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At least 1,009 records · Page 56Linked to original sources
PubMed1995

Human trunk strength profile in lateral flexion and axial rotation.

STUDY DESIGN: To determine the functional capability in asymmetric trunk motion, isometric and isokinetic lateral flexion and axial rotation strengths of a normal and patient samples were measured. Seventy-three normal asymptomatic subjects (41 males and 32 females) and ten patients (9 males and 1 female) were tested. OBJECTIVES: The dual objectives of the study were to develop a database for isometric and isokinetic lateral flexion and axial rotation strength capabilities of a normal sample and to determine the functional impairment of a sample of patients. SUMMARY OF BACKGROUND DATA: More than 60% of low back injuries are associated with trunk twisting. Asymmetric motions are important risk factors. However, strength capability data for axial rotation are sparse and those for lateral flexion nonexistent. METHODS: To achieve the objectives of the study, two devices were designed and fabricated. Isometric lateral flexion was tested bilaterally in neutral posture and at 10 degrees, 20 degrees, and 30 degrees of lateral bending. Isometric axial rotation was tested bilaterally in neutral posture and at 5 degrees, 10 degrees, 15 degrees, and 20 degrees of axial rotation. Isokinetic lateral flexion and axial rotation strengths were tested bilaterally starting from the neutral posture. RESULTS: The strength invariably declined progressively for all groups with increasing postural asymmetry. The strength in isokinetic activities ranged between 60% to 70% of the strength measured in isometric activities. All groups were significantly stronger in lateral flexion compared with axial rotation. The female sample ranged between 60% to 70% values of males for all activities studied. The patient group was weakest, ranging between 45% to 55% for isometric and 52% to 58% for isokinetic activities of their control group.

Adult↗
PubMed1996

The effect of initial head position on active cervical axial rotation range of motion in two age populations.

STUDY DESIGN: This study analyzed cervical axial rotation initiated from five different starting positions in asymptomatic subjects. The results were analyzed to ascertain if rationale for certain clinical assessment methods could be justified. SUMMARY OF BACKGROUND DATA: In the assessment of the cervical spine, many clinicians use assessment techniques that propose to isolate anatomic structures by using various permutations and combinations of the three gross rotational movements, for example, evaluation of axial rotation in flexion and extension. OBJECTIVES: The primary purpose of this study was to compare the magnitude of cervical axial rotation when started from neutral, flexion, extension, protraction, and retraction, and the protraction-retraction range of motion also was determined. METHODS: Two groups of 30 subjects, one group aged 18-30 years and the other group aged 50-65 years and stratified by gender, participated in the study. The 3Space Tracker system (Polhemus, A Kaiser Aero-space and Electronics, Co., Colchester, VT), art electromagnetic tracking device, was used to determine the angular and linear position of the head relative to the sternum by detecting the position and orientation of two sensors attached to the forehead and sternum. RESULTS: Analysis of variance of the data revealed a statistically significant difference (p < 0.05) in axial rotation between all of the five starting positions. The younger age group demonstrated greater range of motion when rotation was initiated from neutral and extension, whereas the older group had greater range when the motion was initiated from protraction, retraction, and flexion. CONCLUSIONS: The results suggest that varying the starting sagittal head position may affect the anatomic structures involved in restraining axial rotation. This supports the clinical approach to range of motion assessment in combined movement patterns.

Adolescent↗
PubMed2001

Morphologic changes in the lumbar intervertebral foramen due to flexion-extension, lateral bending, and axial rotation: an in vitro anatomic and biomechanical study.

