Angular Head Research Articles

РОССИЙСКИЕ ВЕСТИБУЛЯРНЫЕ ИССЛЕДОВАНИЯ НА ОБЕЗЬЯНАХВ ПОЛЕТАХНА БИОСПУТНИКАХ

The BION program with primates included 2 vestibular studies one was focused on coordination of the eye and head movements and activities of the medial vestibular nuclei and cerebellum flocculus during angular head movements in the horizontal plane for gaze fixation and the other, on the central vestibular neurons and otolith-induced cardiac rhythm reaction during linear displacement about the body axis. Sensitivity of the central vestibular neurons to both angular and linear accelerations was found to increase at the beginning of microgravity and then normalized gradually, whereas the flocculus activity remained high throughout the mission.

Development of a conversion model between mechanical and electrical vestibular stimuli.

The vestibular end-organs encode for linear and angular head accelerations in space contributing to our internal representation of self-motion. Activation of the vestibular system with transmastoid electrical current has recently grown in popularity; however, a direct relationship between electrically evoked and mechanically evoked vestibular responses remains elusive in humans. We have developed and tested a mechanical-to-electrical vestibular stimulus conversion model incorporating physiological activation of primary vestibular afferents identified in nonhuman primates. We compared ocular torsional responses between mechanical (chair rotation) and model-derived electrical (binaural-bipolar) stimuli in separate experiments for an angular velocity step change (±10 deg/s over 1 s, ±4-mA peak amplitude; n = 10) and multisine angular velocities (±10 deg/s, 9.7 mA peak to peak, 0.05-1 Hz; n = 5), respectively. Perception of whole body rotation (n = 18) to our step-change stimuli was also evaluated. Ocular torsional slow-phase velocity responses between stimulation types were similar (paired two one-sided tests of equivalence: multiple P < 0.002; one-sample t test: P = 0.178) and correlated (Pearson's coefficient: multiple P < 0.001). Bootstrap analysis of perceived angular velocity likewise showed similarity in perceptual decay dynamics. These data suggest that central processing between stimuli was similar, and our vestibular stimulus conversion model with a conversion factor of ∼0.4 mA per deg/s for an angular velocity step change can generate electrical stimuli that replicates dynamic vestibular activation elicited by mechanical whole body rotations. This proposed vestibular conversion model represents an initial framework for using electrical stimuli to generate mechanically equivalent activation of primary vestibular afferents for use in biomedical applications and immersive reality technologies.NEW & NOTEWORTHY With the growing popularity of electrical vestibular stimulation in biomedical and immersive reality applications, a direct conversion model between electrical and mechanical vestibular stimuli is needed. We developed a model to generate electrical stimuli mimicking the physiological activation of vestibular afferents evoked by mechanical rotations. Ocular and perceptual responses evoked by mechanical and model-derived electrical stimuli were similar, thus providing a critical first step toward generation of electrically induced vestibular responses that have a realistic mechanical equivalent.

