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L Maffei

Publications and source records attributed to L Maffei.

At least 73 records · Page 4Linked to original sources
PubMed1988

The organization of receptive fields in area 18 neurones of the cat varies with the spatio-temporal characteristics of the visual stimulus.

The spatial frequency tuning curves of neurones of area 18 depend upon the velocity of the visual stimulus. The higher the velocity the lower the spatial frequencies to which the cell is tuned. Since in area 17 the size of the cell receptive field is inversely related with the optimal spatial frequency to which the cell responds, we have investigated whether the shift of the optimal spatial frequency with the velocity corresponds to a "change" in the receptive field size. We recorded extracellularly from neurones in area 18; for each cell we selected two gratings, one of high spatial frequency drifting at low velocity and another of low spatial frequency drifting at high velocity to which the cell gave comparable responses. The results show that the masking of the cells receptive field which abolishes the response to the high frequency low velocity grating does not prevent the cell from responding to the low frequency high velocity grating. We conclude that the size of the receptive field of neurones in area 18 depends upon the characteristics (spatial frequency and velocity) of the visual stimulus.

Animals↗
PubMed1987

The transfer of visual information across the corpus callosum: spatial and temporal properties in the cat.

1. The spatial and temporal characteristics of the visual information transmitted across the corpus callosum have been studied in normal cats by recording directly from the corpus callosum and in split-chiasm cats by means of visual evoked potentials (v.e.p.s) and single-unit recordings at the 17/18 border. 2. The modulation transfer functions (m.t.f.s) obtained by recording from the corpus callosum are comparable to the m.t.f.s evaluated by various techniques for the whole visual system of the cat. The spatial and temporal acuities, however, do not reach the values obtained behaviourally or estimated with cortical evoked potentials. 3. In split-chiasm cats, both v.e.p.s and single-unit recordings indicate that the contrast gain of the callosal pathway is considerably lower than the gain of the direct, geniculo-cortical system. Spatial and temporal acuities are lower for the callosal than for the direct system. 4. The same differences in contrast gain between the spatial m.t.f. obtained for the callosal and the direct system have been found in alert split-chiasm cats. 5. Our data suggest that the cross-talk between the hemispheres taking place across the corpus callosum is nearly abolished at low contrasts and high spatial and temporal frequencies.

Animals↗
PubMed1986

Impairment of stereoacuity in cats with oculomotor proprioceptive deafferentation.

Stereoacuity was measured with an operant conditioning technique in adult cats with unilateral deafferentation of oculomotor proprioception (section of the ophthalmic branch of the fifth cranial nerve). Binocular stereoacuity was found not to exceed monocular depth sensitivity, in contrast to what is obtained in normal cats. The results confirm previous findings and indicate a role of oculomotor proprioception in binocular depth perception of the cat.

Animals↗
PubMed1986

Binocular suppression in cortical neurons.

Dichoptic presentation of patterns similar in shape but of very different contrast results in the perception of only the high contrast pattern (binocular suppression). When recording from binocular neurons of the cat visual cortex, we have found an effect which is strikingly similar to this perceptual phenomenon. If a high and a low contrast grating are presented simultaneously, one to each eye, the cell's response to the low contrast stimulus is suppressed.

Animals↗
PubMed1986

Interocular transfer of adaptation after effect in neurons of area 17 and 18 of split chiasm cats.

Responses to sinusoidal gratings for neurons in area 17 and 18 of split chiasm cats were recorded extracellularly, and the interocular transfer of the effect of adaptation to high-contrast gratings was studied. In area 17 all but one of the simple cells showed the phenomenon of adaptation and its interocular transfer; 60% of the complex cells showed the effect of adaptation, and of these cells 35% showed an interocular transfer of adaptation. The adaptation aftereffect was comparable both in strength and duration for the direct and the callosal pathway. The strength of the adaptation aftereffect through the callosal pathway was not related to the strength of the input from the contralateral eye. An interocular transfer of the adaptation aftereffect was found in several neurons with a very weak input from the contralateral eye and in five simple cells apparently responding only to the ipsilateral eye. Fifty-eight percent of the neurons in area 18 showed the effect of adaptation, and 55% of them showed interocular transfer. No interocular transfer of the adaptation aftereffect was found in those neurons where an input from the contralateral eye was undetectable. Interocular transfer of the adaptation was found in all the neurons recorded in area 17 of animals with section of the corpus callosum but intact chiasm. No interocular transfer was found in neurons recorded in area 17 of cats with both the optic chiasm and the corpus callosum sectioned. We conclude that callosal connections are sufficient for the transfer of the adaptation aftereffect, although they are not necessary.

