Postural responses to anterior and posterior perturbations applied to the upper trunk of standing human subjects.

This study concerned the effects of brisk perturbations applied to the shoulders of standing subjects to displace them either forwards or backwards, our aim being to characterise the responses to these disturbances. Subjects stood on a force platform, and acceleration was measured at the level of C7, the sacrum and both tibial tuberosities. Surface EMG was measured from soleus (SOL), tibialis anterior (TA), the hamstrings (HS), quadriceps (QUAD), rectus abdominis (RA) and lumbar paraspinal (PS) muscles. Trials were recorded for each of four conditions: subjects' eyes open (reference) or closed and on a firm (reference) or compliant surface. Observations were also made of voluntary postural reactions to a tap over the deltoid. Anterior perturbations (mean C7 acceleration 251.7 mg) evoked activity within the dorsal muscles (SOL, HS, PS) with a similar latency to voluntary responses to shoulder tapping. Responses to posterior perturbations (mean C7 acceleration -240.4 mg) were more complex beginning, on average, at shorter latency than voluntary activity (median TA 78.0 ms). There was activation of TA, QUAD and SOL associated with initial forward acceleration of the lower legs. The EMG responses consisted of an initial phasic discharge followed by a more prolonged one. These responses differ from the pattern of automatic postural responses that follow displacements at the level of the ankles, and it is unlikely that proprioceptive afferents excited by ankle movement had a role in the initial responses. Vision and surface properties had only minor effects. Perturbations of the upper trunk evoke stereotyped compensatory postural responses for each direction of perturbation. For posterior perturbations, EMG onset occurs earlier than for voluntary responses.

Frequency and phase effects on cervical vestibular evoked myogenic potentials (cVEMPs) to air-conducted sound.

Few previous studies of tuning using air-conducted (AC) stimuli and the cervical vestibular evoked myogenic potential (cVEMP) have compensated for the effects of middle ear (ME) attenuation. Zhang et al. (Exp Brain Res 213:111-116, 2011a) who did allow for ME effects were able to show a secondary peak around 100 Hz for the ocular VEMP (oVEMP). Recently, it has become clear that the otolith afferents responsible for the cVEMP and oVEMP differ and thus the nature of tuning may be more related to the reflex studied determining which otolith receptors are activated rather than the properties of the stimulus. We wished to reinvestigate the tuning for the cVEMP using AC stimuli, to establish whether the low-frequency peak is specific for the oVEMP or a consequence of the stimulus modality itself. In response to recent evidence using a 500 Hz AC stimulus that there was no effect of stimulus phase, we also investigated whether phase (condensation or rarefaction) had an effect at any frequency. We measured corrected cVEMP amplitudes and latencies in response to stimuli between 50 and 1200 Hz in 10 normal volunteers using an AC stimulus adjusted for ME attenuation. We confirmed earlier reports of the similarity of the tuning for both the cVEMP and oVEMP reflexes but found no separate 100 Hz peak for the cVEMP. AC stimulus phase did not affect either amplitude or latency. Both the tuning pattern and the phase effects contrast with those previously reported for bone-conducted (BC) stimuli. Unlike BC stimulation, which shows tuning consistent with an action on the otolith membrane, AC stimuli are likely to act through a different mechanism, most likely directly at the hair cell level.

Contrasting phase effects on vestibular evoked myogenic potentials (VEMPs) produced by air- and bone-conducted stimuli.

We have studied the effects of stimulus phase on the latency and amplitude of cVEMPs and oVEMPs by reanalysing data from Lim et al. (Exp Brain Res 224:437-445, 2013) in which alternating phase was used. Responses for the different initial stimulus phase, either positive or negative, were separated and reaveraged. We found that the phase (compressive or rarefactive) of AC 500-Hz stimuli had no significant effect on either latency or amplitude of the responses. Conversely, phase (positive = motor towards subjects) did alter the effects of BC 500-Hz stimulation. For cVEMPs, phase consistently affected initial latency with earlier responses for positive stimuli, while, for stimulation at the mastoid, negative onset phase gave larger responses. For the oVEMP, effects were different for the two sites of BC stimulation. At the forehead, the response appeared to invert, whereas at the mastoid there appeared to be a delay of the initial response. Related to this, the effect of phase for the two sites was opposite: at the mastoid, positive responses were earlier but negative were larger (particularly for long stimuli). At the forehead, the effect was the opposite: negative onset stimuli evoked earlier responses, whereas positive onset evoked larger responses. These findings indicate a basic difference in the way that AC and BC stimuli activate vestibular receptors and also indicate that the effects of phase of BC stimulation depend on location. Stimulus alternation does little to affect the response to AC stimulation but obscures the effects of BC stimuli, particularly for the oVEMP.

