Non-invasive recording from the human cerebellum during a classical conditioning paradigm using the otolith-evoked blink reflex

Surface EEG Evidence for Cerebellar Control of Distal Upper Limbs in Humans

Background/Objectives: The cerebellum plays a crucial role in motor control, but its direct electrophysiological investigation in humans is challenging. Electrocerebellograms (ECeGs), recorded via surface electrodes below the inion, have been proposed as a non-invasive method to assess cerebellar activity. However, its interpretation is complicated by potential interference from occipital alpha rhythms and neck muscle signals. This study aimed to investigate whether ECeG signals genuinely reflect cerebellar involvement during upper limb movement and to explore possible confounding influences. Methods: We recorded electroencephalograms (EEGs) from occipital (Oz) and cerebellar electrodes (Cb1 and Cb2), alongside EMGs from forearm muscles in healthy individuals performing sinusoidal (~1 Hz) and tremor-like (~4 Hz) wrist movements. To assess occipital contamination, recordings were obtained under both eyes-open and eyes-closed conditions. Results: Occipital alpha power was present in Cb1 and Cb2 but was less affected by eye-opening than at Oz, suggesting a partially distinct neural source. During the tremor condition, movement-frequency power increased at Cb2 and C3 (corresponding to the ipsilateral cerebellar hemisphere and contralateral motor cortex), indicating authentic cerebellar activity. No significant movement-related EEG changes were observed during sinusoidal movements, likely due to weaker neuronal synchronization. Conclusions: These findings suggest that ECeGs can detect cerebellar signals linked to movement, especially during faster and rhythmic motions, and are only moderately affected by occipital contamination. This supports the feasibility of non-invasive cerebellar electrophysiology and underscores the need for further methodological refinement to enhance signal specificity.

Distinct movement related changes in EEG and ECeG power during finger and foot movement

Voluntary movement is known to be associated with cerebrally generated movement-related slow potentials and parallel changes in spectral power. The cerebellar and cerebral cortices are powerfully connected via reciprocal, crossed projections which mediate their coordination in motor, as well as cognitive and affective processes. The cerebellum participates in movement and the question remains as to the nature of movement related changes in power if any which might occur over the cerebellum. In a sample of six healthy adult subjects, we recorded EEG and the electro-cerebellogram (ECeG) with a 10 % cerebellar extension montage during voluntary left and right index finger and foot movements. EMG was recorded from finger extensors and flexors and from the tibialis anterior and soleus muscles and was used to generate triggers for movement related averaging (-2000 to + 2000 ms). Wavelet power was computed over the 4 s epoch for each electrode. For statistical analysis, cerebral and cerebellar grids centred around Cz and SIz were investigated, using both average and linked-ear references. Statistically significant movement related changes were observed in both cerebral and cerebellar power, most significantly in the high delta band (1.5 to 3 Hz), for both montages. In contrast to Cz where power increased premovement, power was reduced over the cerebellum. High-frequency pause-bursting was also observed in the ECeG around the time of movement. Our results indicate that recordings over the cerebellum show distinct changes from those over Cz and in particular show a fall in power during the premovement period.

Cerebellar Non-Invasive Brain Stimulation: A Frontier in Chronic Pain Therapy

Chronic pain poses a widespread and distressing challenge; it can be resistant to conventional therapies, often having significant side effects. Non-invasive brain stimulation (NIBS) techniques offer promising avenues for the safe and swift modulation of brain excitability. NIBS approaches for chronic pain management targeting the primary motor area have yielded variable outcomes. Recently, the cerebellum has emerged as a pivotal hub in human pain processing; however, the clinical application of cerebellar NIBS in chronic pain treatment remains limited. This review delineates the cerebellum's role in pain modulation, recent advancements in NIBS for cerebellar activity modulation, and novel biomarkers for assessing cerebellar function in humans. Despite notable progress in NIBS techniques and cerebellar activity assessment, studies targeting cerebellar NIBS for chronic pain treatment are limited in number. Nevertheless, positive outcomes in pain alleviation have been reported with cerebellar anodal transcranial direct current stimulation. Our review underscores the potential for further integration between cerebellar NIBS and non-invasive assessments of cerebellar function to advance chronic pain treatment strategies.

