Pointing in cervical dystonia patients.

Introduction: The normal hemispheric balance can be altered by the asymmetric sensorimotor signal elicited by Cervical Dystonia (CD), leading to motor and cognitive deficits. Methods: Directional errors, peak velocities, movement and reaction times of pointing towards out-of-reach targets in the horizontal plane were analysed in 18 CD patients and in 11 aged-matched healthy controls. Results: CD patients displayed a larger scatter of individual trials around the average pointing direction (variable error) than normal subjects, whatever the arm used, and the target pointed. When pointing in the left hemispace, all subjects showed a left deviation (constant error) with respect to the target position, which was significantly larger in CD patients than controls, whatever the direction of the abnormal neck torsion could be. Reaction times were larger and peak velocities lower in CD patients than controls. Discussion: Deficits in the pointing precision of CD patients may arise from a disruption of motor commands related to the sensorimotor imbalance, from a subtle increase in shoulder rigidity or from a reduced agonists activation. Their larger left bias in pointing to left targets could be due to an increased right parietal dominance, independently upon the direction of head roll/jaw rotation which expands the left space representation and/or increases left spatial attention. These deficits may potentially extend to tracking and gazing objects in the left hemispace, leading to reduced skills in spatial-dependent motor and cognitive performance.

EEG Theta Dynamics within Frontal and Parietal Cortices for Error Processing during Reaching Movements in a Prism Adaptation Study Altering Visuo-Motor Predictive Planning.

Modulation of frontal midline theta (fmθ) is observed during error commission, but little is known about the role of theta oscillations in correcting motor behaviours. We investigate EEG activity of healthy partipants executing a reaching task under variable degrees of prism-induced visuo-motor distortion and visual occlusion of the initial arm trajectory. This task introduces directional errors of different magnitudes. The discrepancy between predicted and actual movement directions (i.e. the error), at the time when visual feedback (hand appearance) became available, elicits a signal that triggers on-line movement correction. Analysis were performed on 25 EEG channels. For each participant, the median value of the angular error of all reaching trials was used to partition the EEG epochs into high- and low-error conditions. We computed event-related spectral perturbations (ERSP) time-locked either to visual feedback or to the onset of movement correction. ERSP time-locked to the onset of visual feedback showed that fmθ increased in the high- but not in the low-error condition with an approximate time lag of 200 ms. Moreover, when single epochs were sorted by the degree of motor error, fmθ started to increase when a certain level of error was exceeded and, then, scaled with error magnitude. When ERSP were time-locked to the onset of movement correction, the fmθ increase anticipated this event with an approximate time lead of 50 ms. During successive trials, an error reduction was observed which was associated with indices of adaptations (i.e., aftereffects) suggesting the need to explore if theta oscillations may facilitate learning. To our knowledge this is the first study where the EEG signal recorded during reaching movements was time-locked to the onset of the error visual feedback. This allowed us to conclude that theta oscillations putatively generated by anterior cingulate cortex activation are implicated in error processing in semi-naturalistic motor behaviours.

A case of post-traumatic minimally conscious state reversed by midazolam: Clinical aspects and neurophysiological correlates.

PURPOSE: We describe the case of a subject in a post-traumatic Minimally Conscious State (MCS) who retrieved full interaction with the environment after midazolam infusion. We studied EEG correlates of the "awakening reaction" in the different domains of frequency, time and cortical topography, along with the intrinsic connectivity within both the task-positive and the linguistic network. METHODS: EEG recorded before and after midazolam administration has been submitted to spectral power analysis, sLORETA analysis and intrinsic connectivity analysis within both functional networks. RESULTS: A critical change in the power spectrum profile was observed after midazolam: a) the power between 1 and 12 Hz decreased, reaching its maximum difference with respect to pre-infusion at about 7 Hz and b) the power between 12 and 30 Hz increased, with a maximum difference at about 15 Hz. At the same time, midazolam induced significant connectivity changes, especially for these two frequency bands, within both functional networks. CONCLUSIONS: We advance some hypotheses about certain aspects of the recovery from the MCS both in terms of anatomo-functional correlations and functional brain systems and we make inferences about the role that some kind of 'catatonic' symptoms might play in determining and/or maintaining this peculiar clinical state.

