Cerebellar control of a unitary head direction sense.

The head-direction (HD) system, a key neural circuit for navigation, consists of several anatomical structures containing neurons selective to the animal's head direction. HD cells exhibit ubiquitous temporal coordination across brain regions, independently of the animal's behavioral state or sensory inputs. Such temporal coordination mediates a single, stable, and persistent HD signal, which is essential for intact orientation. However, the mechanistic processes behind the temporal organization of HD cells are unknown. By manipulating the cerebellum, we identify pairs of HD cells recorded from two brain structures (anterodorsal thalamus and retrosplenial cortex) that lose their temporal coordination, specifically during the removal of the external sensory inputs. Further, we identify distinct cerebellar mechanisms that participate in the spatial stability of the HD signal depending on sensory signals. We show that while cerebellar protein phosphatase 2B-dependent mechanisms facilitate the anchoring of the HD signal on the external cues, the cerebellar protein kinase C-dependent mechanisms are required for the stability of the HD signal by self-motion cues. These results indicate that the cerebellum contributes to the preservation of a single and stable sense of direction.

Removal of physiological artifacts from simultaneous EEG and fMRI recordings.

OBJECTIVE: Simultaneous recording of the electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) allows a combination of eletrophysiological and haemodynamic information to be used to form a more complete picture of cerebral dynamics. However, EEG recorded within the MRI scanner is contaminated by both imaging artifacts and physiological artifacts. The majority of the techniques used to pre-process such EEG focus on removal of the imaging and balistocardiogram artifacts, with some success, but don't remove all other physiological artifacts. METHODS: We propose a new offline EEG artifact removal method based upon a combination of independent component analysis and fMRI-based head movement estimation to aid the removal of physiological artifacts from EEG recorded during EEG-fMRI recordings. Our method makes novel use of head movement trajectories estimated from the fMRI recording in order to assist with identifying physiological artifacts in the EEG and is designed to be used after removal of the fMRI imaging artifact from the EEG. RESULTS: We evaluate our method on EEG recorded during a joint EEG-fMRI session from healthy adult participants. Our method significantly reduces the influence of all types of physiological artifacts on the EEG. We also compare our method with a state-of-the-art physiological artifact removal method and demonstrate superior performance removing physiological artifacts. CONCLUSIONS: Our proposed method is able to remove significantly more physiological artifact components from the EEG, recorded during a joint EEG-fMRI session, than other state-of-the-art methods. SIGNIFICANCE: Our proposed method represents a marked improvement over current processing pipelines for removing physiological noise from EEG recorded during a joint EEG-fMRI session.

Cervical Muscle Activation Due to an Applied Force in Response to Different Types of Acoustic Warnings.

Mild traumatic brain injury (mTBI) and whiplash-associated disorder are the most common head and neck injuries and result from a sudden head or body acceleration. The head and neck injury potential is correlated with the awareness, level of muscle activation, and posture changes at the time of the perturbation. Environmental acoustic stimuli or a warning system can influence muscle activation and posture during a head perturbation. In this study, different acoustic stimuli, including Non-Directional, Directional, and Startle, were provided 1000 ms before a head impact, and the amplitude and timing of cervical muscle electromyographic (EMG) data were characterized based on the type of warning. The startle warning resulted in 49% faster and 80% greater EMG amplitude compared to the Directional and Non-Directional warnings after warning and before the impact. The post-impact peak EMG amplitudes in Unwarned trials were lower by 18 and 21% in the retraction and rebound muscle groups, respectively, compared to any of the warned conditions. When there was no warning before the impact, the retraction and rebound muscle groups also reached their maximum activation 38 and 54 ms sooner, respectively, compared to the warned trials. Based on these results, the intensity and complexity of information that a warning sound carries change the muscle response before and after a head impact and has implications for injury potential.

Effectiveness of pediatric integrative manual therapy in cervical movement limitation in infants with positional plagiocephaly: a randomized controlled trial.