High-speed helmeted head impacts in motorcycling: A computational study

The motorcyclist is exposed to the risk of falling and impacting ground head-first at a wide range of travelling speeds – from a speed limit of less than 50 km/h on the urban road to the race circuit where speed can reach well above 200 km/h. However, motorcycle helmets today are tested at a single and much lower impact speed, i.e. 30 km/h. There is a knowledge gap in understanding the dynamics and head impact responses at high travelling speeds due to the limitation of existing laboratory rigs.This study used a finite element head model coupled with a motorcycle helmet model to simulate head-first falls at travelling speed (or tangential velocity at impact) from 0 to 216 km/h. The effect of different falling heights (1.6 m and 0.25 m) and coefficient of frictions (0.20 and 0.45) between the helmet outer shell and ground were also examined. The simulation results were analysed together with the analytical model to better comprehend rolling and/or sliding phenomena that are often observed in helmet oblique impacts.Three types of helmet-to-ground interactions are found when the helmet impacts ground from low to high tangential velocities: (1) helmet rolling without slipping; (2) a combination of sliding and rolling; and (3) continuous sliding. The tangential impulse transmitted to the head-helmet system, peak angular head kinematics and brain strain increase almost linearly with the tangential velocity when the helmet rolls but plateaus when the helmet slides. The critical tangential velocity at which the motion transit from the rolling regime to the sliding regime depends on both the falling height and friction coefficient. Typically, for a fall height of 1.63 m and a friction coefficient of 0.45, the rolling/sliding transition occurs at a tangential velocity of 10.8 m/s (38.9 km/h).Low sliding resistance in helmet design, i.e. by the means of a lower friction coefficient between the helmet outer shell and ground, has shown a higher reduction of brain tissue strain in the sliding regime than in the rolling regime. This study uncovers the underlying dynamics of rolling and sliding phenomena in high-speed oblique impacts, which largely affect head impact biomechanics. Besides, the study highlights the importance of testing helmets at speeds covering both the rolling and sliding regime since potential designs for improved head protection at high-speed impacts can be more distinguishable in the sliding regime than in the rolling regime.

Vestibular disorders in roll plane from brainstem to cortex

The aim is to review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs. The focus is particularly on human psychophysics, neurophysiological and imaging data on vestibular disorders in the roll plane. The signs and symptoms are head tilt, vertical divergence of the eyes (skew deviation), ocular torsion, and tilts of subjective visual vertical (SVV) adjustments, all of which represent the so-called ocular tilt reaction (OTR). Furthermore, these signs will be related to mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients. Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex [[1]Brandt T. Dieterich M. The dizzy patient: Don’t forget disorders of the central vestibular system.Nat. Rev. Neurol. 2017 Jun; 13: 352-362https://doi.org/10.1038/nrneurol.2017.58Google Scholar]. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, i.e. components of OTR, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of the function of angular head velocity cells and head direction cells [[2]Glasauer S. Dieterich M. Brandt T. Neuronal network-based mathematical modelling of perceived verticality in acute unilateral vestibular lesions: from nerve to thalamus and cortex.J. Neurol. 2018 May 29; https://doi.org/10.1007/s00415-018-8909-5Google Scholar]. Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. Together with additional ocular motor or brainstem signs they allow precise topographical diagnosis of side and level.

Perioperative vestibular assessment and testing

Vestibular disorders can be difficult to accurately diagnose and manage. A careful history and focused physical examination are typically adequate to establish a diagnosis and initiate medical treatment. Vestibular testing is an important component of the work-up, but it is particularly essential for patients being considered for surgical intervention for a vestibular disorder, where the testing can be used to more definitively confirm a suspected diagnosis and to determine baseline vestibular organ function. In this article, we will first briefly review key components of the history and physical examination of patients with vestibular complaints. We will then discuss the most commonly used vestibular tests and their role in the preoperative assessment of patients undergoing vestibular surgery, including nystagmography, caloric testing, rotary chair testing, video head impulse testing, and vestibular evoked myogenic potential testing.

Why the semicircular canals are not stimulated by linear accelerations

Head accelerations are sensed by the vestibular system in the inner ear. Linear accelerations stimulate the otolith organs, while the semicircular canals (SCC) sense angular accelerations. Fluid–structure interaction (FSI) models of the cupula sensor (simulated with finite element method (FEM)) and the endolymph fluid (simulated with computational fluid dynamics (CFD)) in the semicircular canal offer the possibility to investigate why the SCC are not stimulated by linear accelerations. Two hypotheses exist in the literature. The first hypothesis focusses on the density of the cupula sensor in the SCC, while the second is based on the continuous loop of fluid in the semicircular canal. However, neither increasing the cupula density, nor disrupting the continuous fluid circulation substantially increase the cupula deformation under linear head acceleration, thereby rejecting both existing hypotheses. We propose an alternative hypothesis, based on the circular geometry of the semicircular canal. During angular head acceleration, the cupula intersects the body of endolymph and ‘pushes’ it forward because the cupula seals the semicircular canal like a diaphragm. This results in cupula deflection and neural stimulation. During linear head acceleration, on the other hand, a large part of the canal wall also ‘pushes’ the endolymph forward, which leads to hardly any cupula deflection.

