Electrophysiological correlates of the visual after effect by means of visual evoked potentials.

An attempt was made to determine whether changes of electrical activity could be seen in the posterior cortex during an after image of high frequency luminance gratings. Steady state visual evoked potentials were recorded (midoccipital, right and left temporo-occipital sites) immediately after a period of visual adaptation (15 min) to the stimulus, while the subjects experienced the after image. During this illusion, frequencies of the fast Fourier transform spectra linked to the stimulation differed from the noise and were larger at temporo-occipital sites than at the midoccipital one.

Spatial frequency and right hemisphere: an electrophysiological investigation.

The influence of the spatial frequency of visual stimuli on hemispheric asymmetry has been studied with visual evoked potentials (VEP). Nineteen different sinusoidal gratings (19 SF from 1 to 10 cpd) were presented in an ON-OFF mode to five right-handed subjects. The amplitude of the VEPs and the latency of the first positive component (C1) were analyzed.

The Stroop's test evokes a negative brain potential, the N400.

The Event Related Potential (ERP) of 8 french right handed subjects were recorded with 5 active electrodes located in frontal (Fz), central (Cz), occipital (Oz) and right/left parietal (RH, LH) sites while they were performing a modified version of the test of Stroop. They had either to read the names of basic colors (yellow, green, blue, red) written in the same colors (red written in red: concordant stimuli) or in a different color (red written in blue: discordant stimuli) or to name mentally the color in which was written the name of a color, both colors being concordant or discordant. The ERPs for reading were similar for concordant and discordant stimuli and showed no sign of a N400 wave, this was also the case for the mental naming of a color associated to the written name of the same color.

Hemispheric asymmetries of visual evoked potentials in relation to spatial frequency, handedness and familial left-handedness.

The effects of handedness and of familial left-handedness on the asymmetry of the cerebral hemispheres were investigated by means of visual evoked potentials. Square gratings of different spatial frequencies were presented, at 1 Hz in ON-OFF mode to 60 subjects: 30 right-handers and 30 left-handers, 15 with familial handedness and 15 without in each group. The results show that the patterns of hemispheric asymmetry differ in right- and left-handers.

Role of the cerebellum in spatial orientation in the rat.

Adult DA/HAN strain rats were submitted to a spatial orientation task consisting of finding a reward in an open field. They were first submitted to an initial learning session and 10 days later to a retrieval test. The animals were divided into four groups of five rats each: animals that were cerebellectomized before the initial learning session or after the initial learning session, sham-operated rats, and control (intact) animals.

Role of the cerebellum in habituation exploration behavior in the rat.

Adult control and cerebellectomized DA/HAN-strained male rats were submitted to habituation of exploration behavior in a test environment consisting of a novel cage in which four objects were displayed. Seven days after the initial session of habituation, retention of the habituation was tested. Within-session habituation was observed in cerebellectomized and control rats.

Development of optokinetic neuronal responses in the pretectum and horizontal optokinetic nystagmus in unilaterally enucleated rats.

Responses of single units to constant-velocity rotations of the visual surround (0.25-10 degrees/s) were studied in the pretectum of unilateral enucleated rats at different ages. Enucleation was performed either in the first postnatal week ("early" enucleated rats) or in the adult stage ("late" enucleated rats).

Effects of kainic acid lesions of the nucleus reticularis tegmenti pontis on fast and slow phases of vestibulo-ocular and optokinetic reflexes in the pigmented rat.

The nucleus reticularis tegmenti pontis (NRTP) and adjacent pontine reticular formation were lesioned chemically using the neurotoxic agent kainic acid, and the effects of these lesions on horizontal ocular optokinetic and vestibular nystagmus were examined. Eye position was measured in the alert, NRTP-lesioned animals with the electromagnetic search coil technique. Optokinetic and vestibular stimuli consisted of steps of rotations or sinusoidal oscillations of a fullfield visual pattern surrounding the animal or of the animal in total darkness, respectively.

Responses of nucleus reticularis tegmenti pontis neurons to vestibular stimulation in the rat.

Forty-nine neurons were recorded in the nucleus reticularis tegmenti pontis (NRTP) during horizontal vestibular and/or optokinetic stimulation in immobilized pigmented rats. During optokinetic stimulation, the response of NRTP neurons was either unidirectional (51%) or bidirectional (49%). Histological reconstruction showed that unidirectional neurons were located in the dorsal-medial part of NRTP, and bidirectional neurons in the lateral part.

Dynamic characteristics of vestibular nuclear neurons responses to vestibular and optokinetic stimulation during vestibular compensation in the rat.