BACKGROUND: Positional plagiocephaly (PP) is a cranial deformation frequent amongst children and consisting in a flattened and asymmetrical head shape. PP is associated with excessive time in supine and with congenital muscular torticollis (CMT). Few studies have evaluated the efficiency of a manual therapy approach in PP. The purpose of this parallel randomized controlled trial is to compare the effectiveness of adding a manual therapy approach to a caregiver education program focusing on active rotation range of motion (AROM) and neuromotor development in a PP pediatric sample. METHODS: Thirty-four children with PP and less than 28 week-old were randomly distributed into two groups. AROM and neuromotor development with Alberta Infant Motor Scale (AIMS) were measured. The evaluation was performed by an examiner, blinded to the randomization of the subjects. A pediatric integrative manual therapy (PIMT) group received 10-sessions involving manual therapy and a caregiver education program. Manual therapy was addressed to the upper cervical spine to mobilize the occiput, atlas and axis. The caregiver educational program consisted in exercises to reduce the positional preference and to stimulate motor development. The control group received the caregiver education program exclusively. To compare intervention effectiveness across the groups, improvement indexes of AROM and AIMS were calculated using the difference of the final measurement values minus the baseline measurement values. If the distribution was normal, the improvement indexes were compared using the Student t-test for independent samples; if not, the Mann-Whitney U test was used. The effect size of the interventions was calculated using Cohen's d. RESULTS: All randomized subjects were analysed. After the intervention, the PIMT group showed a significantly higher increase in rotation (29.68 ± 18.41°) than the control group (6.13 ± 17.69°) (p = 0.001). Both groups improved the neuromotor development but no statistically significant differences were found. No harm was reported during the study. CONCLUSION: The PIMT intervention program was more effective in increasing AROM than using only a caregiver education program. The study has been retrospectively registered at clinicaltrials.gov, with identification number NCT03659032 . Registration date: September 1, 2018.

Joint and individual effectiveness of galvanic cutaneous stimulation and tactile stimulation at decreasing Simulator Adaptation Syndrome.

This research was focused on investigating the effectiveness of galvanic cutaneous stimulation and tactile stimulation jointly and individually at mitigating Simulator Adaptation Syndrome. Forty drivers (mean age = 23.1 ± 3.4 years old, twenty women) participated in a driving simulation experiment. Total scores of the Simulator Sickness Questionnaire, head movements (an index of body balance), and driving performance variables were compared across four different stimulation conditions: i) baseline (where no stimulation was presented), ii) galvanic cutaneous stimulation and iii) tactile stimulation deployed individually, and iv) both techniques deployed jointly. The results showed that both techniques presented in conjunction alleviate Simulator Adaptation Syndrome and improve driving performance more effectively than when they are presented in isolation. Importantly, reduced head movements were only revealed when galvanic cutaneous stimulation was applied. We concluded that the reduction of this syndrome is due to an improvement of body balance (elicited by galvanic cutaneous stimulation), and a distraction from the symptoms (elicited by tactile stimulation). We encourage the use of both techniques simultaneously to decrease Simulator Adaptation Syndrome.

A Pilot Longitudinal Study of 3-Dimensional Head and Neck Kinematics During Functional Tasks in Individuals With Chronic Idiopathic Neck Pain Either Wait-Listed for or Receiving Chiropractic Spinal Manipulative Therapy With Exercise.

OBJECTIVE: The purpose of this study was to determine if there is a relationship between pain and movement kinematics during functional tasks, evaluated over time, in individuals with chronic idiopathic neck pain. METHODS: Ten participants with chronic idiopathic neck pain performed 2 functional tasks (overhead reach to the right and putting on a seatbelt) while evaluated using 8 Oqus 300+ cameras. Kinematic variables included joint angles and range of motion (ROM) (°), head segment relative to neck segment (head-neck [HN]); and head/neck segment relative to upper thoracic segment (head/neck-trunk), velocity (m/s), and time (% of movement phase). Pain was quantified using a 100-mm visual analog scale. Linear mixed effects regression models were used to analyze associations between pain and kinematic variables adjusting for treatment group. RESULTS: For overhead reach, higher pain was associated with less HN peak rotation at baseline (ß = -0.33; 95% CI -0.52 to -0.14, P = .003) and less HN total rotation ROM at 6 months (ß = -0.19; 95% CI -0.38 to -0.003, P = .048). For the seatbelt task, higher pain was associated with less HN peak rotation (ß = -0.52; 95% CI -0.74 to -0.30 to -0.74, P < .001) and less HN total rotation ROM at baseline (ß = -0.32; 95% CI -0.53 to -0.10, P = .006). No other movement variables demonstrated meaningful relationships with pain for the reach or seatbelt tasks. CONCLUSION: Higher pain is associated with less HN peak and total rotation during functional reaching tasks requiring head rotation. Recognizing altered functional kinematics in individuals with chronic neck pain may assist patient management.

