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Biomedical subjects

E Godaux

Publications and source records attributed to E Godaux.

At least 37 records · Page 2Linked to original sources
PubMed1998

Kinematics of fast wrist movements in manic-depressive illness chronically treated with lithium carbonate.

Lithium salts have been shown to impair kinematics of fast voluntary movements during acute intoxication. The aim of the present study was to determine whether lithium carbonate affected the kinematics of fast movements in patients chronically treated and who did not exhibit signs of neurotoxicity. We analysed fast wrist flexion movements in 6 healthy subjects, in 5 patients presenting a manic-depressive illness without treatment, and in 8 patients receiving lithium carbonate for a manic-depressive disease. The mean duration of treatment was 3.9 +/- 4.1 years, the mean daily dose 837 +/- 341 mg and the mean serum level 0.95 +/- 0.15 mEq/l. Although mean movement amplitudes were similar in the 3 groups, the variability of fast movements was increased in patients receiving lithium salts. The ratio of maximum to average velocities (Vm/Vave) was significantly higher in patients treated, and their movements were temporally asymmetrical, with a ratio of acceleration duration divided by deceleration duration being lower than in the 2 other groups. These kinematic abnormalities show that a chronic treatment with lithium salts is associated with an impairment of the cerebellar control of fast single-joint movements.

Acceleration↗
PubMed1998

Neuronal activity in the vestibular nuclei after contralateral or bilateral labyrinthectomy in the alert guinea pig.

In the guinea pig, a unilateral labyrinthectomy is followed by an initial depression and a subsequent restoration of the spontaneous activity in the neurons of the ipsilateral vestibular nuclei. In two previous works, we have established the time course of these changes in the alert guinea pig using electrical stimulation as a search stimulus to select the analyzed neurons. The latter criterion was important to capture the many ipsilateral neurons that are silent at rest during the immediate postlabyrinthectomy stage. Because it is known that a pathway originating from the vestibular nuclei on one side crosses the midline and functionally inhibits the activity of the vestibular nuclei on the other side, we investigated in the first part of this study the spiking behavior of the neurons in the vestibular nuclei contralateral to the labyrinthectomy using the same procedure as that used for the ipsilateral neurons. The spiking behavior of 976 neurons was studied during 4-h recording sessions in intact animals and 1 h, 1 day, 2 days, or 1 wk postlabyrinthectomy. Neurons selected according to the electrical activation criterion were classified further as type I (their firing rate increased during ipsilateral rotation), type II (their firing rate increased during contralateral rotation), or unresponsive. The resting activity of type I neurons, which was 38.1 +/- 20.9 spikes/s (mean +/- SD) in the control state, increased statistically significantly 1 h after the lesion (53.3 +/- 29.1 spikes/s) and remained at this level 1 wk later (56.0 +/- 20.3 spikes/s). The sensitivity of type I units, which was 0.80 +/- 0.46 spikes/s per deg/s in the control population, decreased to 0.49 +/- 0.26 spikes/s per deg/s 1 h after the lesion and remained at this level 1 wk later (0.50 +/- 0.39 spikes/s per deg/s). When all monosynaptically activated neurons (type I, type II, unresponsive) were pooled, the sensitivity to horizontal rotation fell from 0.58 +/- 0.51 spikes/s per deg/s in the control state to 0. 15 +/- 0.25 spikes/s per deg/s 1 h after the lesion and to 0.20 +/- 0.32 spikes/s per deg/s 1 wk later. The major findings of the first part of this study in the alert guinea pig are thus in accord with those of Curthoys et al. and Smith and Curthoys in anesthetized guinea pigs. In the second part of this work, we studied the spiking behavior of the neurons in the vestibular nuclei after bilateral labyrinthectomy. After unilateral labyrinthectomy, the resting discharge of the ipsilateral monosynaptically activated vestibular neurons fell from 36.9 +/- 21 spikes/s (basal activity) to 6.7 +/- 17.0 spikes/s 1 h after the lesion and then recovered, reaching 17.4 +/- 18.9 and 40.8 +/- 23.7 spikes/s 1 day and 1 wk after the lesion, respectively. These observations raise the two following questions. What are the relative contributions of the loss of the excitatory influence from the ipsilateral labyrinth (destroyed) and of the persistence of the inhibitory influence from the contralateral labyrinth (intact) in the labyrinthectomy-induced depression of activity? And are the left-right asymmetries caused by a unilateral labyrinthectomy the driving force for restoration of activity? Here, we addressed these two questions by studying the spiking behavior of 473 second-order vestibular neurons in the alert guinea pig after a bilateral labyrinthectomy. In the acute stage, 1 h after bilateral labyrinthectomy, the resting discharge of the second-order vestibular neurons was 16.2 +/- 22.4 spikes/s. From comparison with the results obtained in the acute stage after a unilateral labyrinthectomy, we inferred that the ipsilateral excitatory influence was between two and three times more powerful than the contralateral inhibitory influence. (ABSTRACT TRUNCATED)

