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Biomedical subjects

C Milleret

Publications and source records attributed to C Milleret.

At least 19 recordsLinked to original sources
PubMed2001

Impairment of binocular vision in the adult cat induces plastic changes in the callosal cortical map.

In the primary visual cortex of normally reared adult cat, neurons activated through the corpus callosum are almost entirely located at the 17/18 border. They display small receptive fields distributed along the central vertical meridian of the visual field and are orientation selective. Here we demonstrate that a few weeks of monocular deprivation or unilateral convergent strabismus produced in adulthood does not modify the cortical distribution of these neurons, but leads to an increase of their receptive field size mainly toward the ipsilateral hemifield and to a loss of their orientation selectivity. We conclude that manipulation of binocular vision in the adult modifies neither the location of the primary callosal cortical map nor its retinotopy. In contrast, it induces functional plastic changes in this map which lead to a significant widening of the area of visual space signalled through the corpus callosum. These plastic changes are interpreted as the result of the strengthening of normally hidden subthreshold synaptic inputs.

Animals↗
PubMed2001

Visual interhemispheric transfer to areas 17 and 18 in cats with convergent strabismus.

Commissural connections between primary visual cortical maps of the two hemispheres are essential to unify the split representation of the visual field. In normal adult cats, callosal connections are essentially restricted to the border between areas A17 and A18, where the central vertical meridian is projected. In contrast, early convergent strabismus leads to an expanded callosal-receiving zone, as repeatedly indicated by anatomical experiments. We investigated here the functional correlates of this widespread distribution of callosal terminals by analysing transcallosal visual responses in five anaesthetized and paralysed 4-10-month-old cats whose right eye had been surgically deviated on postnatal day 6. After acute section of the optic chiasm, single-unit activity was recorded from A17 and A18 of the right hemisphere while the left eye was visually stimulated. A total of 108/406 units were transcallosally activated. While they were more frequent at the 17/18 border (46% of the units recorded within this region), numerous transcallosally activated units were located throughout A17 (16%), A18 (27%) or within the white matter (17%). In all regions, transcallosally driven units displayed functional deficits usually associated with strabismus, such as decreased binocularity and ability to respond to fast-moving stimuli, and increased receptive field size. Many units also displayed reduced orientation selectivity and increased position disparity. In addition, transcallosal receptive fields were manifestly located within the hemifield ipsilateral to the explored cortex, with almost no contact with the central vertical meridian. Comparison with data from normal adults revealed that strabismus induced a considerable expansion of the callosal receiving zone, both in terms of the cortical region and of the extent of the visual field involved in interhemispheric transfer, with implications in the integration of visual information across the hemispheres.

Animals↗
PubMed1994

Visual callosal connections and strabismus.

Strabismus is a condition that exists when the visual axes of the two eyes fail to intersect at the fixation point under binocular viewing conditions. When it occurs in mammals during the critical period which corresponds to the period of maximal plasticity early in life, strabismus is known to induce both morphological anomalies and abnormal connections from the retina to the cortex; it further leads to binocular neural changes and to spatial vision deficits, especially at the cortical level. After a brief review of the already known data about the consequences of early strabismus in cats, monkeys and humans on the development of the visual system and of visual perception, new data are presented here concerning interhemispheric connections in the cat. In normally-reared kittens, visual callosal transfer is shown to be almost adult-like as soon as 12 days after birth: it is almost limited to the 17/18 border of the visual cortex when using visual stimulations in spite of the presence of still numerous juvenile exuberant callosal projections. In contrast, callosal transfer of visual information is extended to both areas 17 and 18 after strabismus, leading to the conclusion that at least some juvenile exuberant callosal projections are not only anatomically but also functionally stabilized after such an oculomotor disease. The possibility that similar abnormalities might be present in monkeys and humans is discussed.

Animals↗
PubMed1994

Morphology of callosal axons interconnecting areas 17 and 18 of the cat.

Seventeen callosally projecting axons originating near the border between areas 17 and 18 in adult cats were anterogradely labelled with biocytin and reconstructed in 3-D from serial sections. All axons terminated near the contralateral 17/18 border. However, they differed in their diameter, tangential and radial distributions, and overall geometry of terminal arbors. Diameters of reconstructed axons ranged between 0.45 and 2.25 microns. Most of the axons terminated in multiple terminal columns scattered over several square millimetres of cortex. Thus in general callosal connections are not organized according to simple, point-to-point spatial mapping rules. Usually terminal boutons were more numerous in supragranular layers; some were also found in infragranular layers, none in layer IV. However, a few axons were distributed only or mainly in layer IV, others included this layer in their termination. Thus, different callosal axons may selectively activate distinct cell populations. The geometry of terminal arbors defined two types of architecture, which were sometimes represented in the same axon: parallel architecture was characterized by branches of considerable length which supplied different columns or converged onto the same column; serial architecture was characterized by a tangentially running trunk or main branch with radial collaterals to the cortex. These architectures may relate to temporal aspects of inter-hemispheric interactions. In conclusion, communication between corresponding areas of the two hemispheres appears to use channels with different morphological and probably functional properties.