Baropodometric quantification and implications of muscle coactivation in the lower limbs caused by head movement: A prospective study.

BACKGROUND: In healthy young adults, muscle coactivation can sometimes be induced by remote voluntary contractions when the motor task is forceful, maximal, tiring, or cyclic and brief. OBJECTIVES: To show that a change in plantar pressure is an unequivocal response to backward movement of the head, and to contribute to a better understanding of physiotherapy methods that involve remote muscle activation. METHODS: Involuntary coactivation was quantified as a percentage of the anteroposterior plantar pressure distribution, using a baropodometric platform in a population of young adults. The baropodometric data were collected from a 1s recording after 30 s in the reference condition, and from 1s recordings during the first second and then during the 120th second in the test condition. The results were analyzed with Bayesian statistics (Markov chains and Monte Carlo integration techniques). RESULTS: 90 adults participated in the study (age range: 19-26; 38 males and 52 females). The forefoot plantar pressure increased in all cases, by a mean multiplicative factor (on a logit scale) of 1.12 (from 72.24% to 74.45%) when the head was aligned over the trunk. CONCLUSIONS: This 90-participant trial confirmed our initial hypothesis: a increase in forefoot plantar pressure is a systematic response to the motor task (head movement), and suggests greater recruitment of the plantar flexor muscles. A spinal reflex and/or a previously unknown form of motor overflow might be involved in this phenomenon. These results support the development of inductive physiotherapy techniques based on remote muscle activation in the treatment of musculoskeletal disorders. CLINICALSTRIAL. GOV IDENTIFIER: NCT02320097.

Biomechanical Analysis of the Head Movements of a Person Thrown by the Judo Technique 'Seoi-nage'.

The present study examined the kinematics and biomechanical parameters of the head of a person thrown forward by the judo technique 'Seoi-nage'. A judo expert threw an anthropomorphic test device (the POLAR dummy) five times. Kinematics data were obtained with a high-speed digital video camera. Linear and angular accelerations of the head were measured by accelerometers mounted at the center of gravity of the dummy's head. When Seoi-nage was performed, the dummy fell forward accompanied by contacting the anterior parietal regions of the head to the tatami, and the linear and angular accelerations of most axes reached peak values when the head contacted the tatami. Peak resultant linear and angular accelerations were 20.3 ± 9.8 G and 1890.1 ± 1151.9 rad/s2, respectively (means ± standard deviation). Peak values in linear and angular acceleration did not significantly differ between the three directional axes. Absolute angular accelerations in all axes observed in Seoi-nage were high and the resultant value was approximately equal to the already reported in Ouchi-gari, one of the predominant techniques causing judo-related acute subdural hematoma. However, the remarkable increase of linear acceleration in the longitudinal direction and/or angular acceleration in the sagittal plane, as previously reported in techniques being thrown backward (i.e., Ouchi-gari and Osoto-gari), was not detected. The likely mechanism of acute subdural hematoma caused by Seoi-nage is that a large angular acceleration causes large strains and deformations of the brain surface and subsequent rupture of cortical vessels.

A Comparison of Neural Decoding Methods and Population Coding Across Thalamo-Cortical Head Direction Cells.

Head direction (HD) cells, which fire action potentials whenever an animal points its head in a particular direction, are thought to subserve the animal's sense of spatial orientation. HD cells are found prominently in several thalamo-cortical regions including anterior thalamic nuclei, postsubiculum, medial entorhinal cortex, parasubiculum, and the parietal cortex. While a number of methods in neural decoding have been developed to assess the dynamics of spatial signals within thalamo-cortical regions, studies conducting a quantitative comparison of machine learning and statistical model-based decoding methods on HD cell activity are currently lacking. Here, we compare statistical model-based and machine learning approaches by assessing decoding accuracy and evaluate variables that contribute to population coding across thalamo-cortical HD cells.