Action Potentials↗
PubMed1997

Analysis of single-joint rapid movements in patients with sporadic olivopontocerebellar atrophy.

Patients with pure cerebellar cortical atrophy (CCA) present isolated cerebellar signs, whereas patients with sporadic olivopontocerebellar atrophy (sOPCA) present various combinations of cerebellar and extracerebellar signs. However, the differential diagnosis between these two forms of cerebellar degeneration is often a challenge for the clinician. Therefore, any test helping in this differential diagnosis might have a potential clinical interest. In this study, our goal was to investigate the adaptation to increased inertia in patients with sOPCA exhibiting combined cerebellar and pyramidal signs, during the performance of fast wrist flexions. We found that these patients exhibited a hypermetria which remained unchanged after addition of inertia, because they were unable to increase neither their agonist activity (launching force), nor their antagonist activity (braking force). This contrasts with our previous findings in patients with CCA. In these latter, the hypermetria worsened when the inertial load of the hand increased because those patients were able to increase their agonist activity, but not their antagonist activity. The adaptation to inertia might thus help to differentiate CCA and sOPCA.

Adult↗
PubMed1997

Dissociations between behavioural recovery and restoration of vestibular activity in the unilabyrinthectomized guinea-pig.

1. In the guinea-pig, a unilateral labyrinthectomy induces postural disturbances and an ocular nystagmus which abate or disappear over time. These behavioural changes are accompanied by an initial collapse and a subsequent restoration of the spontaneous activity in the neurones of the ipsilateral vestibular nuclei. Recently, it has been shown that the vestibular neuronal activity remained collapsed over at least 10 h whereas its restoration was complete 1 week after the lesion. The aims of this study were to determine when restoration of spontaneous activity in the partially deafferented vestibular neurones started and to compare the time courses of the behavioural and neuronal recoveries in guinea-pigs that had undergone a unilateral labyrinthectomy. 2. Neuronal discharge measurements were made using chronic extracellular recording of single unit activity. After a left labyrinthectomy, electrodes, were placed on the site of the destroyed labyrinth to enable stimulation of the left vestibular nerve. Behavioural measurements included chronic recording of eye movements by the scleral search coli technique. After a left labyrinthectomy, lateral deviation of the head, twisting of the head, and eye velocity of the slow phases of the nystagmus were measured. 3. The neuronal activity of the rostral part of the vestibular nuclear complex on the lesioned side was recorded in alert guinea-pigs over 4 h recording sessions between 12 and 72 h after the lesion. 4. The criterion used to select vestibular neurones for analysis was their recruitment by an electric shock on the vestibular nerve. In addition, in order to explore a uniform population, we focused on neurones recruited at monosynaptic latencies (0.85-1.15 ms). 5. For each recording period, the mean resting rate was calculated animal by animal and the grand mean of these individual resting rate means was calculated. Previously, a decline in the grand mean resting rate from 35.8 +/- 6.0 spikes s-1 (control state) to 7.1 +/- 4.2 spikes s-1 during the first 4 h after labyrinthectomy has been shown. In the present study, the first sign of recovery was observed during the 12-16 h recording period when the resting rate grand mean increased to 16.3 +/- 3.9 spikes s-1. This grand mean activity did not change significantly during the following 12 h. Thereafter, restoration of neuronal activity improved and was complete 1 week after the lesion. 6. Although the abatement of the vestibular symptoms roughly paralleled the restoration of neuronal activity in the vestibular nuclei, some discrepancies between the time courses of both phenomena emerged. An important step in postural recovery (the animals managed to stand up) and a major part of the abatement of the nystagmus occurred before the recovery of vestibular neuronal activity. In addition, lateral deviation of the head disappeared while restoration of the neuronal activity was incomplete, but significant head twisting was still evident when vestibular resting rates had recovered completely. 7. We conclude that restoration of neuronal activity in the ipsilateral vestibular nuclei starts 12 h after the lesion and that restoration of neuronal activity in the ipsilateral vestibular nuclei is not the only mechanism underlying behavioural vestibular compensation.

