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Results for “Goal-directed control”

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At least 127 records · Page 7Linked to original sources

PubMed1995

Effects of dopamine depletion on the morphology of medium spiny neurons in the shell and core of the rat nucleus accumbens.

Nucleus accumbens receives a dense dopaminergic innervation which is important in regulating motivated states of behavior such as goal-directed actions, stimulus-reward associations and reinforcement of addictive substances. The shell and core territories of this nucleus each receive functionally and morphologically distinct dopaminergic inputs and lesions of the ascending pathways totally deprive the core but not the shell of dopaminergic fibers. Medium spiny neurons are the principal targets of dopaminergic terminals. The present study explored whether the loss of dopamine inputs can affect these neurons and whether cells in the shell and core would be equally susceptible to such a loss. Intracellular injection in fixed slices and neuronal reconstruction were used to analyze the dendritic trees of 62 neurons in the shell and core of animals that received a unilateral, chronic 6-hydroxydopamine lesion of the medial forebrain bundle. In the dopamine-depleted core, dendrites are significantly shorter (16% decrease) than in the intact core and in both the dopamine-depleted core and lateral shell, dendrites are less spiny than in respective control regions. Dopamine loss in the medial shell is associated with significantly more tortuous dendrites that are lower in spine density. However, the number of spines is not reduced which may mean that the increase recorded for segment length, although insignificant in tests, could be responsible for the change in spine density. These data suggest that the loss of dopamine can affect accumbal neuronal morphology and, moreover, can affect neuronal structures differentially in the shell and core.

Animals↗

PubMed1988

Spared-root deafferentation of a cat's hindlimb: hierarchical regulation of pathways mediating recovery of motor behavior.

Previous studies showed that after complete hindlimb deafferentation in cats, the ipsilateral descending pathways mediated recovery of overground, goal-directed locomotion and accurate placement of the deafferented limb. In the present study deafferentations sparing one dorsal root (L6) were performed to see if the descending systems would still be responsible for the recovery. The partially deafferented hindlimb is initially impaired in postural reflexes and accurate placement during locomotion but considerable recovery occurs. A similar pattern of severe impairment and subsequent recovery is observed in cats in which the only lesion is L1 hemisection. When a hemisection is added 6 months later to chronic spared-root deafferentation the recovery (from the latter lesion) is temporarily reversed but the animals recover again in a fashion similar to that after hemisection alone. Since there is no recovery of overground locomotion when hemisection is added to complete deafferentation but there is when deafferentation is incomplete, the descending pathways apparently are not responsible for maintaining the recovery when one dorsal root is spared as they are when all are cut. The results suggest that a competitive or hierarchical control over residual systems may regulate recovery of motor function.

Animals↗

PubMedDate not supplied

Comparison of different exercise programs in the rehabilitation of patients with chronic peripheral vestibular dysfunction.

The purpose of this study was to evaluate the effects of two exercise programs on balance performance in patients with chronic peripheral vestibular dysfunction and to assess whether these exercise programs induce adaptive modifications of the vestibulo-ocular reflex (VOR). Patients were randomly assigned to one of two groups. (1) Those in the Rehab (Reh) group (n = 11) received a comprehensive exercise program that consisted of balance retraining and goal-directed eye-head exercises under combinations of varied visual and somatosensory sensory conditions. Patients received 45-minute training sessions, three times per week for 12 weeks, and were instructed on a custom home exercise program. (2) Those in the Home group (n = 12) were instructed to perform the Cooksey-Cawthorne eye-head exercises at home, on a daily basis, for 12 weeks. In addition, after completion of the exercise program and a follow-up period, 7 of the participants in the Home group (here defined as the A group) chose to enter the Reh program (here defined as the B group). Balance performance was assessed by measuring the peak-to-peak magnitude and total amount of anterior-posterior body sway, and of horizontal (shear) ground reaction force during six test conditions, in which visual and somatosensory orientation cues were reduced or altered by rotation of the visual surround or support surface in proportion to the subject's sway, and in which vision was eliminated (eyes closed). The VOR response to step chair rotations of 60 degrees/s and 120 degrees/s, and the optokinetic reflex (OKN) response to 60 degrees/s constant velocity optokinetic stimuli were recorded. Left-right difference in VOR gain, VOR time constant, and OKN gain were determined. These tests were performed 1 day prior to start of treatment (TD 1), 6 weeks after start of treatment (TD 2), at the end of the 12-week treatment period (TD 3), and 5 months after end of treatment (TD 4). The findings revealed a significant improvement in standing balance performance under dynamic conditions for patients in the Reh program (Reh and B groups) but not for patients performing the eye-head exercise (Home or A groups). Thus, even in patients with chronic vestibular dysfunction, compensation for the loss or disruption of peripheral vestibular inputs can be effectively induced by exercises that provide sensory feedback appropriate for behavioral changes involving sensory substitution or sensory-motor reorganization.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1992

