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We report an experiment to investigate possible vestibular effects on finger tapping to an auditory anapaest rhythm. In a sample of 10 subjects, index finger acceleration and tapping force were recorded along with extensor/flexor ...
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We report an experiment to investigate possible vestibular effects on finger tapping to an auditory anapaest rhythm. In a sample of 10 subjects, index finger acceleration and tapping force were recorded along with extensor/flexor activity and the associated electroencephalographic activity measured at central and cerebellar surface electrodes. In a prior session with a standard short air conducted 500-Hz pip, vestibular evoked myogenic potential thresholds were measured and subsequently used to set the acoustic intensity. During the main experiment subjects were asked to synchronise tapping to the pips arranged in the anapaest at two different frequencies, 500 Hz vs 5 kHz, so that only the low-frequency high-intensity condition was a vestibular, as well as an auditory stimulus. We hypothesised that a vestibular effect would manifest in an interaction between the frequency and intensity factors for a range of dependent measures of tapping performance. No clear evidence was found for vestibular effects, but this was likely due to the confounding effects of an independent effect of intensity and the relative weakness of the acoustic vestibular stimulus. However, the data did show novel evidence for two distinct timing processes for the flexion and extension stages of a tap cycle and two distinct timing strategies, which we refer to as 'staccato' and 'legato; characterised by different profiles of force and extension.
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Vestibular cerebellar evoked potentials (VsCEPs) were recorded from over the occipital and cerebellar regions of the scalp using bone-conducted (BC) stimuli applied at the mastoids (impulsive accelerations and 500 Hz) and 500 Hz a...
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Vestibular cerebellar evoked potentials (VsCEPs) were recorded from over the occipital and cerebellar regions of the scalp using bone-conducted (BC) stimuli applied at the mastoids (impulsive accelerations and 500 Hz) and 500 Hz acoustic tones (AC). Ten healthy subjects were tested. Electrodes were positioned over the midline (Oz, Iz, CBz) and at 3, 6 and 9 cm intervals lateral to the midline electrodes bilaterally. Additional electrodes were also positioned over posterior neck muscles (SPL1 and SPL2). The largest evoked potentials on average were recorded from the electrodes 3 and 6 cm lateral to the Iz and CBz midline locations. BC stimuli produced short latency potentials on the side contralateral to the stimulated mastoid and were dependent on stimulus polarity. Positive polarity stimuli produced biphasic VsCEPs at approximately 12 and 17 ms (P12-N17) for BC impulses and 10 and 15 ms (P10-N15) for BC 500 Hz stimuli. Following the initial excitation, there was a period of suppression of background activity lasting an average of 16.8 ms for positive polarity BC impulses. Negative polarity stimuli produced later VsCEPs both for BC impulses (P20-N26) and BC 500 Hz (P13-N18). VsCEPs to AC 500 Hz stimuli lateralised to the contralateral side and were larger for right than left ear stimulation. Stimulus polarity (condensation and rarefaction) did not alter the timing of the VsCEPs to AC 500 Hz tones. No evoked response was recorded to somatosensory (median and radial nerve) stimulation. Four patients with cerebellar disease were tested and two showed abnormal VsCEPs with initial negativities. VsCEPs show distinct mapping over the posterior fossa and are likely to reflect climbing fibre responses via crossed otolith-cerebellar pathways.
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We studied 12 patients with Parkinson's disease (PD): 6 with postural instability (Hoehn and Yahr Stage 3) and 6 without (Stage 2 or 2.5), using a quantitative test based on the clinical pull test. Their findings were compared wit...
