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PubMed1998

Epidermal growth factor receptor transmembrane domain: 2H NMR implications for orientation and motion in a bilayer environment.

As part of a study of receptor tyrosine kinase behavior in membranes, we have collected extensive NMR data from three well-defined probe locations within the transmembrane region of the human EGF receptor. Spectra were obtained for selectively deuterated alanine residues in a series of peptides corresponding to the putative transmembrane domain (with short extramembranous extensions). Peptides were incorporated into fluid unsonicated liposomes of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and POPC containing 33 mol % cholesterol to mimic common lipid composition of cell plasma membranes. The peptide concentration was in the range of 1-6 mol % relative to that of phospholipid. Data acquired at 35 degreesC have been analyzed quantitatively to determine their implications to receptor spatial orientation and dynamics. If it is presumed that the single transmembrane portion approximates an alpha-helix of 3.6 residues per turn, this helix was found to be tilted away from the membrane perpendicular, about which there was rapid axial diffusion. However, rotation about the peptide long axis was static on the NMR time scale of 10(-)4 s, and the peptide appeared to have a preferred direction(s) of lean. The results for this peptide, whose hydrophobic length is greater than the membrane hydrophobic thickness, were very similar between membranes of POPC and membranes of POPC containing 33 mol % cholesterol, despite considerable host matrix differences in thickness and order. Allowed values of peptide tilt occupied a narrow range: between 10 and 14 degrees in POPC and between 10 and 12 degrees in POPC/cholesterol. Although the existence of some preferred direction(s) of lean was demanded by the results, the direction of lean was not uniquely determined. We have interpreted these results, which were essentially unchanged at 65 degreesC, as reflecting the behavior of peptide monomers undergoing rapidly reversible peptide-peptide interactions. For transmembrane monomers, interference with rotation about the peptide long axis might be understood to arise from an energy benefit (in a tilted peptide) to prevention of particular amino acid side chains near the membrane surfaces from moving in and out of hydrophobic or hydrophilic environments. It will be desirable to test the conclusion of preferential lean of a monomeric receptor since such behavior could provide a mechanism for modulating monomer association with other species (i.e., signal transduction).

Alanine↗

PubMed1998

[Image processing in the primary visual cortex].

INTRODUCTION: Area 17 or the primary visual area forms the first link in the chain of cerebral analysis of a visual image. The neurones forming the primary visual cortex are characterized by the extreme precision of their connections, functional specialization and hierarchic organization. The spatial precision of the connections within the system for vision permit retinotopic representation in the visual cortex, so that each point of the retina is projected into a specific area of the cortex. The cortical neurones which analyze the characteristics of the image situated in a precise zone of the visual field are themselves organized into a basic functional unit known as a hypercolumn. Within each hypercolumn there are various columnar cell systems with receptive fields having similar characteristics. Thus, each hypercolumn is made up of multiple orientation columns, two ocular dominance columns and 'blob' regions. All these systems permit the analysis of different aspects of the image. The neurones belonging to the orientation columns are sensitive to the orientation, spatial frequency and movement of a visual stimulus; those of the 'blob' regions to colour, and the binocular neurones of the ocular dominance columns to depth. Within each column, the hierarchical pattern of neurone interconnections determines the successive appearance of cells with receptive fields having new properties.

Geniculate Bodies↗

PubMed1992

Behavioural, biochemical and histological effects of AF64A following injection into the third ventricle of the mouse.