Spectral parameters modulation and source localization of blink-related alpha and low-beta oscillations differentiate minimally conscious state from vegetative state/unresponsive wakefulness syndrome.

Recently, the cortical source of blink-related delta oscillations (delta BROs) in resting healthy subjects has been localized in the posterior cingulate cortex/precuneus (PCC/PCu), one of the main core-hubs of the default-mode network. This has been interpreted as the electrophysiological signature of the automatic monitoring of the surrounding environment while subjects are immersed in self-reflecting mental activities. Although delta BROs were directly correlated to the degree of consciousness impairment in patients with disorders of consciousness, they failed to differentiate vegetative state/unresponsive wakefulness syndrome (VS/UWS) from minimally conscious state (MCS). In the present study, we have extended the analysis of BROs to frequency bands other than delta in the attempt to find a biological marker that could support the differential diagnosis between VS/UWS and MCS. Four patients with VS/UWS, 5 patients with MCS, and 12 healthy matched controls (CTRL) underwent standard 19-channels EEG recordings during resting conditions. Three-second-lasting EEG epochs centred on each blink instance were submitted to time-frequency analyses in order to extract the normalized Blink-Related Synchronization/Desynchronization (nBRS/BRD) of three bands of interest (low-alpha, high-alpha and low-beta) in the time-window of 50-550 ms after the blink-peak and to estimate the corresponding cortical sources of electrical activity. VS/UWS nBRS/BRD levels of all three bands were lower than those related to both CTRL and MCS, thus enabling the differential diagnosis between MCS and VS/UWS. Furthermore, MCS showed an intermediate signal intensity on PCC/PCu between CTRL and VS/UWS and a higher signal intensity on the left temporo-parieto-occipital junction and inferior occipito-temporal regions when compared to VS/UWS. This peculiar pattern of activation leads us to hypothesize that resting MCS patients have a bottom-up driven activation of the task positive network and thus are tendentially prone to respond to environmental stimuli, even though in an almost unintentional way.

Cortical source of blink-related delta oscillations and their correlation with levels of consciousness.

Recently, blink-related delta oscillations (delta BROs) have been observed in healthy subjects during spontaneous blinking at rest. Delta BROs have been linked with continuous gathering of information from the surrounding environment, which is classically attributed to the precuneus. Furthermore, fMRI studies have shown that precuneal activity is reduced or missing when consciousness is low or absent. We therefore hypothesized that the source of delta BROs in healthy subjects could be located in the precuneus and that delta BROs could be absent or reduced in patients with disorders of consciousness (DOC). To test these hypotheses, electroencephalographic (EEG) activity at rest was recorded in 12 healthy controls and nine patients with DOC (four vegetative states, and five minimally conscious states). Three-second-lasting EEG epochs centred on each blink instance were analyzed in both time- (BROs) and frequency domains (event-related spectral perturbation or ERSP and intertrial coherence or ITC). Cortical sources of the maximum blink-related delta power, corresponding to the positive peak of the delta BROs, were estimated by standardized Low Resolution Electromagnetic Tomography. In control subjects, as expected, the source of delta BROs was located in the precuneus, whereas in DOC patients, delta BROs were not recognizable and no precuneal localization was possible. Furthermore, we observed a direct relationship between spectral indexes and levels of cognitive functioning in all subjects participating in the study. This reinforces the hypothesis that delta BROs reflect neural processes linked with awareness of the self and of the environment.

Reciprocal dynamics of EEG alpha and delta oscillations during spontaneous blinking at rest: a survey on a default mode-based visuo-spatial awareness.