Effects of weak antagonist on fast elbow flexion movements in man.

By using a mathematical model and experiments involving electrical simulation of antagonistic muscles, we have formed the hypothesis (Wierzbicka et al. 1986) that in one-joint movements the antagonist muscle not only provides braking torque but also controls movement time. To get additional experimental support for this hypothesis, we studied elbow flexion movements performed by patients with spinal cord injury at the C5-6 level who had relatively normal strength in their biceps muscle and little or no voluntary control of the triceps. Seven quadriplegic patients and six control subjects performed elbow flexion movements of 10 degrees, 20 degrees, and 30 degrees "as fast and accurately as possible". Despite the lack of antagonist, patients used the same "pulse height" strategy as control subjects to scale their responses with movement amplitude. However, patients' movement time was on average twice that of control subjects, and durations of both accelerative and decelerative phases of movement were increased. Movement speed and acceleration were reduced to 20-50% of the corresponding values of control subjects. Patients tended to overshoot the target to a larger extent than control subjects, particularly 10 degrees targets, with nearly twice the error. We performed the same experiments using an external torque motor to assist the weak triceps. When a constant extensor torque of 2.5 or 5 Nm was provided by the motor, patients were able to move faster, and movement accuracy improved to within the normal range. These results provide direct evidence that the lack of an antagonist has an important effect on completion time and accuracy of fast goal-directed movements.

Adult↗

PubMed1984

Source density analysis of scalp potentials during evaluated action. I. Coronal distribution.

The distribution of source densities (the "Laplacean") of event related potentials (ERPs) over the scalp during a goal-directed task has been derived by a novel method which presents seven samples in a hexagonal array, using an economical computing technique that affords much freedom from artefactual contamination. The task had four phases: waiting for a ball to appear, observing its coordinates and estimating action needed to get it through a goal-mouth, acting and awaiting the outcome, and finally evaluating the outcome as success or failure. Different phases of the task were characterized by significantly different distributions of sources. Failures were distinguished from success to consistent features of the last phase of the ERP. All locations within the reference hexagon (spanning a circle of approximately 12 cm diameter on the scalp) showed the latter features. In control experiments, the effects of response mode and of different cognitive interpretations of the input/output situation were studied. A check showed that with monopolar recording involuntary tongue movements can totally vitiate conclusions in such investigations. The Laplacean derivations proved relatively free of such artefactual contamination.

Arousal↗

PubMed1995

The experiential meaning of eating, handicap, adaptedness, and confirmation in living with esophageal dysphagia.

