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Biomedical subjects

M Ptito

Publications and source records attributed to M Ptito.

At least 73 records · Page 4Linked to original sources
PubMed1986

Stereoperception in cats following section of the corpus callosum and/or the optic chiasma.

The spatial separation of the eyes in animals with overlapping visual fields means that parts of a three dimensional object project to slightly disparate retinal points in each eye. This disparity, once interpreted by the brain, is thought to be a sufficient condition for stereoperception. In the present experiment, stereopsis based on spatial disparity cues was evaluated in cats using Julesz random-dot stereograms before and after sections of the optic chiasm, the corpus callosum or both. Normal cats were able to solve the random-dot problem. Optic chiasm transection drastically diminished this ability, callosal section had little effect and combined lesions of these two structures abolished stereoperception. These results suggest that central stereopsis based on spatial disparity is mainly mediated by binocular cortical cells receiving their input via the ipsilateral and the through-the-chiasm contralateral thalamo-cortical pathways.

Animals↗
PubMed1985

Intracortical connections of the anterior ectosylvian and lateral suprasylvian visual areas in the cat.

Intra- and interhemispheric connections between the anterior ectosylvian visual area (AEV) and other visual cortical areas including the lateral suprasylvian (LSS) were examined in the cat using the retrograde double-label fluorescence technique. The areal and laminar distributions of labeled neurons were mapped following injections of different tracers: Evans Blue (EB), Fast Blue (FB) and Nuclear Yellow (NY) made separately into AEV and LSS of the same or opposite hemispheres. The results indicated: (1) reciprocal and bilateral AEV-LSS connections stemming from layers V and VI in addition to a predominant efferent LSS projection upon AEV from both layer III and the posterior lateral (PLLS) subdivision of LSS; (2) homotopic interhemispheric connections to AEV arising from layers III, V and VI and from layers III and V of ipsilateral areas 20 and 21a; (3) differential laminar distributions of the cell populations projecting to the two cortical sites injected including neurons in layer III of LSS which project to contralateral LSS and AEV of either hemisphere via collateral axon branching (double-labeled). The anatomical findings support the functional similarities between AEV and LSS and the possible role of AEV in interhemispheric transfer of visual information is discussed.

Animals↗
PubMed1983

Interocular transfer in cats with early callosal transection.

The visual system is capable of reorganization following experimental interventions, provided that these are carried out before the 'critical period' early in life. Direct evidence suggests that this plasticity may also apply to the commissural system. In the present experiment, we sectioned the posterior two-thirds of the corpus callosum in kittens either before this structure attained maturity, as defined by various anatomical and physiological parameters, or after callosal maturation but before the end of the critical period for most other visual functions. As adult, further transection of the optic chiasma was carried out and these animals were then compared with adult split-brain cats for their ability to transfer monocularly learned pattern discriminations from one hemisphere to the other. Our results indicate that only the first group of animals with the earlier callosal transection demonstrated significant interhemispheric transfer. This suggests that the secondary commissural system is subject to at least some degree of functional plasticity. However, its critical period is very brief and possibly pre-dates the optimal activation of the callosal pathway.

Age Factors↗
PubMed1983

Effects of unilateral and bilateral lesions of the lateral suprasylvian area on learning and interhemispheric transfer of pattern discrimination in the cat.

The aim of the present experiment was to evaluate the hypothesis that the lateral suprasylvian area is involved in the interhemispheric transfer of visual information. This area was surgically removed in 10 cats which had previously undergone a midsagittal transection of their optic chiasmas. The animals then learned a pattern discrimination using either one or the other hemisphere and were tested for transfer using the other, untrained hemisphere. The lateral suprasylvian area in the intact hemisphere was next ablated in 6 of these cats. Each hemisphere was trained on a new pattern discrimination and tested for transfer using the other. The results obtained with the unilaterally lesioned animals indicated that: (a) learning with the lesioned hemisphere was as rapid as with the intact hemisphere; and (b) that transfer in either direction was normal although slightly retarded, but not significantly so, when the information proceeded from the intact to the lesioned hemisphere. Learning with either hemisphere of the bilaterally lesioned animals also appeared to be normal. Learning with the hemisphere which was lesioned second and transferring to the one which was ablated first was within normal range whereas transfer was generally not as immediate when the procedure was reversed. As a whole, the results, when coupled with those of others, would tend to indicate that the lateral suprasylvian area is involved in interhemispheric transfer but shares this function with other callosally connected areas of the primary visual cortex.

Animals↗
PubMed1983

Harmaline-induced rhythmic activities of bulbar reticular cells and antagonistic muscles in the rat: a simultaneous recording study.

The harmaline-induced tremor of antagonistic muscles is studied in the anaesthetized rat. By recording simultaneously both the rhythmic EMG-activities in flexor and extensor muscles and the concomitant tremorogenic bulbar reticular discharges, we discovered two facts. 1) The extensor burst precedes the flexor muscle discharge by about 10 msec, contrarily to the close synchrony expected from anterior descriptions of harmaline tremor. 2) The previously observed periodical modulation of olivary and Purkinje cell rhythmic activities is transferred, through the reticular formation to the spinal level, in the form of an alteration of periods with tremor and periods with tonic coactivation of antagonistic muscles. The implication of the myotatic loop in the second fact is discussed.

