Biomedical subjects

Terence D Sanger

Publications and source records attributed to Terence D Sanger.

6 recordsLinked to original sources

PubMed2003

Abnormal coupling of knee and hip moments during maximal exertions in persons with cerebral palsy.

The motions of lower-limb extension, adduction, and internal rotation are frequently coupled in persons with cerebral palsy (CP) and are commonly referred to as an extension synergy. However, the underlying joint moments that give rise to these coupled motions are not well understood. We hypothesized that maximal voluntary exertions in a direction of one component of a synergy (e.g., hip extension) would result in the concurrent presence of other components of the synergy in subjects with CP but not in control subjects. To test this hypothesis, we measured three-dimensional moments about the hip and knee as nine subjects with spastic CP and six control subjects performed maximal isometric exertions of the hip and knee flexors and extensors. During maximal hip extension exertions, control subjects simultaneously generated a knee flexion moment, whereas CP subjects generated a knee extension moment (P < 0.05) and a larger hip internal rotation moment than did controls (P < 0.05). During maximal knee extension exertions, control subjects generated a hip flexion moment, whereas CP subjects generated a hip extension moment (P < 0.05). The patterns of joint moments generated by CP subjects are consistent with an extension synergy and may underlie the coupled motion patterns of the lower extremity in such persons.

Adolescent↗

PubMed2003

Neural population codes.

In many regions of the brain, information is represented by patterns of activity occurring over populations of neurons. Understanding the encoding of information in neural population activity is important both for grasping the fundamental computations underlying brain function, and for interpreting signals that may be useful for the control of prosthetic devices. We concentrate on the representation of information in neurons with Poisson spike statistics, in which information is contained in the average spike firing rate. We analyze the properties of population codes in terms of the tuning functions that describe individual neuron behavior. The discussion centers on three computational questions: first, what information is encoded in a population; second, how does the brain compute using populations; and third, when is a population optimal? To answer these questions, we discuss several methods for decoding population activity in an experimental setting. We also discuss how computation can be performed within the brain in networks of interconnected populations. Finally, we examine questions of optimal design of population codes that may help to explain their particular form and the set of variables that are best represented. We show that for population codes based on neurons that have a Poisson distribution of spike probabilities, the behavior and computational properties of the code can be understood in terms of the tuning properties of individual cells.

Action Potentials↗

PubMed2003

Pediatric movement disorders.

PURPOSE OF REVIEW: Pediatric movement disorders are a heterogeneous group of symptoms that occur in the context of a large number of different neurological diseases. Accurate diagnosis and quantification of these disorders is essential for determining outcome, appropriate treatment, and criteria for inclusion in research trials. The purpose of this review is to summarize recent advances in diagnosis and treatment for childhood movement disorders. RECENT FINDINGS: The ultimate goal is to discover new treatments that can lead to measurable improvement in functional outcome for affected children. In order to accomplish this goal, we must have consistent definitions and accurate measurements to determine the diagnosis and severity for each child in a clinic or research trial. Recent progress in defining childhood movement disorders has led to consensus definitions of different types of hypertonia. There has also been progress in the development of outcome measures that relate to meaningful functional performance in a variety of skill areas. Most exciting is the prospect of new treatments, and we survey the current non-medical, medical, and surgical therapies for childhood motor disorders. SUMMARY: Although pediatric movement disorders are a complex and often poorly understood group of symptoms, recent work has shown that there is a possibility of defining, measuring, and ultimately treating these debilitating diseases.

Anticonvulsants↗

PubMed2003

Classification and definition of disorders causing hypertonia in childhood.

OBJECTIVE: This report describes the consensus outcome of an interdisciplinary workshop that was held at the National Institutes of Health in April 2001. The purpose of the workshop and this article are to define the terms "spasticity," "dystonia," and "rigidity" as they are used to describe clinical features of hypertonia in children. The definitions presented here are designed to allow differentiation of clinical features even when more than 1 is present simultaneously. METHODS: A consensus agreement was obtained on the best current definitions and their application in clinical situations. RESULTS: "Spasticity" is defined as hypertonia in which 1 or both of the following signs are present: 1) resistance to externally imposed movement increases with increasing speed of stretch and varies with the direction of joint movement, and/or 2) resistance to externally imposed movement rises rapidly above a threshold speed or joint angle. "Dystonia" is defined as a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. "Rigidity" is defined as hypertonia in which all of the following are true: 1) the resistance to externally imposed joint movement is present at very low speeds of movement, does not depend on imposed speed, and does not exhibit a speed or angle threshold; 2) simultaneous co-contraction of agonists and antagonists may occur, and this is reflected in an immediate resistance to a reversal of the direction of movement about a joint; 3) the limb does not tend to return toward a particular fixed posture or extreme joint angle; and 4) voluntary activity in distant muscle groups does not lead to involuntary movements about the rigid joints, although rigidity may worsen. CONCLUSION: We have provided a set of definitions for the purpose of identifying different components of childhood hypertonia. We encourage the development of clinical rating scales that are based on these definitions, and we encourage research to relate the degree of hypertonia to the degree of functional ability, change over time, and societal participation in children with motor disorders.

Child↗

PubMed2002

Nonlinear sensory cortex response to simultaneous tactile stimuli in writer's cramp.

Writer's cramp is a task-specific dystonia that leads to involuntary hand postures during writing. Abnormalities of sensory processing may play a pathophysiological role in this disorder. Electrophysiology studies in a monkey model of focal dystonia have revealed de-differentiation of sensory maps and the existence of single cells in hand regions of area 3b with enlarged receptive fields that extend to the surfaces of more than one digit. These changes may lead to abnormal processing of simultaneous sensory inputs. To study abnormal processing of simultaneous sensory information in adult humans with writer's cramp, we used functional magnetic resonance imaging to compare the response in primary sensory cortex with simultaneous tactile stimulation of the index and middle finger, with the response to stimulation of each finger alone. We tested five patients with writer's cramp and seven unaffected (normal) subjects. In the normal subjects, a linear combination of the activation patterns for individual finger stimulation predicts the pattern of activity for combined stimulation with 12% error. In writer's cramp patients, the linear combination predicted the combined stimulation pattern with 30% error. Results indicate a nonlinear interaction between the sensory cortical response to individual finger stimulation in writer's cramp. This altered interaction may contribute to the motor abnormalities.

Brain↗

PubMed2002

Decoding neural spike trains: calculating the probability that a spike train and an external signal are related.

Experimental and clinical applications of extracellular recordings of spiking cell activity frequently are used to relate the activity of a cell to externally measurable signals such as surface potentials, sensory stimuli, or movement measurements. When the external signal is time-varying, correlation methods have traditionally been used to quantify the degree of relation with the neural firing. However, in some circumstances correlation methods can give misleading results. A new algorithm is described that estimates the extent to which a spike train is related to a continuous time-varying signal. The technique calculates the probability of generating a spike train with Poisson statistics if the time-varying signal determines the Poisson rate. This is accomplished by successive division of the signal and the spike train into halves and recursive calculation of the probability of each half-signal. The performance of the new algorithm is compared with the performance of correlation methods on simulated data.

Action Potentials↗