Head Orientation Modulates Vestibular Cerebellar Evoked Potentials (VsCEPs) and Reflexes Produced by Impulsive Mastoid and Midline Skull Stimulation

The cerebellum plays a critical role in the modulation of vestibular reflexes, dependent on input from proprioceptive afferents. The mechanism of this cerebellar control is not well understood. In a sample of 11 healthy human subjects, we investigated the effects of head orientation on ocular, cervical, postural and cerebellar short latency potentials evoked by impulsive stimuli applied at both mastoids and midline skull sites. Subjects were instructed to lean backwards with the head positioned straight ahead or held rotated in different degrees of yaw towards the right and left sides. Impulsive mastoid stimulation, a potent method of utricular stimulation, produced localised vestibular cerebellar evoked potentials (VsCEPs: P12-N17) which were strongly modulated by head orientation. The response was larger on the side opposite to the direction of head rotation and with stimulation on the side of rotation. In contrast, ocular VEMPs (oVEMPs: n10-p16) were present but showed little change with head posture, while cervical VEMPs (cVEMPs: p15-n23) were larger with the head held rotated away from the side of the recording. Postural effects with lateral vestibular stimulation were strongly modulated by head rotation, with more powerful effects occurring bilaterally with stimulation on the side of rotation. The duration of the postural EMG changes was similar to the post-excitation inhibition of the electrocerebellogram (ECeG), consistent with cerebellar participation. We conclude that head rotation selectively affects evoked vestibular reflexes towards different targets, consistent with their physiological roles. Changes in VsCEPs may contribute to the modulation of postural reflexes by the cerebellum.

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.

The blink reflex and its modulation - Part 1: Physiological mechanisms

The blink reflex (BR) is a protective eye-closure reflex mediated by brainstem circuits. The BR is usually evoked by electrical supraorbital nerve stimulation but can be elicited by a variety of sensory modalities. It has a long history in clinical neurophysiology practice. Less is known, however, about the many ways to modulate the BR. Various neurophysiological techniques can be applied to examine different aspects of afferent and efferent BR modulation. In this line, classical conditioning, prepulse and paired-pulse stimulation, and BR elicitation by self-stimulation may serve to investigate various aspects of brainstem connectivity. The BR may be used as a tool to quantify top-down modulation based on implicit assessment of the value of blinking in a given situation, e.g., depending on changes in stimulus location and probability of occurrence. Understanding the role of non-nociceptive and nociceptive fibers in eliciting a BR is important to get insight into the underlying neural circuitry. Finally, the use of BRs and other brainstem reflexes under general anesthesia may help to advance our knowledge of the brainstem in areas not amenable in awake intact humans. This review summarizes talks held by the Brainstem Special Interest Group of the International Federation of Clinical Neurophysiology at the International Congress of Clinical Neurophysiology 2022 in Geneva, Switzerland, and provides a state-of-the-art overview of the physiology of BR modulation. Understanding the principles of BR modulation is fundamental for a valid and thoughtful clinical application (reviewed in part 2) (Gunduz et al., submitted).

Electrophysiological activity from over the cerebellum and cerebrum during eye blink conditioning in human subjects

We report the results of an experiment in which electrophysiological activity was recorded from the human cerebellum and cerebrum in a sample of 14 healthy subjects before, during and after a classical eye blink conditioning procedure with an auditory tone as conditional stimulus and a maxillary nerve unconditional stimulus. The primary aim was to show changes in the cerebellum and cerebrum correlated with behavioral ocular responses. Electrodes recorded EMG and EOG at peri-ocular sites, EEG from over the frontal eye-fields and the electrocerebellogram (ECeG) from over the posterior fossa. Of the 14 subjects half strongly conditioned while the other half were resistant. We confirmed that conditionability was linked under our conditions to the personality dimension of extraversion-introversion. Inhibition of cerebellar activity was shown prior to the conditioned response, as predicted by Albus (1971). However, pausing in high frequency ECeG and the appearance of a contingent negative variation (CNV) in both central leads occurred in all subjects. These led us to conclude that while conditioned cerebellar pausing may be necessary, it is not sufficient alone to produce overt behavioral conditioning, implying the existence of another central mechanism. The outcomes of this experiment indicate the potential value of the noninvasive electrophysiology of the cerebellum.