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Responses of Purkinje-cells of the cerebellar anterior vermis to stimulation of vestibular and somatosensory receptors.
No full textIn decerebrate cats, sinusoidal rotation of the forepaw around the wrist modifies the activity of the ipsilateral forelimb extensor triceps brachii (TB) and leads to plastic changes of adaptive nature in the gain of vestibulospinal (VS) reflexes (VSRs). Both effects are depressed by functional inactivation of the cerebellar anterior vermis, which also decreases the gain of VSRs. In order to better understand the mechanisms of these phenomena, the simple spike activity of Purkinje (P-) cells was recorded from the vermal cortex of the cerebellar anterior lobe during individual and/or combined stimulation of somatosensory wrist, neck and vestibular receptors. About one third of the recorded units were affected by sinusoidal rotation of the ipsilateral forepaw around the wrist axis (0.16 Hz, ±10°). Most of these neurons (∼60%) increased their activity during ventral flexion of the wrist and decreased it during the oppositely directed movement, with an average phase lag of −141° with respect to the position of maximal dorsiflexion. The remaining cells (∼40%) were excited during dorsiflexion of the wrist, with an average phase lead of 59° with respect to the extreme dorsal flexion. Both populations showed comparable response gains, with an average value of 0.42±0.52, S.D., imp/s/deg. About half of the recorded units were also tested during sinusoidal roll tilt of the animal around the longitudinal axis (0.16 Hz, ±10°), leading to stimulation of labyrinthine receptors. When both stimuli were applied simultaneously, the responses to combined stimulation usually corresponded to the sum of individual responses. While the phase distribution of somatosensory responses was clearly bimodal, vestibular responses showed phase angle values uniformly scattered between ±180° and 0°, so that, during combined stimulation, each neuron could be maximally activated by coupling the two stimuli with a particular phase relation. Finally, a proportion of the recorded neurons was also tested during sinusoidal rotation of the body around its longitudinal axis, with the head fixed in space, leading to stimulation of neck receptors. The proportion of neurons affected by individual stimulation of vestibular or neck receptors (81% and 72%, respectively) was larger than that of wrist-driven neurons. Convergence of signals from vestibular, somatosensory wrist and neck receptors was found in 18% of the neurons analyzed. In conclusion, the results of this study show that somatosensory signals from the forelimb: i) modulate the activity of a sizeable proportion of neurons located within the cerebellar anterior vermis and ii) interact widely with labyrinthine and neck signals at this level. Moreover, iii) this corticocerebellar region is largely dominated by vestibular and neck signals that may be utilized to build up a neuronal representation of the position of body in space. These findings suggest that: 1) the modulation of TB activity induced by rotation of the ipsilateral wrist may at least partially depend upon the simultaneous changes in P-cell activity and 2) the interaction of vestibular and somatosensory wrist signals at P-cell level may represent the substrate of the plastic changes that affect the VSR when animal tilt and wrist rotation are driven together. A preliminary report of these data has been presented [Bruschini L, Manzoni D, Pompeiano O (2000) Responses of cerebellar Purkinje cells to forepaw rotation in decerebrate cat. Pflügers Arch 440:R31]
Coupling sensory inputs to the appropriate motor responses: new aspects of cerebellar function.
No full textAbstract
It is known that proprioceptive signals modify the spatial organization of the postural reflexes, thus leading to body stability. The neurophysiological basis of this phenomenon are at present unknown. The present report documents that, in decerebrate cat, body-to-head rotation in the horizontal plane modified the preferred response direction to labyrinthine stimulation of the forelimb extensor triceps brachii. Such direction resulted always perpendicular to the longitudinal body axis of the animal, whatever its relative position with respect to the head could be. The rotation of the preferred response direction of the triceps was greatly reduced by functional inactivation of the ipsilateral cerebellar vermis. On the other hand, following body-to-head displacement, the preferred response directions of the corresponding P-cells tended, on the average, to rotate in the same direction and by the same angle as the body. We propose that the neck input finely tunes parallel vestibular channels, endowed with different spatial and temporal properties, impinging upon P-cells, thus modifying their responses to animal tilt and, as a consequence, the spatial properties of VS reflexes. It is possible that, by a similar mechanism, the cerebellum may contribute to the changes in reference frame occurring in sensorimotor transformations of reflex and voluntary nature
Causal Symbolic Information Transfer for the Assessment of functional Brain-Heart Interplay through EEG Microstates Occurrences: a proof-of-concept study
No full textElectroencephalography (EEG) microstates analysis provides a sequence of topographies representing the scalp-related electric field over time, and each microstate is synthetically represented by a symbol. Despite recent advances on functional brain-heart interplay (BHI) assessment, to our knowledge no methodology takes EEG microstates into account to relate the causal heartbeat dynamics. Moreover, standard BHI methods are tailored to a single EEG-channel analysis, neglecting the comprehensive information associated with a multichannel cluster or a whole-brain activity. To overcome these limitations, we devised a novel methodological frame-work for the assessment of functional BHI that exploits the symbolic representation of both EEG microstates and heart rate variability (HRV) series. Directional BHI quantification is then performed through Kullback-Leibler Divergence (KLD) and Transfer Entropy. The proposed methodology is here preliminarily tested on a dataset gathered from healthy subjects undergoing a resting state and a mental arithmetic task. Except for the KLD in the from-brain-to-heart direction, all other estimates showed significant differences between the two experimental conditions. We conclude that the proposed frame-work may promisingly provide novel insights on brain-heart phenomena through a whole-brain symbolic representation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Neck influences on the spatial properties of vestibulospinal reflexes in decerebrate cats: role of the cerebellar anterior vermis.
