Elderly subjects in senior residences were recruited by poster announcements or by word of mouth. All subjects were tested by a clinical neurologist to determine that they were without neurological symptoms and in good physical condition. Eligibility criteria were lucidity, independence in everyday activities, and the absence of motor handicaps such as functional impairment due to arthritis or other causes of joint immobility. Subjects with significant visual or hearing loss, cerebro-vascular or spinal diseases, pathological tremor, or any functional limitations of the upper limbs as a consequence of stroke or Parkinson's disease were excluded from the study. Medication taken by the subjects was documented to prevent the influence of drugs that may affect the central nervous system. An assessment of cognitive abilities was made using the “Mini Mental State Examination” 
. Only persons with scores of 27 to 30 out of 30 possible points (indicative of “no dementia”) participated in the study. Accordingly, the subjects included in our study represent a subpopulation clearly biased towards mental and physical fitness. Young subjects were recruited by poster announcements from the university community. These individuals reported no known neurological disorders.
Hand preference was determined throughout the study with the “Edinburgh Handedness Inventory” (EHI) 
which classifies handedness on the basis of a short interview on hand preference in the performance of routine practical tasks. The questionnaire evaluates handedness values from –100 for extreme left hand use to +100 for extreme right hand use. Only persons with unambiguous right hand dominance (≥ +70 points) and without a history of hand switching during their lifetime were included. The study was performed in accordance with the Declaration of Helsinki. Subjects gave written informed consent, and the protocol was approved by the local ethics committee of the Ruhr-University Bochum.
Sixty healthy volunteers (34 females and 26 males) participated in this study. Their self-rated handedness (EHI) was compared to the computer-based assessment of their dexterity. Subjects were divided into four age groups designated “25,” “50,” “70,” and “80” in accordance with the average age of the group. Group 25 included 14 subjects (9 females and 5 males) with a mean age of 24.8±3.1 years; group 50 included 14 subjects (8 females and 6 males) with a mean age of 51.8±3.2 years; group 70 included 18 subjects (9 females and 5 males) with a mean age of 70.9±2.7 years, and group 80 included 14 subjects (8 female and 6 males) with a mean age of 80.7±4.7 years.
Self-rated hand dominance revealed no significant differences between the four groups (Oneway ANOVA, F(3,59)
0.989). The EHI scores were calculated as 85.00±7.60 for group 25, 83.08±9.58 for group 50, 83.89±9.48 for group 70, and 83.93±11.63 for group 80.
Motor performance test-series
According to Fleishman 
, fine motor movements can be factorized with regard to speed, accuracy, and maintenance of upper limb positions. We investigated these aspects during execution of fine motor movements of the arms, hands, and fingers using the four separate tests described below.
“Steadiness” () describes the ability to obtain a prescribed arm-hand position and to maintain it for a defined time period. “Line tracing” () describes the ability to fulfill precise, simultaneous arm-hand movements. “Aiming” () describes the ability to accomplish fast arm-hand movements for small targets. “Tapping” () describes the ability to perform very fast, repetitive wrist-finger movements with little emphasis on precision of movement.
Examination of fine motor performance
All tests are available in the commercial test-series “MLS” (Dr. G. Schuhfried GmbH, Austria). The MLS is a computerized device for the accurate analysis of fine motor performance. Data registration was performed with the “Vienna-test-system” software, Version 5.05 (Dr. G. Schuhfried GmbH, Austria). We conducted a short form of the tests (10–15 minutes) in order to create a convenient test-situation for the elderly subjects.
The test board for the MLS can be used in both horizontal and vertical orientations. Two contact pencils are connected to the sides. The number and duration of contacts between pencils and test board are measured by closing electrical circuits (5V, 20mA). Data are transferred via an interface to a computer for analysis. The plain surface of the test board contains holes of different diameters, two rows of small contact plates, two large square contact plates, and a long groove.