Specificity and variability of trunk kinematics on a mechanical horse.

As perturbation training is gaining popularity, it is important to better understand postural control during complex three-dimensional stimuli. One clinically relevant and commonly used three-dimensional stimulus is found in hippotherapy and simulated hippotherapy on a mechanical horse. We tested nine healthy participants on a horse simulator, measured head and trunk kinematics, and characterized data in time (root-mean-square and variability) and frequency (amplitude spectra, gains, and phases) domains. We addressed three fundamental questions: 1) What is the specificity of postural responses to the simulator? 2) Which plane of motion is associated with the most and least variability (repeatable movements across repeated stimuli and across participants)? 3) To what extent are postural responses influenced by different degrees of stability (addition of pelvis straps and trunk support)? We found head and trunk responses were highly specific to the three-dimensional simulator perturbation direction and frequency. Frontal plane responses had the least variability across repetitions and participants whereas transverse motion was most variable. Head motion was more variable than the trunk at low frequencies and exhibited a marked decrease in tilt in the sagittal plane. Finally, the inclusion of pelvis straps had minimal effect on kinematics at low frequencies but altered higher frequencies; whereas added trunk support reduced head and trunk responses to perturbations and altered timing characteristics in all three planes. In conclusion, the present study suggests that frontal plane motion was under a high level of control, and results support the idea that specific head and trunk postural responses can be elicited from a complex three-dimensional stimuli, such as those found in hippotherapy. Researchers and clinicians can use results from this study to help interpret variability, implement mechanical adjustments to stability, and assess responses in pathological populations.

Asymmetric Thickness of Oblique Capitis Inferior and Cervical Kinesthesia in Patients With Unilateral Cervicogenic Headache.

OBJECTIVE: The purpose of this study was to compare the thickness of the oblique cervical inferior (OCI) and the error of the head reposition test between the painful and nonpainful sides of patients with cervicogenic headache (CeH) and between the patients and the asymptomatic group. METHODS: Thirteen patients (24.5 ± 4.8 years) and 14 asymptomatic participants (23.9 ± 2.7 years) were included. The head reposition test was recorded by a 3-dimensional motion analysis system. The thickness of the OCI was recorded by ultrasonography. The measured outcomes were compared between the painful and nonpainful sides and with the asymptomatic participants. RESULTS: The thickness of the OCI in the rest condition on the painful side (9.92 ± 2.31 mm) was smaller than that of the nonpainful side (10.56 ± 2.24 mm). The constant error of the head-to-target test toward the nonpainful side was smaller in the patients with CeH (-1.6 ± 4.3°) than in the asymptomatic group (3.3 ± 3.7°, P = 0.005). CONCLUSION: Asymmetric OCI and cervical proprioception were demonstrated in patients with CeH.

Pharmacological profile of vestibular inhibitory inputs to superior oblique motoneurons.

Vestibulo-ocular reflexes (VOR) are mediated by three-neuronal brainstem pathways that transform semicircular canal and otolith sensory signals into motor commands for the contraction of spatially specific sets of eye muscles. The vestibular excitation and inhibition of extraocular motoneurons underlying this reflex is reciprocally organized and allows coordinated activation of particular eye muscles and concurrent relaxation of their antagonistic counterparts. Here, we demonstrate in isolated preparations of Xenopus laevis tadpoles that the discharge modulation of superior oblique motoneurons during cyclic head motion derives from an alternating excitation and inhibition. The latter component is mediated exclusively by GABA, at variance with the glycinergic inhibitory component in lateral rectus motoneurons. The different pharmacological profile of the inhibition correlates with rhombomere-specific origins of vestibulo-ocular projection neurons and the complementary segmental abundance of GABAergic and glycinergic vestibular neurons. The evolutionary conserved rhombomeric topography of vestibulo-ocular projections makes it likely that a similar pharmacological organization of inhibitory VOR neurons as reported here for anurans is also implemented in mammalian species including humans.