Animals↗
PubMed1997

Emergence of clusters in the hidden layer of a dynamic recurrent neural network.

The neural integrator of the oculomotor system is a privileged field for artificial neural network simulation. In this paper, we were interested in an improvement of the biologically plausible features of the Arnold-Robinson network. This improvement was done by fixing the sign of the connection weights in the network (in order to respect the biological Dale's Law). We also introduced a notion of distance in the network in the form of transmission delays between its units. These modifications necessitated the introduction of a general supervisor in order to train the network to act as a leaky integrator. When examining the lateral connection weights of the hidden layer, the distribution of the weights values was found to exhibit a conspicuous structure: the high-value weights were grouped in what we call clusters. Other zones are quite flat and characterized by low-value weights. Clusters are defined as particular groups of adjoining neurons which have strong and privileged connections with another neighborhood of neurons. The clusters of the trained network are reminiscent of the small clusters or patches that have been found experimentally in the nucleus prepositus hypoglossi, where the neural integrator is located. A study was conducted to determine the conditions of emergence of these clusters in our network: they include the fixation of the weight sign, the introduction of a distance, and a convergence of the information from the hidden layer to the motoneurons. We conclude that this spontaneous emergence of clusters in artificial neural networks; performing a temporal integration, is due to computational constraints, with a restricted space of solutions. Thus, information processing could induce the emergence of iterated patterns in biological neural networks.

Animals↗
PubMed1996

The hypothesis of the uniqueness of the oculomotor neural integrator: direct experimental evidence in the cat.

1. As far as horizontal eye movements are concerned, the well-known hypothesis, not yet experimentally proved, of the common neural integrator states that the eye-position signal is generated by a common network, regardless of the type of versional movement. The aim of this study was to evaluate the validity of this hypothesis by checking whether the sensitivity to eye position of the neurones of the nucleus prepositus hypoglossi (NPH) (the main component of the system integrating the different incoming velocity signals) would be the same regardless of the type of versional movement. 2. The discharge of sixty-five NPH neurones was recorded in the alert cat during spontaneous eye movements made in the light and in response to sinusoidal rotations of the head in complete darkness. 3. For each NPH neurone, the sensitivity to eye position was determined from measurements carried out during intersaccadic fixation. The discharge rate of the studied neurone was plotted against eye position. The slope of the resulting regression line gave the sensitivity (measured during intersaccadic fixation in the light) of the neurone to eye position, which was termed K(f). 4. A new method was developed to measure the sensitivity to eye position (K(v)) of neurones during vestibular slow phases. The difficulty came from the fact that, during slow phases, eye velocity and eye position changed simultaneously and that each of those two variables could influence neuronal activity. For each neurone, the instantaneous firing rate was measured each time the eye passed through a given position during any slow phase generated during any vestibulo-ocular reflex. At a given position, the discharge rate of the neurone under study was plotted against the eye velocity. From the resulting linear regression line, two interesting values were obtained: its slope, corresponding to the sensitivity of the neurone to eye velocity, R(v), (at that given eye position) and its 'y'-intercept, F(0), the interpolated firing rate when the eye velocity was zero. This procedure was repeated for different eye positions. The values of F(0) were then plotted against the eye positions. The slope of the resulting regression line gave the sensitivity (measured during vestibular stimulation) of the neurone to eye position, which was termed K(v). 5. The errors on the individual values of K(f) and K(v) were assessed in order to allow a statistical comparison at the single unit level. 6. We found that, for each of our sixty-five neurones, the sensitivity to eye position measured during intersaccadic fixation in the light was equal to the sensitivity to eye position measured during the vestibulo-ocular reflex (VOR) elicited in complete darkness. We conclude that our results favour the hypothesis of a unique horizontal oculomotor integrator for all versional movements.