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We studied 12 patients with Parkinson's disease (PD): 6 with postural instability (Hoehn and Yahr Stage 3) and 6 without (Stage 2 or 2.5), using a quantitative test based on the clinical pull test. Their findings were compared with those for 12 healthy controls. The patients on their usual medications were pulled either forwards or backwards at the level of the shoulders and asked not to take a step in a series of five trials. Acceleration was monitored for the upper trunk, sacrum, and both tibias. EMG was measured in soleus and tibialis anterior (TA) muscles in all and for thigh and truncal muscles in a subgroup. A target of 0.2g trunk acceleration was used, but smaller perturbations were used in very unstable patients. All the Stage 3 patients lost balance in at least one trial for the posterior perturbations but none for the anterior ones. None of the Stage 2 patients lost balance. There was increased tonic EMG and agonist activity but no difference in EMG onset or initial force production compared to healthy controls. For posterior perturbations, there were two related disorders that separated the PD patients from controls. There was a significantly higher ratio of sacral-to-applied acceleration and both PD groups showed reduced knee acceleration and shortened latency, more so for the Stage 3 group. The increased sacral-to-C7 acceleration ratio was correlated with the tonic level of activation of the hamstrings (HS), quadriceps, and lumbar paraspinal muscles (PS), while the tibial acceleration latency was also correlated with the level of tonic PS activation. We also found that the size of balance responses, 0-200ms post-perturbation, correlated significantly with the level of tonic activation in nearly all the muscles studied. We confirmed that PD patients show greater instability posteriorly than anteriorly to applied perturbations. Our findings support increasing axial and limb rigidity as the cause of the impaired pull test rather than postural bradykinesia and suggest that tonic truncal and thigh muscle activation may be an important underlying cause.
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This study investigated the effect of eye gaze and head position on vestibular-evoked potentials (VsEPs). Head position would be expected to affect myogenic sources, and eye position is known to affect ocular myogenic responses (o...
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This study investigated the effect of eye gaze and head position on vestibular-evoked potentials (VsEPs). Head position would be expected to affect myogenic sources, and eye position is known to affect ocular myogenic responses (ocular vestibular-evoked myogenic potentials), whereas a neurogenic source should behave otherwise. Eleven healthy subjects were recruited, and VsEPs, using 72-channel EEG, were recorded at a fixed intensity above the vestibular threshold. Three eye gaze and three head positions were tested (-20 degrees, 0 degrees, and +20 degrees to the horizontal). Short-latency potentials showed that in addition to the expected effect of gaze on infraocular (IO') leads, where up-gaze gives a maximum response, significant changes in amplitude were also observed in electrodes remote from the eyes and in particular, from contralateral parietal-occipital (PO) and neck (CB') leads. Shortlatency potentials of similar latency were observed (p10/n17 and n10/p17, respectively). The pattern of change with gaze in the PO leads was distinct from that observed for the IO' leads. For the PO leads, the maximum response was obtained with neutral gaze, and this was also distinct from that observed for CB' electrodes, where a maximal response was observed with head flexion in the second wave but not the first. Evidence of modulation of N42 and N1 potentials with both eye and head position was also observed. Head-and eye-position manipulation thus suggests that the inion response consists of an early neurogenic component, as well as myogenic responses. The p10/n17 at PO, in particular, may be an indicator of vestibulocerebellar projections.
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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 soleu...
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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.
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Our object was to investigate the effect of location and phase on the properties of oVEMPs and cVEMPs evoked by two bone conducted (BC) stimuli, 500 Hz and an impulsive stimulus for midline skull sites from Nz to Iz, in normal vol...