Behavioural, biochemical and histological effects were assessed following AF64A injected into the third ventricle of female NMRI mice. Doses from 3 to 7 nmol produced significant changes in behaviour, causing hyperactivity, reduced hole-board exploration, rotational behaviour in a symmetrical Y-maze corresponding to a loss of alternation, abnormal behaviour in a plus-maze task of fear/anxiety with markedly increased exploration of the open arms and finally deficits in passive avoidance responding and spatial orientation in a Morris-type water maze. In this latter test, a cue learning deficit was noted for the two highest doses only. No histological changes of consequence were observed up to 5 nmol. Beyond this dose, at 6 and particularly 7 nmol, necrosis of parts of the hippocampus and septum was apparent. ChAT and AChE activity were decreased in the hippocampus but not in the cortex although the decreases were smaller than generally reported for AF64A-treated rats. ChAT and AChE reductions correlated highly with hyperactivity in the open-field and to a lesser extent, with spatial learning deficits. Monoaminergic activity was also affected in the hippocampus, but not in the cortex, at 4 nmol and above. NE and particularly 5-HT and 5-HIAA levels were reduced although the rate of 5-HT turnover was unaltered. A highly significant correlation was obtained between 5-HT effects and the increased open arm exploration in the plus-maze task of fear/anxiety. The behavioural effects and biochemical changes lasted at least 8-9 weeks postop.

Acetylcholinesterase↗

PubMed2006

The effect of the orientation of the radial head on the kinematics of the ulnohumeral joint and force transmission through the radiocapitellar joint.

Background. The treatment of radial head fractures that are not amenable to an open reduction and internal fixation, remains to be a difficult issue. A potential problem with prosthetic replacement of the radial head is the shape of current radial head prostheses. The purpose of this study was to determine the effect of the shape of the radial head on kinematics and load transfer of the elbow. Methods. Kinematics of the elbow and radiocapitellar force transmission were measured in 6 fresh frozen upper extremities. The effect of radial head shape was tested by rotating the head 90 degrees , with a custom-made 'native' radial head prosthesis. 3-D spatial orientation of the ulna showed an average difference in ulnohumeral laxity, between the nominal and 90 degrees conditions, of 0.1 degrees throughout the arc of motion with neutral forearm rotation (maximum: 2 degrees ). Findings. We found an average difference in ulnar axial rotation, of 0.1 degrees (maximum: 1.9 degrees ). No differences showed statistical significance. Radiohumeral joint force was measured and maximally showed a 32 times increase of force in the altered shape conditions. Interpretation. Our results show that the kinematics of the elbow was not affected by altering the shape of the radial head, but it did adversely affect the forces in the radiohumeral joint. This could possibly generate degenerative changes in the elbow.

Biomechanical Phenomena↗

PubMed1994

Orientation-conserved transfer of symmetric Krebs cycle intermediates in mammalian tissue.

Metabolism of [2-13C]-, [3-13C]-, and [1,2,3-13C]propionate in perfused rat livers and [2-13C]-acetate in perfused rat hearts has been examined in tissue extracts by 13C NMR. Label from [2-13C]-propionate was preferentially incorporated into the C2 carbon of lactate, alanine, and aspartate in liver tissue while label from [3-13C]propionate appeared preferentially in the C3 carbon of those same molecules. These data suggest that 13C may not be completely randomized in the symmetric citric acid cycle intermediates succinate and fumarate as is normally assumed but that some fraction of those intermediates may be transferred between enzymes in this span of the cycle with conservation of spatial orientation, consistent with recent results obtained in yeast [Sumegi et al. (1990) Biochemistry 29, 9106-9110]. This was confirmed by performing similar experiments with [1,2,3-13C]propionate. Time-dependent asymmetry was also observed between the intensities of the glutamate C2 and C3 resonances and between the aspartate C2 and C3 resonances in 13C NMR spectra of intact hearts and heart extracts during early perfusion with [2-13C]-acetate. A model is presented which predicts that isotopic asymmetry is observed only during the first 2-3 turns of the cycle pools when isotope enters the cycle via acetyl-CoA even if all symmetric cycle intermediates retain a unique molecular orientation on each pass through the citric acid cycle.

Acetates↗

PubMed2005

Angular orientation of trabecular bone in the femoral head and its relationship to hip joint loads in leaping primates.