STUDY DESIGN: A biomechanical and anatomic study with human cadaveric lumbar spine. OBJECTIVES: The purpose of this study is to examine the morphologic changes in the intervertebral foramen during flexion, extension, lateral bending, and axial rotation of the lumbar spine and to correlate these changes with the flexibility of the spinal motion segments. SUMMARY OF BACKGROUND DATA: Previous studies showed morphologic changes in the intervertebral foramen during flexion and extension; however, those changes during lateral bending and axial rotation were not well known. METHODS: There were 81 motion segments obtained from 39 human cadaveric lumbar spines (mean age 69 years). The motion segments were imaged with CT scanner with 1-mm thick consecutive sections. For biomechanical testing each motion segment was applied with incremental pure moments of flexion, extension, lateral bending, and axial rotation. Rotational movements of the motion segment were measured using VICON cameras. After application of the last load, the specimens were frozen under load, and then CT was performed with the same technique described above. Six parameters of the intervertebral foramen were measured, including foraminal width (maximum and minimum), foraminal height, disc bulging, thickness of ligamentum flavum, and cross-sectional area of the foramen. RESULTS: Flexion increased the foraminal width (maximum and minimum), height, and area significantly while significantly decreasing the disc bulging and thickness of ligamentum flavum (P < 0.05). However, extension decreased the foraminal width (maximum and minimum), height, and area significantly. Lateral bending significantly decreased the foraminal width (maximum and minimum), height, and area at the bending side, whereas lateral bending significantly increased the foraminal width (minimum), height, and area at the opposite side of bending. Likewise, axial rotation decreased the foraminal width (minimum) and area at the rotation side significantly while significantly increasing the foraminal height and foraminal area at the opposite side. The percent change in the foraminal area was found significantly correlated with the amount of segmental spinal motion except for the extension motion. CONCLUSIONS: This study showed that the intervertebral foramen of the lumbar spine changed significantly not only on flexion-extension but also on lateral bending and axial rotation. The percent change in cross-sectional foraminal area was correlated with the amount of segmental motion except for extension motions. Further studies are needed to assess the morphologic changes in the intervertebral foramen in vivo and to correlate clinically.

Adult↗
PubMed2001

Canal and intervertebral foramen encroachments of a burst fracture: effects from the center of rotation.

STUDY DESIGN: The neural spaces of thoracolumbar burst fractures were investigated in an in vitro biomechanical study. OBJECTIVE: To evaluate encroachments of spinal canal diameter and intervertebral foramen area as functions of where the center of rotation is located during flexion and extension. SUMMARY OF BACKGROUND DATA: Decompression of the neural spaces is important for the recovery of neural function in a patient with a burst fracture injury. A few biomechanical studies have documented the decompression of the neural elements by adjustment of posterior fixation devices. However, the device adjustments have been device specific and ill defined. No study has investigated the neural decompression phenomenon with precisely defined multiple adjustments. METHODS: Burst fractures were produced at L1 vertebra in nine T11-L3 human spinal segments. Specimens were flexed and extended around five different centers of rotation located in the mid-L1 plane. The spinal canal diameter and intervertebral foramen area encroachments were quantified in maximum flexion and extension around each center of rotation using lateral radiographs. RESULTS: The average canal encroachment of 42.6% changed in flexion (32.2-48.5%) and extension (36.3-44.2%) by location of the center of rotation. The average intervertebral foramen area encroachment was decreased to a greater extent more often in flexion than in extension because of where the center of rotation was located. CONCLUSIONS: Both flexion and extension can decompress canal and foramina, depending on the choice for the location of the center of rotation. If lordotic posture is preferred clinically, then the optimal choice may be extension around the center of rotation located at the tip of the spinous process of the burst vertebra.

Adult↗
PubMed2003

Magnetic resonance imaging in quantitative analysis of rotator cuff muscle volume.

