Downbeat nystagmus: a clinical and pathophysiological review.

Downbeat nystagmus (DBN) is a neuro-otological finding frequently encountered by clinicians dealing with patients with vertigo. Since DBN is a finding that should be understood because of central vestibular dysfunction, it is necessary to know how to frame it promptly to suggest the correct diagnostic-therapeutic pathway to the patient. As knowledge of its pathophysiology has progressed, the importance of this clinical sign has been increasingly understood.

Locally Synthetized 17-β-Estradiol Reverses Amyloid-β-42-Induced Hippocampal Long-Term Potentiation Deficits.

Amyloid beta 1-42 (Aβ42) aggregates acutely impair hippocampal long-term potentiation (LTP) of synaptic transmission, and 17β-estradiol is crucial for hippocampal LTP. We tested whether boosting the synthesis of neural-derived 17β-estradiol (nE2) saves hippocampal LTP by the neurotoxic action of Aβ42. Electrophysiological recordings were performed to measure dentate gyrus (DG) LTP in rat hippocampal slices.

Evaluation of Cochlear Symptoms in Migraine Patients without Vestibular Migraine and/or Ménière's Disease.

Migraine pathogenic pathways may selectively target the cochlea. A qualitative and quantitative analysis of cochlear symptoms in migraine patients without vestibular migraine and/or Méniere's disease was conducted. We examined 60 consecutive patients with history of cochlear symptoms, including fullness, tinnitus, and hearing loss.

Effectiveness of Focal Muscle Vibration in the Recovery of Neuromotor Hypofunction: A Systematic Review.

Adequate physical recovery after trauma, injury, disease, a long period of hypomobility, or simply ageing is a difficult goal because rehabilitation protocols are long-lasting and often cannot ensure complete motor recovery. Therefore, the optimisation of rehabilitation procedures is an important target to be achieved. The possibility of restoring motor functions by acting on proprioceptive signals by unspecific repetitive muscle vibration, focally applied on single muscles (RFV), instead of only training muscle function, is a new perspective, as suggested by the effects on the motor performance evidenced by healthy persons.

Skull-vibration-induced nystagmus test in patients who are candidates for intratympanic gentamicin injection.

Objective: This study aims to evaluate the utility of the skull-vibration-induced nystagmus test (SVINT) in the selection of patients with Ménière's disease (MD) for intratympanic injection of gentamicin. To date the indications for this treatment have been based only on subjective elements.

Methods: A retrospective study was performed in 20 patients diagnosed with unilateral MD.

Induction and Cancellation of Self-Motion Misperception by Asymmetric Rotation in the Light.

Asymmetrical sinusoidal whole-body rotation sequences with half-cycles at different velocities induce self-motion misperception. This is due to an adaptive process of the vestibular system that progressively reduces the perception of slow motion and increases that of fast motion. It was found that perceptual responses were conditioned by four previous cycles of asymmetric rotation in the dark, as the perception of self-motion during slow and fast rotations remained altered for several minutes.

Plastic changes induced by muscle focal vibration: A possible mechanism for long-term motor improvements.

Repetitive focal vibrations can induce positive and persistent after-effects. There is still no satisfactory interpretation of the underlying mechanisms. A rationale, which can provide consistency among different results, is highly desirable to guide both the use of the application and future research.

Adaptive perceptual responses to asymmetric rotation for testing otolithic function.

This study aimed to test the role of the otolithic system in self-motion perception by examining adaptive responses to asymmetric off-axis vertical rotation. Self-movement perception was examined after a conditioning procedure consisting of prolonged asymmetric sinusoidal yaw rotation of the head on a stationary body with hemicycle faster than the other hemicycle. This asymmetric velocity rotation results in a cumulative error in spatial self-motion perception in the upright position that persists over time.

Electroencephalographic response to transient adaptation of vestibular perception.

When given a series of sinusoidal oscillations in which the two hemicycles have equal amplitude but asymmetric velocity, healthy subjects lose perception of the slower hemicycle (SHC), reporting a drift towards the faster hemicycle (FHC). This response is not reflected in the vestibular-ocular reflex, suggesting that the adaptation is of higher order. This study aimed to define EEG correlates of this adaptive response.

Inhibition of androgenic pathway impairs encoding of cerebellar-dependent motor learning in male rats.