Adaptation, Ocular↗
PubMed1985

Deafferentation of oculomotor proprioception affects depth discrimination in adult cats.

Depth discrimination was tested behaviourally in adult cats prior to and after chronic section of the ophthalmic branch of the Vth cranial nerve, that contains the majority of oculomotor proprioceptive fibers. Binocular depth discrimination was considerably impaired following either unilateral or bilateral oculomotor proprioceptive deafferentation.

Afferent Pathways↗
PubMed1985

Pattern ERG in the monkey after section of the optic nerve.

Electroretinographic responses (ERG) to homogeneous light flashes and to alternating gratings were recorded from either eye of monkeys in which one optic nerve had been previously sectioned. Three weeks after optic nerve section the ERG response of the operated eye to alternating gratings was drastically reduced in amplitude and 5 weeks after surgery it was reduced to noise level. The uniform field ERG was unaffected. Histological examination of whole-mounted retinas of monkeys sacrificed 6 and 8 weeks after optic nerve section showed a loss of ganglion cells in the operated eye. It is concluded that the integrity of ganglion cells is essential for the generation of a normal ERG response to gratings.

Animals↗
PubMed1985

Functional organization of the cat's visual cortex after prenatal interruption of binocular interactions.

The functional consequences of interrupting in utero binocular interactions were studied by recording from single cells in area 17 of adult cats that had one eye removed at least 2 wk before birth. In these animals all cortical neurons could be driven by the remaining eye, and in tangential microelectrode penetrations, sequences of neurons containing a full 180-degree cycle of preferred orientations were encountered. Other response properties of cortical neurons in the prenatally enucleated animals were also normal with the notable exception that the dimensions of receptive fields were significantly smaller when compared with those of control animals. Our results indicate that orientation columns in the visual cortex can develop independently of ocular dominance columns, and they suggest that interruption of binocular interactions during prenatal development of the visual pathways may enhance the resolving power of the remaining eye.

Animals↗
PubMed1985

Spatial-frequency characteristics of neurones of area 18 in the cat: dependence on the velocity of the visual stimulus.

The spatial and temporal response properties of neurones of areas 17 and 18 were studied in single units (165) of anaesthetized and paralysed cats. The visual stimuli were drifting or alternating gratings. We confirmed and extended the observation by Tolhurst & Movshon (1975) showing that the spatial-frequency characteristics of neurones of area 17 are largely independent of the temporal parameters of drifting or alternating gratings. The spatial-frequency tuning curves of neurones of area 18 shift along the spatial-frequency axis when the velocity or the temporal frequency of the drifting grating are changed. The effect of an increase either of velocity or temporal frequency is to shift the cell spatial-frequency tuning curve down the spatial-frequency scale, keeping relatively constant the strength and band width of the response. The spatial-frequency tuning curves of neurones of area 18 do not show this temporal-frequency-dependent phenomenon when the stimuli are gratings alternated in phase. In this case neurones of areas 17 and 18 show a similar behaviour. The response properties of neurones of area 18 are compared with recent psychophysical results obtained in similar experimental conditions. The hypothesis is advanced that both areas 17 and 18 are devoted to the processing of spatial information. Area 17 would be responsible for the processing of patterns in stationary or quasi-stationary situations while area 18 would be responsible for that of patterns moving at high velocities.

Animals↗
PubMed1985

Dopaminergic drugs improve human visual contrast sensitivity.

Effects of dopaminergic drugs (L-dopa plus benserazide, or nomifensine) on human visual function have been tested in healthy volunteers by measuring the psychophysical contrast sensitivity for sinusoidal gratings of various spatial frequencies. After drug administration the contrast sensitivity improved in all subjects over a limited range of medium to high spatial frequencies.

Adult↗
PubMed1984

Electroretinographic responses and retrograde changes of retinal morphology after intracranial optic nerve section. A quantitative analysis in the cat.

Previous experiments have shown that the ERG response to alternating gratings vanishes gradually within 4 months after transection of the optic nerve, changes begin after 2-3 weeks. The response to gratings of low spatial frequencies deteriorates earlier than the response to gratings of high spatial frequencies (Maffei and Fiorentini 1981). Quantitative analysis of ganglion cell sizes in retinal wholemounts shows that ganglion cell shrinkage and ganglion cell loss begin at three weeks in the periphery of the retina, particularly in the temporal retina. The same morphological alteration subsequently becomes apparent also in the area centralis and the nasal retina, respectively. The main and early cell loss occurs among medium sized ganglion cells, supposedly the beta-cells. Among the alpha-cells only shrinkage is observed up to two months postoperatively. Light- and electron microscopic examination of cross sections through the retina show that pathological changes are restricted to the innermost layers.