No full textAbstract
The vestibulospinal (VS) reflexes elicited by animal rotation modify the activity of limb musculature, thus preserving balance and postural stability. We investigated whether the orientation of these postural responses is strictly dependent upon the direction of head displacement or else can be modified by extralabyrinthine inputs to the goal of stabilizing body position. The experiments were performed in decerebrate cats, in which the effects of static body-to-head displacements were tested on the multiunit EMG responses of the medial head of the triceps brachii to wobble of the whole animal at 0.15 Hz, 10°, both in the clockwise (CW) and counterclockwise (CCW) direction. These stimuli allowed us to determine the muscle response vector, whose orientation component corresponds to the direction of head displacement giving rise to the maximal EMG response. When the animal body was kept straight with respect to the head, the triceps response vector was always oriented close to the transverse axis, pointing to the side-down direction. Following 30°of body-to-head displacement around a vertical axis passing through the first-second cervical joints, the response vectors of both the left and the right muscles shifted in the same direction of body rotation, thus remaining approximately perpendicular to the body axis. The change in muscle vector orientation corresponded on the average to the angle of body-to-head displacement. Only slight changes in amplitude of the muscle responses were observed. These findings imply that the maximal activation of the triceps brachii always occurred for the same direction of body displacement, irrespective of the pattern of discharge of vestibular afferents, which is determined by the direction of head displacement. The rotation of the triceps response vector induced by body-to-head displacement was reduced or suppressed by inactivation of the ipsilateral cerebellar anterior vermis, following local microinjection of the GABA(A) agonist muscimol. These findings indicate that 1) the sensory input which results from changing the body position with respect to the head, probably originating from neck receptors, is able to modify the pattern of the VS reflexes, which appear to be organized in a body-centered reference frame, and 2) the cerebellar vermis is required for the proper execution of this sensorimotor transformation
Responses of Purkinje cells in the cerebellar anterior vermis to off-vertical axis rotation in decerebrate cats.
No full textAbstract
Responses of 67 Purkinje cells (P-cells) and 44 unidentified neurons (U-cells) located in the cerebellar anterior vermis were recorded in decerebrate cats during off-vertical axis rotation (OVER). This stimulus consisted of a slow constant velocity (9.4°/s) rotation in the clockwise (CW) and counterclockwise (CCW) directions around an axis inclined by 5° with respect to the vertical. OVAR imposes on the animal head a 5° tilt, whose direction changes continuously over the horizontal plane, thus eliciting a selective stimulation of macular receptors. A total of 27/67 P-cells (40%) and 24/44 U-cells (55%) responded to both CW and CCW rotations. For these bidirectiol tal units, the direction of maximum sensitivity to tilt (S(max) could be identified. S(max) directions were distributed over the whole horizontal plane of stimulation. Among bidirectional. neurons, 48% of the P-cells and 33% of the U-cells displayed an equal amplitude of modulation during CW and CCW rotations, indicating a cosine-tuned behaviour. In these instances, the temporal phase of the unit response to a given direction of tilt remained constant, while the sensitivity was maximal along the S(max) direction and declined with the cosine of the angle between S(max) and the tilt direction. The remaining bidirectional units displayed unequal amplitudes of modulation during CW and CCW rotations. For these neurons, a nonzero sensitivity along the null direction was expected and the response phase varied as a function of stimulus direction. Finally, 31% and 23% of P-cells and U-cells, respectively, responded during OVAR in one direction only (undirectional units). This behaviour predicts equal sensitivities along any tilt direction in the horizontal plane and a response phase that changes linearly with the stimulus direction. The possibility that the tested neurons formed a population which coded the direction of head tilt in space was also investigated. The data from the whole population of cells were analysed using a modified version of vectorial analysis. This model assumes that for a particular tilt each cell makes vectorial contributions; the vectorial sum of these contributions represent