Analysis of 3D spatial trajectories in Parkinsonian, essential and physiological tremors.

The clinical differentiation of the tremor in Parkinson's disease (PD) and essential tremor (ET) can sometimes be challenging, especially in the early stage of the disease. As different neural oscillators are involved in the generation of these two types of tremor, their trajectorial analysis could also be different. The goal of this study was to investigate whether some disease-specific patterns related to their tremor trajectories in fact exist. The three-axial accelerometer signals of the hand tremor obtained from a total of 369 participants [49 with PD, 25 with isolated resting tremor (iRT), 133 with ET, and finally 162 normal subjects with physiological tremor (Ph)] were subjected to vector analysis using a custom-made mathematical program. Subsequently, detailed trajectorial analysis was performed. The key discrimination ability between the PD and ET groups was represented by the ratio of the vector in the y-z plane and the spatial vector. The great majority of the patients with PD and iRT showed significantly higher values as compared to those with ET. The differences between the PD and iRT groups and between ET and Ph were not statistically significant. We suggest that the newly introduced three-axial accelerometry with analysis of tremor trajectories could be beneficial in differentiating between tremors in PD and ET.

Some quantitative EEG features in default mode resting state network under general anaesthesia.

OBJECTIVES: The default mode resting state network (DMRSN) constitutes a circuit which is active in conditions when the subject is at rest. We tested the hypothesis that its function will be altered during unconsciousness. METHODS: Changes in the mean squared coherences in five conventional frequency bands (delta to gamma) in DMRSN during general anaesthesia (GA) were investigated in 39 patients. They were compared with the normal EEG of 86 alert subjects, severely abnormal EEG of 112 patients with dementia and/or encephalopathy, and the mathematical model of brain death. RESULTS: Anaesthetised patients showed significant decrease in the gamma coherence in the posterior area of the DMRSN compared to both the control group and the patients with dementia and/or encephalopathy. Among the anaesthetized patients 21 had a clear burst suppression pattern with prolonged epochs of suppression in EEG. In suppressed EEG segment the differences between the connections of the anterior to posterior parts and connections between the posterior parts of the DMRSN were almost lost. However, they still showed highly significant differences in most items when compared with coherences in the mathematical model of brain death. CONCLUSION: The functional connectivity in the DMRSN could be a reliable and robust method for assessing the depth of anaesthesia and maybe also disorders of consciousness in general. The mean squared coherences in the gamma frequency band indicated the highest sensitivity for the depth of unconsciousness. The measure is not dependent on the diffused slowing in dementia or encephalopathy patients as long as they remain in a full consciousness.

Direction-dependent excitatory and inhibitory ocular vestibular-evoked myogenic potentials (oVEMP) produced by oppositely directed accelerations along the midsagittal axis of the head [corrected].

Oppositely directed displacements of the head need oppositely directed vestibulo-ocular reflexes (VOR), i.e. compensatory responses. Ocular vestibular-evoked myogenic potentials (oVEMPs) mainly reflect the synchronous extraocular muscle activity involved in the process of generating the VOR. The oVEMPs recorded beneath the eyes when looking up represent electro-myographic responses mainly of the inferior oblique muscle. We aimed: (1) to study the properties of these responses as they were produced by head acceleration impulses to the forehead and to the back of the head; (2) to investigate the relationships between these responses and the 3-D linear head accelerations that might reflect the true stimulus that acts on the vestibular hair cells. We produced backward- and forward-directed acceleration stimuli in four conditions (positive and negative head acceleration impulses to the hairline and to the inion) in 16 normal subjects. The oVEMPs produced by backward- and forward-directed accelerations of the head showed consistent differences. They were opposite in the phase. The responses produced by backward accelerations of the head began with an initial negativity, n11; conversely, those produced by accelerations directed forward showed initially a positive response, p11. There was a high inter-subject correlation of head accelerations along the head anteroposterior and transverse axes, but almost no correlation of accelerations along the vertical axis of the head. We concluded that backward-directed head accelerations produced an initial excitatory response, and forward-directed accelerations of the head were accompanied by an initial inhibitory response. These responses showed dependence on acceleration direction in the horizontal plane of the head. This could be consistent with activation of the utricle.

Vestibulo-ocular (oVEMP) responses produced by bone-conducted sound stimuli applied to the mid-sagittal plane of the head.