Psychophysical evidence for auditory motion parallax.

Distance is important: From an ecological perspective, knowledge about the distance to either prey or predator is vital. However, the distance of an unknown sound source is particularly difficult to assess, especially in anechoic environments. In vision, changes in perspective resulting from observer motion produce a reliable, consistent, and unambiguous impression of depth known as motion parallax. Here we demonstrate with formal psychophysics that humans can exploit auditory motion parallax, i.e., the change in the dynamic binaural cues elicited by self-motion, to assess the relative depths of two sound sources. Our data show that sensitivity to relative depth is best when subjects move actively; performance deteriorates when subjects are moved by a motion platform or when the sound sources themselves move. This is true even though the dynamic binaural cues elicited by these three types of motion are identical. Our data demonstrate a perceptual strategy to segregate intermittent sound sources in depth and highlight the tight interaction between self-motion and binaural processing that allows assessment of the spatial layout of complex acoustic scenes.

Real-time Correction of Motion and Imager Instability Artifacts during 3D γ-Aminobutyric Acid-edited MR Spectroscopic Imaging.

Purpose To compare the involuntary head motion, frequency and B0 shim changes, and effects on data quality during real-time-corrected three-dimensional γ-aminobutyric acid-edited magnetic resonance (MR) spectroscopic imaging in subjects with mild cognitive impairment (MCI), patients with Parkinson disease (PD), and young and older healthy volunteers. Materials and Methods In this prospective study, MR spectroscopic imaging datasets were acquired at 3 T after written informed consent was obtained. Translational and rotational head movement, frequency, and B0 shim were determined with an integrated volumetric navigator. Head motion patterns and imager instability were investigated in 33 young healthy control subjects (mean age ± standard deviation, 31 years ± 5), 34 older healthy control subjects (mean age, 67 years ± 8), 34 subjects with MCI (mean age, 72 years ± 5), and 44 patients with PD (mean age, 64 years ± 8). Spectral quality was assessed by means of region-of-interest analysis. Group differences were evaluated with Bonferroni-corrected Mann-Whitney tests. Results Three patients with PD and four subjects with MCI were excluded because of excessive head motion (ie, > 0.8 mm translation per repetition time of 1.6 seconds throughout >10 minutes). Older control subjects, patients with PD, and subjects with MCI demonstrated 1.5, 2, and 2.5 times stronger head movement, respectively, than did young control subjects (1.79 mm ± 0.77) (P < .001). Of young control subjects, older control subjects, patients with PD, and subjects with MCI, 6%, 35%, 38%, and 51%, respectively, moved more than 3 mm during the MR spectroscopic imaging acquisition of approximately 20 minutes. The predominant movements were head nodding and "sliding out" of the imager. Frequency changes were 1.1- and 1.4-fold higher in patients with PD (P = .007) and subjects with MCI (P < .001), respectively, and B0 shim changes were 1.3-, 1.5-, and 1.9-fold higher in older control subjects (P = .005), patients with PD (P < .001), and patients with MCI (P < .001), respectively, compared with those of young control subjects (12.59 Hz ± 2.49, 3.61 Hz · cm-1 ± 1.25). Real-time correction provided high spectral quality in all four groups (signal-to-noise ratio >15, Cramér-Rao lower bounds < 20%). Conclusion Real-time motion and B0 monitoring provides valuable information about motion patterns and B0 field variations in subjects with different predispositions for head movement. Immediate correction improves data quality, particularly in patients who have difficulty avoiding movement. © RSNA, 2017 Online supplemental material is available for this article.

Assessment of vestibulo-ocular function without measuring eye movements.