Tears of the rotator cuff are accompanied by muscle atrophy, which has direct implications on patient outcome after rotator cuff surgery. However, no reliable method exists to determine muscle volumes in situ. The current authors evaluated the reliability of magnetic resonance imaging in assessing rotator cuff muscle volumes. Muscle volumes were determined in 10 shoulders from cadavers using two methods: (1). oblique sagittal shoulder scans were obtained, the contours of the supraspinatus, infraspinatus and teres minor, and subscapularis muscles were traced, and muscle volumes were calculated using image analysis software; and (2). rotator cuff muscles were dissected and muscle volumes were measured by water displacement. The average magnetic resonance imaging volume of the supraspinatus, infraspinatus and teres minor, and subscapularis muscles were 36 +/- 12, 96 +/- 41, and 99 +/- 33 mL, respectively. There was a significant correlation between magnetic resonance imaging and water displacement measurements. The intraobserver and interobserver variabilities were less than 4%. The results indicate the magnetic resonance imaging is a reliable method to determine rotator cuff muscle volumes with good intraobserver and interobserver variability. This method may prove valuable preoperative assessment of rotator cuff muscles and prediction of outcome after rotator cuff repair.

Aged↗
PubMed2005

Intraoperative diagnosis of syndesmosis injuries in external rotation ankle fractures.

OBJECTIVE: This study was designed to compare intraoperative fluoroscopic stress testing, static radiographs, and biomechanical criteria for the diagnosis of distal tibiofibular syndesmotic instability associated with external rotation type ankle fractures. DESIGN: Prospective, consecutive series. SETTING: Academic level 1 trauma center. PATIENTS/PARTICIPANTS: Thirty-eight skeletally mature patients with unstable unilateral external rotation ankle fractures were prospectively recruited. INTERVENTION: Before surgery, the treating surgeon detailed the operative treatment plan, including need for syndesmotic fixation. In pronation-external rotation injuries, biomechanical criteria were applied to predict syndesmotic instability. Ankles were examined using intraoperative fluoroscopic external rotation stress tests. The contralateral uninjured limb was used as a control. A 7.2-Nm force was applied for the external rotation stress examination. Stress testing was performed after lateral malleolar fixation and repeated after medial and syndesmotic fixation. MAIN OUTCOME MEASURES: The incidence of syndesmotic instability was determined based on radiographic clear space measurements and compared with previously published criteria. RESULTS: Intraoperative fluoroscopy detected unpredicted syndesmotic instability in 37% of ankles. In supination-external rotation (OTA 44B) injuries, unpredicted syndesmosis instability was found in 10 of 30 patients (33%). In pronation-external rotation injuries (OTA 44C), 4 of 7 patients (57%) were associated with syndesmosis disruption not predicted by biomechanical criteria. In bimalleolar fractures, syndesmosis fixation improved stability compared with rigid bimalleolar fixation alone (P < 0.01). CONCLUSIONS: Preoperative radiographs and biomechanical criteria are unable to routinely predict the presence or absence of syndesmosis instability. Rigid bimalleolar fixation was frequently not sufficient to stabilize syndesmotic disruption. Intraoperative stress fluoroscopy is a valuable tool for detection of unstable syndesmotic injuries.

Adolescent↗
PubMedDate not supplied

The effect of tibial rotation on varus deformity measurement.

PURPOSE: Tibial osteotomy is used to treat a variety of orthopedic conditions, including reduction in pain and improvement of deformity and function. In templating for surgery, accurate radiographic measurement aids in planning for correction. The purpose of our study was to examine the effect of internal rotation and external rotation on measurement of tibial sawbone models with 5 closing wedge varus deformities at 10-degree increments between 10 and 50 degrees. One sawbone without deformity served as the control. STUDY DESIGN: A total of 66 radiographs were measured by 5 individuals. Measurement deviations from the control in each of the 10 positions of rotation were assessed. RESULTS: In the analysis of variance models, increased rotation and varus angulation were associated with increased deviation compared with the control. In external rotation for every 10 degrees of varus angulation, the degree deviation increased 0.69 degrees. In IR for every 10 degrees of angulation, the degree deviation increased by 0.84 degrees. Internal rotation had the greatest impact. Mean differences between different rater's measurements were small (1.1+/-1.2 degrees) and correlations suggested high interrater reliability. CONCLUSIONS: As the degree of rotation from neutral increased and varus angulation increased, deviation from neutral increased. CLINICAL RELEVANCE: Clinically, the results of this study support the importance of proper alignment of the tibia during radiography to more precisely template surgery.

