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Biomedical subjects

H Forssberg

Publications and source records attributed to H Forssberg.

87 records · Page 5Linked to original sources
PubMed1985

Ontogeny of human locomotor control. I. Infant stepping, supported locomotion and transition to independent locomotion.

Locomotor patterns of human infants were studied during stepping in the newborn period (first two months of life), during supported locomotion (6-12 months of age) and during independent locomotion in children who just were able to walk by themselves without external support (10-18 months of age). Leg movements, pattern of muscular activity and reaction forces were studied by a computerized system. The locomotor pattern during the newborn period lacked the specific functions that are unique for human plantigrade locomotion. There was no heel strike in front of the body; the foot was placed instead on its forepart straight under the body. Hip and knee joints were hyperflexed during the whole step cycle and flexed synchronously during swing. The specific knee-ankle coordination of human adults was missing. The ankle extensors were activated prior to touch down together with other extensor muscles. There was no propulsive force. A similar immature non-plantigrade pattern recurred after an inactive period. During the subsequent period of supported locomotion there was a gradual transformation of the infantile pattern towards the plantigrade pattern continuing after establishment of independent locomotion. It is suggested that innate pattern generators in the spinal cord produce the infant stepping and also generate the basic locomotor rhythm in adults, but that neural circuits specific for humans develop late in ontogeny and transform the original, non-plantigrade motor activity to a plantigrade locomotor pattern.

Biomechanical Phenomena↗
PubMed1984

Is parkinsonian gait caused by a regression to an immature walking pattern?

The gait of 6 patients with Parkinson's disease was analyzed by movement, EMG, and force recordings. In certain important details, a regression towards a more immature walking pattern was seen. It is suggested that the characteristic parkinsonian gait in addition to hypokinesia is caused by deficits in the neural circuits controlling plantigrade locomotion.

Adult↗
PubMed1983

Hardwired locomotor network in cat revealed by a retained motor pattern to gastrocnemius after muscle transposition.

Locomotor output to the gastrocnemius muscle was studied after a transposition giving the muscle a dorsi-flexing action around the ankle. Except for a slight prolongation of the activity, the old extensor pattern was retained in all cats throughout the study. A peak of activity before termination was seen in one cat at higher walking speed. It is concluded that neither the spinal locomotor network controlling the gastrocnemius muscle nor the supraspinal circuits influencing the network exhibit a high degree of plasticity in response to locating the muscle in a position antagonistic to the original.

Animals↗
PubMed1982

Ontogenetic development of postural control in man: adaptation to altered support and visual conditions during stance.

Normal young children ranging in age from 1 1/2 to 10 years were assessed in a number of experimental paradigms testing the ability to adapt quickly their strategy of control to altered support surface and visual conditions. The experimental protocols, using a movable platform and visual surround, and the analytic techniques, using EMGs and measures of reaction forces and body motions, were identical to those employed in a complementary study in this issue (Nashner, L. M., F. O. Black, and C. Wall, III (1982) J. Neurosci. 2: 536-544). The structure of automatic postural adjustments in young children was, with the exception of greater variability, similar to that of adult subjects studied previously. However, young children below the age of 7 1/2 years were unable to suppress systematically the influence of inputs derived from the support surface or from vision when these provided inappropriate orientation information due to the motion of these surfaces. The discussion emphasizes that the automatic postural adjustments and the context-dependent reweighting of support surface, vestibular, and visual inputs are organizationally separate processes and that the hierarchically lower level automatic process matures before the higher level adaptive processes.

Acclimatization↗
PubMed1981

Peripheral feedback mechanisms acting on the central pattern generators for locomotion in fish and cat.

The feedback mechanisms taking part in the control of locomotion in cat and fish are reviewed, particularly with regard to position- and movement-related feedback. It is shown that in both fish and cat there is a powerful position-dependent negative feedback which will act only in the position range where the muscle activity normally changes, e.g., from extensor to flexor activity. In addition, there is positive feedback in the middle of the movement range which will act in certain conditions, e.g., to promote and maintain flexor activity during the flexion of the hind limb.

Animals↗
PubMed1980

The locomotion of the low spinal cat. I. Coordination within a hindlimb.

Kittens were subjected to a complete transection of the spinal cord (Th 10--12) 1--2 weeks after birth. A few days after the operation they could perform alternating limb movements and somewhat later walking movements with their hindlimbs on a treadmill. The stepcycle of the hindlimbs could be divided into a flexion phase (F) and a first (E1), second (E2) and third (E3) extension phase. The duration of the support phase decreased markedly with treadmill velocity while the swing phase decreased to a much smaller extent. The pattern of electromyographical activity in hip, knee, ankle and toe muscles during treadmill locomotion was very similar to that of the intact cat. This related to both the timing and the general shape of locomotor bursts. The extensor muscles were thus activated well before the placement of the foot and able to produce enough force to support the body. The propulsive thrust in each step was, however, decreased and the animals showed more severe deficits particularly in their equilibrium control. It is concluded, however, that neural networks in the spinal cord (with its peripheral inflow intact but without supraspinal influences) have the capacity to generate a specific and detailed locomotor pattern.

Animals↗
PubMed1980

The locomotion of the low spinal cat. II. Interlimb coordination.