3D modelling of angular spindle’s head for machining centre

The unified design of the angular spindle head of the machining centre for drilling-milling and boring type is considered. Three-dimensional modeling of the angular head assembly in CAD KOMPAS-3D is performed using a specialized application “Shafts and 3D mechanical transmissions” including a three-dimensional representation of the machining centre kinematic scheme. The photorealistic visualization module Artisan Rendering, which is integrated into the KOMPAS-3D CAD contour, was used to create presentations and promote this construction to the machine tool industry. A two-stage procedure for analyzing the structure by the stiffness criterion is proposed: at the early stages of the design by the matrix initial parameters method; at the stage of the working project by the finite element method in the APM FEM module. The procedure for determining the stress-strain state of the angular head spindle with end mills realized.

Asymmetric cupula displacement due to endolymph vortex in the human semicircular canal.

The vestibular system in the inner ear senses angular head manoeuvres by endolymph fluid which deforms a gelatinous sensory structure (the cupula). We constructed computer models that include both the endolymph flow (using CFD modelling), the cupula deformation (using FEM modelling), and the interaction between both (using fluid-structure interaction modelling). In the wide utricle, we observe an endolymph vortex. In the initial time steps, both the displacement of the cupula and its restorative forces are still small. As a result, the endolymph vortex causes the cupula to deform asymmetrically in an S-shape. The asymmetric deflection increases the cupula strain near the crista and, as a result, enhances the sensitivity of the vestibular system. Throughout the head manoeuvre, the maximal cupula strain is located at the centre of the crista. The hair cells at the crista centre supply irregularly spiking afferents, which are more sensitive than the afferents from the periphery. Hence, the location of the maximal strain at the crista may also increase the sensitivity of the semicircular canal, but this remains to be tested. The cupula overshoots its relaxed position in a simulation of the Dix-Hallpike head manoeuvre (3s in total). A much faster head manoeuvre of 0.222s showed to be too short to cause substantial cupula overshoot, because the cupula time scale of both models (estimated to be 3.3s) is an order of magnitude larger than the duration of this manoeuvre.

Perception of Verticality and Vestibular Disorders of Balance and Falls.

Objective: To review current knowledge of the perception of verticality, its normal function and disorders. This is based on an integrative graviceptive input from the vertical semicircular canals and the otolith organs.Methods: The special focus is on human psychophysics, neurophysiological and imaging data on the adjustments of subjective visual vertical (SVV) and the subjective postural vertical. Furthermore, examples of mathematical modeling of specific vestibular cell functions for orientation in space in rodents and in patients are briefly presented.Results: Pathological tilts of the SVV in the roll plane are most sensitive and frequent clinical vestibular signs of unilateral lesions extending from the labyrinths via the brainstem and thalamus to the parieto-insular vestibular cortex. Due to crossings of ascending graviceptive fibers, peripheral vestibular and pontomedullary lesions cause ipsilateral tilts of the SVV; ponto-mesencephalic lesions cause contralateral tilts. In contrast, SVV tilts, which are measured in unilateral vestibular lesions at thalamic and cortical levels, have two different characteristic features: (i) they may be ipsi- or contralateral, and (ii) they are smaller than those found in lower brainstem or peripheral lesions. Motor signs such as head tilt and body lateropulsion, components of ocular tilt reaction, are typical for vestibular lesions of the peripheral vestibular organ and the pontomedullary brainstem (vestibular nucleus). They are less frequent in midbrain lesions (interstitial nucleus of Cajal) and rare in cortical lesions. Isolated body lateropulsion is chiefly found in caudal lateral medullary brainstem lesions. Vestibular function in the roll plane and its disorders can be mathematically modeled by an attractor model of angular head velocity cell and head direction cell function. Disorders manifesting with misperception of the body vertical are the pusher syndrome, the progressive supranuclear palsy, or the normal pressure hydrocephalus; they may affect roll and/or pitch plane.Conclusion: Clinical determinations of the SVV are easy and reliable. They indicate acute unilateral vestibular dysfunctions, the causative lesion of which extends from labyrinth to cortex. They allow precise topographical diagnosis of side and level in unilateral brainstem or peripheral vestibular disorders. SVV tilts may coincide with or differ from the perception of body vertical, e.g., in isolated body lateropulsion.