Artifacts↗
PubMed2006

Pedicle rotation in scoliosis: a marker for occult intrathecal abnormalities.

STUDY DESIGN: The Perdriolle method was used to assess retrospectively radiographic pedicle rotation for association with occult intrathecal abnormalities in patients with scoliosis. OBJECTIVE: To determine if pedicle rotation can be predictive of underlying intrathecal abnormalities. SUMMARY OF BACKGROUND DATA: Scoliosis associated with intrathecal abnormalities is thought to produce less rotation than true idiopathic scoliosis. No supporting evidence was found in the literature. METHODS: A consecutive series of patients with a presenting diagnosis of idiopathic scoliosis were reviewed for anteroposterior radiographs and spinal magnetic resonance imaging (MRI). A blinded single examiner evaluated radiographic curve parameters. MRI reports were reviewed for the presence or absence of intrathecal abnormalities. RESULTS: A total of 78 MRIs included 15 intrathecal abnormalities and 63 normals. The abnormal MRI group had more males and apex left curves. Primary curve in the intrathecal abnormality group had a mean of 9.6 degrees of apical vertebrae rotation compared to 17.7 degrees in idiopathic curves (average 37 degrees and 40 degrees Cobb angles, respectively). Of angulation, 1 degrees correlated with 0.21 degrees and 0.34 degrees of rotation in intrathecal abnormality versus no abnormality groups, respectively. CONCLUSIONS: Curves with occult intrathecal pathology had significantly less rotation than those without. Pedicle rotation assessment is a useful adjuvant for identifying scoliosis with intrathecal abnormalities.

Adolescent↗
PubMed2006

Analysis of preexistent vertebral rotation in the normal spine.

STUDY DESIGN: A newly developed CT measurement method was used to investigate axial rotation from T2 to L5 in the normal, nonscoliotic spine. OBJECTIVES: To identify a preexistent rotational pattern in the normal, nonscoliotic spine. SUMMARY OF BACKGROUND DATA: The data available on axial rotation measurements in the normal spine are scant and limited to only a few vertebrae. Systematic analysis of the thoracic and lumbar vertebrae of the normal spine, based on computed tomography has, to our knowledge, not been performed. METHODS: CT scans of the thorax and abdomen of 50 persons without clinical or radiologic evidence of scoliosis were used to measure vertebral axial rotation from T2 to L5 with a newly developed semiautomatic computerized method. RESULTS: The results of the present study showed a predominant rotation to the left of the high thoracic vertebrae, and to the right of the mid and lower thoracic vertebrae in the normal, nonscoliotic spine, which differed significantly from an equal right-left distribution. This rotational pattern is present in both males and females. CONCLUSION: The normal, nonscoliotic spine demonstrates a preexistent pattern of vertebral rotation that corresponds to what is seen in the most prevalent types of thoracic idiopathic scoliosis.

Adolescent↗
PubMed2006

Low back pain patients demonstrate increased hip extensor muscle activity during standardized submaximal rotation efforts.