The interaction of the two hindlimbs were investigated by an analysis of the muscular activity and the movements in 14 chronic spinal kittens during treadmill locomotion (i.e. in kittens subjected to a transection of the spinal cord (Th10--12)) one or two weeks after birth). At low speed the limbs were alternating (walk or trot). At higher they were activated more simultaneous, as during gallop. The two limbs could walk at different velocities, as during walking in a circle, when the two belts of the treadmill were driven at different speeds. The duration of the support phases was mainly influenced by the speed of the belt on which the limb was walking. The limbs could still maintain a common rhythm up to a two or three fold speed difference, as the flexion or the first extension phase of the limb walking on the "fast" belt was prolonged and the flexion phase of "slow limb" was shortened. At extreme speed differences the limb on the "fast belt" performed 2, 3 and even 4 steps during one stepcycle of the "slow limb". The placement of the feet was found to maintain the most stable relationship during alternating gaits at different speed differences. It is concluded that all phases of the step cycle are modifiable and that there are several mechanisms coordinating the limbs within the spinal cord.

Animals↗
PubMed1979

Stumbling corrective reaction: a phase-dependent compensatory reaction during locomotion.

1. Tactile stimuli to the paw consisting of a stick making contact or an air puff aimed at the dorsum were used to study the phasic influence of locomotor activity on the reflex pattern elicited in extensor and flexor muscles and on the induced compensatory movements in intact cats. The resulting movements and reflex pattern are called "stumbling corrective reactions." 2. The basic reflex pattern and movements of the stumbling corrective reaction are: a) if the stimulus occurs during the swing phase, a short-latency activation of the flexor muscles, which induces an additional flexion of the limb lifting the paw over the obstacle; b) if the stimulus occurs during the support phase, an inhibition followed by an excitation of the extensor muscles, which neither increase nor decrease the extension. However, the stimulus evokes an increased flexor activity in the succeeding swing phase, which induces a brisker flexion. 3. Tactile stimuli to the proximal part of the limb or to the belly in front of the knee evoked the same type of phase-dependent compensatory reactions. Such reactions would presumably be beneficial for the animal to avoid high obstacles that impede movement. 4. A nonnoxious electrical stimulus (typically 2 mA; 1 ms) applied to the dorsum of the paw was used to study systematically the reflex pattern of the stumbling corrective reaction. Two pathways were defined to the knee flexor (semitendinosus). One early burst was evoked at about 10 ms and one later at about 25 ms after the stimulus. Short inhibitory pathways and longer excitatory pathways (20-50 ms) projected to the extensor nuclei. A short-latency (10 ms) excitatory pathway to the ankle extensor (lateral gastrocnemius) was also activated. 5. A painful electrical stimulus applied to the dorsum of the paw evoked large flexor responses during the whole step cycle. During the support phase the locomotion was disrupted as the supporting limb was withdrawn. 6. The results demonstrate that intact cats are able to compensate rapidly for unpredicted perturbations and that the reflex pattern and the induced corrective movements are adapted to the locomotor activity so that functionally meaningful movements are evoked in each phase of the step cycle. 7. The evoked reflexes and their modulation are consistent with those previously found in chronic spinal cats during walking and in paralyzed spinal cats performing "fictive locomotion." It is suggested that the same spinal pathways are used, and that they are controlled by the spinal "locomotor generator."

Animals↗
PubMed1977

Phasic gain control of reflexes from the dorsum of the paw during spinal locomotion.

In chronic spinal cats walking with their hindlimbs on a treadmill belt, tactile stimuli were applied to the dorsum of the paw during various phases of the step cycle. A stimulation during the swing phase evoked a flexion response with a concomitant crossed extension, whereas in stance it induced an increased ipsilateral extension. EMG-recordings show short latency reflex responses in flexors and extensors, respectively. The responses are organized such that latencies of knee muscles are shorter than those of ankle and hip muscles. The movements induced by the stimulations appear to be very meaningful during normal conditions in compensating for any unpredicted obstacle disturbing the movement of the paw during locomotion. Responses during forward flexion and during the support phase are well adapted to the ongoing locomotor activity and do not influence the interlimb coordination whereas a stimulation when the foot approaches the ground after the end of flexion disturbs the regular alternating pattern. Different possible mechanisms underlying this phase-dependent reflex reversal are discussed.

Animals↗
PubMedDate not supplied

Temporal resolution of auditory perception in relation to perception, memory, and language skills in typical children.

This study examined temporal resolution of auditory perception (TRAP) in relation to speech perception and phonological working memory in one experiment and in relation to measures of rapid naming, understanding of grammatical contrasts, and phonological awareness in a second experiment. In the TRAP test, 6- to 9-year-old children discriminated four pairs of two sine tones, 878 Hz and 1350 Hz, presented in blocks with stepwise decreasing interstimulus intervals from 256 ms to 8 ms. In Experiment 1, weak but significant correlations between TRAP and speech perception and phonological working memory were found, as well as a significantly lower TRAP performance by girls. Experiment 2 indicated a significant relation between TRAP and the phonological awareness task. The results give qualified support to the notion of a weak relationship between TRAP and speech perception and language skills among typical children. However, the gender differences in TRAP performance, the limited variance explained by the regression models, and the finding that only one of the language parameters correlated with TRAP do not support the notion of a causal relationship between language skills and TRAP. The possibility that TRAP is connected to general neurological maturation rather than specifically to language abilities is discussed.

Auditory Perceptual Disorders↗