the outcome of the population code and points in the direction of head tilt in space. Thus, a dynamic head tilt along four representative directions was simulated. For each of the four directions, 12 population vectors were calculated at regular time intervals so as to cover an entire cycle of head tilt. The results indicate that for each selected time in the cycle the direction of the population vector closely corresponded to that of the head tilt, while its amplitude was related to the amount of head tilt. These data were particularly obtained for the P-cells. In view of their efferent connections, the cerebellar anterior vermis may provide a framework for the spatial organization of vestibulospinal reflexes induced by stimulation of otolith receptors
Injections of ß-noradrenergic substances in the cerebellar anterior vermis of cats affect adaptation of the vestibulospinal reflex gain
No full textAbstract
In precollicular decerebrate cats, intermittent sinusoidal roll tilt of the whole animal (at 0.15 Hz, +/- 10 degrees) produced a vestibulospinal reflex (VSR), characterized by an increased EMG activity of the forelimb extensor triceps brachii during side-down and a decreased activity during side-up tilt. This reflex was first tested during and after a 3-h period of sustained animal tilt at the same parameters indicated above. An adaptive increase in gain of the VSR progressively developed in some experiments, but not in others. In a second group of experiments, however, sinusoidal roll tilt of the head (0.15 Hz, +/- 10 degrees) was associated with a synchronous roll tilt of the body (at 0.15 Hz, +/- 12.5 degrees). This additional stimulus led to 2.5 degrees of neck rotation, which was thus out of phase with respect to head rotation. In all these experiments, submitted to a 3-h period of sustained neck-vestibular stimulation, the gain of the VSR tested every 10-15 min consistently increased to reach the maximum at the end of the third hour of stimulation. This adaptive process was followed up to 1 h after stimulation. Microinjection into the hemivermal cortex of the cerebellar anterior lobe of the beta-noradrenergic antagonists propranolol or sotalol (0.25-0.50 microliter at 8 micrograms/microliter saline) produced only slight and short-lasting changes in the basic amplitude of the VSR, but always decreased or prevented the occurrence of the adaptive increase in gain of the VSR during sustained out of phase head-neck rotation. The same agents also suppressed the increase in gain of the VSR which occurred in some experiments during sustained roll tilt of the whole animal (at 0.15 Hz, +/- 10 degrees), leading to selective stimulation of labyrinth receptors. On the other hand, the beta-noradrenergic agonist isoproterenol (0.25 microliters at 8 micrograms/microliters saline) brought to the light the adaptive process in other experiments in which no adaptation occurred during sustained animal rotation. These effects occurred when the sites of injection were located within the zone B of the cerebellar anterior vermis, which projects to the lateral vestibular nucleus. In conclusion, the results indicate that the adaptive changes affecting the gain of the VSR in decerebrate cats are facilitated by the noradrenergic afferent system acting on the cerebellar vermis through beta-adrenoceptors
Contribution of the cerebellar anterior vermis to the gain and spatiotemporal properties of the vestibulospinal reflexes: a behavioural and cellular analysis.
No full textAbstract
Functional inactivation of the lobules IV-V of the cerebellar vermis obtained by local microinjection of the GABA-A agonist muscimol, depresses, in decerebrate cats, the amplitude of the VS reflex recorded from the forelimb extensor TB and may occasionally affect its spatial and/or temporal properties. The activity changes induced by tilting the animal head in all the possible directions were uniformly reduced. Experiments of unit recording from the same region submitted in other experiments to the drug injection, revealed that a large proportion of P-cells (67%) showed spatially tuned responses to the labyrinth input, characterized by preferred directions which were uniformly scattered over the horizontal plane. Neurons with opposite orientations could be found within a relatively narrow volume of corticocerebellar tissue, that could have been easily inactivated by injected volumes (0.25 μl, 8 μg/μl) of muscimol. We proposed that the spatial tuning of the P-cell responses to the labyrinth input is a basic property which allows the cerebellum to control the gain of VS reflexes elicited by head tilts in a broad directional range
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