Animals↗
PubMed1996

Cerebellar hypermetria associated with a selective decrease in the rate of rise of antagonist activity.

Classically, cerebellar hypermetria observed during fast and accurate movements is ascribed to a delayed onset of the electromyographic activity of the antagonist muscle. We describe here 3 patients presenting a late-onset cerebellar degeneration and exhibiting a hypermetria during their fast and accurate movements in spite of a normal onset latency of the antagonist activity. Hypermetria was found to be due to a slower rate of rise of the antagonist activity.

Adult↗
PubMed1996

Analysis of cerebellar dysmetria associated with lithium intoxication.

By contrast to the permanent cerebellar sequelae developing over the weeks following a lithium intoxication, the cerebellar dysfunction occurring in the acute phase is poorly documented. In this study, we analysed the fast and accurate wrist flexion movements and the associated electromyographic activities in 6 patients as soon as possible after a lithium intoxication and three months later. Movements were recorded before and after increasing the inertial load of the moving hand. During the acute phase of the disease, three patients performed dysmetric movements, which became hypermetric when the inertia was increased. In the three other patients, the overshooting of the target which was already observed in the basal condition (no load), was even larger when masses were added. In all the patients, addition of loads increased the onset latency of the antagonist activity during the acute stage of the intoxication. Three of the six patients who presented fever, renal failure and did not undergo hemodialysis developed permanent cerebellar deficits. The three others who presented no fever, no renal failure and underwent hemodialysis recovered completely.

Acute Disease↗
PubMed1996

Discharge properties of brain stem neurons projecting to the flocculus in the alert cat. I. Medical vestibular nucleus.

1. The aim of this study was to characterize the signals transmitted by neurons of the medial vestibular nucleus (MVN) to the middle zone of the flocculus in alert cats. 2. Bipolar stimulating electrodes were implanted into the middle zone of each flocculus, because this zone is known to be involved in the control of horizontal eye movements. Correct implantation of the stimulating electrodes was ensured by 1) recording of Purkinje cells whose activity was related to horizontal eye movements and 2) elicitation of slow abduction of the ipsilateral eye upon electrical stimulation. 3. The rostral two-thirds of the MVN were investigated by microelectrodes during stimulation of both flocculi. Antidromically activated neurons were found only in the central part of the explored area. Forty-four units were activated from the contralateral, eight from the ipsilateral flocculus. Neurons could never be activated from both flocculi. 4. Neurons included in this study were MVN neurons that had 1) to be antidromically activated from one flocculus and 2) to modulate their firing rate during the horizontal vestibuloocular reflex (VOR) elicited by sinusoidal stimulation (0.1 Hz; 10, 20, 30 or 40 degrees). The 39 neurons matching both criteria were classified in 2 groups: 22 neurons changed their firing rate during spontaneous horizontal eye movements (EM-neurons), 17 modulated their activity only during head rotation and were labeled vestibular-only neurons (VO-neurons). 5. Sufficient data were obtained from 13 EM-neurons to allow a quantitative analysis. Among those, 12 were activated from the contralateral and 1 from the ipsilateral flocculus. Their sensitivity to horizontal eye position during intersaccadic fixation was 3.54 +/- 2.75 (SD) spikes.s-1/deg. Eight EM-neurons behaved as type I neurons, five as type II neurons. During the slow phases of the VOR, all of these neurons combined some head-velocity sensitivity (1.50 +/- 0.43 spikes.s-1/deg.s-1) with some horizontal eye-position sensitivity (3.61 +/- 2.45 spikes.s-1/deg). Additionally, seven of these neurons presented a sensitivity to eye velocity (1.34 +/- 0.55 spikes.s-1/deg.s-1). The phase difference between the modulation of firing rate and eye position varied substantially between neurons. The observed phase lead with respect to eye position ranged from 2 to 110 degrees (41.9 +/- 31.8 degrees). 6. Sufficient data were obtained from 10 VO-neurons to allow a quantitative analysis. Among those, nine were activated from the contralateral and one from the ipsilateral flocculus. All of these neurons behaved as type I neurons. The sensitivity to head velocity was 1.64 +/- 1.07 spikes.s-1/deg.s-1. The phase lead of the modulation of spike activity with respect to head velocity ranged from 4.5 to 30.5 degrees (16.4 +/- 8.9 degrees). 7. We conclude that the MVN provides the horizontal zone of the flocculus (with a strong contralateral preference) with information about head velocity (through VO-neurons and EM-neurons) and about eye velocity and position (through EM-neurons).