Animals↗
PubMed1994

Pattern of development of the callosal transfer of visual information to cortical areas 17 and 18 in the cat.

The aim of this study was to investigate the development of visual callosal transfer in the normally reared cat. Two- to nine-week-old kittens and adults (used as controls) underwent section of the optic chiasm. Three days later, the animals were placed under anesthesia and paralysed; unit activities were recorded from visual cortical areas 17 and 18 and from the white matter in one hemisphere. The units were tested for their responses to visual stimulation of each eye successively. Out of 1036 recorded neurons, 185 could be activated through the eye contralateral to the explored cortex via callosal transfer. Most of them could also be driven through the ipsilateral eye via the 'direct' geniculo-cortical pathway. For animals aged > or = 2 weeks, virtually all of these units were located at the 17/18 border zone, with a majority in the supragranular layers. When activated through the corpus callosum, they displayed receptive fields located either on the central vertical meridian of the visual field or in the hemifield ipsilateral to the explored cortex. Such extension into the ipsilateral hemifield as well as receptive field disparities of binocular units decreased with age, while spontaneous activity, strength of response, orientation selectivity and ability to respond to slits moving at middle-range velocity increased. The main conclusion is that the transient callosal projections described by anatomists, which are present until 3 months of age, do not achieve supraliminar synaptic contacts with parts of areas 17 and 18 other than the 17/18 border zone, at least from 12 days after birth. However the visual callosal transfer in young animals displays some characteristics which disappear with age.

Aging↗
PubMed1993

The sensitive period for strabismic amblyopia in humans.

PURPOSE: In order to assess the sensitive period for strabismic amblyopia, the period of susceptibility to monocular occlusion was investigated in 407 children who ranged in age from 21 months to 12 years. METHODS: Patients were treated between 1975 and 1990 by occlusion of the best eye. The efficiency of the treatment was measured as the ratio of reduction of the amblyopia at the end of the occlusion. RESULTS: The efficiency of the occlusion is shown to depend on the age of the onset of the treatment: recovery of acuity of the amblyopic eye was maximum when the occlusion was initiated before 3 years of age, decreased as a function of age and was about null by the time the patient was 12 years of age. CONCLUSION: This is assumed to be an indication of the sensitive period for strabismic amblyopia in humans. The results are discussed on the basis of the neurophysiological mechanisms of amblyopia established in animals.

Age Factors↗
PubMed1993

Alpha rhythm in the cat thalamus.

In cats, electrocortical rhythms at about 10 Hz displaying common characteristics with the human alpha rhythm [1] were recorded from the part of the visual cortex that includes the anterior half of areas 17 (on the cortical convexity), of area 18 and of their common limit, representing the projection of the lower contralateral visual quadrant and that of the lower vertical meridian. It is shown here that activities highly correlated with these rhythms and at the same frequency, were recorded from the anterior half of the laminar dorsal lateral geniculate body (mediodorsal part of layer A), and also from a limited area medial to this nucleus. The cat thalamocortical alpha system thus appears to concern only the projection of the lower quadrants, probably excluding the area centralis itself.

Alpha Rhythm↗
PubMed1992

A 10 Hz "alpha-like" rhythm in the visual cortex of the waking cat.

Rhythms at about 10 Hz were recorded from the primary visual cortex of the cat (anterior part of area 18), with characteristics close to those of the alpha rhythm in man: frequency band (7-14 Hz), localization and reactivity to visual stimulation. Coherence analysis of this activity with the "mu" rhythms on the somatosensory cortex showed that although both types develop in the same overall behavioural situations (quiet waking and/or expectancy of an event to occur), they are independent.

Alpha Rhythm↗
PubMed1990

[Dissymmetry in the interhemispheric transfer between visual areas in the adult cat, induced by chiasmotomy and monocular occlusion].

In the adult cat, a midsagittal section of the optic chiasm, which deprives each hemisphere of about half of its visual afferences, is followed after 6 weeks by a change in the callosal interhemispheric transfer, if one eye was occluded during the whole postoperative recovery period, thus depriving one hemisphere of direct visual messages related to patterned vision: with respect to controls only chiasmotomized, with binocular visual experience during an identical postoperative period, the deprived hemisphere displayed a significantly larger callosal afferent traffic while its own callosal efferences were on the contrary significantly reduced. This dissymmetry reveals that important postoperative changes can thus take place even in the adult animal.