Animals↗
PubMed1984

Complementation analyses of differentiation-defective embryonal carcinoma cells.

We have generated cell hybrids by fusing embryonal carcinoma (EC) cells which fail to differentiate in response to retinoic acid (RA) and/or hexamethylenebisacetamide (HMBA). The first two classes of hybrids were between an RA- line (also unresponsive to HMBA) that lacks cellular RA binding protein (cRABP) activity and HMBA- lines which possess cRABP and differentiate in the presence of RA. All of the hybrid clones possessed cRABP and differentiated normally upon exposure to either RA or HMBA. When the aforementioned RA- mutant was fused with a second mutant which was refractory to RA and HMBA but possessed cRABP activity, the resultant hybrid clones were responsive to both RA and HMBA and had cRABP activity. These results suggest that all of these mutants were recessive and complementary. Tumors from these hybrid lines differentiated extensively, in some instances much more so than the mutant parental lines and even the wild-type lines from which the mutants were derived. Based upon these observations, we propose that various EC lines might differentiate poorly in tumor form for different reasons. Hybrids between two differentiation-defective, cRABP- lines appeared to be at least partially complemented for responsiveness to RA and HMBA. These hybrids contained low but detectable levels of cRABP. This is not a consequence of tetraploidy since fusions between cells from the same mutant line retained their differentiation-defective phenotype and possessed little or no cRABP activity. Unlike tumors from the other hybrids described above, tumors from these hybrid lines expressed a very restricted pattern of differentiated cell types. This might be because the mutant lines in the latter hybrids originally derived from the same wild-type EC line.

Acetamides↗
PubMed1983

Pattern electroretinograms and visual-evoked potentials in glaucoma and multiple sclerosis.

Steady-state visual-evoked potentials and electroretinograms were simultaneously recorded in four patients with glaucoma and in five patients with multiple sclerosis. The stimuli included a homogenous field and a 2.3 cycles per degree sinusoidal grating that were counter-phase modulated at the rate of 7.5 Hz. We used narrow bandwidth spectral analysis to measure the response amplitudes and signal-to-noise ratios. Transient pattern visual-evoked potentials (1 Hz) were also measured for latency in each eye. We found abnormal pattern electroretinograms, based on the absence of a significant second harmonic component, in three of the four glaucomatous eyes although the homogenous field electroretinograms were normal. In the patients with multiple sclerosis, the pattern electroretinograms were abnormal in two eyes, but the transient visual-evoked potential latency had the highest diagnostic yield (seven of ten eyes).

Adult↗
PubMed1983

The role of high spatial frequencies in face perception.

The relevance of low and high spatial-frequency information for the recognition of photographs of faces has been investigated by testing recognition of faces that have been either low-pass (LP) or high-pass (HP) filtered in the spatial-frequency domain. The highest resolvable spatial frequency was set at 15 cycles per face width (cycles fw-1). Recognition was much less accurate for images that contained only the low spatial frequencies (up to 5 cycles fw-1) than for images that contained only spatial frequencies higher than 5 cycles fw-1. For faces HP filtered above 8 cycles fw-1, recognition was almost as accurate as for faces LP filtered below 8 cycles fw-1, although the energy content of the latter greatly exceeded that of the former. These findings show that information conveyed by the higher spatial frequencies is not redundant. Rather, it is sufficient by itself to ensure recognition.

Discrimination, Psychological↗
PubMed1982

Functional implications of cross-orientation inhibition of cortical visual cells. I. Neurophysiological evidence.

Simple and complex cells of striate cortex of anaesthetized and paralysed cats were stimulated with two superimposed one-dimensional grating stimuli of different orientations to investigate inhibitory effects of non-optimally oriented stimuli. We confirmed that a stimulus of orientation orthogonal to a cell's long axis significantly reduces the cell's discharge rate. Further experiments revealed the following. (i) The inhibition was typically stronger for simple than for complex cells. (ii) It is very broadly tuned for orientation, all orientations outside the cell's tuning band having a comparable inhibitory effect. (iii) Similarly, it is broadly tuned for spatial frequency. These last two results suggest that the inhibition arises not from a single cell but from a pool of cells. (iv) The pattern of the discharge of the inhibition in response to stimulation by phase-reversed sinusoidal gratings is consistent with the notion that the inhibition arises from complex cells. A second series of recordings of stimulation by visual noise patterns demonstrated how 'cross-orientation inhibition' prevents simple cells from responding to two-dimensional visual noise while allowing them to respond to comparable one-dimensional noise patterns. We suggest that this mechanism may serve to render simple cells selectively sensitive to one-dimensional stimuli, such as the contours or borders of visual objects.

Action Potentials↗