Vestibular-dependent inter-stimulus interval effects on sound evoked potentials of central origin

Electrophysiological Activity from the Eye Muscles, Cerebellum and Cerebrum During Reflexive (Classical Pavlovian) Versus Voluntary (Ivanov-Smolensky) Eye-Blink Conditioning

We report an experiment to investigate the role of the cerebellum and cerebrum in motor learning of timed movements. Eleven healthy human subjects were recruited to perform two experiments, the first was a classical eye-blink conditioning procedure with an auditory tone as conditional stimulus (CS) and vestibular unconditional stimulus (US) in the form of a double head-tap. In the second experiment, subjects were asked to blink voluntarily in synchrony with the double head-tap US preceded by a CS, a form of Ivanov-Smolensky conditioning in which a command or instruction is associated with the US. Electrophysiological recordings were made of extra-ocular EMG and EOG at infra-ocular sites (IO1/2), EEG from over the frontal eye fields (C3'/C4') and from over the posterior fossa over the cerebellum for the electrocerebellogram (ECeG). The behavioural outcomes of the experiments showed weak reflexive conditioning for the first experiment despite the double tap but robust, well-synchronised voluntary conditioning for the second. Voluntary conditioned blinks were larger than the reflex ones. For the voluntary conditioning experiment, a contingent negative variation (CNV) was also present in the EEG leads prior to movement, and modulation of the high-frequency EEG occurred during movement. US-related cerebellar activity was prominent in the high-frequency ECeG for both experiments, while conditioned response-related cerebellar activity was additionally present in the voluntary conditioning experiment. These results demonstrate a role for the cerebellum in voluntary (Ivanov-Smolensky) as well as in reflexive (classical Pavlovian) conditioning.

Central Representation of Cervical Vestibular Evoked Myogenic Potentials

Sensitivity of vestibular system to sounds (SVSS) can be measureable by cervical vestibular evoked myogenic potentials (cVEMPs). The aim of this study is to investigate central representation of vestibular system sensitivity to sound. The research was conducted in 2022-2023 by searching English language databases. The criterion for selecting documents was their overlap with the aim of this work. The animals studies were not included. The saccule is stimulated by sounds, that are transmitted through air and bone conduction. Utricle and semicircular canals are activated only by the vibrations. The afferent nerve fibers of the vestibular system project to the temporal, frontal, parietal, primary visual cortex, insula and the cingulate cortex. There is a relationship between normal results of the cVEMPs and these parameters. Improved phonemes recognition scores and word recognition scores in white noise, the efficiency of auditory training, incraed amplitude of the auditory brainstem responses to 500 HZ tone burst. Learning the first words is not only based on the hearing and other senses participate. The auditory object is a three-dimensional imaging in people's minds, when they hear a word. The words expressed by a speaker create different auditory objects in people's minds. Each of these auditory objects has its own color, shape, aroma and characteristics. For the formation of the auditory objects, all senses and whole areas of the brain contribute. Like other senses, central representation of vestibular system sensitivity to sound are also involved in the formation of auditory objects.

Vestibular-Evoked Cerebral Potentials

The human vestibular cortex has mostly been approached using functional magnetic resonance imaging and positron emission tomography combined with artificial stimulation of the vestibular receptors or nerve. Few studies have used electroencephalography and benefited from its high temporal resolution to describe the spatiotemporal dynamics of vestibular information processing from the first milliseconds following vestibular stimulation. Evoked potentials (EPs) are largely used to describe neural processing of other sensory signals, but they remain poorly developed and standardized in vestibular neuroscience and neuro-otology. Yet, vestibular EPs of brainstem, cerebellar, and cortical origin have been reported as early as the 1960s. This review article summarizes and compares results from studies that have used a large range of vestibular stimulation, including natural vestibular stimulation on rotating chairs and motion platforms, as well as artificial vestibular stimulation (e.g., sounds, impulsive acceleration stimulation, galvanic stimulation). These studies identified vestibular EPs with short latency (<20 ms), middle latency (from 20 to 50 ms), and late latency (>50 ms). Analysis of the generators (source analysis) of these responses offers new insights into the neuroimaging of the vestibular system. Generators were consistently found in the parieto-insular and temporo-parietal junction-the core of the vestibular cortex-as well as in the prefrontal and frontal areas, superior parietal, and temporal areas. We discuss the relevance of vestibular EPs for basic research and clinical neuroscience and highlight their limitations.

