The impulse response of optic flow-sensitive descending neurons to roll m-sequences

ABSTRACT When animals move through the world, their own movements generate widefield optic flow across their eyes. In insects, such widefield motion is encoded by optic lobe neurons. These lobula plate tangential cells (LPTCs) synapse with optic flow-sensitive descending neurons, which in turn project to areas that control neck, wing and leg movements. As the descending neurons play a role in sensorimotor transformation, it is important to understand their spatio-temporal response properties. Recent work shows that a relatively fast and efficient way to quantify such response properties is to use m-sequences or other white noise techniques. Therefore, here we used m-sequences to quantify the impulse responses of optic flow-sensitive descending neurons in male Eristalis tenax hoverflies. We focused on roll impulse responses as hoverflies perform exquisite head roll stabilizing reflexes, and the descending neurons respond particularly well to roll. We found that the roll impulse responses were fast, peaking after 16.5–18.0 ms. This is similar to the impulse response time to peak (18.3 ms) to widefield horizontal motion recorded in hoverfly LPTCs. We found that the roll impulse response amplitude scaled with the size of the stimulus impulse, and that its shape could be affected by the addition of constant velocity roll or lift. For example, the roll impulse response became faster and stronger with the addition of excitatory stimuli, and vice versa. We also found that the roll impulse response had a long return to baseline, which was significantly and substantially reduced by the addition of either roll or lift.

Unilateral Multicanalicular Vestibular Lithiasis of Right Horizontal and Posterior Semicircular Canals: An Unusual Case

Vestibular lithiasis (canalolithiasis as well as cupulolithiasis) commonly exists in monocanalicular forms involving one of the three semicircular canals, frequent posterior, less frequent horizontal, and very rarely anterior. It is treated with canal clearing maneuvers intended to reposition the otoconia from the semicircular canal (where they have inappropriately entered) through the utricular exit in the nonampullary arm of the semicircular canal to the utricle (where they normally remain as a part of utricular gelatinous matrix). The cases of multicanalicular vestibular lithiasis with the involvement of more than one semicircular canal require meticulous identification of the involved canals and multiple different canal-clearing maneuvers for effective treatment. A 70-year-old male patient with no significant history of previous medical or otologic illnesses or head trauma presented with a 1-day history of vertigo with positional aggravation. A one-time performed diagnostic supine head roll test elicited three different patterns of positional nystagmus, each with an accurate localizing and lateralizing value. Diagnosis of unilateral multicanalicular vestibular lithiasis of right horizontal and posterior semicircular canals was entertained based on the pattern of the elicited positional nystagmi on the supine roll test. The upbeating torsional nystagmus that localizes the involvement to the posterior semicircular canal was paradoxically elicited by supine head roll test and not by the Dix–Hallpike test. As horizontal semicircular canalolithiasis causes severe symptoms, its treatment preceded that of concurrent posterior semicircular canalolithiasis. The patient was successfully treated with multiple sessions of canalith repositioning maneuvers (CRMs) spread over 24 hours. It is important to perform both positional tests, namely Dix–Hallpike maneuver, and supine head roll test, in cases suspected to have multicanalicular vestibular lithiasis. The positionings may need to be repeated several times to unveil multiple nystagmi, each with different localizing and lateralizing values. Identifying treatment priorities with CRM for the individual semicircular canals is crucial, and the canal that is liable to cause severe symptoms needs early clearance of the otoconial debris. If a CRM fails to clear a semicircular canal, an alternative maneuver may need to be executed. Clinicians involved in the care of cases with multicanalicular vestibular lithiasis should be well versed with all possible backup maneuvers for clearing each of the three semicircular canals.

Active head rolls enhance sonar-based auditory localization performance

Animals utilize a variety of active sensing mechanisms to perceive the world around them. Echolocating bats are an excellent model for the study of active auditory localization. The big brown bat (Eptesicus fuscus), for instance, employs active head roll movements during sonar prey tracking. The function of head rolls in sound source localization is not well understood. Here, we propose an echolocation model with multi-axis head rotation to investigate the effect of active head roll movements on sound localization performance. The model autonomously learns to align the bat’s head direction towards the target. We show that a model with active head roll movements better localizes targets than a model without head rolls. Furthermore, we demonstrate that active head rolls also reduce the time required for localization in elevation. Finally, our model offers key insights to sound localization cues used by echolocating bats employing active head movements during echolocation.