Animals↗
PubMed1989

Effects of afferent signals from the extraocular muscles upon units in the cerebellum, vestibular nuclear complex and oculomotor nucleus of the trout.

The responses of single units in the cerebellum, the vestibular nuclear complex and adjacent regions of the brainstem and in the oculomotor nucleus were studied in decerebrate, paralysed rainbow trout (Salmo gairdneri). Natural vestibular stimulation was provided by horizontal, sinusoidal oscillation of the fish and extraocular muscle afferents of the eye ipsilateral to the recording were activated either by passive eye-movement or by electrical stimulation of the trochlear (IV) nerve in the orbit. Unit responses to vestibular and/or orbital stimuli were examined in peristimulus-time histograms interleaved in time. In the cerebellum and brainstem, of 124 units exposed to both types of stimulus, 26 (21%) responded only to vestibular input, 26 (21%) were affected only by the orbital signal and 23 (18%) received both signals. The remaining 49 units (39%) responded to mechanical stimulation of the head or body or to vibration; they were labelled "polymodal" and discarded. The recording sites of 56 units were verified by histology; 30 were in the cerebellum and 26 in the brainstem. Input from the eye muscles had excitatory or inhibitory effects upon the vestibular responses. The effects of the orbital signal were usually phasic but rare tonic responses also occurred. About half (15 of 34) of the units which responded to passive eye-movement showed statistically significant differences in the magnitude of their responses to horizontal and to vertical eye-movement. More units preferred horizontal movement (11) than preferred vertical passive eye-movement (four). Note that the plane of vestibular stimulation was always horizontal. In the region of the oculomotor nucleus, of 19 units, five (26%) gave vestibular responses only and three (16%) were affected only by the orbital signal; three units (16%) with polymodal responses were discarded. Of the eight units carrying both signals, histological confirmation that the recording site lay in the column of cells forming the oculomotor/trochlear nuclei was obtained in four. The responses and interactions were similar to those found in the brainstem. The results present two principal points of interest. 1. They reinforce the accumulating body of evidence that, in species with widely different oculomotor and visual behaviour, signals from extraocular muscle proprioceptors reach the vestibulo-ocular system; this, in turn, suggests that these signals may play some rather fundamental role in the oculomotor system.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Comparative development of cell properties in cortical area 18 of normal and dark-reared kittens.

The development of visual cell properties was studied in cortical Area 18 (A18) of normal (NRs) and dark-reared kittens (DRs), from 2 weeks of age to adulthood. In addition to the orientation selective (S) and non-selective (NS) cells, we describe a new type of non-selective cell with a peripheral zone (NSp), which could be either an intermediate form between NS and S cells and included in a sequential model or an immature form of the S cells whose responses are affected by peripheral stimulations. Using accurate coordinates for the area centralis position relative to the optic disc projection as a function of age, we show that: a) the extent of the visual field increases with age in DRs and NRs; b) the retinotopic organization is always present; c) receptive fields, large in the NS cells, reduce to the size of mature S cells as soon as the cells acquire orientation selectivity. This process can occur after only 6 h of visual experience; d) velocity preference shifts toward high velocities, though more so in NRs than in DRs. An interpretation of the development of these properties is proposed, taking into account eye growth, the growth of dendritic fields and the formation of new connections. A comparison with previous results obtained in Area 17 (A17) shows a similar time course of the specification (NRs) and of the despecification (DRs) processes, although the development of A18 is postponed by about 2 weeks. Moreover, the "adult-like" binocular distribution of ocular dominance depends upon visual experience in A18, while it does not in A17.

Animals↗
PubMed1988

Development of the kitten visual cortex depends on the relationship between the plane of eye movements and visual inputs.