The elastic properties and mechanical behavior of trabecular bone are largely determined by its three-dimensional (3D) fabric structure. Recent work demonstrating a correlation between the primary mechanical and material axes in trabecular bone specimens suggests that fabric orientation may be used to infer directional components of the material strength and, by extension, the hypothetical loading regime. Here we quantify the principal orientation of trabecular bone in the femoral head and relate these principal fabric directions to loading patterns during various locomotor behaviors. The proximal femora of a diverse sample of prosimians were scanned using a high-resolution X-ray computed tomography scanner with resolution of better than 50 mum. Spherical volumes of interest were defined within the femoral heads and the 3D fabric anisotropy was calculated using the mean intercept length and star volume distribution methods. In addition to differences in bone volume and anisotropy, significant differences were found in the spatial orientation of the principal trabecular axes depending on locomotor behavior. The principal orientations for leapers (Galago, Tarsius, Avahi) are relatively tightly clustered (alpha(95) confidence limit: 8.2; angular variance s: 18.2 degrees ) and oriented in a superoanterior direction, while those of nonleapers are more variable across a range of directions (alpha(95): 16.8; s: 42.0 degrees ). The mean principal directions are significantly different for leaping vs. nonleaping taxa. These results further suggest a relationship between bone microstructure in the hip joint and locomotor behavior and indicate a similarity of loading across leapers despite differences in kinematics and phylogeny.

Animals↗

PubMed1986

Heavy riboflavin synthase from Bacillus subtilis. Particle dimensions, crystal packing and molecular symmetry.

Heavy riboflavin synthase from Bacillus subtilis is an enzyme complex consisting of approximately three alpha-subunits (Mr 23.5 X 10(3)) and 60 beta-subunits (Mr 16 X 10(3)). The enzyme has been crystallized from phosphate buffer in a hexagonal crystal modification that belongs to space group P6(3)22. The asymmetric unit of the crystal cell contains ten beta-subunits. The structure of this unusual 10(6) Mr protein has been studied by small-angle X-ray scattering, electron microscopy of three-dimensional crystals, and crystallographic methods. The scattering curves can be interpreted in terms of a hollow sphere model with a ratio of inner and outer radius of 0.3:1. A diameter of 168 A was estimated from the scattering curves, in close agreement with electron microscopic studies. An aggregate with the stoichiometry beta 60, which was obtained by ligand-driven reaggregation of isolated beta-subunits, showed similar shape and dimensions, but a larger value for the ratio Ri/Ra. Electron micrographs of freeze-etched enzyme crystals showed approximately spherical molecules, which were arranged in hexagonal layers. The lattice constants found from the micrographs are in good agreement with the values derived from X-ray diffraction data. Rotation function calculations in Patterson space showed a set of peaks for 2-fold, 3-fold and 5-fold local rotation axes, accurately consistent with icosahedral symmetry and with the particle orientation A shown in the Appendix. The crystal packing can be described as follows: enzyme particles with icosahedral symmetry (point group 532) are located at points 32 of the hexagonal cell, corresponding to positions (0, 0, 0) and (0, 0, 1/2) on the 6-fold screw axes. From the data reported, it may be concluded that the enzyme structure can be described as an icosahedral capsid of 60 beta-subunits with the triangulation number T = 1. The alpha-subunits are located in the central core space of the capsid, but their spatial orientation is incompletely understood.

Bacillus subtilis↗

PubMed1977

Global spatial disorientation. Clinico-pathologic correlations.

Two patients presenting with the acute onset of bilateral parietal lobe damage showed initially the features of Balint's syndrome. After most of its manifestations had cleared, both patients exhibited severe disorders of spatial orientation: acoustic ataxia, inability to localize objects in space. In addition, 1 patient showed a topographical disorientation and abnormalities of whole body movements. This patient came to post-mortem examination, which revealed bilateral and fairly symmetrical old and recent infarctions of the superior parietal lobules. In the light of these observations and previous reports, it is suggested that the reported abnormalities of whole body movements can be explained on the basis of a visuo-motor intrahemispheric disconnection due to the bilateral lesion of the dorsal parietal lobe. In addition, the global spatial disorientation is analysed and is thought to be the manifestation of a derangement of a specific function centered in the parietal lobe. Moreover, it is pointed out that topographic disorientation does not require the concomitant failure of oculomotor mechanisms for its production. The topography of the anatomical lesion is considered in relation to current concepts on brain damage after severe hypotension and cardiac arrest. It is concluded that this group of patients is most likely at risk of developing behavioural abnormalities akin to the ones here reported.