BACKGROUND: The vestibulo-ocular reflex (VOR) maintains stable gaze during head motion. Deficiencies lead to apparent world motion due to incomplete stabilization of eyes in space. VOR measurement requires specialized apparatus, trained operators, and significant setup time. NEW METHOD: We present a system (VON: vestibulo-ocular nulling) for rapid vestibulo-ocular assessment without measuring eye movements per se. VON uses a head-mounted motion sensor, laptop computer with user input control, and laser target whose position is controlled by the computer. As the head moves, the target is made to move in the same manner with a gain set by the subject. When the subject sets the gain so the target appears stationary in space, it is stationary on the retinas. One can determine from this gain the extent to which the eyes move in space when the head moves, which is the amount by which the VOR is deficient. From this the gain of the compensatory eye movements is derived. RESULTS: VON was compared with conventional video-based VOR measures. Both methods track expected changes in gain over 20min of adaptation to minifying spectacles. VON measures are more consistent across subjects, and pre-adaptation values are closer to compensatory. COMPARISON WITH EXISTING METHOD: VON is a rapid means to assess vestibulo-ocular performance. As a functional perceptual measure, it accounts for gaze-stabilizing contributions that are not apparent in the standard VOR, such as pursuit and perceptual tolerance. CONCLUSIONS: VON assesses functional VOR performance. Future implementations will make VOR assessment widely available to investigators and clinicians.

Exploring the body through reflexology: Physical behaviors observed during application.

Recent studies on reflexology describe the appearance of different application-associated effects, attributed to a self-regulatory mechanism related to treatment efficacy. On the other hand, sleep is a physiological process of vital importance for health. Its main value lies in restoring the natural balance between neuronal centers. Among its associated behavioral characteristics are spontaneous movements and eye movements. The aim of this study is to investigate the effects that occur during application of reflexology and that are not described in the literature. This is a descriptive observational study with a quantitative methodology. Abivariate anlysis has been conductec through chi-square test or Anova as apropiate. A total of 111 clients of a therapy center in Tarragona have participated in the study. They were assigned into four groups (musculoskeletal, stress, anxiety, mantenance). Reflexology was administered and observered the manifestations that occured during the session. The findings have identified four categories of effects, of which there was no previous reference. These effects can be related to any of the stages of sleep. This study shows that reflexology promotes its application for different effects, such as eye movements and spontaneous movements. These data reveal the need to investigate these effects and their impact on health as well as their possible relationship with sleep.

The Human Retrosplenial Cortex and Thalamus Code Head Direction in a Global Reference Frame.

UNLABELLED: Spatial navigation is a multisensory process involving integration of visual and body-based cues. In rodents, head direction (HD) cells, which are most abundant in the thalamus, integrate these cues to code facing direction. Human fMRI studies examining HD coding in virtual environments (VE) have reported effects in retrosplenial complex and (pre-)subiculum, but not the thalamus. Furthermore, HD coding appeared insensitive to global landmarks. These tasks, however, provided only visual cues for orientation, and attending to global landmarks did not benefit task performance. In the present study, participants explored a VE comprising four separate locales, surrounded by four global landmarks. To provide body-based cues, participants wore a head-mounted display so that physical rotations changed facing direction in the VE. During subsequent MRI scanning, subjects saw stationary views of the environment and judged whether their orientation was the same as in the preceding trial. Parameter estimates extracted from retrosplenial cortex and the thalamus revealed significantly reduced BOLD responses when HD was repeated. Moreover, consistent with rodent findings, the signal did not continue to adapt over repetitions of the same HD. These results were supported by a whole-brain analysis showing additional repetition suppression in the precuneus. Together, our findings suggest that: (1) consistent with the rodent literature, the human thalamus may integrate visual and body-based, orientation cues; (2) global reference frame cues can be used to integrate HD across separate individual locales; and (3) immersive training procedures providing full body-based cues may help to elucidate the neural mechanisms supporting spatial navigation. SIGNIFICANCE STATEMENT: In rodents, head direction (HD) cells signal facing direction in the environment via increased firing when the animal assumes a certain orientation. Distinct brain regions, the retrosplenial cortex (RSC) and thalamus, code for visual and vestibular cues of orientation, respectively. Putative HD signals have been observed in human RSC but not the thalamus, potentially because body-based cues were not provided. Here, participants encoded HD in a novel virtual environment while wearing a head-mounted display to provide body-based cues for orientation. In subsequent fMRI scanning, we found evidence of an HD signal in RSC, thalamus, and precuneus. These findings harmonize rodent and human data, and suggest that immersive training procedures provide a viable way to examine the neural basis of navigation.

Dependence of auditory spatial updating on vestibular, proprioceptive, and efference copy signals.