Axially evoked postural reflexes: influence of task.

Postural reflexes were recorded in healthy subjects (n = 17) using brief axial accelerations and tap stimuli applied at the vertebra prominens (C7) and manubrium sterni. Short latency (SL) responses were recorded from the soleus, hamstrings and tibialis anterior muscles and expressed as a percentage of the background EMG prior to stimulus onset. In the majority of postural conditions tested, subjects were recorded standing erect and leaning forward with their feet together. The SL response was larger for soleus than for the hamstrings during standing (soleus vs hamstrings; 70.4 vs 28.1%), whereas the opposite occurred during kneeling (25.3 vs 127.3%). Concordant head and trunk accelerations produced larger SL responses than discordant accelerations for soleus and hamstrings, but the evoked excitatory response was independent of head direction and as expected for the direction of truncal acceleration. Postural reflexes for soleus and tibialis anterior were strongly affected by conditions that posed a significant threat to postural stability; stimulation at C7 was associated with significant SL enhancement for soleus during anterior lean while sternal stimulation showed SL enhancement for tibialis anterior during posterior lean. Cutaneous anaesthesia applied over the C7 stimulation site had no significant effect on EMG responses, nor did vision or surface type (rigid or compliant). This study provides further evidence that postural reflexes produced by brief axial accelerations are independent of cutaneous receptors, vestibular afferents and ankle proprioceptors, and demonstrates that postural tasks and truncal orientation significantly affect the evoked response, consistent with a role in stabilising posture.

Recruitment properties and significance of short latency reflexes in neck and eye muscles evoked by brief lateral head accelerations.

Short lateral head accelerations were applied to investigate the recruitment properties of the reflexes underlying the earliest ocular and cervical electromyographic reflex responses to these disturbances. Components of both reflexes are vestibular dependent and have been termed "ocular vestibular evoked myogenic potentials" and "cervical vestibular evoked myogenic potentials", respectively. Previous investigations using a unilateral vestibular stimulus have indicated that some but not all these vestibular-dependent reflexes show a simple power law relationship to stimulus intensity. In particular, crossed otolith-ocular reflexes showed evidence of an inflection separating two types of behaviour. The present stimulus acts bilaterally, and only the earliest crossed otolith-ocular reflex, previously shown to have a strictly unilateral origin, showed evidence of an inflection. Reflex changes in ocular torsion could, in principle, correct for the changes associated with translation for an elevated eye, but our findings indicated that the responses were consistent with previous reports of tilt-type reflexes. For the neck, both vestibular and segmental (muscle spindle) reflexes were evoked and followed power law relationships, without any clear separation in sensitivity. Our findings are consistent with previous evidence of "tilt-like" reflexes evoked by lateral acceleration and suggest that the departure from a power law occurs as a consequence of a unilateral crossed pathway. For the neck, responses to transients are likely to always consist of both vestibular and non-vestibular (segmental) components. Most of the translation-evoked ocular and cervical reflexes appear to follow power law relationship to stimulus amplitude over a physiological range.

Differential effects of duration for ocular and cervical vestibular evoked myogenic potentials evoked by air- and bone-conducted stimuli.

We investigated the changes in cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic potentials in response to differing stimulus durations. cVEMPs (n = 12 subjects) and oVEMPs (n = 13 subjects) were recorded using air-conducted (AC: 500 Hz) and bone-conducted (BC: 500 Hz) tone burst stimuli with durations varying from 2 to 10 ms. BC stimulation was applied both frontally and to the mastoid. AC cVEMPs showed an increase in amplitude with stimuli up to 6-ms duration associated with a prolonged latency, as previously reported. In contrast, AC oVEMP amplitude decreased with increasing stimulus duration. BC stimuli showed no significant increase in amplitude with increasing stimulus duration for either reflex using either location of stimulation. BC cVEMPS following forehead stimulation showed a significant decrease as duration increased, and BC oVEMPs to mastoid stimulation were largest at 2 ms and decreased thereafter. We conclude that an increase in amplitude with increasing stimulus duration, using 500 Hz stimuli, only occurs for AC cVEMPs. There is no definite benefit in using longer stimuli than 2 ms for BC or oVEMP studies. Shorter stimuli also minimise subject exposure to sound and vibration.

The perceived long-term impact of COVID-19 on OCD symptomology.