Underestimation of self-tilt increases in reduced gravity conditions

BACKGROUND: During large angles of self-tilt in the roll plane on Earth, measurements of the subjective visual vertical (SVV) in the dark show a bias towards the longitudinal body axis, reflecting a systematic underestimation of self-tilt. OBJECTIVE: This study tested the hypothesis that self-tilt is underestimated in partial gravity conditions, and more so at lower gravity levels. METHODS: The SVV was measured in parabolic flight at three partial gravity levels: 0.25, 0.50, and 0.75 g. Self-tilt was varied amongst 0, 15, 30, and 45 deg, using a tiltable seat. The participants indicated their SVV by setting a linear array of dots projected inside a head mounted display to the perceived vertical. The angles of participants’ body and head roll tilt relative to the gravito-inertial vertical were measured by two separate inertial measurement units. RESULTS: Data on six participants were collected. Per G-level, a regression analysis was performed with SVV setting as dependent variable and head tilt as independent variable. The latter was used instead of chair tilt, because not all the participants’ heads were aligned with their bodies. The estimated regression slopes significantly decreased with smaller G-levels, reflecting an increased bias of the SVV towards the longitudinal body axis. On average, the regression slopes were 0.95 (±0.38) at 0.75 g; 0.84 (±0.22) at 0.5 g; and 0.63 (±0.33) at 0.25 g. CONCLUSIONS: The results of this study show that reduced gravity conditions lead to increased underestimation of roll self-tilt.

An evaluation of serum Otolin-1 & Vitamin-D in benign paroxysmal positional vertigo

BACKGROUND: Serum otolin-1 is an inner ear protein exclusively expressed in otoconia and cells of vestibule and cochlea. Serum otolin-1 is found to be quantifiable in patients with BPPV. Low Vitamin-D is associated with pathogenesis of BPPV. Since otoconia degeneration contributes to BPPV, lack of Vitamin-D may impact otoconia structure and integrity. OBJECTIVE: We aimed at studying the s.otolin-1 as biomarker and significance of vit-D in BPPV. MATERIAL AND METHOD: 23 patients in test and control groups respectively were chosen within the age of 20 to 65 years. All the patients were diagnosed using Dix Hallpike menouver and head roll test, patients were treated with appropriate Canal Reposition Menouver (CRM). RESULTS: Serum Otolin-1 levels among the test ranged from 366 to 882 pg/mL with mean of 585.17 pg/mL whereas in control group ranged from 223 to 462 pg/mL with mean of 335.26 pg/mL. Mean Vitamin-D levels among the test group was 22.67 ng/mL (Range = 6.3–68.4) and that of control 15.43 pg/mL (Range = 5.4–27.7) respectively. The relationship between the serum Otolin-1 and Vitamin-D was not statistically significant. CONCLUSION: Otolin-1 levels is increased in BPPV patients and is sensitive in BPPV, specificity needs to be validated. Role of vitamin-D with respect to inner ear proteins needs further investigation.

Spontaneous Direction-Changing or Reversing Positional Nystagmus without Changing Head Position during Head-Roll/Head-Hanging Maneuvers: Biphasic Positional Nystagmus

Background and Objectives: Conflicting mechanisms have been reported about spontaneous reversal of positional nystagmus during head-roll maneuver in patients with benign paroxysmal positional vertigo (BPPV). The objective of this study is to review the reports about the characteristics and possible mechanisms of reversing positional nystagmus and to present seven new cases.Subjects and Methods: Seven cases (5 males, 2 females; 4 left-sided, 3 right-sided) were recruited among 732 patients with BPPV seen outpatient clinic between 2009 and 2019. Diagnosis of lateral canal canalolithiasis was confirmed when transient geotropic nystagmus was documented during head-roll test. Reversing positional nystagmus was analyzed in each case and clinical characteristics of the patients were documented.Results: The age of patients was ranging between 30 to 64 years (46.44±10.91). Duration of symptoms was short (21.34±19.74). Six of them had a story of head trauma. Initial latency was short. First, intense geotropic nystagmus was observed following provocative head-roll position on the affected side. There was short “silent phase”. Then, a longer second-phase of reversed nystagmus was noted. Total duration of nystagmus was 78.40±6.82 seconds. Maximal slow phase velocity was 24.05±6.34 deg/sec. All patients were cured with barbeque maneuver.Conclusions: Ipsilateral reversing positional nystagmus during head-roll maneuver is due to lateral canal canalolithiasis. Mechanism is likely to be due to endolymphatic double flow. Bilateral cases may be due to simultaneous co-existence of canalolithiasis and cupulolithiasis. Longer recording of nystagmus is recommended not to miss the cases with spontaneous direction-changing positional nystagmus.