Humans localize sounds by comparing inputs across the two ears, resulting in a head-centered representation of sound-source position. When the head moves, information about head movement must be combined with the head-centered estimate to correctly update the world-centered sound-source position. Spatial updating has been extensively studied in the visual system, but less is known about how head movement signals interact with binaural information during auditory spatial updating. In the current experiments, listeners compared the world-centered azimuthal position of two sound sources presented before and after a head rotation that depended on condition. In the active condition, subjects rotated their head by ∼35° to the left or right, following a pretrained trajectory. In the passive condition, subjects were rotated along the same trajectory in a rotating chair. In the cancellation condition, subjects rotated their head as in the active condition, but the chair was counter-rotated on the basis of head-tracking data such that the head effectively remained fixed in space while the body rotated beneath it. Subjects updated most accurately in the passive condition but erred in the active and cancellation conditions. Performance is interpreted as reflecting the accuracy of perceived head rotation across conditions, which is modeled as a linear combination of proprioceptive/efference copy signals and vestibular signals. Resulting weights suggest that auditory updating is dominated by vestibular signals but with significant contributions from proprioception/efference copy. Overall, results shed light on the interplay of sensory and motor signals that determine the accuracy of auditory spatial updating.

Neuromodulation using percutaneous electrical nerve stimulation for the management of trigeminal-mediated headshaking: A safe procedure resulting in medium-term remission in five of seven horses.

REASONS FOR PERFORMING STUDY: There are no consistently safe and effective methods for the treatment of trigeminal-mediated headshaking in horses. In affected horses, the trigeminal nerve is sensitised, appearing to result in neuropathic pain. Percutaneous electrical nerve stimulation (PENS) therapy is a minimally invasive neuromodulatory treatment used in people to manage neuropathic pain. OBJECTIVES: To determine whether PENS therapy is safe, tolerated and effective for the management of trigeminal-mediated headshaking in horses. STUDY DESIGN: Descriptive case series. METHODS: Seven horses diagnosed with trigeminal-mediated headshaking and currently showing clinical signs were studied. All procedures were carried out in sedated horses with a needle-prick sized area of skin desensitised with local anaesthetic to facilitate probe insertion. A disposable PENS probe was advanced subcutaneously adjacent to the nerve, rostral to the infraorbital foramen under ultrasonographic guidance. The nerve was stimulated for 25 min following a protocol of alternating frequencies and a perception threshold based on human clinical data. The probe was removed and the procedure repeated on the contralateral side. The protocol used comprised a series of 3 or 4 treatments, with treatments being repeated when signs of headshaking recurred. RESULTS: All horses tolerated the procedure well. Three horses developed a haematoma at the site on one occasion and 2 had increased clinical signs for up to 3 days following first treatment. Six horses demonstrated a positive response to their first treatment, returning to ridden work at the same level as prior to onset of headshaking, with 5 continuing to respond. Median remission time for first treatment was 3.8 days (range 0-8 days, n = 7), second treatment 2.5 weeks (0-8 weeks, n = 7), third treatment 15.5 weeks (0-24 weeks, n = 5) and fourth treatment 20 weeks (12-28 weeks ongoing, n = 2). CONCLUSIONS: Percutaneous electrical nerve stimulation therapy is a safe, well tolerated, minimally invasive, repeatable management option for trigeminal-mediated headshaking, with encouraging efficacy for amelioration of clinical signs in the short- to medium term.

Dynamic sound localization in cats.

Sound localization in cats and humans relies on head-centered acoustic cues. Studies have shown that humans are able to localize sounds during rapid head movements that are directed toward the target or other objects of interest. We studied whether cats are able to utilize similar dynamic acoustic cues to localize acoustic targets delivered during rapid eye-head gaze shifts. We trained cats with visual-auditory two-step tasks in which we presented a brief sound burst during saccadic eye-head gaze shifts toward a prior visual target. No consistent or significant differences in accuracy or precision were found between this dynamic task (2-step saccade) and the comparable static task (single saccade when the head is stable) in either horizontal or vertical direction. Cats appear to be able to process dynamic auditory cues and execute complex motor adjustments to accurately localize auditory targets during rapid eye-head gaze shifts.