ABSTRACT
The velocity of impact between an object and the human head is a critical factor influencing brain injury outcomes but has not been explored in any detail in animal models. Here we provide a comprehensive overview of the interplay between impact velocity and injury severity in a well-established weight-drop impact acceleration (WDIA) model of diffuse brain injury in rodents. We modified the standard WDIA model to produce impact velocities of 5.4, 5.85 and 6.15 m/s while keeping constant the weight and the drop height. Gradations in impact velocity produced progressive degrees of injury severity measured behaviourally, electrophysiologically and anatomically, with the former two methods showing greater sensitivity to changes in impact velocity. There were impact velocity-dependent reductions in sensorimotor performance and in cortical depth-related depression of sensory cortex responses; however axonal injury (demonstrated by immunohistochemistry for ß-amyloid precursor protein and neurofilament heavy-chain) was discernible only at the highest impact velocity. We conclude that the WDIA model is capable of producing graded axonal injury in a repeatable manner, and as such will prove useful in the study of the biomechanics, pathophysiology and potential treatment of diffuse axonal injury.
Subject(s)
Diffuse Axonal Injury/pathology , Diffuse Axonal Injury/physiopathology , Diffuse Axonal Injury/psychology , Acceleration , Animals , Biomechanical Phenomena , Corpus Callosum/pathology , Disease Models, Animal , Lateral Ventricles/pathology , Male , Neurons/physiology , Rats, Sprague-Dawley , Rotarod Performance Test , Somatosensory Cortex/physiopathologyABSTRACT
Eight humans participated in a two-choice signal-detection task in which stimulus disparity was varied over four levels. Two procedures arranged asymmetrical numbers of reinforcers received for correct left- and right-key responses (the reinforcer ratio). The controlled procedure ensured that the obtained reinforcer ratio remained constant over changes in stimulus disparity, irrespective of subjects' performances. In the uncontrolled procedure, the asymmetrical reinforcer ratio could covary with subjects' performances. The receiver operating characteristic (ROC) patterns obtained from the controlled procedure approximated isobias functions predicted by criterion location measures of bias. The uncontrolled procedure produced variable ROC patterns that were somewhat like the isobias predictions made by likelihood ratio measures of bias; however, the obtained reinforcer ratio became more extreme as discriminability decreased. The obtained pattern of bias was directly related to the obtained reinforcer ratio. This research indicates that criterion location measures seem to be preferable indices of response bias.
Subject(s)
Motivation , Reinforcement Schedule , Signal Detection, Psychological , Adult , Choice Behavior , Discrimination Learning , Female , Humans , Male , Psychomotor Performance , PsychophysicsABSTRACT
The incidence of skeletal tuberculosis in New Zealand as measured by both hospital morbidity and notification data has fallen since the introduction of chemotherapy to low levels comparable with other developed societies. The decline has been greatest in the 5-14 year age group and least in the over 65 group. Individual surgeons can now expect to see few cases in a practising lifetime. Effective chemotherapy is the key to successful treatment. Adequate biopsy is essential, but apart from the drainage of large abscesses the place of surgery in the early management of osteoarticular tuberculosis is discretionary. Early activity can usually be encouraged once chemotherapy is instituted, late reconstruction by joint arthroplasty being available if adequate function is not achieved.