Animals↗
PubMed1996

Discharge properties of brain stem neurons projecting to the flocculus in the alert cat. II. Prepositus hypoglossal nucleus.

1. The aim of this study was to characterize the signals transmitted by the neurons of the nucleus prepositus hypoglossal (NPH) to the middle zone of the flocculus of the cat. The methods, the behavioral testing, and the animals used in this study were the same as those used in the accompanying paper on medial vestibular nucleus neurons. 2. The rostral two-thirds of the NPH was explored in alert animals with microelectrodes during stimulation of the middle zone of both flocculi. Discharges of neurons were analyzed during spontaneous eye movements (head fixed) and during horizontal vestibuloocular reflex (VOR) activity elicited by sinusoidal stimulation (10, 20, 30, or 40 degrees at 0.1 Hz). Forty neurons were found to be antidromically activated from only one or the other of the two flocculi (latency: 0.99 +/- 0.17 ms, mean +/- SD): 37 from the contralateral flocculus and 3 from the ipsilateral one. None of the neurons could be activated antidromically from both flocculi. Floccular stimulation never resulted in direct inhibition of these NPH neurons. 3. Of the 37 units antidromically activated from the contralateral flocculus, 26 were recorded sufficiently long to allow full quantitative analysis. Most of these (20 neurons) were classified as burst-tonic (BT) neurons. The BT neurons exhibited during each saccade made in one direction (the ON direction) a burst of spikes, and during postsaccadic fixation a tonic activity that increased with gaze displacement in the ON direction. The mean sensitivity of the neurons to eye velocity during the "ON" saccades was 3.3 +/- 1.6 spikes.s-1.deg-1.s-1. During intersaccadic fixation, the mean sensitivity to eye position was 3.6 +/- 2.5 spikes.s-1.deg-1. During the VOR, the majority showed modulation in relation to both eye position and eye velocity. The mean sensitivity to eye position during the VOR was 3.4 +/- 2.6 spikes.s-1.deg-1 (range: 0.2-8.1 spikes.s-1.deg-1). The mean sensitivity to eye velocity during the VOR was 2.1 +/- 1.3 spikes.s-1.deg-1.s-1. The mean phase lead of with respect to eye position was 16.4 +/- 6.8 degrees (range: 6.0-28.9 degrees). Eighty percent of the BT neurons behaved as type I neurons. Forty-seven percent of the BT neurons also presented some head velocity sensitivity (1.48 +/- 0.6 spikes.s-1.deg-1.s-1, mean +/- SD). 4. Other NPH cells antidromically activated from the contralateral flocculus were classified in two groups: bidirectional burst (BB) neurons (n = 4) and burst-driving (BD) neurons (n = 2). The BB neurons were characterized by a burst discharge during every horizontal saccade or VOR quick phase, irrespective of the direction. The mean sensitivity of the BB neurons to eye velocity during saccades was 3.3 +/- 7.8 (SD) spikes.s-1.deg-1.s-1. Both BD neurons increased their firing rate during the slow VOR phases induced by an ipsilateral rotation (type I neurons) and exhibited high-frequency bursts in association with ipsilaterally directed quick phases. 5. The results indicate that the main projection of the NPH onto the middle zone of the flocculus comes from contralaterally located type I BT neurons. Signals transmitted in this path associate a high sensitivity for eye velocity with a high sensitivity for eye position. This type of input is consistent with the suggestion that the main function of the flocculus is to control the gain of downstream reflexes and to perform a fine adjustment of the gaze holding command.