Circulating Mitochondrial DNA Levels in Collegiate Football Players: A Pilot Study

Traumatic injury causes the release of circulating mitochondrial alarmins or damage‐associated molecular patterns (DAMPs) including mitochondrial DNA (mtDNA), peptides, and lipids from intracellular molecules into the extracellular space. Here, we sought to investigate whether circulating mtDNA concentration is a valuable hallmark of the sports‐related subconcussive brain injuries in collegiate football players.MethodsBlood samples were collected in K2EDTA vacutainers from male, collegiate football players (n = 13, aged 20.0 ± 1.0, BMI 32.1 ± 5.3 kg/m2) at 4 different time points: pre‐full‐contact practice, post‐full‐contact practice, pre‐season, and post‐season. These subjects include 8 defensive and 5 offensive line players. Samples are analyzed to determine the absolute amount of circulating mtDNA markers (COX3 and ND1, ng/ml) using a RT‐PCR method. Analysis of Bac16s levels was included in each run as a negative control to ensure reliability. The absolute mtDNA/ml of plasma sample was determined using a standard curve constructed using Lambda DNA of known concentration. Head impact kinematics data were collected during a full‐contact practice session using the Vector mouth guard (Biometrics Inc) which measures linear and angular head kinematics during impact. Data used in this study include number of hits, sum of peak linear acceleration, sum of peak angular acceleration, and sum and average of head injury criterion. A p‐value less than 0.05 was deemed significant for all comparisons.ResultsThere were no significant changes in the level of circulating mtDNA between pre‐full‐contact‐practice and post‐full‐contact practice in both offensive and defensive players. There were no statistically significant correlations of the changes in the value of circulating mtDNA the pre‐ vs. post‐practice with head impact kinematics data recorded during the practice sessions. Kinematics data in conjunction with mtDNA data indicated that circulating mtDNA levels are more indicative of activity level, rather than the degree of subconcussive head impacts. For the Pre‐ vs. Post‐season comparisons, the levels of circulating mtDNA were not significantly increased post‐season. However, the offensive group exhibited higher levels of COX 3 and ND1 levels in post‐season, as compared to those of the defensive group. Specifically, COX3 concentrations were 0.012 ± 0.004 ng/ml (pre‐season, defensive), 0.011 ± 0.004 (post‐season, defensive), 0.022 ± 0.009 (pre‐season, offensive) and 0.022 ± 0.002 (post‐season, offensive). ND1 concentrations were 0.007 ± 0.002 (pre‐season, defensive), 0.006 ± 0.002 (post‐season, defensive), 0.013 ± 0.006 (pre‐season, offensive) and 0.013 ± 0.001 (post‐season, offensive).ConclusionHigher circulating mtDNA level was observed in offensive line payers who sustains less frequent, but greater magnitude of head and body impacts during play. Our preliminary results warrant further study in a larger group of collegiate athletes engaged in contact sports.Support or Funding InformationSupported by NIH Grant R01NS102157This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

The Validity of an Oculus Rift to Assess Postural Changes During Balance Tasks.