Cerebellar-dependent learning is essential for the adaptation of motor and no motor behaviors to changing contexts, and neuroactive steroids-mainly referred to as estrogens-may regulate this process. However, the role of androgens in this process has not been established, although they may affect cerebellar physiology. Thus, this study aims to determine whether the activation of androgenic neural pathways may take part in controlling the vestibuloocular (VOR) and optokinetic reflexes (OKR), which depend on a defined cerebellar circuitry.

Disruption of self-motion perception without vestibular reflex alteration in ménière's disease.

Background: Self-motion misperception has been observed in vestibular patients during asymmetric body oscillations. This misperception is correlated with the patient's vestibular discomfort.

Objective: To investigate whether or not self-motion misperception persists in post-ictal patients with Ménière's disease (MD).

Is the Focal Muscle Vibration an Effective Motor Conditioning Intervention? A Systematic Review.

Mechanical vibration, applied to single or few muscles, can be a selective stimulus for muscle spindles, able to modify neuromuscular management, inducing short and long-term effects, are now mainly employed in clinic studies. Several studies reported as treatments with focal vibratory (FVT) can influence neuromuscular parameters also in healthy people. However, the application modalities and the consequent effects are remarkably fragmented.

Adaptive Balance in Posterior Cerebellum.

Vestibular and optokinetic space is represented in three-dimensions in vermal lobules IX-X (uvula, nodulus) and hemisphere lobule X (flocculus) of the cerebellum. Vermal lobules IX-X encodes gravity and head movement using the utricular otolith and the two vertical semicircular canals. Hemispheric lobule X encodes self-motion using optokinetic feedback about the three axes of the semicircular canals.

Auditory perception is influenced by the orientation of the trunk relative to a sound source.

The study investigated how hearing depends on the whole body, head and trunk orientation relative to a sound source. In normal hearing humans we examined auditory thresholds and their ability to recognize logatomes (bi-syllabic non-sense words) at different whole body, head and trunk rotation relative to a sound source. We found that auditory threshold was increased and logatome recognition was impaired when the body or the trunk were rotated 40° away from a sound source compared to when the body or the trunk was oriented towards the sound source.

Rapid Estrogenic and Androgenic Neurosteroids Effects in the Induction of Long-Term Synaptic Changes: Implication for Early Memory Formation.

Mounting experimental evidence demonstrate that sex neuroactive steroids (neurosteroids) are essential for memory formation. Neurosteroids have a profound impact on the function and structure of neural circuits and their local synthesis is necessary for the induction of both long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission and for neural spine formation in different areas of the central nervous system (CNS). Several studies demonstrated that in the hippocampus, 17β-estradiol (E2) is necessary for inducing LTP, while 5α-dihydrotestosterone (DHT) is necessary for inducing LTD.

Different time course of compensation of subjective visual vertical and ocular torsion after acute unilateral vestibular lesion.

Purpose: Time course of the recovery of otolithic dis-function caused by superior vestibular neuritis has been examined in fifteen patients.

Methods: The subjective visual vertical (SVV) and the ocular cyclotorsion (OT) have been measured four times after the acute episode up to 1 year RESULTS: In most of the patients the SVV tilt returned to control values within few months (3-6 months) after the acute episode, while OT remained out of normal range in almost all patients a year later.

Conclusion: The abnormal OT observed after 1 year from the acute episode of vestibular neuritis, suggests that the otolithic receptors remained altered for several months and the OT may be a good indicator of the entity of the residual peripheral otolithic lesion.

Sensory inflow manipulation induces learning-like phenomena in motor behavior.

Purpose: Perceptual and goal-directed behaviors may be improved by repetitive sensory stimulations without practice-based training. Focal muscle vibration (f-MV) modulating the spatiotemporal properties of proprioceptive inflow is well-suited to investigate the effectiveness of sensory stimulation in influencing motor outcomes. Thus, in this study, we verified whether optimized f-MV stimulation patterns might affect motor control of upper limb movements.

Bidirectional Synaptic Plasticity Is Driven by Sex Neurosteroids Targeting Estrogen and Androgen Receptors in Hippocampal CA1 Pyramidal Neurons.

Neuroactive estrogenic and androgenic steroids influence synaptic transmission, finely modulating synaptic plasticity in several brain regions including the hippocampus. While estrogens facilitate long-term potentiation (LTP), androgens are involved in the induction of long-term depression (LTD) and depotentiation (DP) of synaptic transmission. To examine sex neurosteroid-dependent LTP and LTD in single cells, patch-clamp recordings from hippocampal CA1 pyramidal neurons of male rats and selective antagonists for estrogen receptors (ERs) and androgen (AR) receptors were used.