Animals↗
PubMed1995

Detection of silent cerebellar lesions by increasing the inertial load of the moving hand.

In a previous study, we analyzed the hypermetria of wrist flexion movements in patients with a cerebellar syndrome. We found that hypermetria augmented when the inertial load of the moving hand was artificially increased. In the present study, we applied the same protocol to patients with an apparently normal neurological examination, in spite of a cerebellar lesion documented by magnetic resonance imaging. In all of these patients, the addition of a mass to the moving hand caused the appearance of a hypermetria. This lack of adaptation of fast and accurate movements to an increased inertia thus appears as a new diagnostic tool enabling the detection of silent cerebellar lesions.

Adaptation, Physiological↗
PubMed1995

Recovery of hypermetria after a cerebellar stroke occurs as a multistage process.

In a prospective study, we repeatedly recorded fast goal-directed wrist movements of 8 patients who had experienced an acute cerebellar hypermetria due to a stroke and who had subsequently recovered clinically. Movements and the associated agonist and antagonist electromyographic (EMG) activities were recorded before and after addition of inertial loads. Four stages characterized the recovery process. At stage 1, hypermetria was present in the basal state and was not modified by the addition of inerital loads. At stage 2, hypermetria, which was present in the basal state, was enlarged by mass addition. At stage 3, hypermetria was absent in the basal state, but was revealed by an inertial load increase. At stage 4, as in healthy subjects, there was no hypermetria without or with addition of inertial loads. At stage 1, the patients presented several defects. (1) Facing an increased inertia, they could not increase their agonist EMG activity. (2) The onset latency of their antagonist EMG activity was delayed. (3) Facing an increased inertia, they could not increase their antagonist EMG activity. Among these three defects, the first disappeared at stage 2, the second at stage 3, and the third at stage 4.

Adult↗
PubMed1995

Existence in the nucleus incertus of the cat of horizontal-eye-movement-related neurons projecting to the cerebellar flocculus.

1. Properties of nucleus incertus (NIC) neurons projecting to the cerebellar flocculus were studied in alert cats by using chronic unit and eye movement recording and antidromic activation. Projection of these neurons onto the flocculus was verified with retrograde transport of horseradish peroxidase after injections in the flocculus. 2. Bipolar stimulation electrodes were implanted into the "middle" zone of each flocculus because this zone is known to be involved in the control of horizontal eye movements. The dorsomedial aspect of the pontine tegmentum was explored with microelectrodes during stimulation of both flocculi. The majority of neurons antidromically activated from the flocculus were found in the caudal part of the NIC. 3. Of the 69 neurons activated from the flocculus, 44 were classified as burst-tonic (BT) neurons; 34 discharged in relation with horizontal movements of the eye, 10 in relation with vertical movements. Of the 14 remaining neurons, 6 were not related to eye movements and 8 were classified as burst neurons. The BT neurons of the NIC displayed a great sensitivity to both horizontal eye position and horizontal eye velocity. 4. This study demonstrates the presence of a new group of horizontal eye movement related BT neurons situated in the NIC. The fact that they project to the horizontal floccular zone emphasizes the importance of the functional specialization of the different Purkinje cell zones.

Animals↗