STUDY DESIGN: A comparative study of trunk and hip extensor muscle recruitment patterns in 2 subject groups. OBJECTIVE: To examine for changes in recruitment of the hip and back extensor muscles during low level isometric trunk rotation efforts in chronic low back pain (CLBP) subjects by comparison with matched asymptomatic control subjects. SUMMARY OF BACKGROUND DATA: Anatomic and biomechanical models have provided evidence that muscles attaching to the thoracolumbar fascia (TLF) are important for providing stabilization to the lumbopelvic region during trunk rotation. This has guided rehabilitation programs. The muscles that link diagonally to the posterior layer of the TLF have not previously been examined individually and compared during low-level trunk rotation efforts in CLBP patients and matched controls. METHODS: Thirty CLBP patients and 30 matched controls were assessed using surface electromyography (EMG) as they performed low-level isometric rotation efforts while standing upright. Muscles studied included latissimus dorsi, erector spinae, upper and lower gluteus maximus, and biceps femoris. Subjects performed the rotation exertion with various levels of external trunk support, related to different functional tasks. RESULTS: EMG results demonstrated that subjects with CLBP had significantly higher levels of recruitment for the lower and upper gluteus maximus (P < 0.05), hamstrings (P < 0.05), and erector spinae muscles (P < 0.05) during rotation to the left compared with the control subjects. CONCLUSION: This study provided evidence of increased muscle recruitment in CLBP patients when performing a standardized trunk rotation task. These results may have implications for the design of therapeutic exercise programs for CLBP patients.

Adult↗
PubMedDate not supplied

Evaluation of a pumping assist lung that uses a rotating fiber bundle.

A paracorporeal respiratory assist lung (PRAL) is being developed for supplemental gas exchange to allow the native lungs of acute lung failure patients to heal. The device consists of a rotating annular microporous hollow fiber membrane bundle. The rotation augments the gas exchange efficiency of the device at constant flow-rate thereby uncoupling gas exchange and flow rate. The rotating fibers also enable the PRAL to pump the blood without the need for an additional pump or arterial cannulation. Blood flow rates will be between 500 and 750 ml/min with CO(2) removal rates of 100-130 ml/min. A prototype was manufactured with an overall surface area of 0.25 m. When rotated at 1500 rpm, CO(2) removal increased by 133% and O(2) transfer increased by 157% during an in vitro bovine blood study. The pumping of the rotating fiber bundle was assessed in a glycerol/water solution. At 1500 rpm, the PRAL generated 750 ml/min against 52 mm Hg pressure. Hemolysis of the device was assessed using in vitro bovine blood from a slaughterhouse. Plasma free hemoglobin levels were similar regardless of whether the rotating fibers were present in the PRAL, indicating that a rotating fiber bundle can be used to increase gas exchange without causing blood trauma.

Animals↗
PubMed2006

Navigation with three-dimensional rotational radiographic data for transpedicular percutaneous needle introduction: feasibility and comparison with fluoroscopic guidance.

PURPOSE: To investigate the feasibility of navigation with three-dimensional (3D) rotational radiographic data for transpedicular percutaneous needle introduction and to compare navigation with 3D rotational radiographic data with conventional fluoroscopic guidance. MATERIALS AND METHODS: A navigation system was coupled to a 3D rotational radiographic imaging system. In a cadaver study, 60 biopsy needles were introduced into vertebral bodies with fluoroscopic guidance or navigation with 3D rotational radiographic data by two interventionalists with different levels of experience in percutaneous procedures. Radiation exposure, fluoroscopy and introduction times, and needle position were evaluated and compared. RESULTS: For 3D rotational radiographic navigation, the needle position was equivalent for both interventionalists (7 mm). For fluoroscopic guidance, the interventionalist with less experience in percutaneous procedures had significantly more pedicle cortex violations than the other interventionalist (eight vs one). Radiation exposure measured at the operators' hand was lower for 3D rotational radiography-guided needle introductions. Radiation exposure measured at the body wall of the cadaver was equivalent between modalities (9 mGy). CONCLUSIONS: Navigation with 3D rotational radiographic image data is feasible for transpedicular percutaneous needle introduction and has two advantages compared with fluoroscopic guidance: it poses less strict requirements on the expertise of the interventionalist, and it reduces radiation exposure to the interventionalist.

Biopsy, Needle↗
PubMed2005

Incidence and severity of biceps long head tendon lesion in patients with complete rotator cuff tears.