Adult↗

PubMed2005

Gaze direction modulates auditory spatial deficits in stroke patients with neglect.

We investigated the effects of eye position on auditory spatial deficits in four patients with left neglect and right-hemisphere damage, using three blocked gaze directions (35 degrees to the right, central, or 35 degrees to the left), while preventing any head-movement to ensure that initial auditory inputs remained constant regardless of eye-in-orbit position. The auditory task required speeded discrimination of sound elevation, with patients moving a central lever up or down according to the vertical position of a peripheral target sound, regardless of its side (left or right). Replicating previous auditory research, the patients' vertical discrimination performance was worse for auditory targets on the contralesional (left) versus the ipsilesional side, indicating neglect-related auditory deficits on this task. Critically, while this worse performance for left than right auditory targets was present (for both reaction times and errors) when gaze was directed centrally or rightwards, it was considerably reduced when gaze was directed leftwards. These results demonstrate that lateral gaze-direction can modulate neglect-related auditory spatial deficits, even though eye-position did not alter the initial auditory inputs. This outcome may relate to audio-visual links in spatial orienting and potentially some retinocentric influences on perceived sound location, although the latter alone could not explain all our results. Such findings might involve multisensory brain structures in which responses to sounds are modulated by eye-in-orbit position.

Attention↗

PubMedDate not supplied

Integration of olfactory information in a spatial representation enabling accurate arm choice in the radial arm maze.

The aim of the present study was to determine whether and how rats can use local olfactory cues for spatial orientation. Rats were trained in an eight-arm radial maze under different conditions as defined by the presence or absence of supplementary olfactory cues marking each arm, the availability of distant visuospatial information, and the illumination of the maze (light or darkness). The different visual conditions were designed to dissociate among the effects of light per se and those of visuospatial cues, on the use of olfactory cues for accurate arm choice. Different procedures with modifications of the arrangement of olfactory cues were used to determine if rats formed a representation of the spatial configuration of the olfactory cues and if they could rely on such a representation for accurate arm choice in the radial maze. The present study demonstrated that the use of olfactory cues to direct arm choice in the radial arm maze was critically dependent on the illumination conditions and implied two different modes of processing of olfactory information according to the presence or the absence of light. Olfactory cues were used in an explicit manner and enabled accurate arm choice only in the absence of light. Rats, however, had an implicit memory of the location of the olfactory cues and formed a representation of the spatial position of these cues, whatever the lighting conditions. They did not memorize the spatial configuration of the olfactory cues per se but needed these cues to be linked to the external spatial frame of reference.

Animals↗

PubMed1995

Proprioceptive sensory codes mediating movement trajectory perception: human hand vibration-induced drawing illusions.

To study the organization of the proprioceptive sensory codes subserving movement trajectory perception, complex hand drawing illusions were elicited using various vibration patterns applied to the wrist muscles of nine human subjects. It was established that it is possible to elicit kinesthetic illusions involving spatially oriented lines and geometrical shapes such as rectilinear or curvilinear figures by activating four groups of muscle tendons at the wrist level. The vibration sequences specifically evoking each shape were determined by varying the vibration frequency, the duration of each stimulus applied, and the vibrator onsets, and by applying the vibrations either successively or simultaneously. The proprioceptive coding of a trajectory can be modelled in terms of a series of vectors, the direction of which depends on the anatomical sites of the muscles that are stretched and shortened during the movement. The vector giving the spatial path of a movement is the sum vector of the vectors determined on the basis of the proprioceptive inputs originating from each muscle, and the modulus of the resulting vector is the instantaneous velocity of the movement. In line with previous cortical data, our results suggest that the perception of the spatial paths of limb segment movements is coded in joint space kinematic coordinates on the basis of the relevant ongoing proprioceptive information. It therefore emerges from the results of this study that muscle proprioception is able to generate spatiotemporal afferent patterns that may mediate complex cognitive operations such as those involved in the memorizing and recognition of motor forms.