To investigate whether shifts in head position, measured via an Oculus Rift head-mounted display (HMD), is a valid measure of whole-body postural stability. The inverted single-link pendulum model of balance suggests shifts in whole-body center of mass can be estimated from individual body segments. However, whether head position describes postural stability such as center-of-pressure (COP) remains unclear. Participants (N = 10) performed six conditions while wearing an HMD and performing a previously validated virtual reality (VR)-based balance assessment. COP was recorded with a Wii Balance Board force plate (WBB), while an HMD recorded linear and angular head displacement. Visual input was presented in the HMD (stable scene, dark scene, or dynamic scene) and somatosensory information (with or without foam) was varied across each condition. The HMD time series data were compared with the criterion-measure WBB. Significant correlations were found between COP measures (standard deviation, range, sway area, velocity) and head-centered angular and linear displacements (roll, pitch, mediolateral and anteroposterior directions). The Oculus Rift HMD shows promise as a measure of postural stability without additional posturography equipment. These findings support the application of VR HMD technology for assessment of postural stability across a variety of challenging conditions. The human factors and ergonomic benefit of such an approach is in its portability, low cost, and widespread availability for clinic and home-based investigation of postural disturbances. Fall injury affects millions of people annually, so assessment of fall risk and treatment of the underlying causes has enormous public health benefit.

Inertial Sensors Reveal Subtle Motor Deficits When Walking With Horizontal Head Turns After Concussion.

To examine whether horizontal head turns while seated or while walking, when instrumented with inertial sensors, were sensitive to the acute effects of concussion and whether horizontal head turns had utility for concussion management. Applied field setting, athletic training room. Twenty-four collegiate athletes with sports-related concussion and 25 healthy control athletes. Case-control; longitudinal. Peak head angular velocity and peak head angle (range of motion) when performing head turns toward an auditory cue while seated or walking. Gait speed when walking with and without head turns. Athletes with acute sports-related concussion turned their head slower than healthy control subjects initially (group β = -49.47; SE = 16.33; P = .003) and gradually recovered to healthy control levels within 10 days postconcussion (group × time β = 4.80; SE = 1.41; P < .001). Peak head velocity had fair diagnostic accuracy in differentiating subjects with acute concussion compared with controls (areas under the receiver operating characteristic curve [AUC] = 0.71-0.73). Peak head angle (P = .17) and gait speed (P = .64) were not different between groups and showed poor diagnostic utility (AUC = 0.57-0.62). Inertial sensors can improve traditional clinical assessments by quantifying subtle, nonobservable deficits in people following sports-related concussion.

Strategies for Gaze Stabilization Critically Depend on Locomotor Speed

Locomotion involves complex combinations of translational and rotational head movements. For gaze stability, this necessitates the interplay of angular and linear vestibulo-ocular reflexes (VOR) as well as the integration of visual feedback about the desired viewing distance. Furthermore, gaze stabilizing systems must be able to cope with vast differences in head motion brought about by changing locomotor speeds and patterns (walking vs. running). The present study investigated horizontal and vertical angular VOR (aVOR) and linear gaze stabilization (lGS) as well as compensation for linear head movements by angular counter rotation of the head during treadmill walking and running at different velocities (0.4 to 2.4 m/s) while fixating either a close (0.5 m) or distant (2.0 m) target. In the horizontal plane, the aVOR predominated throughout all locomotor speeds, whereas the compensation of linear translations was highly variable and generally insufficient. In contrast, in the vertical plane, eye and angular head motion steadily became more in phase with increasing locomotor speed, which served to optimize linear motion compensation. Furthermore, the timing of the vertical aVOR became more automated and independent of visual feedback during faster locomotion. Thus, horizontal and vertical gaze stabilization strategies appear to be considerably different. Whereas horizontal gaze control is likely governed by passive sensorimotor reflexes throughout all locomotor speeds, vertical gaze stabilization switches to an automated feed-forward control at faster locomotion. This switch is presumably driven by efference copies from spinal locomotor commands that were previously shown to govern gaze stabilization in animal models during stereotypic locomotion.