A pandemic outbreak can lead to excessive, maladaptive levels of anxiety, particularly among individuals who already suffer from obsessive-compulsive disorder (OCD). The Coronavirus Disease 2019 (COVID-19) provided a novel opportunity to examine the possibility that individuals with OCD, compared to those without OCD, might experience greater distress from this common stressor. The present study examined the lasting effects of COVID-19 in the year after the outbreak. Additionally, there is limited research regarding the stability of OCD dimensions; therefore, this study examined whether the COVID-19 pandemic impacted the stability of OCD dimensions. One hundred and forty-three adults who reported they had been diagnosed with OCD and ninety-eight adults without OCD, completed an online survey assessing the impact the COVID-19 pandemic had on symptoms of OCD in the year after the initial outbreak. The OCD group showed greater concern about the pandemic and greater concern about future pandemics compared to the comparison group. In addition, COVID-19 related distress differentially related to OCD symptoms dimensions, showing the strongest association with the contamination dimension. Lastly, results showed that many individuals reported that their OCD dimension shifted to obsessions about COVID-19 from their pre-existing OCD dimension.

Correction to: A Perfect Storm? Health Anxiety, Contamination Fears, and COVID-19: Lessons Learned from Past Pandemics and Current Challenges.

[This corrects the article DOI: 10.1007/s41811-021-00109-7.].

A Perfect Storm? Health Anxiety, Contamination Fears, and COVID-19: Lessons Learned from Past Pandemics and Current Challenges.

The novel coronavirus disease 2019 (COVID-19) rapidly spread, becoming a global pandemic with significant health, economic, and social impacts. COVID-19 has caused widespread anxiety, which at healthy levels leads to adaptive, protective behavioral changes. For some individuals, a pandemic outbreak can lead to excessive, maladaptive levels of anxiety, particularly among those with obsessive-compulsive disorder (OCD) and health anxiety. In the present paper, we review past research studies that examined anxiety in response to other disease outbreaks (including Swine Flu, Zika, and Ebola) to serve as a guide for expectable responses to COVID-19. Our review focused on the role of belief-based cognitive variables (obsessive beliefs, contamination cognitions), transdiagnostic processes (disgust sensitivity, anxiety sensitivity, an intolerance of uncertainty), social factors, and environmental/situational variables as contributing factors to excessive concerns about past pandemics. These factors in combination with unique characteristics of the virus (disease, behavioral, social and economic factors) and media consumption might enhance vulnerability to excessive anxiety about COVID-19, in line with a diathesis-stress model. COVID-19 is also unique from past pandemics due to its severity, easy transmissibility, and the nature of prescribed behavioral responses (i.e., hand washing and social distancing). We therefore discuss the ways in which COVID-19 may disproportionately affect individuals with OCD and health anxiety. We conclude with important topics for clinical and research attention to help mental health professionals respond in this time of crisis.

Sound-evoked vestibular projections to the splenius capitis in humans: comparison with the sternocleidomastoid muscle.

The short-latency vestibulo-collic reflex in humans is well defined for only the sternocleidomastoid (SCM) neck muscle. However, other neck muscles also receive input from the balance organs and participate in neck stabilization. We therefore investigated the sound-evoked vestibular projection to the splenius capitis (SC) muscles by comparing surface and single motor unit responses in the SC and SCM muscles in 10 normal volunteers. We also recorded surface responses in patients with unilateral vestibular loss but preserved hearing and hearing loss but preserved vestibular function. The single motor unit responses were predominantly inhibitory, and the strongest responses were recorded in the contralateral SC and ipsilateral SCM. In both cases there was a significant decrease or gap in single motor unit activity, in SC at 11.7 ms for 46/66 units and in SCM at 12.7 ms for 51/58 motor units. There were fewer significant responses in the ipsilateral SC and contralateral SCM muscles, and they consisted primarily of weak increases in activity. Surface responses recorded over the contralateral SC were positive-negative during neck rotation, similar to the ipsilateral cervical vestibular evoked myogenic potential in SCM. Responses in SC were present in the patients with hearing loss and absent in the patient with vestibular loss, confirming their vestibular origin. The results describe a pattern of inhibition consistent with the synergistic relationship between these muscles for axial head rotation, with the crossed vestibular projection to the contralateral SC being weaker than the ipsilateral projection to the SCM. NEW & NOTEWORTHY We used acoustic vestibular stimulation to investigate the saccular projections to the splenius capitis (SC) and sternocleidomastoid (SCM) muscles in humans. Single motor unit recordings from within the muscles demonstrated strong inhibitory projections to the contralateral SC and ipsilateral SCM muscles and weak excitatory projections to the opposite muscle pair. This synergistic pattern of activation is consistent with a role for the reflex in axial rotation of the head.

