PubMed Health⌕ Search

Biomedical subjects

Y Frégnac

Publications and source records attributed to Y Frégnac.

30 records · Page 2Linked to original sources
PubMed1987

The period of susceptibility of visual cortical binocularity to unilateral proprioceptive deafferentation of extraocular muscles.

1. The electrophysiological effects of section of extraocular muscle proprioceptive afferents have been investigated in kitten area 17. Extraocular proprioceptive afferents were interrupted by cutting the ophthalmic branch of the fifth trigeminal nerve (V1 nerve) unilaterally in 15 normally reared kittens (NR) between 3 and 12 wk postnatal, in 3 NR adult cats, and in 7 dark-reared (DR) kittens at 6 wk postnatal. Bilateral sections of the V1 nerve were performed in two kittens at 6 wk postnatal. NR kittens were maintained in a normal environment after the section. DR kittens were returned to the darkroom until the recording session. Receptive-field properties of area 17 neurons were studied after a postsurgical delay of 4-7 wk in most NR kittens and of 4 days to 5 wk in DR kittens. In one NR kitten and in the operated adult cats, the delay was 1-2.5 yr. This study is based on a total sample of 1,190 visual cortical units. 2. When performed in NR kittens between 4 and 8 wk of age, the unilateral section of extraocular proprioceptive afferents significantly reduced the proportion of binocular cells: 1 mo after the section of the V1 nerve, half of the visual cortical cells were monocularly activated. A similar reduction in the proportion of binocular cells was also observed in DR kittens operated at 6 wk of age and then maintained in the dark for 5-7 wk. In contrast to the unilateral section, the bilateral section of the V1 nerve performed in 6-wk-old NR kittens did not disrupt cortical binocularity. 3. In 10 of the 22 kittens that had undergone unilateral sections, there was a strong asymmetry in the ocular dominance distribution in favor of one eye. This asymmetry was not related to the side of the section and was the same in both hemispheres for a given kitten. 4. The postsurgical delay played an important role in the appearance of the cortical deficit: binocularity loss was not found within the week following the section but was present 1 mo after the section. This functional impairment appeared to be permanent, since it was still observed 2.5 yr after the section. 5. Cortical cells were classified in two ways on the basis of their receptive-field organization: 1) into S- or C-types (38, 73), and 2) into small area slow (SAS), large area slow (LAS), or Fast (F)-types (42, 57).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Role of extraocular muscle proprioception in the development of depth perception in cats.

1. The ophthalmic branch of the trigeminal nerve (V1), which carries extraocular proprioceptive afferents, was sectioned unilaterally or bilaterally in kittens and adult cats. Depth perception was measured behaviorally in these sectioned cats, as well as in control cats. 2. For kittens that underwent unilateral V1 sections at 6-11 wk of age, postsurgical values of binocular depth perception--measured 1.5-3 mo later--were 2-3 times worse than in normal control animals. Cats that underwent unilateral V1 sections as adults, however, showed no postsurgical deficits in binocular depth perception. 3. For kittens that underwent bilateral V1 sections at 6.5-7.5 wk of age, similar longterm impairments were found in binocular depth perception. No impairment was found in two kittens bilaterally sectioned at 11.5 wk of age. A cat that underwent bilateral sections as an adult also showed no binocular depth perception deficits. 4. Although these behavioral effects were observed only when unilateral and bilateral V1 sections were performed up to a certain age in development, they differed in two ways. 1) Imbalance of extraocular proprioceptive inflow produced by unilateral section had a deleterious effect at an age when the final adult level had been reached. At that stage, complete suppression of inflow produced by the bilateral section failed to impair the final level of binocular performance. 2) Short-term effects observed during the week following the section appeared in bilaterally operated animals as a transient freezing of the presurgical binocular performance whatever the age of the section during the sensitive period. In contrast, short-term effects produced by unilateral section were found to be age dependent: a progressive slowing down in the normal rate of improvement of binocular thresholds was observed following a section performed at 5 wk of age; an arrest in development was found when surgery was done at 6-7 wk of age. A significant impairment appeared within 2 days when the section was performed at 11 wk of age. 5. In all experimental kittens, monocular depth perception thresholds were unaffected or impaired only to a minor extent (less than 15% change) following the unilateral or bilateral section. In unilaterally operated kittens, there were no consistent differences associated with the side of the section. 6. A sham-operated kitten, in which the V1 was visualized but not cut, showed no impairments in binocular or monocular depth perception.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1985

Noradrenaline and functional plasticity in kitten visual cortex: a re-examination.