Head impact magnitudes that occur from purposeful soccer heading depend on the game scenario and head impact location

PurposeThis study quantified the linear and angular kinematics that result from purposeful heading during youth soccer games, and the influence of game scenario and head impact location on these magnitudes. MethodThis observational study recruited thirty-six female soccer players (13.4 ± 0.9 years old) from three elite youth soccer teams (U13, U14, U15) and followed for an entire soccer season. Players wore wireless sensors during each game to quantify head impact magnitudes. A total of 60 regular season games (20 games per team) were video recorded, and purposeful heading events were categorized by game scenario (e.g. throw in), and head impact location (e.g. front of head). ResultsGame scenario had a statistically significant effect on the linear head acceleration, and rotational head velocity, that resulted from purposeful headers. Rotational velocity from purposeful headers varied significantly between head impact locations, with impacts to the top of the head (improper technique) resulting in larger peak rotational velocities than impacts to the front of the head (proper technique); this was also the case for the linear acceleration for punts. ConclusionOur findings suggest that the magnitude for both linear and angular head impact kinematics depend on the game scenario and head impact location. Headers performed with the top of the head (improper technique) result in larger rotational velocities compared to the front of the head (proper technique). Accordingly, youth players should be educated on how to execute proper heading technique to reduce head impact accelerations.

Application of NSGA-II for optimisation of cylindrical plunge grinding process parameters

Cylindrical grinding (finishing) operation is widely used for obtaining accurate surface finish on components in automobile sectors. Present industries are facing a challenge of producing high quality components with low power consumption and low manufacturing cost due to increased competition. In this paper, optimum process parameters values are obtained for dressing depth of cut, dressing cross feed rate and grinding feed rate of cylindrical plunge grinding operation. Experiments were performed as per L9 orthogonal array with replica on computer numerical control angular head grinding machine. Mathematical model has been developed using response surface methodology for determining grinding responses. The results of RSM are further used to obtain Pareto front optimal solutions using NSGA-II approach. A novel method is developed to obtain grinding ratio. The established results are helpful to decide optimal grinding parameters.

Central positional nystagmus: Characteristics and model-based explanations.

The central vestibular system operates to precisely estimate the rotational velocity and gravity orientation using the inherently ambiguous information from peripheral vestibular system. Therefore, any lesions disrupting this function can generate positional nystagmus. Central positional nystagmus (CPN) can be classified into the paroxysmal (transient) and persistent forms. The paroxysmal CPN has the features suggesting a semicircular canal origin regarding the latency, duration, and direction of nystagmus. Patients with paroxysmal CPN commonly show several different types of nystagmus classified according to the provoking positioning. The persistent form of CPN mostly appears as downbeat nystagmus while prone or supine, or apogeotropic or geotropic horizontal nystagmus when the head is turned to either side while supine. CPN may be ascribed to erroneous neural processing within the velocity-storage circuit that functions in estimating angular head velocity, gravity direction, and inertia. Paroxysmal CPN appears to be post-rotatory rebound nystagmus due to lesions involving the cerebellar nodulus and uvula. In contrast, persistent CPN may arise from erroneous gravity estimation. The overlap of lesion location responsible for both paroxysmal and persistent CPN may account for the frequent coexistence of both forms of nystagmus in a single patient.

Application of NSGA-II for optimisation of cylindrical plunge grinding process parameters

Cylindrical grinding (finishing) operation is widely used for obtaining accurate surface finish on components in automobile sectors. Present industries are facing a challenge of producing high quality components with low power consumption and low manufacturing cost due to increased competition. In this paper, optimum process parameters values are obtained for dressing depth of cut, dressing cross feed rate and grinding feed rate of cylindrical plunge grinding operation. Experiments were performed as per L9 orthogonal array with replica on computer numerical control angular head grinding machine. Mathematical model has been developed using response surface methodology for determining grinding responses. The results of RSM are further used to obtain Pareto front optimal solutions using NSGA-II approach. A novel method is developed to obtain grinding ratio. The established results are helpful to decide optimal grinding parameters.

