled beneath the table surface. Magnetic coupling transfers the sleds movement to the target object on the tabletop. This arrangement allows fast movements of the object (up to 5 m/s) and at the same time protects subjects from any harm due to the moving parts. The system is connected to LC shutter glasses, a 3-D movement registration device, and a switch that detects the onset of hand motion. This allows the selective withdrawal of vision during the reaching task or the introduction of changes in the object motion depending on the subjects reactions.

Completing queries: rewriting of incomplete web queries under schema constraints

Web queries have been and will remain an essential tool for accessing, processing, and, ultimately, reasoning with data on the Web. With the vast data size on the Web and Semantic Web, reducing costs of data transfer and query evaluation for Web queries is crucial. To reduce costs, it is necessary to narrow the data candidates to query, simplify complex queries and reduce intermediate results. n nThis article describes a static approach to optimization of web queries. We introduce a set of rules which achieves the desired optimization by schema and type based query rewriting. The approach consists in using schema information for removing incompleteness (as expressed by descendant constructs and disjunctions) from queries. The approach is presented on the query language Xcerpt, though applicable to other query languages like XQuery. The approach is an application of rules in many aspects--query rules are optimized using rewriting rules based on schema or type information specified in grammar rules.

Ein echtzeitfähiges, autonomes Greifobjekt zur Evaluation feinmotorischer Funktionen

Die Registrierung der Griffkrafte und der kinematischen Bewegungsparameter bei feinmotorischen Objektmanipulationen hat sich als eine hochsensitive Methode zur Erfassung physiologischer Leistungen gesunder Probanden und pathologischer Leistungseinbusen bei Patienten mit peripheren oder zentralen Schadigungen des Nervensystems erwiesen. Laboraufbauten zur Erfassung der Leistungen sind oft aufwendig und mit Einschrankungen bei der Durchfuhrung, z.B. durch Kabel, verbunden. Wunschenswert ist ein flexibles, einfach zu bedienendes und robustes Messsystem, dessen Anwendung die Bewegungsaufgaben nicht behindert und das bei geringem Zeitaufwand zu klar interpretierbaren Ergebnissen fuhrt. Ein Teil der Anforderungen wurde von uns in einem autonomen Messgerat mit einem Sensor zur Messung der Griffkraft und 3-dimensionaler Beschleunigungsmessung realisiert („Thunfischdose“). Dank interner A/D-Wandlung und Daten-Speicherung war wahrend der Messung keine behindernde Kabelverbindung notwendig. Dieses Konzept wurde mit dem hier vorgestellten System modernisiert, verfeinert und ausgebaut. Das Greifobjekt („Sandwich“) beinhaltet neben der etablierten Sensorik eine getrennte Messung der Griffkrafte der opponierenden Finger. Ein zentraler Vorteil ist die Unterstutzung von etablierter Funktechnik, so dass die Messung ohne mechanische Einschrankungen extern gesteuert und kontrolliert werden kann und die Ergebnisse on-line mit gewohnlicher PC- oder PDA-Technik analysiert werden konnen. Zudem wurde im Interesse langer Akkulaufzeit ein rigides Energiekonzept umgesetzt und ein energie-optimierter Mikroprozessor verwendet. Moderne Halbleiter-Speicher erlauben daruber hinaus hohe Datendichten. Erfullt werden diese Anforderungen durch den Einsatz eigens entwickelter Kraftmesstechnik, Halbleiter-Beschleunigungssensoren, Flash-Speicher, des Bluetooth-Protokolls und der Prozessorfamilie MSP430. Ein Einsatzfall fur das Mess-System ist beispielsweise die Analyse der Effekte unterschiedlicher Interventionen bei neurologischen Patienten, wie etwa physio- oder ergotherapeutischer Behandlungen, Trainingsprogramme, oder auch neue, auf kortikaler Stimulation basierende Verfahren. Ein anderer Einsatzfall sind wiederholte Messungen zur Studie circadianer Modulation von Sensomotorik und zur Evaluation von den Effekten der Arbeitsbelastung (Schichtarbeit) auf feinmotorische Leistungen. Gefordert durch die Gottfried Daimler- und Karl Benz-Stiftung