A quantitative re-examination was made of the influence of noradrenergic depletion on the epigenesis of kitten visual cortex. Two methods were used to deplete noradrenaline at the cortical level: stereotaxically controlled injection of 6-hydroxydopamine (6-OHDA) in the coeruleus complex, from which the noradrenergic input to visual cortex arises; intraventricular injection of 6-OHDA. The latter chemical lesion also depleted dopamine levels in the brain. Lesion of the noradrenergic or catecholaminergic systems was performed neonatally or at an age of 3-4 weeks in kittens submitted to five different rearing procedures: normal rearing, dark rearing, monocular rearing, monocular exposure following dark rearing and monocular deprivation following normal rearing. Forty-two kittens between 3 and 12 weeks of age were used for this biochemical and electrophysiological study. Noradrenaline and dopamine levels were measured by a radioenzymatic method in the primary visual cortex of twenty-six kittens. A total of 1263 cells were recorded in area 17 of twenty-six kittens. Combined biochemical and electrophysiological data were obtained in ten 6-OHDA-lesioned kittens. Whatever the mode of chemical lesion used, cortical noradrenergic depletion failed to block either maturation or vision-dependent processes which are known to affect orientation selectivity and/or ocular dominance during the critical period. However, in some cases, the amplitude of the epigenetic functional modifications was slightly reduced in 6-OHDA-treated kittens. The cortical effects of monocular deprivation starting from the age of 5 weeks were studied quantitatively both in lesioned and intact kittens. Disappearance of noradrenaline in area 17 did not prevent the loss of binocularity in cortical cells. However, even when monocular occlusion had been maintained for 2 or 3 weeks in 6-OHDA-treated kittens, ocular dominance shifts were limited to a stage equivalent to that observed in the intact kitten after 5-8 days of monocular occlusion. The amplitude of this partial protective effect was found to be unrelated either to the delay following the chemical lesion, or to the level of noradrenaline remaining in lesioned kitten cortex. Although a putative gating role of noradrenaline cannot be excluded in the development of the intact animal, this report shows that its presence is not required for functional plasticity to occur in kitten area 17.

Animals↗
PubMed1981

[Period of sensitivity of the primary visual cortex of the cat to the unilateral suppression of extraocular proprioceptive afferents].

Unilateral suppression of extraocular proprioceptive afferents, which run through the ophthalmic branch of the Vth nerve, disrupted binocular integration in the primary visual cortex of normally reared kittens, when it was performed between 4 and 8 weeks of postnatal age. One month later, half the visual cortical cells were exclusively activated through one eye. A similar disorganization of binocularity was observed in visually deprived Kittens when unilateral lesion was performed at 6 weeks of age. We conclude that the loss of binocular integration is caused by non visual factors, probably related to asymmetry between proprioceptive informations from each eye.

Afferent Pathways↗
PubMed1981

Effect of neonatal unilateral enucleation on the development of orientation selectivity in the primary visual cortex of normally and dark-reared kittens.

The developmental properties of 573 neurones have been investigated in the primary visual cortex of eight binocularly intact and twelve unilaterally enucleated kittens. It is shown that removal of one eye at birth alters the development of orientation selectivity observed in the presence or absence of visual experience. In 6-week-old deprived kittens, there remain significantly more orientation selective cells in enucleated than in binocularly deprived kittens. These deprivation-resistant cells respond preferentially to horizontal or vertical orientations and are recorded mainly in the cortex contralateral to the remaining eye. In six-week-old kittens with visual experience, the process of tuning maturation appears to be unaffected by unilateral enucleation at birth. However, a larger over-representation of horizontal and vertical orientation preferences is observed in uniocular kittens than in binocularly intact kittens, suggesting that the development of oblique orientation preference depends upon the presence of binocular afferents in the visual pathway.

Animals↗
PubMed1979

Development of orientation selectivity in the primary visual cortex of normally and dark reared kittens. I. Kinetics.

Kinetics of the development of orientation tuning are inferred from quantitative analysis of extracellular recordings in the primary visual cortex of normally and dark reared kittens. 712 visual cells were classified in three functional groups: a) non-specific cells, and b) immature cells which are not as orientation selective as c) specific cells. Power regression and covariance analysis indicate that the "critical period" begins before 19 days and that the kinetics of the immature pool are the same in both rearing conditions. A catenary process of development of orientation selectivity is proposed, the immature compartment being a transit pool between non-specific and specific cells. Two sequential stages occur: 1) the realisation of an intrinsic programme of maturation, by which cortical specificity appears at eye opening and increases independently of visual experience 2) a phase of "epigenesis" beginning at 19 days, during which functional modification depends on visual experience.

Animals↗
PubMed1979

Development of orientation selectivity in the primary visual cortex of normally and dark reared kittens. II. Models.

The development of orientation selectivity in the primary visual cortex is described by first-order kinetics between three functional compartments chained in a catenary mode. A first model is presented, in which two unidirectional kinetics with constant exchange coefficients, symmetrical in their effects, function in an alternating mode depending on the presence or absence of visual experience. The failure of this model to simulate the modifications induced by a delayed visual experience, when the exchange coefficients are identified to fit normal and dark rearing, supports the hypothesis that the maturation process consequent to interaction with visual environment is dependent on the date at which it is allowed to take place. A second model is then proposed, in which exchange coefficients are piecewise linear functions of time. In order to correctly predict the functional effects of restricted visual experience following prior dark rearing, it is assumed that visuomotor experience during the critical period permits the expression of a non-linear "modifiability gradient" which may have been masked up to this point by the absence of vision or eye movements.

Animals↗
PubMed1978

Early development of visual cortical cells in normal and dark-reared kittens: relationship between orientation selectivity and ocular dominance.