This article is mainly based on interview studies of pensioners' (n = 62), patients' (n = 19), and students' (n = 87) experiences of living with longstanding esophageal dysphagia. The aim is to describe the experiential meaning of dysphagic patients' lives by interpreting their experiences, problems, and emotions and by specifying these into scales according to the model of goal-directed action by Pörn [43-49]. The experiential meaning will be articulated in terms of attainment or nonattainment of goals in relation to eating, handicap, adaptedness, and confirmation. In the experiential meaning of eating, the emphasis is on the attainment of nourishing goals or goals attained by means of food with desired hedonistic qualities and linked with feelings of hope or no hope of a shared life. The experiential meaning of handicap is interpreted as the dysphagic individual's experiences of an actual nonattainment of eating goals due to swallowing disabilities and with experiences of nonattainment of other important goals and related emotions; for example, shame for human incompetence. The experiential meaning of adaptedness is understood as the dysphagic individual's experiences of actual capacity for goal attainments interpreted as a sense of control in the daily living with dysphagia and linked with security, or in the negative case, reduced self-esteem and feelings of panic or fear. The experiential meaning of confirmation is interpreted as the dysphagic individual's experiences of actual or potential repertoire for goal attainment, i.e., self-assessment strengthened by evidence obtained in relationships linked with emotions of hope of self-realization. In conclusion, a specific model for understanding the dysphagic patient's concealment of dysphagia in the medical encounter has been developed.

Adaptation, Physiological↗

PubMed1986

The role of fixation and visual attention in the occurrence of express saccades in man.

The differential influence of fixation and directed visual attention on reaction times of goal-directed saccades and especially on the occurrence of express saccades was investigated. In all the experiments the subjects were instructed first to keep their direction of gaze at the center of a translucent screen with or without a central fixation point. When a new stimulus appeared, the subjects had to look at it as soon as possible. In some control experiments the subjects had to direct their gaze to the screen center and simultaneously direct their attention to a peripheral light spot before the target for the saccade appeared. Many express saccades occurred when either active fixation of a central fixation point or attention directed to a peripheral visual target (regardless of its position) was interrupted 200 ms before the target for the saccade appeared. Express saccades were almost completely abolished in the presence of fixation and/or directed visual attention at the moment in which the saccade target appeared. We conclude that express saccades occur if visual attention has already been released at the moment when the target for the saccade appears. This disengagement needs some time which adds to the reaction time.

Adult↗

PubMed1992

Intention and outcome: key components of causal structure facilitating mapping in children's analogical transfer.

The consequences of two key features of causal structure in source stories, intention and positive outcome, for analogical transfer were examined in kindergarten and second graders. In Experiment 1, children received either structure-complete, structure-incomplete, or irrelevant source stories. Structure-incomplete stories lacked either the intention to solve a problem (a goal-directed component), evidence of a successful consequence (an outcome-related component), or both as part of the solution activity described in source stories. Evidence for transfer was obtained for second graders when a goal-directed component, and to a lesser extent, an outcome-related component were connected to the solution action in source stories. Differences among conditions for kindergartners were less evident, although they revealed a pattern of performance similar to the second graders. A second experiment was conducted to determine whether memory and an orientation to use the source story information might account for these findings. Efforts to ensure memory for and hints to use information in the source stories, however, did not benefit solution transfer when intention and positive outcome were absent. These results suggest that a complete causal structure, including goal and outcome, in source stories augments transfer in young children by promoting mapping of the analogical relationship between source stories and the target problem.

Achievement↗

PubMed1990

Dynamic properties of human goal-directed arm movements.

In the present study, the velocity of pointing movements towards visual targets was analyzed. In accordance with the literature, tangential velocity was found to exhibit rather smooth, single-peaked profiles. In contrast, however, the profiles of the velocity components in the Cartesian coordinates of space were conspicuously multi-peaked, and suggestive of sums of a smooth curve and an oscillation. Oscillation frequency was 4-6 Hz, and its amplitude 200-600 mm/s; the phase shift between horizontal and vertical oscillation was about 180 degrees. The oscillation remained unaltered when the external load of the arm, the size of the visual target, or the required movement direction were changed. The relationship between the present findings and previously documented rhythmic properties of motor control is discussed, and it is concluded that the oscillations may have been generated by neural circuits with inherent oscillatory properties.

Acceleration↗

PubMed1987

The properties of goal-directed eye movements evoked by microstimulation of the cerebellar vermis in the cat.