17 beta-estradiol synthesis modulates cerebellar dependent motor memory formation in adult male rats.

Neurosteroid 17 beta-estradiol (E2) is a steroid synthesized de novo in the nervous system that might influence neuronal activity and behavior. Nevertheless, the impact of E2 on the functioning of those neural systems in which it is slightly synthesized is less questioned. The vestibulo-ocular reflex (VOR) adaptation, may provide an ideal arena for investigating this issue.

Acute inhibition of estradiol synthesis impacts vestibulo-ocular reflex adaptation and cerebellar long-term potentiation in male rats.

The vestibulo-ocular reflex (VOR) adaptation is an ideal model for investigating how the neurosteroid 17 beta-estradiol (E2) contributes to the modification of behavior by regulating synaptic activities. We hypothesized that E2 impacts VOR adaptation by affecting cerebellar synaptic plasticity at the parallel fiber-Purkinje cell (PF) synapse. To verify this hypothesis, we investigated the acute effect of blocking E2 synthesis on gain increases and decreases in adaptation of the VOR in male rats using an oral dose (2.

Sensorimotor Control of the Shoulder in Professional Volleyball Players With Isolated Infraspinatus Muscle Atrophy.

Context: Isolated infraspinatus muscle atrophy (IIMA) affects only the hitting shoulder of overhead-activity athletes and is caused by suprascapular nerve neuropathy. No study has assessed the static and dynamic stability of the shoulder in overhead professional athletes with IIMA to reveal possible shoulder sensorimotor alterations.

Objective: To assess the shoulder static stability, dynamic stability, and strength in professional volleyball players with IIMA and in healthy control players.

Knee flexion with quadriceps cocontraction: A new therapeutic exercise for the early stage of ACL rehabilitation.

Quadriceps strengthening exercises designed for the early phase of anterior cruciate ligament (ACL) rehabilitation should limit the anterior tibial translation developed by quadriceps contraction near full knee extension, in order to avoid excessive strain on the healing tissue. We hypothesize that knee-flexion exercises with simultaneous voluntary contraction of quadriceps (voluntary quadriceps cocontraction) can yield considerable levels of quadriceps activation while preventing the tibia from translating forward relative to the femur. Electromyographic activity in quadriceps and hamstring muscles was measured in 20 healthy males during isometric knee-flexion exercises executed near full knee extension with maximal voluntary effort of quadriceps cocontraction and external resistance (R) ranging from 0% to 60% of the 1-repetition maximum (1RM).

Adaptive Changes in the Perception of Fast and Slow Movement at Different Head Positions.

Background: This paper examines the subjective sense of orientation during asymmetric body rotations in normal subjects.

Methods: Self-motion perception was investigated in 10 healthy individuals during asymmetric whole-body rotation with different head orientations. Both on-vertical axis and off-vertical axis rotations were employed.

Different synaptic stimulation patterns influence the local androgenic and estrogenic neurosteroid availability triggering hippocampal synaptic plasticity in the male rat.

Electrophysiological recordings were used to investigate the role of the local synthesis of 17β-estradiol (E2) and 5α-dihydrotestosterone (DHT) on synaptic long-term effects induced in the hippocampal CA1 region of male rat slices. Long-term depression (LTD) and long-term potentiation (LTP), induced by different stimulation patterns, were examined under the block of the DHT synthesis by finasteride (FIN), and the E2 synthesis by letrozole (LET). We used low frequency stimulation (LFS) for LTD, high frequency stimulation (HFS) for LTP, and intermediate patterns differing in duration or frequency.

Neo-synthesis of estrogenic or androgenic neurosteroids determine whether long-term potentiation or depression is induced in hippocampus of male rat.

Estrogenic and androgenic steroids synthesized in the brain may rapidly modulate synaptic plasticity interacting with specific membrane receptors. We explored by electrophysiological recordings in hippocampal slices of male rat the influence of 17β-estradiol (E2) and 5α-dihydrotestosterone (DHT) neo-synthesis on the synaptic changes induced in the CA1 region. Induction of long-term depression (LTD) and depotentiation (DP) by low frequency stimulation (LFS, 15 min-1 Hz) and of long-term potentiation (LTP) by high frequency stimulation (HFS, 1 s-100 Hz), medium (MFS, 1 s-50 Hz), or weak (WFS, 1 s-25 Hz) frequency stimulation was assayed under inhibitors of enzymes converting testosterone (T) into DHT (5α-reductase) and T into E2 (P450-aromatase).