1. 535 units were recorded in the primary visual cortex in twelve normally reared and fifteen dark-reared kittens aged between 8 and 50 days. These results were pooled with a previous study of 582 units recorded from thirty-five kittens reared in similar conditions. 2. These 1117 cells were classified into four functional classes of neurones: (a) visually unresponsive cells, (b) non-specific cells which were sensitive to spots or slits of light moving in any direction, (c) immature cells which were preferentially activated by a rectilinear stimulus but unselective regarding its precise orientation and (d) specific cells that appeared to be as selective for orientation as the simple or complex cells in the adult cat. 3. The results confirm that cells having the same orientation-specific response properties as adult cortical visual neurones are present in the earliest stages of post-natal development, independently of visual experience. However, to maintain and develop these specific cells after the third week of post-natal life, visual experience is necessary. 4. The ocular dominance of visual cells is not constant from the earliest stages of development. A significant increase in binocularly driven neurones occurs with age. 5. Before 3 weeks of age, whatever the rearing conditions, there are more specific cells coding horizontal and vertical orientations than those coding oblique orientations. These 'horizontal and vertical detectors' are preferentially driven by the contralateral eye. 5. After 4 weeks of age, specific neurones are found at all orientations in normally reared kittens. At this stage of development the ocular dominance is independent of orientation preference, of the functional class of neurones considered and of the rearing conditions. The proportion of binocularly driven cells is slightly below adult standard. 7. A hypothesis of differential plasticity is proposed: contralateral, monocular 'horizontal and vertical detectors' are supposed to be stable; they would remain so until they become binocular. Binocular cells, for which competition between two inputs occurs, are the labile units which can be despecified or specified under the control of visual experience.

Action Potentials↗
PubMedDate not supplied

The visual cortical association field: a Gestalt concept or a psychophysiological entity?

The receptive field of a visual neurone is classically defined as the region of space (or retina) where a visual stimulus evokes a change in its firing activity. Intracellular recordings in cat area 17 show that the visually evoked synaptic integration field extends over a much larger area than that established on the basis of spike activity. Synaptic depolarizing (dominant excitation) responses decrease in strength for stimuli that are flashed at increasing distances away from the centre of the discharge field, while their onset latency increases. A detailed spatio-temporal analysis of these electrophysiological data shows that subthreshold synaptic responses observed in the 'silent' surround of cortical receptive fields result from the intracortical spread of activation waves carried by slowly conducting horizontal axons within primary visual cortex. They also predict that a perceptual facilitation may occur when feedforward activation produced by the motion signal in the retina travels in phase in the primary visual cortex with the visually induced spread of horizontal activation. A psychophysical correlate has been obtained in humans, showing that apparent motion produced by a sequence of co-linear Gabor patches, known to preferentially activate V1 orientation selective cells, are perceived by human observers as much faster than non co-linear sequences of the same physical speed.

Animals↗
PubMedDate not supplied

A phenomenological model of visually evoked spike trains in cat geniculate nonlagged X-cells.

The visual information that first-order cortical cells receive is contained in the visually evoked spike trains of geniculate relay cells. To address functional issues such as the ON/OFF structure of visual cortical receptive fields with modelling studies, a geniculate cell model is needed where the spatial and temporal characteristics of the visual response are described quantitatively. We propose a model simulating the spike trains produced by cat geniculate nonlagged X-cells, based on a review of the electrophysiological literature. The level of description chosen is phenomenological, fitting the dynamics and amplitude of phasic and tonic responses, center/surround antagonism, surround excitatory responses, and the statistical properties of both spontaneous and visually evoked spike trains. The model, which has been constrained so as to reproduce the responses to centered light spots of expanding size and optimal light and dark annuli, predicts responses to thin and large bars flashed in various positions of the receptive field. The switching gamma renewal process method has been introduced for modelling spontaneous and visually evoked spike trains within the same mathematical framework. The statistical structure of the spike process is assumed to be more regular during phasic than tonic visual responses. On the whole, this model generates more realistic geniculate input to cortex than the currently used retinal models.

Animals↗
PubMedDate not supplied

Paradoxical signal transduction in neurobiological systems.

Information processing in neurobiological systems is commonly thought to rely on the assessment of a signal-to-noise ratio as the key mechanism of signal detection; it assumes and requires that both signal and noise are concurrently available. An alternative theory holds that detection proceeds by the system appreciating any instantaneous input by the input's departure from the moving average of past activity. The evidence reviewed here suggests that this latter transduction mechanism provides a unique, formal account of the highly dynamic, neuroadaptative plasticity (i.e., tolerance, dependence, sensitization) that ensues upon mu-opioid receptor activation. The mechanism would appear already to operate with the receptor-G protein coupling that occurs upon agonist binding to mu-opioid receptors, and also with highly integrated responses such as whole-organism analgesia. The mechanism may perhaps operate ubiquitously with further neuronal and non-neuronal, cell surface, and intracellular-signaling systems, and may govern the experience-dependent regulation of synaptic strength. The transduction mechanism defines a continuously evolving process; the process's most peculiar feature is that it makes any input generate not one but two outcomes that are paradoxical, or opposite in sign.

Analgesics↗