BACKGROUND: Biceps long head tendon lesion is commonly associated with rotator cuff tendon pathology. This study is to determine the pathologic spectrum of biceps long head tendon in surgical cases with complete full thickness rotator cuff tear. METHODS: Between 1993 and 2002, 122 complete rotator cuff tears with surgery were included for the analysis. During surgery, biceps long head tendon was grossly examined or evaluated via arthroscopy. A simplified classification was used to describe the biceps lesion. RESULTS: 50 (41%) patients had type 1 lesion (tendinitis), 10 (8%) patients had type 2 lesion (subluxation), 12 (10%) patients had type 3 (dislocation), 15 (12%) patients had type 4 (partial tear), and 6 patients (5%) had type 5 (complete rupture). The remaining 29 patients (24%) did not have obvious pathology. All chronic rotator cuff tear (> 3 months) were associated with biceps tendon pathology. A rotator cuff tear greater than 5 cm as determined at surgery was strongly associated with an advanced biceps lesion. CONCLUSION: Biceps tendon injuries are associated with complete rotator cuff tears and there may be a causal relationship due to the impingement that occurs. Early identification and repair of rotator cuff lesions may prevent further deterioration of the biceps tendon.

Adult↗
PubMed1991

Evidence that the unilateral activation of 5-HT1D receptors in the substantia nigra of the guinea-pig elicits contralateral rotation.

1. The effects of various 5-hydroxytryptamine (5-HT) receptor agonists were examined following unilateral infusion into the substantia nigra (SN) of the guinea-pig. 2. The 5-HT1 receptor agonists, 5-carboxamidotryptamine (5-CT) (2-25 micrograms), sumatriptan (10-25 micrograms) and RU24969 (25 micrograms) all induced a marked contralateral rotation. In contrast, the selective 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH DPAT, 10-25 micrograms) produced only a very small response, whilst the selective 5-HT1C/5-HT2 receptor agonist (+-)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride ((+/-)-DOI) (25 micrograms) and the 5-HT3 receptor agonist, 2-methyl 5-HT (2-Me5-HT, 25 micrograms) were without effect. 3. The contralateral rotation induced by 5-CT (10 micrograms) was attenuated following pretreatment with the non-selective 5-HT1/5-HT2 receptor antagonists methiothepin (1 mg kg-1, s.c.) and metergoline (5-10 mg kg-1, s.c.) but not the 5-HT1C/5-HT2 antagonist ritanserin (1 mg kg-1, s.c.) or the 5-HT3 antagonist, ondansetron (0.5 mg kg-1, s.c.). An involvement of dopaminergic systems in the rotational response to 5-CT was implied by the antagonism of 5-CT-induced rotation by haloperidol (0.3 mg kg-1, s.c.). 4. At doses lower than those required to produce contralateral rotation, 5-CT (0.08-0.4 micrograms) and sumatriptan (2 micrograms) induced a small, but nonetheless consistent, ipsilateral rotation. 5. The data with agonists and antagonists taken together suggest that 5-CT-induced contralateral rotation may be mediated by 5-HTID receptor activation but definitive classification of the receptor will not be possible until selective 5-HTID-antagonists become available. This may therefore represent the first model to study this receptor subtype in vivo.

Animals↗
PubMed1977

Operational definitions of mandibular morphogenetic and positional rotations.

A material of 30 patients with metallic implants was used in a longitudinal study, based on lateral headplates, of the mandibular rotational pattern. The complexity of the rotational phenomenon in the mandibular rotation has necessitated the proposal of some operational definitions: morphogenetic and positional rotations of the mandible. A relationship has been established between the variation of the gonial angle and the variation of both morphogenetic and positional rotations of the mandible. A relationship has been established between the variation of the condylar growth direction and the variation of both morphogenetc and positional rotations of the mandible: this relationship is the strongest when the morphogenetic rotation of the corpus is considered.

Dental Implantation↗
PubMed1985

Rotational behaviour elicited by intracerebral injections of apomorphine and pergolide in 6-hydroxy-dopamine-lesioned rats. I: Comparison between systemic and intrastriatal injections.