Properties of cervical and ocular vestibular evoked myogenic potentials (cVEMPs and oVEMPs) evoked by 500 Hz and 100 Hz bone vibration at the mastoid.

OBJECTIVE: To define and compare the input-output properties of 500 Hz and 100 Hz bone-conducted (BC) transmastoid stimulation when evoking cVEMPs and oVEMPs. The findings for 500 Hz were compared with those previously reported for air-conducted (AC) 500 Hz stimulation. METHODS: Twelve healthy subjects (18-57 years old) participated in this study, with simultaneous recordings of cVEMPs and oVEMPs bilaterally. Initial intensities of 138 dB (FL) were used and then reduced in 3 or 6 dB increments to 105 dB. RESULTS: For BC 500 Hz, like AC 500 Hz, the relationship between the stimulus and reflex output fitted a power law for most peaks, but not the initial peak of the oVEMP. Some of the subjects did not have early crossed oVEMP responses for BC 500 Hz but all did for 100 Hz. For BC 100 Hz, while the initial waveforms were similar, many of the peaks showed a tendency to saturate at the higher intensities. For both BC 500 Hz and 100 Hz, the initial (contralateral) oVEMP peaks had a higher threshold than for the (ipsilateral) cVEMP responses although this difference was more marked for 500 Hz. CONCLUSIONS: BC 500 Hz shows similar properties to AC 500 Hz, consistent with an overlapping spectrum of afferents being excited by both, with bilateral effects for the BC stimulus. BC 100 Hz evokes more non-vestibular peaks, presumably from muscle afferents, for the SCM recordings but is a more reliable method of evoking the early crossed potentials of the oVEMP. SIGNIFICANCE: BC 500 Hz is a useful adjunct to the AC 500 Hz stimulus and has similar properties. The BC 100 Hz stimulus may be a more reliable method of evoking the early crossed oVEMP responses.

Electrode montage and gaze effects on ocular vestibular evoked myogenic potentials (oVEMPs).

OBJECTIVES: To investigate the properties of lateral electrode locations compared to the conventional ones and to bipolar compared to chin-referenced montages for recording ocular vestibular evoked myogenic potentials (oVEMPs). METHODS: A total of 18 subjects were studied using 5 electrode locations around the eye, including the conventional location and more lateral ones (i.e. M, ML and L electrodes near the orbital margin, R1 and R2 electrodes below the two more medial ones). Unilateral air-conducted (AC) sound, bone-conducted (BC) impulses at the mastoid and BC vibration (500Hz) at the forehead were used. These were applied while the subjects looked in neutral gaze and with 4 levels of increasing elevation. A subset of 10 subjects were also studied when looking downwards at 4 levels. Five bipolar montages were created offline by subtraction. RESULTS: The M and ML electrodes had the largest responses but responses were seen for all 5 electrodes. The chin reference was associated with substantial pickup from the contralateral side (as judged using unilateral AC stimulation). The M-R1 (conventional) montage showed a significantly non-linear response to gaze angle, unlike the ML montages. The ML-R1 montage gave the largest responses. There was a clear change in latency for the conventional montage with downgaze for the AC and BC impulsive stimuli. CONCLUSIONS: The ML active electrode has a more stable n1 latency, a larger and a more linear response to gaze angle than the conventional recording site, probably due to contamination by pickup of inferior rectus activity when using the conventional site. SIGNIFICANCE: The ML location is a better site for the active pickup for recording oVEMPs if the main object of study is the inferior oblique muscle and particularly if subjects have difficulty with upgaze.

Properties of 500Hz air- and bone-conducted vestibular evoked myogenic potentials (VEMPs) in superior canal dehiscence.