Source analyses of axial and vestibular evoked potentials associated with brainstem-spinal reflexes show cerebellar and cortical contributions

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.

The role of delta and theta oscillations during ego-motion in healthy adult volunteers

The successful cortical processing of multisensory input typically requires the integration of data represented in different reference systems to perform many fundamental tasks, such as bipedal locomotion. Animal studies have provided insights into the integration processes performed by the neocortex and have identified region specific tuning curves for different reference frames during ego-motion. Yet, there remains almost no data on this topic in humans.

In this study, an experiment originally performed in animal research with the aim to identify brain regions modulated by the position of the head and eyes relative to a translational ego-motion was adapted for humans. Subjects sitting on a motion platform were accelerated along a translational pathway with either eyes and head aligned or a 20° yaw-plane offset relative to the motion direction while EEG was recorded.

Using a distributed source localization approach, it was found that activity in area PFm, a part of Brodmann area 40, was modulated by the congruency of translational motion direction, eye, and head position. In addition, an asymmetry between the hemispheres in the opercular-insular region was observed during the cortical processing of the vestibular input. A frequency specific analysis revealed that low-frequency oscillations in the delta- and theta-band are modulated by vestibular stimulation. Source-localization estimated that the observed low-frequency oscillations are generated by vestibular core-regions, such as the parieto-opercular region and frontal areas like the mid-orbital gyrus and the medial frontal gyrus.

Investigating the vestibular system using modern imaging techniques-A review on the available stimulation and imaging methods

The vestibular organs, located in the inner ear, sense linear and rotational acceleration of the head and its position relative to the gravitational field of the earth. These signals are essential for many fundamental skills such as the coordination of eye and head movements in the three-dimensional space or the bipedal locomotion of humans. Furthermore, the vestibular signals have been shown to contribute to higher cognitive functions such as navigation. As the main aim of the vestibular system is the sensation of motion it is a challenging system to be studied in combination with modern imaging methods. Over the last years various different methods were used for stimulating the vestibular system. These methods range from artificial approaches like galvanic or caloric vestibular stimulation to passive full body accelerations using hexapod motion platforms, or rotatory chairs. In the first section of this review we provide an overview over all methods used in vestibular stimulation in combination with imaging methods (fMRI, PET, E/MEG, fNIRS). The advantages and disadvantages of every method are discussed, and we summarize typical settings and parameters used in previous studies. In the second section the role of the four imaging techniques are discussed in the context of vestibular research and their potential strengths and interactions with the presented stimulation methods are outlined.

Vestibular cerebellar evoked potentials in humans and their modulation during optokinetic stimulation

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 ~12 and 17 ms ipsilateral to head acceleration direction (P12-N17) and a slightly later, contralateral, biphasic positive-negative wave with latencies ~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.

NEW & NOTEWORTHY We report likely vestibular cerebellar evoked potentials (VsCEPs) produced by lateral head impulses recorded in intact humans over the posterior fossa. VsCEPs occurred as short-latency P12-N17 waves ipsilateral to the direction of head motion and as P19-N23 contralaterally and were present in half our subjects. Their properties suggest that the VsCEPs may be of a climbing-fiber origin. VsCEPs are related to the perception of motion and, possibly, control of linear vestibular ocular reflex gain.

The inion response revisited: evidence for a possible cerebellar contribution to vestibular-evoked potentials produced by air-conducted sound stimulation

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°, 0°, and +20° 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. Short-latency 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.NEW & NOTEWORTHY Loud sounds were used to activate vestibular receptors in human volunteers and the effects of head and eye position studied for short-latency responses. A potential (p10/n17) recorded in the parieto-occipital leads showed behavior not expected for a response with a myogenic origin. Source modeling suggested a possible origin from the cerebellum. It may represent a new indicator of human vestibulocerebellar function.