By means of a narrowband wavelet analysis (0.5-6Hz), EEG delta event-related oscillations (EROs), both time- and phase-locked to spontaneous blinking (delta blink-related oscillations or delta BROs), have recently been demonstrated. On the basis of their spatiotemporal characteristics, delta BROs have been proposed as being involved in an automatic mechanism of maintaining awareness in a visuo-spatial context. The aim of the present study was: a) to investigate whether spontaneous blinking was also able to modulate alpha oscillations and, if so, b) whether this modulation was consistent with delta BROs, in order c) to acquire additional information for a better understanding of the cognitive phenomena underlying blinking. Using a broadband (0.5-100 Hz) continuous wavelet transform (CWT), we analysed a total of 189 three-second EEG epochs time-locked to the blinks of seven healthy volunteers. The EEG signals were submitted both to band-pass filtered cross-trial averaging (to obtain frequency-specific BROs) and to alpha event-related synchronization/desynchronization (i.e., blink-related synchronization/desynchronization, BRS/BRD). The alpha oscillations showed: a) an early BRS; b) a BRD in the same temporal window of the delta BROs and, c) a late BRS. We postulate that: a) the early BRS represents the short-term memory maintenance of the last visually perceived trace of the surroundings; b) the alpha BRD is associated with the comparison between the newly perceived image of the environment and its mnestic representation, and, lastly, c) the late BRS is connected with neuronal recovery phenomena.

Blink-related delta oscillations in the resting-state EEG: a wavelet analysis.

Over the past decades, many studies have linked the variations in frequency of spontaneous blinking with certain aspects of information processing and in particular with attention and working memory functions. On the other hand, according to the theory postulated by Crick and Koch, the actual function of primary consciousness is based on the reciprocal interaction between attention and working memory in the automatic and serial mode. The purpose of this study was to investigate for electrophysiological correlates compatible with the cognitive nature of spontaneous blinking, by using the EEG recordings obtained in a group of seven healthy volunteers while they rested quietly though awake, with their eyes open, but not actively engaged in attention-demanding goal-directed behaviours. The global wavelet analysis - at total of 189 three-second EEG epochs time-locked to the blink - revealed an increase in the delta band signal corresponding to the blink. In particular, a reconstruction of the EEG signal by means of inverse-wavelet transform (IWT) showed a blink-related P300-like wave at mid-parietal site. We assumed this phenomenon to represent an electrophysiological sign of the automatic processing of contextual environmental information. This might play a role in maintaining perceptive awareness of the environment at a low level of processing, while the subject is not engaged in attention-demanding tasks but rather introspectively oriented mental activities or free association(s).

Hipnic modulation of cerebellar information processing: implications for the cerebro-cerebellar dialogue.

Recent evidence indicates that during the sleep-waking cycle the forebrain and the cerebellum show parallel changes of their operating capabilities and suggest that cooperation between these two structures plays a different role in the different behavioral states. In particular, a high degree of cerebro-cerebellar cooperation is expected in waking and in paradoxical sleep when enhanced information processing within the cerebellum and the cortex is associated with effective reciprocal cerebro-cerebellar signal transmission. We first speculate that during waking, a state in which a wide range of behaviors is produced by the interaction with the external world, the cerebellum might assist the cortex to develop the neural dynamic patterns which underlie behaviors and that this could be accomplished via cerebellar modulation of both short- and long-range cortical synchronization. In particular, we propose that the cerebellum might favour the automatic triggering of the patterns already acquired, when requested by the context, as well as the acquisition of novel patterns, when found to be of adaptive value, and might even modulate the access to consciousness of brain operations, if producing unpredicted results, by regulating pattern complexity. This proposal is based on the experimental evidence that oscillatory activity may flow within the cerebro-cerebellar loops and that stimulation or lesion of the cerebellar structures affects cortical synchronization. Then we report evidence indicating that during paradoxical sleep, when brain activation occurs in the absence of sensory inflow and motor output, cerebro-cerebellar cooperation mainly favours consolidation of newly acquired waking patterns and/or savings of old patterns from disruption possibly through a non-utilitarian replay process. Finally, we propose that cerebro-cerebellar cooperation weakens during slow wave sleep, given that in this sleep state neuronal activity and excitability decrease both in the cerebellum and in the forebrain and cerebello-cortical signal transmission is at least partially gated at the thalamic level.