OBJECTIVES: To compare threshold and amplitude properties for air- (AC) and mastoid bone-conducted (BC) cervical (cVEMP) and ocular (oVEMP) vestibular evoked myogenic potentials in superior canal dehiscence (SCD). METHODS: Thirteen patients (53±14yrs) clinically diagnosed with SCD were tested using AC 500Hz sound and BC 500Hz transmastoid vibration. Baseline intensities of 135dBpSPL and 138dBpFL respectively were used and reduced until the response amplitudes were less than 2.5 standard deviations of the prestimulus baseline mean. SCD VEMP amplitudes, response gradients and threshold parameters for the initial peaks for the cVEMP (ipsilateral) and the oVEMP (contralateral) were compared with results for normal subjects over a range of intensities. RESULTS: Despite higher amplitudes, reflex gradients against intensity for AC and BC cVEMPs were significantly less in SCD than normals (P≪0.001) while AC and BC oVEMP gradients were not significantly different between the groups. Abnormally low thresholds for AC 500Hz were present for 85% of cVEMPs and 62% of oVEMPs. Abnormally low BC 500Hz thresholds were seen for 33% of cVEMPs and 83% of oVEMPs. Amplitudes for AC 500Hz were compared over the 135-105dBpSPL intensity range. The cVEMP showed more pathologically large amplitude responses with the lower stimulus intensities (135dBpSPL: 5%, 105dBpSPL: 100%) whereas the oVEMP demonstrated high rates of amplitude increases for all intensities (129-111dBpSPL: 92%). The pattern of pathologically large amplitudes evoked by BC 500Hz was similar for both reflexes such that both cVEMPs and oVEMPs showed maximum prevalence of abnormally large responses around 117dBpFL (cVEMP: 58%, oVEMP: 83%). CONCLUSIONS: In SCD, both AC and BC evoked cVEMPs show evidence of saturation but this is not evident for oVEMPs. Both cVEMPs and oVEMPs show frequent abnormalities of amplitudes and thresholds in SCD compared to normal subjects but the sensitivities differed between measures. SIGNIFICANCE: Previous evidence of saturation of cVEMP responses in SCD was confirmed. For diagnosis, AC cVEMP amplitudes at 105dBpSPL or AC-evoked oVEMP amplitudes both have over 90% sensitivity in separating SCD from normal responses.

Vestibular evoked myogenic potentials (VEMPs) evoked by air- and bone-conducted stimuli in vestibular neuritis.

OBJECTIVE: To compare and characterise abnormalities for short latency vestibular evoked myogenic potentials (VEMPs) elicited by air- (AC) and two differing types of bone-conducted (BC) stimuli during vestibular neuritis (VN). METHODS: AC (500Hz short tone bursts) and two BC stimuli (500Hz at the forehead and impulses at the mastoids) were used to evoke cervical and ocular potentials (cVEMPs and oVEMPs) in VN patients (n=22) and healthy subjects. RESULTS: More abnormalities were observed for the oVEMP than the cVEMP when using either AC 500Hz or BC 500Hz. The AC stimulus showed slightly more abnormalities than the BC 500Hz stimulus. In contrast, BC impulses produced frequent abnormalities for both oVEMPs and cVEMPs. The findings were modelled, based upon presumed selective lesions of the superior nerve. CONCLUSIONS: AC 500Hz stimulation was slightly better than BC 500Hz in demonstrating abnormalities in patients with VN. BC impulses behave as expected for a predominantly utricular stimulus. The relative contributions of saccular and utricular fibres differ for stimulus type and target reflex. SIGNIFICANCE: AC 500Hz is as effective as BC 500Hz for investigating VN. BC impulses act most strongly on utricular afferents.

Differing response properties of cervical and ocular vestibular evoked myogenic potentials evoked by air-conducted stimulation.

OBJECTIVE: To determine the amplitude changes of vestibular evoked myogenic potentials (VEMPs) recorded simultaneously from the neck (cVEMPs) and eyes (oVEMPs) in response to 500 Hz, 2 ms air-conducted sound pips over a 30 dB range. METHODS: Fifteen healthy volunteers (mean age 29, range 18-57 years old) and one patient with unilateral superior canal dehiscence (SCD) were studied. The stimulus was reduced in increments to 105 dB pSPL for the normals (81 dB pSPL for the SCD patient). A statistical criterion was used to detect responses. RESULTS: Ipsilateral (i-p13/n23) and contralateral (c-n12/p24/n30) peaks for the cVEMP montage and contralateral (c-n10/p16/n21) and ipsilateral (i-n13) peaks for the oVEMP montage were present for the baseline intensity. For the lowest intensity, 6/15 subjects had responses for the i-p13 cVEMP potential and 4/15 had c-n10 oVEMP responses. The SCD patient showed larger responses for nearly all intensities. The cVEMP potentials were generally well fitted by a power law relationship, but the oVEMP c-n10, p16 and n21 potentials showed a significant increase in gradient for the higher intensities. CONCLUSION: Most oVEMP and cVEMP responses follow a power law relationship but crossed oVEMP responses showed a change in gradient above a threshold. SIGNIFICANCE: The pattern of response to AC stimulation may be a property of the pathways underlying the potentials.