Alkaloids↗
PubMed1983

[Structures of telencephalic projection in the pigeon. Identification by marking with horseradish peroxidase].

The sites of origin of afferents to the telencephalon in the pigeon were investigated using the HRP technique (TMB). Following large multiple injections of the enzyme into the cerebral hemisphere, peroxidase-positive neurons were identified at diencephalic levels: ipsilaterally in DLM, DMA, DLP, DIP, DMP, Rt, Ov, SRt and SCE/SCI; bilaterally in DLA and SPC. At mesencephalic and posterior brainstem levels, HRP-labeled neurons were found: ipsilaterally in AVT, ZpNIII, ICo, FRM, FRL, TP and SCv; bilaterally in GCt, ZpFLM, neurons were found: ipsilaterally in AVT, ZpNIII, ICo, FRM, FRL, TP and SCv; bilaterally in GCt, ZpFLM, Annul, LoC, LC and PrV. Smaller injections of HRP into different regions of the telencephalon demonstrated, for some of the latter structures, either single or multiple projections upon topographically distinct subdivisions.

Afferent Pathways↗
PubMed1981

Classification of receptive field properties in cat visual cortex.

The properties of the receptive fields of visual cortex neurons of cats were studied manually and by a computer controlled system using single lines, double lines and multiple lines (gratings). The multiple selectivities of each of the receptive fields studied make it necessary to abandon the concept that each cell functions as a feature detector. Instead, an attempt was made to classify the receptive field properties with the aim to delineate the transfer functions (of the total networks) served for each property. When tested with one-line stimulus, cells with simple receptive field properties differed from cells with complex receptive field properties as to their velocity selectivity (simple: 1 degree to 3 degrees/s; complex: 4 degrees to 10 degrees/s), spontaneous activity (lower for cells with simple properties) optimal firing rate (lower for cells with simple properties) and receptive field size (smaller for cells with simple properties) but not for orientation and direction selectivity. When tested with a 2-lines moving stimulus, the responses of cells with simple properties were facilitated by the progressive separation of the lines whereas the responses of cells with complex receptive field properties were inhibited. When multiple line, i.e., gratings, were used, an equivalence between simple and X properties and complex and Y properties was shown, while the sustained/transient classification proved to be independent of the simple/complex (X/Y) classification. Thus, receptive field properties can be classified into three categories: one reflects the input to the receptive fields; a second deals with the interactive properties of the fields; while a third appears more related to the overall properties of the network.

Animals↗
PubMed1981

Intracerebral influences on the microstructure of receptive fields of cat visual cortex.

Effects of electrical stimulation of the basal ganglia (caudate nucleus and putamen) and cortex (gyrus proreus and compositus) on the receptive fields and response properties of units in the visual cortex of cats were assessed using single lines, double lines and multiple lines (gratings). In the single line experiment caudate stimulation, significantly increased the spontaneous activity, optimal firing rate and receptive field size of visual cortex neurons whereas putamen stimulation decreased these parameters. Stimulation of gyrus proreus enhanced, while that of gyrus compositus diminished optimal firing rate without affecting spontaneous activity; in addition, stimulation of ipsilateral proreus and compositus increased the receptive field size whereas their contralateral homologues decreased it. In the double line experiment, proreus and caudate stimulation increased the magnitude of the facilitatory effect of progressive separation of the lines over certain ranges whereas compositus and putamen stimulation increased the inhibitory influences. Orientation selectivity and spatial frequency tuning characteristics were unaffected by the electrical stimulation of any of the four sites. Thus three categories of network properties were delineated: those characterized by remaining invariant to any cerebral stimulation; those characterized by overall activation as by basal ganglia stimulation; and those characterized as interactive which were responsive especially to cortical stimulation.

Animals↗
PubMed1981

[Role of the contralateral cortex on the receptive field properties in the visual cortex of cats].

The aim of this series of experiments was to evaluate the receptive field properties of visual cells receiving part of their input the corpus callosum. Normal (control) and chiasma sectioned cats were recorded using conventional methods. The recording sites were the 17-18 border and the lateral suprasylvian (LS) cortex. The results indicated (a) the ocular dominance distribution was shifted towards the ipsilateral eye in the split chiasma cats; (b) orientation tunning and/or directional specificity were identical for the two eyes; (c) R.F. positions of binocular cells were also similar for each eye and were clustered near the vertical meridian, which they sometimes straddled; (d) R.F. sizes were larger in L.S. than in primary visual cortex but generally of equal dimensions for each eye. The results are interpreted with respect to the various functions which have been postulated for the corpus callosum.

Animals↗
PubMed1981

[The role of the corpus callosum and other commissures in the interhemispheric transfer of visual information].

In order to assess the contribution of the lateral suprasylvian area and subcortical pathways other than the corpus callosum in learning and interhemispheric transfer, a series of studies was undertaken in the cat. Groups of animals which received different types of cortical and subcortical lesions were tested for learning and interocular transfer of visual pattern discriminations. Results have shown that : 1. the lateral suprasylvian area is of equal importance in learning and transfer as areas 17, 18 and 19; 2. in the absence of the corpus callosum, other commissures could preserve interocular transfer of visual information. The results obtained on commissurotomized neonate kittens clearly support this assumption.

Animals↗