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Our object was to investigate the effect of location and phase on the properties of oVEMPs and cVEMPs evoked by two bone conducted (BC) stimuli, 500 Hz and an impulsive stimulus for midline skull sites from Nz to Iz, in normal volunteers. Compressive and rarefactive onset phases were used and the induced linear and rotational accelerations measured. We confirmed our previous finding of marked changes in the polarity of oVEMPs with location. For cVEMPs using the 500Hz stimulus there were few changes with location or phase, but the impulsive stimulus showed clear phase-related changes at several locations, with the shortest latencies occurring with compressive stimuli at AFz and Fz and the largest amplitudes at Iz. For oVEMPs, both stimuli showed clear effects of phase, with the shortest latencies with compressive stimuli at AFz and Fz and with the largest negativity at Oz or Iz. Whereas the effectiveness at Iz is consistent with a role in the linear VOR, the inversion of polarity and shorter latency around AFz and Fz is not and could not be explained by changes in acceleration of the head. The latency for BC 500Hz oVEMPs for AFz was the same as that for air-conducted (AC) stimuli. We suggest that whereas BC stimuli at most sites work through displacement of the otolith membrane, BC oVEMPs evoked at AFz and Fz may work through a direct action on utricular hair cells. Our findings have implications for clinical testing of VEMPs using midline BC stimuli.
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In this work we examine the possible neural basis for two brainstem-spinal reflexes using source analyses of brain activity recorded over the cortex and posterior fossa. In a sample of 5 healthy adult subjects, using axial and ves...
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In this work we examine the possible neural basis for two brainstem-spinal reflexes using source analyses of brain activity recorded over the cortex and posterior fossa. In a sample of 5 healthy adult subjects, using axial and vestibular stimulation by means of applied impulsive forces, evoked potentials were recorded with 63 channels using a 10 % cerebellar extension montage. In parallel, EMG was recorded from soleus and tibialis anterior muscles and accelerometry from the lower leg. Recordings over the cerebellum (ECeG) confirmed the presence of short latency (SL) potentials and these were associated with changes in high-frequency power. The SL responses to the two stimulus modalities differed in that the axial stimulation produced an initial pause and then a burst in the high-frequency ECeG, followed by excitation/inhibition in soleus while vestibular stimulation produced an initial burst then a pause, followed by inhibition/excitation in soleus. These short latency responses were followed by longer latency N1/P2/N2 responses in the averaged EEG, which were maximal at FCz. Brain Electrical Source Analysis (BESA) demonstrated both cerebellar and cerebral cortical contributions to the short-latency responses and primarily frontal cortex contributions to the long-latency EPs. The latency and polarity of the SL EPs, in conjunction with changes in high-frequency spontaneous activity, are consistent with cerebellar involvement in the control of brainstem-spinal reflexes. The early involvement of frontal cortex and subsequent later activity may be an indicator of the activation of the cortical motor-related system for rapid responses which may follow the reflexive components. These findings provide evidence of the feasibility of non-invasive electrophysiology of the human cerebellum and have demonstrated cerebellar and frontal activations associated with postural-related stimuli.
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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. ...
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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.
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We recorded evoked potentials (EPs) from over the posterior fossa and in parallel ocular vestibular evoked myogenic potentials (OVEMPs) during visuo-vestibular stimulation in a sample of 7 male and 11 female human subjects. In 9 o...
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We recorded evoked potentials (EPs) from over the posterior fossa and in parallel ocular vestibular evoked myogenic potentials (OVEMPs) during visuo-vestibular stimulation in a sample of 7 male and 11 female human subjects. In 9 of the 18 subjects we were able to record EPs reliably in the form of an early biphasic positive-negative wave with latencies similar to 12 and 17 ms ipsilateral to head acceleration direction (P12-N17) and a slightly later, contralateral, biphasic positive-negative wave with latencies similar to 19 and 23 ms (P19-N23). The amplitudes of the responses varied widely between subjects. Both P12 and N23 EPs were modulated by the mode of visual stimulation, larger for vection (sense of movement) compared with optokinetic nystagmus and for congruent movement. We suggest that the EPs measured over the posterior fossa are a manifestation of climbing fiber responses of cerebellar cortical Purkinje cells. i.e.. a form of vestibular cerebellar EP (VsCEP). The two subject groups with and without VsCEPs were distinguished by the magnitude of their OVEMPs and their subjective experience of vection. The modulation of VsCEPs by visual context may be a manifestation of cerebellar control of linear vestibular ocular reflex gain.
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