The properties of eye movements evoked by microstimulation of the cerebellar vermis, lobules V VII, were investigated in encéphale isolé cats. The evoked eye movements tended to reach the same final goal in the orbit irrespective of initial eye position. The goal position depended on stimulus intensity. In contrast with the monkey, the goal of the eye movement lay within the oculomotor range. The goal position of the eye movements evoked by simultaneous stimuli delivered to two sites corresponded with the point which was obtained by the vectorial addition of the two eye movements evoked by the stimulation of each site. These findings suggest that the cat vermal lobules V VII play an important role in the control of horizontal and vertical eye position in the orbit.

Animals↗

PubMed2026

The effects of visuomotor training and tDCS stimulation on visuomotor integration and visual processing: an electrophysiological approach.

BACKGROUND: Visuomotor integration coordinates visual and motor cortical activity to produce goal-directed responses and can be indexed by Rolandic Mu-rhythm suppression and visual evoked potential (VEP) P100 parameters. Perceptual-motor training improves visuomotor performance, and transcranial direct current stimulation (tDCS) over primary motor cortex (M1) has been reported to enhance motor learning when paired with training. This study examined whether anodal M1 tDCS augments the effects of Senaptec visuomotor training in healthy adults. METHODS: Sixty participants were randomized to active anodal tDCS (five 10-minute sessions, 1 mA; n = 31) or sham (n = 29) over M1 immediately before each Senaptec training session; 53 completed all sessions and post-testing. Outcomes were Mu-suppression ratios, VEP P100 latency and amplitude, and Senaptec measures of visual sensitivity and visuomotor control. RESULTS: Active tDCS produced no augmentation of any outcome, with no significant group × time interaction for any measure, consistent across composite and task-level analyses. Training alone produced no change in Mu suppression or visuomotor control. By contrast, both groups showed significant training-related gains in visual sensitivity, including near-far quickness and stereopsis, accompanied by shorter P100 latencies and larger amplitudes, indicating more efficient early visual processing. CONCLUSIONS: A clear dissociation emerged: training produced robust improvements in early visual processing, whereas neither tDCS nor training altered sensorimotor (Mu) or visuomotor-control measures. The tDCS results should be interpreted cautiously given the modest dose and limited power to detect small effects, rather than as evidence of inefficacy. Tablet-based perceptual training enhanced visual processing independent of neuromodulation.

Humans↗

PubMed1981

Different effects involved in the interaction of saccades and the vestibulo-ocular reflex.

The accuracy of human goal-directed saccades during passive sinusoidal whole-body rotation is the same as that of normal saccades with the head still. Two mechanisms contribute to this accuracy: 1. There is an incomplete summation (70% on the average) of saccade and VOR velocities. 2. The duration of saccades during head rotation is lengthened if VOR and saccade velocities have the same direction, and is shortened if their direction is opposite. The latter finding supports the hypothesis that saccades are controlled by local feedback.

Eye Movements↗

PubMed1994

Pictorial support for discourse comprehension.

Discourse comprehension often involves the construction of a mental model of a situation and its updating as the discourse progresses. Theory suggests that a picture which depicts the initial physical situation in a story could help young children construct a functional mental model which they might maintain as the story progresses, thereby supporting comprehension. This was tested with young children, 4 to 6 years of age. The ability of those who saw the picture to model the final story event was enhanced and, even though the picture did not depict the main character's goal directly, recall of the goal was increased. This could be explained in terms of the creation of a functional mental model and the increased opportunity that it provides for linking goal-directed events with the goal as the model is updated. Mental representation theory was found useful here for predicting how to support comprehension in ways which could translate readily into practice in the classroom. Some potential applications of the findings in teaching young children are described.

Child Development↗

PubMed1994

Correlates of temporal perspective.