Female↗

PubMed1997

Spatial coherence: a new method of quantifying myocardial electrical organization using multichannel epicardial electrograms.

A new technique has been developed to quantify the organization of myocardial electrical activity. The spatial coherence technique employs the use of the magnitude-squared coherence (MSC) spectrum to analyze multichannel electrograms obtained during cardiac mapping. In this study, MSC values for all possible pairs of electrograms recorded from an epicardial plaque consisting of 112 electrodes were computed and systematically integrated to form a three-dimensional coherence surface, that is, a graphical representation of average coherence values versus the spatial orientation of one electrode to another. From this surface, two-dimensional graphs of average coherence versus electrode separation distance were derived, and the data were fitted to an exponentially decaying curve. Two novel parameters indicative of myocardial organization were then extracted from the curves, the coherence length parameter and the coherence plateau parameter. Higher values for these parameters were hypothesized to reflect greater levels of organization of the rhythm. A total of 164 mapping sessions were performed on nine dogs. Three-second data segments of normal sinus rhythm (NSR) and ventricular fibrillation (VF) were analyzed by using spatial coherence. Coherence lengths were found to be significantly longer (24.3 +/- 13.4 vs 0.165 +/- 0.053 mm, P = .0001) and coherence plateau values significantly higher (0.896 +/- 0.104 vs 0.098 +/- 0.008, P = .0001) for NSR than for VF. In addition, one instance of ventricular tachycardia, a rhythm more organized than VF, had coherence parameter values greater than those for VF but less than those for NSR (coherence length = 1.23 mm, coherence plateau value = 0.597). These results suggest that spatial coherence may be an effective means of quantifying the electrical organization of a particular cardiac rhythm. The advantages of this technique are (1) it extracts a single parameter from the vast amount of data that is generated in a typical mapping study, thus allowing easy characterization of different cardiac rhythms in terms of their level of organization, and (2) it does not require activation time detection, a process that is difficult when studying arrhythmias such as ventricular fibrillation.

Animals↗

PubMedDate not supplied

Tensile strength of the supraspinatus after reimplantation into a bony trough: an experimental study in rabbits.

The goals of this study were to determine the strength of the supraspinatus tendon after reimplantation into a bony trough and to find out whether the fibrocartilaginous enthesis reformed. In 21 rabbits, the supraspinatus tendon was transected and reinserted into a bony trough at the greater tuberosity. After sacrifice at 8 and 12 weeks, tensile strength was measured. Microscopically, the presence of fibrocartilage and the spatial orientation of the cartilage columns and collagen fibers were assessed. At sacrifice, 14 of 21 reinserted specimens had healed successfully and were studied. Most mechanical failures occurred through bone, and none failed at the site of reimplantation. The mean peak loads of the operated tendons were significantly lower than their controls (8 weeks, 134.8 +/- 49.9 N vs 223.1 +/- 33.4 N, and 12 weeks, 172.2 +/- 68.2 N vs 274.1 +/- 70.0; P =.013 and P =.025, respectively). Histologically, at 8 weeks, the fibrocartilaginous enthesis had partially reformed; it was narrower than normal, and the collagen fibers had only partially assumed their normal spatial arrangement. Twelve weeks after reimplantation, 4 of 7 entheses had a normal histologic appearance. We conclude that return of strength of the supraspinatus tendon is evident 8 weeks after surgical reattachment into a bony trough and that the fibrocartilaginous enthesis is normal in over half of the specimens at 12 weeks. The subchondral bone was weaker than the reinserted tendon. The results support the clinical practice of surgical reimplantation. Avoiding active exercises early while promoting them later could improve the surgical results and reduce the effects of disuse.