Each task was explained by reading a standardized instruction sheet, and then the task was demonstrated to ensure that the subjects fully understood what they had to do. While the subjects sat in front of the board, support of the test arm was not permitted. All tests were performed with both the right and the left hands. To prevent systematic errors, subjects were randomly allocated to use the right or the left hand first.
The subject's task was to place the pencil into a small circular hole (5.8 mm) of the vertically positioned board, and hold it there without touching the edges for 32 seconds without support to steady the hand (). This tested for the ability to hold a steady position, and for the absence of postural tremor 
. Dependent variables were the number of errors, meaning the number of contacts the pencil made with the circumference the hole.
Subjects were instructed to insert the pencil perpendicular to the groove in the horizontally positioned board and follow its course without touching the edges (). This tested ataxia and action tremor by assessing the ability to make visually-controlled, steady, guided movements 
. Subjects were instructed to make as few errors as possible. Dependent variables were number of errors and the total time required to complete the task. Arm movements were carried out from the periphery to midline for each respective hand.
Subjects had to consecutively hit each of a row of 20 linearly arranged small contact fields (diameter 5 mm, midpoint separation 9 mm) with the test pencil (). This test assessed the degree of ataxia and the speed of movement by the ability to make rapid repeated aimed movements 
. Again, the dependent variables were the number of errors (missed contact fields) and the total time needed to complete the task.
Subjects were required to hit a square contact plate (40 by 40 mm) on the test board with the test pencil as frequently as possible (). The measured parameter was number of hits achieved in a time interval of 32 seconds and thereby the speed of antagonistic oscillation 
. Because, in this task, support of the forearm was allowed, the repetitive contacts had to be accomplished by wrist movements.
Another group of 36 healthy volunteers (16 females and 20 males) participated in the second experiment. This time, the self-rated handedness (EHI) was compared with the sensory-based assessment of hand use in everyday activities. As in the first experiment, the groups were designated according to the average age of the group. Group 25 included 13 subjects (6 females and 7 males) with a mean age of 27.3±4.8 years, group 50 had 9 subjects (3 females and 6 males) with a mean age of 52.4±3.1 years, and group 70 had 14 subjects (7 females and 7 males) with a mean age 72.9±3.6 years.
Self-rated hand dominance revealed no significant difference between the three groups (Oneway ANOVA, F(2,35)
0.950). The EHI scores were 88.46±24.44 for group 25, 87.78±6.67 for group 50, and 88.87±10.27 for group 70.
Assessment of hand movements in everyday activities
In order to obtain an objective measure of the use of the dominant and non-dominant hands in everyday activities, two ActiTrac® monitors (IM Systems Inc, USA) containing ceramic biaxial piezoelectric accelerometer sensors were used to record physical motion in two planes (vertical and front-to-back axes). The devices were fixed on the wrist of each hand, using belt-clips to allow unrestricted mobility of the subjects during recording, for several hours. The ActiTrac monitors measured acceleration at a rate of 40 Hz and accumulated the acceleration signals every 2 s resulting in 30 epochs per minute in units of mG (sensitivity 1.25 mG), which were stored for off-line analysis.
Data obtained for dominant and non-dominant hands in both experiments were analyzed using ANOVAs for the factors “GENDER” and “AGE-GROUP”, and repeated measures ANOVA designed for the factor “HAND”. In order to detect possible relationships between performance and age, single parameters were correlated with age (Pearson-correlation). To allow a direct comparison between the extent of age-dependency, correlation coefficients were Fisher-transformed and listed as Z-values. In order to discover possible changes in hand dominance, a laterality index (l−r)/(l+r) [l
left hand performance, r
right hand performance] was calculated based on the results obtained in the practical tests (Experiment 1), or hand use in everyday activities (Experiment 2). The indices describe the extent of hand dominance for a given task within a continuum ranging from 1 to −1 (left hand dominance). All indices were aligned so that positive values indicate right hand dominance within a given task. These indices were also correlated with age via Pearson correlations. All statistical analyses were calculated using SPSS version 12.0 (SPSS Inc, USA). A p value of <0.05 was considered significant.