The present study examined both dispositional and behavioral indices of future and present temporal perspective as measured by the 1985 Gonzalez and Zimbardo scale. To examine the behavioral consequences of individual temporal perspective, the 1988 Robinson method of time diaries was used. Four dispositional indices and their association with individual temporal perspective were examined, need for achievement, work ethic orientation, self-monitoring, and evaluation anxiety. Individuals with a future time perspective placed a strong emphasis on success via goal-directed behavior, paid attention to environmental cues, and engaged in a large number of activities to achieve these goals. Implications for research are discussed.

Activities of Daily Living↗

PubMed1992

Goal-directed care: caring for aggressive nursing home residents with dementia.

1. Aggressive behavior in elders with dementia occurs most often during personal care. It is often a response to invasion of private space and may be prevented or reduced by interpersonal approaches that reflect a set of individualized goals for the resident. 2. Five resident goals for preventing or reducing aggressive behavior are to feel safe, to feel physically comfortable, to experience a sense of control, to experience optimal stress, and to experience pleasure. 3. These goals provide a framework for humane care that respects the personhood of the individual and minimizes the need for psychotropic medications and physical restraints.

Aged↗

PubMed1991

The effects of task preference on performance during purposeful and nonpurposeful activities.

This study examined the number of repetitions, increase in heart rate, increase in blood pressure, and rating of perceived exertion of subjects performing the most-preferred and least-preferred tasks from a predetermined list under purposeful and nonpurposeful conditions. Twenty healthy women completed the four experimental tests in random order for a period of 10 min each. The results indicated that there was no significant interaction (p greater than .05) between task choice and condition, thus implying that the subjects' performance was not influenced by task preference regardless of whether the activity was purposeful or nonpurposeful. Comparisons between the purposeful and nonpurposeful conditions revealed that the increase in heart rate and rating of perceived exertion were significantly higher (p less than .05) during nonpurposeful activity for both the most-preferred and the least-preferred tasks. On the basis of these results, it is recommended that therapists use purposeful, or goal-directed, activities in their practice, even if they are unable to provide their patients with a choice of therapeutic tasks.

Adult↗

PubMed1991

Compensatory muscle activity for sitting posture during upper extremity task performance in paraplegic persons.

Compensation for the loss of postural activity of the erector spinae (ES) muscle in spinal cord injured (SCI) subjects was investigated. All SCI subjects had clinically complete lesions below the T3 level. Body disbalance was invoked by requiring sitting subjects to execute reaching movements over individually predetermined distances in a horizontal plane. Myoelectric activity of the latissimus dorsi (LD) muscle and the trapezius pars ascendens (TPA) muscle both in the SCI subjects and in controls was recorded. The body disbalance was measured in terms of changes in the position of the body centre of gravity. The effects of anticipation for body displacement were examined by cuing the direction of the reaching movement. Our results indicate that paraplegic subjects use both LD and TPA to stabilize their sitting posture, in contrast to non-disabled persons. Secondly, the movement anticipation is in general slower in persons with paraplegia. Furthermore, the paraplegic subjects showed considerable impairments concerning the processing of precued information prior to a goal-directed upper extremity movement.

Adolescent↗

PubMed1986

Adaptive gain control of saccadic eye movements.

Properties of gain adaptivity in the saccadic system were studied. Subjects had to track a target which moved in single or double steps. The first target step which elicited the primary saccade had an amplitude in the range of 8-16 deg. The primary saccade triggered a further target displacement of 4 deg either in the same or--in different experimental sessions--in the opposite direction of the first target step. These consistent intrasaccadic target displacements lead to adaptive changes of saccadic amplitudes. The experimental data show that the saccadic system adapts to the stimulus sequence in a simple, parametric manner, namely by changing its gain. Consequently, it is assumed that a single gain element determines saccade sizes for all target eccentricities. Further, it is shown that adaptation has different time courses for gain increase and decrease, and its performance is close to completeness. The results are discussed with respect to the undershooting behaviour of goal-directed saccades and the functional demands to the saccadic system.

Adaptation, Ocular↗