Animals↗

PubMed1991

Molecular and crystal structures of 2-(2-pyridyl)thioacetamide derivatives and possible relationship with inhibitory activity for gastric acid secretion.

As a possible method to determine the key atoms and their spatial orientation which are necessary for the gastric mucosal protective and antisecretory activity, crystal structures of sixteen 2-(2-pyridyl) thioacetamide derivatives have been analyzed by the X-ray diffraction method. The characteristics of the molecular and crystal structures of the derivatives are described in this paper. The energetic stability of the molecular conformation is also investigated by means of the molecular force field method. Using the conformational data, a possible relationship between the stereostructure and inhibitory activity for gastric acid secretion is considered by QSAR analyses. The results suggest that the activity is related to the overall molecular conformation, and that the spatial distribution of the side-chain polar atoms with respect to the fixed pyridine is especially important for the activity.

Animals↗

PubMed2003

Midline sagittal sacral fractures in anterior-posterior compression pelvic ring injuries.

OBJECTIVE: To evaluate the outcome of an uncommon variant of the anterior-posterior compression pelvic injury, in which the posterior ring injury is a midline sagittal sacral fracture extending into the spinal canal. DESIGN: Prospective, consecutive series. SETTING Two regional trauma centers. PATIENTS: A consecutive series of 10 patients with rotationally displaced, vertically stable anterior-posterior compression pelvic ring fractures (OTA type 61-B1) in which the posterior ring injury is a midline sagittally oriented sacral fracture involving the spinal canal (Denis zone III). This injury pattern comprised 0.6% of pelvic fractures and 1.4% of sacral fractures treated at these two institutions during a 10-year period. INTERVENTION: Patients were treated according to the same principles used in more commonly seen types of anterior-posterior compression pelvic ring injuries. Nine patients were treated with reduction and anterior pelvic stabilization at an average of 5 days after injury, 8 of whom were treated with open reduction and internal fixation and 1 with external fixation. No posterior pelvic fixation was used. One patient with nondisplaced bilateral pubic ramus fractures was treated nonoperatively. Immediate weight bearing was allowed as tolerated. MAIN OUTCOME MEASUREMENTS: Prospectively collected clinical follow-up data emphasized a detailed neurologic examination, whereas radiographic evaluation involved anteroposterior, inlet, and outlet plain radiographic views of the pelvis. RESULTS: An anatomical or near-anatomical reduction of the pelvis was achieved and maintained in all patients. Fractures healed at an average of 10 weeks. At an average follow-up of 31 months (range 20-46 months), there were no objective neurologic deficits that could be attributed to sacral root injury and no significant residual pain or gait disturbance related to the pelvic fracture. Loss of bowel or bladder function, loss of perianal sensation or sphincter tone, and lumbosacral radicular pain or sensorimotor deficit were specifically absent in all patients. Three patients, however, complained of sexual dysfunction at final follow-up. None of these patients had clinical evidence of sacral root/plexus injury secondary to the fracture. One additional patient, who sustained a urethral tear, required a chronic suprapubic catheter because of stricture. Six patients, one of whom had needed repair of a retroperitoneal bladder tear, had no urogenital sequelae. DISCUSSION AND CONCLUSION: Patients who sustain sagittally oriented midline fractures of the sacrum that extend into the spinal canal (Denis zone III) as part of displaced, vertically stable anterior-posterior compression pelvic injuries, have a low incidence of neurologic deficit attributable to sacral root or plexus injury. This is in contrast to the high rate of neurologic deficit (>50%) otherwise reported in zone III sacral fractures, particularly in those associated with a displaced transverse component. In the midline sagittal fracture variant, simultaneous lateral displacement of both bony and neural elements through the midline may protect the sacral roots and plexi from significant traction or shear injury by maintaining the spatial orientation between the sacral foramina and sciatic notch. Long-term sequelae were related to urogenital complaints rather than to musculoskeletal problems, as 4 of the 10 patients in this series had either sexual or urologic dysfunction.