Objective and subjective responses to motion sickness: the group and the individual

We investigated and modeled the temporal evolution of motion sickness in a highly dynamic sickening drive. Slalom maneuvers were performed in a passenger vehicle, resulting in lateral accelerations of 0.4 g at 0.2 Hz, to which participants were subjected as passengers for up to 30 min. Subjective motion sickness was recorded throughout the sickening drive using the MISC scale. In addition, physiological and postural responses were evaluated by recording head roll, galvanic skin response (GSR) and electrocardiography (ECG). Experiment 1 compared external vision (normal view through front and side car windows) to internal vision (obscured view through front and side windows). Experiment 2 tested hypersensitivity with a second exposure a few minutes after the first drive and tested repeatability of individuals’ sickness responses by measuring these two exposures three times in three successive sessions. An adapted form of Oman’s model of nausea was used to quantify sickness development, repeatability, and motion sickness hypersensitivity at an individual level. Internal vision was more sickening compared to external vision with a higher mean MISC (4.2 vs. 2.3), a higher MISC rate (0.59 vs. 0.10 min−1) and more dropouts (66% vs. 33%) for whom the experiment was terminated due to reaching a MISC level of 7 (moderate nausea). The adapted Oman model successfully captured the development of sickness, with a mean model error, including the decay during rest and hypersensitivity upon further exposure, of 11.3%. Importantly, we note that knowledge of an individuals’ previous motion sickness response to sickening stimuli increases individual modeling accuracy by a factor of 2 when compared to group-based modeling, indicating individual repeatability. Head roll did not vary significantly with motion sickness. ECG varied slightly with motion sickness and time. GSR clearly varied with motion sickness, where the tonic and phasic GSR increased 42.5% and 90%, respectively, above baseline at high MISC levels, but GSR also increased in time independent of motion sickness, accompanied with substantial scatter.

Upright BPPV Protocol: Feasibility of a New Diagnostic Paradigm for Lateral Semicircular Canal Benign Paroxysmal Positional Vertigo Compared to Standard Diagnostic Maneuvers

Background: The diagnosis of benign paroxysmal positional vertigo (BPPV) involving the lateral semicircular canal (LSC) is traditionally entrusted to the supine head roll test, also known as supine head yaw test (SHYT), which usually allows identification of the pathologic side and BPPV form (geotropic vs. apogeotropic). Nevertheless, SHYT may not always allow easy detection of the affected canal, resulting in similar responses on both sides and intense autonomic symptoms in patients with recent onset of vertigo. The newly introduced upright head roll test (UHRT) represents a diagnostic maneuver for LSC-BPPV, supplementing the already-known head pitch test (HPT) in the sitting position. The combination of these two tests should enable clinicians to determine the precise location of debris within LSC, avoiding disturbing symptoms related to supine positionings. Therefore, we proposed the upright BPPV protocol (UBP), a test battery exclusively performed in the upright position, including the evaluation of pseudo-spontaneous nystagmus (PSN), HPT and UHRT. The purpose of this multicenter study is to determine the feasibility of UBP in the diagnosis of LSC-BPPV.Methods: We retrospectively reviewed the clinical data of 134 consecutive patients diagnosed with LSC-BPPV. All of them received both UBP and the complete diagnostic protocol (CDP), including the evaluation of PSN and data resulting from HPT, UHRT, seated-supine positioning test (SSPT), and SHYT.Results: A correct diagnosis for LSC-BPPV was achieved in 95.5% of cases using exclusively the UBP, with a highly significant concordance with the CDP (p < 0.000, Cohen's kappa = 0.94), regardless of the time elapsed from symptom onset to diagnosis. The concordance between UBP and CDP was not impaired even when cases in which HPT and/or UHRT provided incomplete results were included (p < 0.000). Correct diagnosis using the supine diagnostic protocol (SDP, including SSPT + SHYT) or the sole SHYT was achieved in 85.1% of cases, with similar statistical concordance (p < 0.000) and weaker strength of relationship (Cohen's kappa = 0.80).Conclusion: UBP allows correct diagnosis in LSC-BPPV from the sitting position in most cases, sparing the patient supine positionings and related symptoms. UBP could also allow clinicians to proceed directly with repositioning maneuvers from the upright position.