Semicircular canal biomechanics in health and disease.

The semicircular canals are responsible for sensing angular head motion in three-dimensional space and for providing neural inputs to the central nervous system (CNS) essential for agile mobility, stable vision, and autonomic control of the cardiovascular and other gravity-sensitive systems. Sensation relies on fluid mechanics within the labyrinth to selectively convert angular head acceleration into sensory hair bundle displacements in each of three inner ear sensory organs. Canal afferent neurons encode the direction and time course of head movements over a broad range of movement frequencies and amplitudes. Disorders altering canal mechanics result in pathological inputs to the CNS, often leading to debilitating symptoms. Vestibular disorders and conditions with mechanical substrates include benign paroxysmal positional nystagmus, direction-changing positional nystagmus, alcohol positional nystagmus, caloric nystagmus, Tullio phenomena, and others. Here, the mechanics of angular motion transduction and how it contributes to neural encoding by the semicircular canals is reviewed in both health and disease.

Functional and anatomical relationships between the medial precentral cortex, dorsal striatum, and head direction cell circuitry. I. Recording studies.

Head direction (HD) cells fire as a function of the animal's directional heading and provide the animal with a sense of direction. In rodents, these neurons are located primarily within the limbic system, but small populations of HD cells are found in two extralimbic areas: the medial precentral cortex (PrCM) and dorsal striatum (DS). HD cell activity in these structures could be driven by output from the limbic HD circuit or generated intrinsically. We examined these possibilities by recording the activity of PrCM and DS neurons in control rats and in rats with anterodorsal thalamic nucleus (ADN) lesions, a manipulation that disrupts the limbic HD signal. HD cells in the PrCM and DS of control animals displayed characteristics similar to those of limbic HD cells, and these extralimbic HD signals were eliminated in animals with complete ADN lesions, suggesting that the PrCM and DS HD signals are conveyed from the limbic HD circuit. Angular head velocity cells recorded in the PrCM and DS were unaffected by ADN lesions. Next, we determined if the PrCM and DS convey necessary self-motion signals to the limbic HD circuit. Limbic HD cell activity recorded in the ADN remained intact following combined lesions of the PrCM and DS. Collectively, these experiments reveal a unidirectional functional relationship between the limbic HD circuit and the PrCM and DS; the limbic system generates the HD signal and transmits it to the PrCM and DS, but these extralimbic areas do not provide critical input or feedback to limbic HD cells. NEW & NOTEWORTHY Head direction (HD) cells have been extensively studied within the limbic system. The lesion and recording experiments reported here examined two relatively understudied populations of HD cells located outside of the canonical limbic HD circuit in the medial precentral cortex and dorsal striatum. We found that HD cell activity in these two extralimbic areas is driven by output from the limbic HD circuit, revealing that HD cell circuitry functionally extends beyond the limbic system.

Hero worship at all costs?

The new landmark of Gdansk is a leaning tower made of glass, steel, and red concrete located on the Motława River. The panorama windows of the restaurant at the Museum of the Second World War offer the only view of the old Hanseatic city with its town houses and its Brama Żuraw (crane gate). The legendary Lenin Shipyard (now Gdansk Shipyard), where the Solidarność was once launched, is just a short walk away. Lech Wałęsa’s fame as an anti-communist workers’ hero has faded though. The present leaders of Poland consider Wałęsa as a communist agent and traitor of the nation because of his alliance with the much-hated liberals. The new hero is Jarosław Kaczyński, leader of the PiS-Party (Prawo i Sprawiedliwość, Law and Justice). A Gdansk graffiti artist immortalized him on a firewall across from the museum, as an angular head with a Roman toga. The great chairman currently exercises his power over many people, even in the new leaning tower by the Motława.