Recently several studies have yielded evidence that impulses of bone-conducted (BC) sound can produce short-latency myogenic responses in the extraocular muscles, which are probably mediated by otolithic afferents. These responses, although miniscule, can be recorded with surface electrodes and are termed ocular vestibular evoked myogenic potentials (oVEMP). It is assumed that in response to low-frequency BC-sound stimuli the head moves predominantly along the axis from the site of the applied stimulus to the opposite side. Thus, oppositely-directed accelerations along a particular axis would produce oppositely-directed compensatory vestibulo-ocular responses (VOR) and oVEMPs. The aim of this study was to investigate whether the oVEMPs would reflect these direction-dependent VOR responses. Single cycles of 125 and 250 Hz BC tones were applied to opposite sides of two approximately orthogonal, naso-occipital (x) and vertical (z) axes of the head. oVEMP responses were recorded with standard bilateral vertical EOG montages. The responses in all twelve healthy subjects showed consistent differences with regard to the latency and/or shape of the response to stimuli applied to opposite sides of the head. These differences likely reflect different patterns of electro-myographic activity of the extraocular muscles, which may be mediated by groups of vestibular (probably otolithic) afferents with differently-orientated spatial polarization vectors.

Influence of cerebellar stereotactic stimulation on left-right electrodermal information transference in a patient with cerebral palsy.

BACKGROUND AND OBJECTIVES: Recent evidence indicates that cerebral palsy is connected to specific autonomic dysregulation between sympathetic and parasympathetic efferent pathways, likely linked to hemispheric influences. These findings suggest a hypothesis that contralateral interhemispheric disinhibition, which may occur on various levels of brain processing including motor functions, could be linked to specific functional dysregulation and structural lesions, which may play a specific role in the modulation of autonomic functions and lead to autonomic dysregulation in cerebral palsy. METHOD: With the aim of comparing autonomic functions as they relate to interhemispheric modulatory influences during therapeutically indicated stereotactic cerebellar stimulation, we have performed bilateral electrodermal activity measurement and calculations of pointwise transinformation (PTI) in a patient with cerebral palsy. Measurement was performed during therapeutic deep cerebellar stimulation in two cerebellar areas in anterior cerebellar lobe-culmen (left electrode) and central lobule-superior cerebellar peduncle (right electrode). RESULTS: The results indicate that information transference (PTI) is able to distinguish the states related to specific cerebellar stimulations and that lowest levels of the PTI have been found during stimulation of the central lobule-superior cerebellar peduncle (electrode deepest contact 1), indicating a significantly increased level of inhibition between the left and right sides. CONCLUSION: The results may present potentially useful clinical findings indicating that increased PTI calculated from electrodermal activity could indirectly indicate disinhibitory activity as a possible indicator of a failure of interhemispheric communication that could explain some specific pathogenetic mechanisms in cerebral palsy. Nevertheless, these results need detailed confirmation in further research, as well as reliable clinical evaluation of their usefulness in the therapy of cerebral palsy.

Galvanic ocular vestibular evoked myogenic potentials provide new insight into vestibulo-ocular reflexes and unilateral vestibular loss.

OBJECTIVE: Synchronous extraocular muscle activity can be recorded from around the eyes at the beginning of a vestibular-evoked eye movement (ocular vestibular evoked myogenic potentials, OVEMPs). As galvanic vestibular stimulation (GVS) evokes the vestibulo-ocular reflex, we wished to investigate GVS-evoked OVEMPs. METHODS: We stimulated 10 normals and 6 patients with unilateral vestibular loss (uVL) with bi/unipolar 4 mA, 2 ms current steps at the mastoid. OVEMPs were recorded from electrodes placed superior and inferior to the eyes. RESULTS: OVEMPs were present beneath both eyes in all normal subjects: an initial positivity ipsilateral to the cathodal electrode (peak latency 9.9 ms, amplitude 1.3 microV) and an initial negativity contralateral to the cathode (8.8 ms, 2.4 microV). In the patients, stimulation of the affected side produced little or no response. Stimulation of the intact side produced only contralateral responses. CONCLUSIONS: The infra-orbital response is likely produced primarily by the inferior obliques, producing conjugate torsion away from the cathode. The projection to the ipsilateral eye depends upon normal vestibular function on the contralateral side. SIGNIFICANCE: OVEMPs can be evoked by GVS. While bilateral effects are obtained with unilateral stimulation in normals, the primary vestibular pathway to the inferior oblique in humans is crossed.