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At least 253 records · Page 14Linked to original sources
PubMed2004

Dexterous finger movements in primate without monosynaptic corticomotoneuronal excitation.

It is generally accepted that the precision grip and independent finger movements (IFMs) in monkey and man are controlled by the direct (monosynaptic) corticomotoneuronal (CM) pathway. This view is based on previous observations that pyramidotomy causes near permanent deficits of IFMs. However, in addition to the direct CM pathway, pyramidotomy interrupts several corticofugal connections to the brain stem and upper cervical segments. Indirect (oligosynaptic) CM pathways, which are phylogenetically older, have been considered to be of little or no importance in prehension. In three adult macaque monkeys, complete transection of the direct CM pathway was made in C4/C5, which is rostral to the forelimb segments (C6-Th1). Electrophysiological recordings revealed lack of the direct lateral corticospinal tract (LCST) volley, monosynaptic extracellular field potentials in the motor nuclei, and monosynaptic CM excitation. However, a disynaptic volley, disynaptic field potentials and disynaptic CM excitation mediated via C3-C4 propriospinal neurons remained after the lesion. Thus the lesion interrupted the monosynaptic CM pathway and oligosynaptic LCST pathways mediated by interneurons in the forelimb segments. Precision grip and IFMs were observed already after 1-28 days postoperatively. Weakness in force and deficits in preshaping remained for an observation period of 3 mo. Indirect CM pathways may be important for neuro-rehabilitation.

Animals↗
PubMed2000

Visual and tactile information about object-curvature control fingertip forces and grasp kinematics in human dexterous manipulation.

Most objects that we manipulate have curved surfaces. We have analyzed how subjects during a prototypical manipulatory task use visual and tactile sensory information for adapting fingertip actions to changes in object curvature. Subjects grasped an elongated object at one end using a precision grip and lifted it while instructed to keep it level. The principal load of the grasp was tangential torque due to the location of the center of mass of the object in relation to the horizontal grip axis joining the centers of the opposing grasp surfaces. The curvature strongly influenced the grip forces required to prevent rotational slips. Likewise the curvature influenced the rotational yield of the grasp that developed under the tangential torque load due to the viscoelastic properties of the fingertip pulps. Subjects scaled the grip forces parametrically with object curvature for grasp stability. Moreover in a curvature-dependent manner, subjects twisted the grasp around the grip axis by a radial flexion of the wrist to keep the desired object orientation despite the rotational yield. To adapt these fingertip actions to object curvature, subjects could use both vision and tactile sensibility integrated with predictive control. During combined blindfolding and digital anesthesia, however, the motor output failed to predict the consequences of the prevailing curvature. Subjects used vision to identify the curvature for efficient feedforward retrieval of grip force requirements before executing the motor commands. Digital anesthesia caused little impairment of grip force control when subjects had vision available, but the adaptation of the twist became delayed. Visual cues about the form of the grasp surface obtained before contact was used to scale the grip force, whereas the scaling of the twist depended on visual cues related to object movement. Thus subjects apparently relied on different visuomotor mechanisms for adaptation of grip force and grasp kinematics. In contrast, blindfolded subjects used tactile cues about the prevailing curvature obtained after contact with the object for feedforward adaptation of both grip force and twist. We conclude that humans use both vision and tactile sensibility for feedforward parametric adaptation of grip forces and grasp kinematics to object curvature. Normal control of the twist action, however, requires digital afferent input, and different visuomotor mechanisms support the control of the grasp twist and the grip force. This differential use of vision may have a bearing to the two-stream model of human visual processing.

Adult↗
PubMed1998

Manual dexterity and keyboard use in spastic hemiparesis: a comparison between the impaired hand and the 'good' hand on a number of performance measures.

OBJECTIVE: To assess the functional deficits in tapping performance of subjects with spastic hemiparesis. DESIGN: In a pilot study, typing performance on a computer keyboard was examined on a number of performance measures. SETTING: Department of Research and Development at the Werkenrode Institute. SUBJECTS: Four subjects (mean age 16.4 years, standard deviation 1.8 years) with cerebral palsy and diagnosed as having spastic hemiparesis. INTERVENTIONS: Subjects had to type a sequence of one or more keys as quickly as possible within an 8 second period with the fingers of both hands separately. MAIN OUTCOME MEASURES: The average number of good and false responses were calculated. Within the false response category, four, mutually exclusive, types of errors were distinguished; wrong key, repetition, registrations under 75 ms and holding. Speed and regularity of the typing responses were also established. RESULTS: The 'good' hand outperformed the impaired hand on all performance measures except on the amount of repetition errors made. The holding error was only present for the impaired hand, and there was an increase in holding errors from the index to the little finger in this hand. In addition, the impaired hand performed the task with a slower speed and in a more irregular fashion. CONCLUSIONS: The results are discussed with reference to keyboard design. It is concluded that the standard 'QWERTY' keyboard hampers typing performance extensively, especially for subjects with left spastic hemiparesis. A learning method is presented in which the role of an external pacer (e.g. metronome) is discussed. This device can initially be used to decrease movement variability and, eventually, for increasing movement speed.

Adolescent↗