Rotational behaviour in unilaterally 6-hydroxy-dopamine-denervated rats has been attributed to stimulation of dopamine receptors on striatal as well as limbic areas. In the present study the rotational behaviour elicited by local intrastriatal injections of apomorphine or pergolide was compared to the rotation elicited by systemic injections of the drugs. We found that intrastriatal injections induced rotational behaviour almost identical to the behaviour occurring after systemic treatment. Furthermore, studies of the spread of [3H]apomorphine in brain tissue showed that at the peak of rotation the radioactivity was confined within the limits of the striatum. Non-significant amounts of radioactivity was found in the nucleus accumbens. On the basis of these data we conclude that rotational behaviour elicited by systemic injections of apomorphine or pergolide originates from stimulation of striatal sites. The difference in rotational patterns elicited by these drugs is more likely to relate to differences in receptor stimulation within the striatum than differences in, for example, relative distribution between limbic and striatal areas.

Animals↗
PubMed1987

The dopamine-gamma aminobutyric acid interaction in the striatum of the rat is differently regulated by dopamine D-1 and D-2 types of receptor: evidence obtained with rotational behavioural experiments.

The effects of GABA antagonists on apomorphine- and pergolide-induced rotational behaviour were studied with models combining intracerebral and systemic pharmacological treatments. Whether given systemically or intrastriatally to 6-hydroxydopamine-lesioned rats, the GABA antagonist picrotoxin inhibited the rotational responses produced by s.c. administration of the dopamine (DA) D-1/D-2 agonist apomorphine while it enhanced the rotational behaviour produced by the DA D-2 agonist pergolide. Following unilateral injection of picrotoxin or bicuculline into the striatum of naive rats, apomorphine produced ispsilateral rotation, while pergolide produced contralateral rotation. These contrasting effects are compared to the behavioural responses produced by intracerebral administration of GABAergic drugs alone. Intrapallidal injection of picrotoxin produced contralateral rotational behaviour which was independent of pallido-nigral pathways. Contralateral rotation was also produced by GABA agonists, but only following intranigral injections. The results are discussed in terms of differences in the localization of DA D-1 and DA D-2 receptors on striatal GABAergic neurons. The DA D-2 receptor agonist pergolide may induce inhibition of striato-pallidal GABAergic neurons, as well as of a local GABAergic circuit exerting inhibition on a striato--pallidal enkephalinergic pathway. However, the DA D-1/D-2 receptor agonist apomorphine may inhibit striatal interneurons exerting inhibition on a striato-nigral GABAergic projection. Such a neuronal arrangement may explain that striatal DA stimulation increases GABA release from the striato-nigral terminals.

Animals↗
PubMed2005

Virtual head rotation reveals a process of route reconstruction from human vestibular signals.

The vestibular organs can feed perceptual processes that build a picture of our route as we move about in the world. However, raw vestibular signals do not define the path taken because, during travel, the head can undergo accelerations unrelated to the route and also be orientated in any direction to vary the signal. This study investigated the computational process by which the brain transforms raw vestibular signals for the purpose of route reconstruction. We electrically stimulated the vestibular nerves of human subjects to evoke a virtual head rotation fixed in skull co-ordinates and measure its perceptual effect. The virtual head rotation caused subjects to perceive an illusory whole-body rotation that was a cyclic function of head-pitch angle. They perceived whole-body yaw rotation in one direction with the head pitched forwards, the opposite direction with the head pitched backwards, and no rotation with the head in an intermediate position. A model based on vector operations and the anatomy and firing properties of semicircular canals precisely predicted these perceptions. In effect, a neural process computes the vector dot product between the craniocentric vestibular vector of head rotation and the gravitational unit vector. This computation yields the signal of body rotation in the horizontal plane that feeds our perception of the route travelled.

Adult↗