1. Previous experiments have demonstrated that eye movements, acting through the extraocular muscle (EOM) proprioceptive afferents, are necessary for the development of orientation selectivity in the cells of the kitten visual cortex. New experiments were carried out to study the effect of the plane of eye movements on the preferred orientation acquired by the visual cortical cells. 2. Dark-reared (DR) kittens were operated on at 5-6 weeks of age. In the first series of experiments, 4 out of the 6 EOMs were removed bilaterally in such a way that both eyes could only move in a single plane, either vertical or horizontal. In the second series of experiments, the same operation was performed on one eye which was also sutured shut and, on the other side, the EOM were deafferented by intracranial section of the ophthalmic branch of Vth nerve and the eye left open. 3. 1-4 days after surgery the kittens were given 6 h of visual experience and 12 h later were prepared for visual cell recording in Area 17. 4. In kittens of the first series: orientation selectivity developed in the majority (60-65%) of visual cells, most of which encoded horizontal orientations when the eyes had moved in the vertical plane and vertical orientations when the eyes had moved in the horizontal plane. These results show that the plane of eye movements during early visual experience influences the distribution of preferred orientations with an orthogonal relation. Ocular dominance histograms were "strabismic like". 5. In kittens of the second series: orientation selectivity developed in 40-50% of cells, about half of which were tuned for the orientation orthogonal to the direction of movement of the occluded eye, as in experiment I. The seeing, deafferented eye, presumably would have sent normal visual inputs centrally, corresponding to displacements on the retina in every direction since the ocular motility of that eye had not been disturbed. However, proprioceptive information about its movements was suppressed. As only some of the EOMs of the occluded eye were still present and connected, the conclusion is that the observed influence of the plane of eye movements acts through the proprioceptive afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Afferent signals from cat extraocular muscles in the medial vestibular nucleus, the nucleus praepositus hypoglossi and adjacent brainstem structures.

The responses of single units in the vestibular nuclei, nucleus praepositus hypoglossi and in the brainstem, deep and posterior to the abducens nucleus, were studied in anaesthetized, paralysed cats. Natural vestibular stimulation was provided by horizontal, sinusoidal oscillation of the animal and extraocular muscle afferents of the ipsilateral eye were activated either by passive eye-movement or by electrical stimulation of the inferior oblique branch of the oculomotor nerve in the orbit. Unit responses to vestibular and/or orbital stimuli were examined in sets of peristimulus time histograms interleaved in time. Of 127 units exposed to both types of stimulus, 40 (32%) responded only to vestibular input; 46 (32%) were affected only by the orbital afferent signal and 19 (15%) received both signals; the remaining 22 units (17%) were discarded because they had polymodal (usually somaesthetic) input. Of the 93 units whose recording sites were determined histologically, 24 were in the medial vestibular nucleus, 16 in the n. praepositus hypoglossi and 45 in the magnocellular nucleus of the reticular formation posterior and deep to the abducens nucleus. In these three nuclei 19 units in total were found which carried the orbital proprioceptive afferent signal and also responded to horizontal vestibular stimulation. The input from the eye muscles proved able to modify the vestibular response by adding excitation or inhibition or both. Effects of the orbital signal were generally phasic. About half of the units which responded to passive eye-movement showed statistically significant differences between their responses to horizontal and to vertical eye-movement. We have shown previously that signals from extraocular muscle proprioceptors reach the vestibulo-oculomotor system in an amphibian and a bony fish; the present experiments show that this is the case in a mammal also. The fact that the visual and visuomotor behaviour of these three species is very different suggests that the proprioceptive signal may play some rather fundamental role in the vestibulo-ocular system. The principal interest of the present results is that they demonstrate that units in the central vestibular system of the cat, in structures which are known to be concerned in oculomotor control, and particularly in the organization of horizontal eye-movement, receive an afferent signal from the eye muscles during passive eye-movement. These brainstem nuclei are known to receive various combinations of input from the vestibular and visual systems and of signals which represent neck movement and eye position and velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Area centralis position relative to the optic disc projection in kittens as a function of age.

Changes during development of the optic disc projection relative to the area centralis position in the visual field were studied in the kitten. The determinations were based both on direct measurement and physiological location of these retinal landmark projections. The results showed that the relative distance between these retinal landmarks in visual space became shorter with age, indicating that the visual field coordinates change extensively with age. Since the area centralis cannot be seen in most young kittens, the mean distances we have determined for the landmarks in the visual field may provide a useful means of estimating the position of area centralis from the projected position of the optic disc. Our results also confirm the nonuniform growth of the retina suggested already from anatomical observations. Taking into account both eye growth and the changes in the visual field coordinates allowed some reinterpretation of changes in physiological properties of the visual cells known to occur during development, such as decreased size of the visual receptive fields, increased spatial resolution and increased responsiveness to high velocity visual stimuli.

Aging↗
PubMed1987

[Reorganization of callosal interhemispheric connections in the adult cat: effects of monocular occlusion after chiasmotomy].

Two groups of adult cats were chiasmotomized and their cortical receptive fields (17-18 boundary) were compared after a postoperative period of ca 6 weeks. In one group, binocular vision was maintained during that period, in the other one, one eye was sutured at the time of the chiasmotomy, depriving one hemisphere from patterned vision through the direct pathway. In monocular chiasmotomized animals, the receptive fields to stimulation of the contralateral eye were significantly larger than in the binocular ones.

Animals↗