In albino rats and pigmented rats, neurons were recorded extracellularly in the vestibular nuclei during the first 2 weeks after unilateral labyrinthectomy in order to study the neuronal events occurring during vestibular compensation and the effect of unilateral vestibular lesion on the optokinetic responses of neurons in the vestibular nuclei. It was found in albino rats that a re-equilibration took place in the gains of type I neurons between both lesioned and intact sides. The gain of the rare type I neurons on the deafferented side, which was low just after the lesion (t less than 48 h) subsequently increased (48 h less than t less than 14 d) while on the intact side the gain was greater just after the lesion, and then decreased.

Responses of prepositus hypoglossi neurons to optokinetic and vestibular stimulations in the rat.

The responses of 47 nucleus prepositus hypoglossi neurons to vestibular optokinetic stimulations in the horizontal plane were recorded in immobilized, pigmented rats. During sinusoidal vestibular stimulation in the dark, type II (62%) and type I (38%) responses were recorded. In addition to the sinusoidal modulation of firing rate, units often showed fast rhythmic increases or decreases in firing (nystagmic modulation).

An electrophysiological study of pathways mediating optokinetic responses to the vestibular nucleus in the rat.

Intra- and extracellular responses of neurons in the pretectum (Pt), the nucleus reticularis tegmenti pontis (NRTP), the prepositus hypoglossal complex (NPH) and the vestibular nuclei (VN) were recorded during orthodromic/antidromic stimulation of their afferent/efferent fibers. In the Pt, many neurons were excited by stimulation of the contralateral optic nerve (ONc). Comparison of the latencies of evoked presynaptic action potentials and EPSPs yielded a time difference corresponding to one synaptic delay.

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats.

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity.

Non-cerebellar visual afferents to the vestibular nuclei involving the prepositus hypoglossal complex: an autoradiographic study in the rat.

Radioactive amino-acids were injected into the nucleus reticularis tegmenti pontis (NRTP) and the pretectum (PT) in the rat. Beside the labeling of the several nuclei which are known to receive afferents of either the NRTP and/or the PT, monosynaptic projections from these two structures to the prepositus hypoglossal complex (PHN) were demonstrated. Pretectal visual inputs to the vestibular nuclei (VN) may thus be conveyed not only by the classical PT-inferior olive-cerebellar route, but also by two other non-cerebellar ones involving the strong efferent projections of the PHN onto the VN.

Development of optokinetic responses in vestibular nuclear neurons in the young rat.

Responses of vestibular nuclear neurons (Vn) of the horizontal canal system to optokinetic stimulation could not be elicited before postnatal day 22. Between days 22 and 29 response magnitude gradually increased whereas response phase remained constant. At the end of the first postnatal month the sensitivity of the optokinetic responses was still much less than that measured in adult animals.

Firing characteristics of neurons mediating optokinetic responses to rat's vestibular neurons.

1) The responses of single units in the pretectum (Pt) and in the n. reticularis tegmenti pontis (NRTP) to constant velocity horizontal rotation (0.25--60 deg/s) of a large-field visual pattern were studied in immobilized, non-anesthetized DA-HAN rats.

Response of central vestibular neurons to horizontal linear acceleration in the rat.

Responses of central vestibular neurons to horizontal sinusoidal translation (F:0.25Hz) were recorded in albino rat. 57.

Pathways mediating optokinetic responses of vestibular nucleus neurons in the rat.

1. The effects of various brain lesions on the responses of vestibular nuclear neurons (Vn) of the horizontal semicircular canal system to optokinetic stimulations were studied to elucidate the optokinetic path from the retina to the vestibular nuclei. A previous study performed in intact rats served as a control [2].

The postnatal development of functional properties of central vestibular neurons in the rat.

The postnatal development of the responses of rat central vestibular neurons to horizontal angular acceleration was studied in the time and frequency domain. The resting discharge was very low and irregular during the first postnatal days, increased gradually and became more regular throughout the first month and reached adult values approximately by the end of the first month. The relative distribution of type I and type II units was the same in all age groups.

Responses to tilting of fibers of the frog's saccular nerve.

The activity of single fibers from the saccular nerve has been recorded in isolated head preparations in the frog (Rana esculenta). Nearly all the fibers present an activation or a depression of their activity during the tilting movement in a given direction. This is considered to correspond to the existence of two anatomical populations of haircells in the saccular macula which differ in their functional polarization.

[Response of the saccule to the direct vibratory stimulation of the macula in frogs].

Direct stimulation of the frog's saccular macula shows that the saccular fibers are sensitive to vibrations between 10(-1) (at least) and 8.10(3) Hz and that their response depends on 1) the frequency of the vibration, 2) the origin of the fiber in the macula.