Adult↗

PubMed2006

Remodeling of myocardial sleeve and gap junctions in canine superior vena cava after rapid pacing.

OBJECTIVE: We studied the response of the superior vena cava (SVC) myocardial sleeve to atrial fibrillation (AF). METHODS AND RESULTS: We examined adult male dogs without pacing (N=6) and after rapid atrial pacing (600 bpm) for 2 weeks (P2w; N=5) and 6-8 weeks (P6-8w; N=5). After pacing, the sleeve was increased in thickness (non-paced vs. either paced group, both P<0.05). This was associated with an increase in proliferative activity, which was higher in the P2w than the P6-8w animals (P<0.05). In addition, collagen content increased, and the component cardiomyocytes become more unevenly oriented and shorter and narrower in shape (non-paced vs. either paced group, both P<0.05). Pacing had different effects on connexin40 (Cx40) and Cx43 gap junctions. There was a 98% increase in Cx43 signal in P2w, and a 74% increase in P6-8w animals (non-paced vs. each paced group, both P<0.05). In contrast, Cx40 signal decreased 47% in P2w but increased 44% in P6-8w animals (non-paced vs. each paced group, both P<0.05). CONCLUSIONS: Rapid atrial pacing results in a specific pattern of remodeling of the canine SVC sleeve, including changes in size and shape, spatial orientation, and gap junction expression profile of the component cardiomyocytes. These changes may co-operatively affect the electrical properties and contribute to the formation and maintenance of the arrhythmogenic substrate of AF.

Animals↗

PubMed1973

The neural signal of angular head position in primary afferent vestibular nerve axons.

1. The relation between discharge frequency and angular head position was determined for a population of regularly discharging single first-order vestibular neurones in the eighth nerve of the barbiturate anaesthetized cat.2. Each axon had a characteristic head position which was maximally excitatory to it, and a diametrically opposed head position which was minimally excitatory.3. After correction for phase shifts introduced by the orientation of preferred excitability, discharge rate in statoreceptor afferents varied as a power function of the sine of angular head position with exponents ranging from 0.9 to 1.6.4. Experimentally determined discharge rates were compared with the predictions of a computer simulation model incorporating the idea that shearing force acting on morphologically polarized receptors is the adequate stimulus for macular receptor cells.5. This approach permitted the identification of a population of first-order vestibular afferents whose discharge frequency varied with head position as did the magnitude of shear force computed for individual receptors, each most excited in a particular head position.6. The majority of the spatial orientations of maximal sensitivity defined a surface which is tilted by approximately 30 degrees with reference to the Horsley-Clarke horizontal plane, implying that most statoreceptor afferents are maximally sensitive to position changes when the cat's head is at or near its normal position.

Action Potentials↗

PubMed2005

Planning and drawing complex shapes.

Arm and hand movements are generally controlled using a combination of sensory-based and memory-based guidance mechanisms. This study examined similarities and differences in visually-guided and memory-guided arm movements, and sought to determine as to what extent certain control principles apply to each type of movement. In particular, the 2/3 power law is a principle that appears to govern the formation of complex, curved hand trajectories; it specifies that the tangential velocity should be proportional to the radius of curvature raised to an exponent of 1/3. A virtual reality system was used to project complex target paths in three-dimensional (3D) space. Human subjects first tracked (with the tip of a handheld pen) a single target moving along an unseen path. The entire target path then became visible and the subject traced the shape. Finally, the target shape disappeared and the subject was to draw it, in the same 3D space, from memory. Most aspects of the movements (speed, path size, shape and arm postures) were very similar across the three conditions. However, subjects adhered to the 2/3 power law most closely in the tracing condition, when the entire target path was visible. Also, only within the tracing condition, there were significant differences in the value of the exponent depending on the size and the spatial orientation of the trajectory. In the tracking and drawing conditions, the exponent was greater than 1/3, indicating that subjects spent more time in areas of tight curvature. This may represent a strategy for learning and remembering the complex shape.

Adult↗