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Biomedical subjects

L Maffei

Publications and source records attributed to L Maffei.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1982

Electroretinographic responses to alternating gratings in the cat.

Electroretinographic (ERG) responses to alternating sinusoidal gratings were investigated in the anaesthetized cat. The alternating grating ERG, but not the flash ERG, is reduced in amplitude during electrical stimulation of the optic nerve. Temporary retinal ischaemia caused either by clamping of the retinal artery or by increased intraocular pressure differentially affects the ERG responses to gratings or flashes. It has also been confirmed that following retrograde degeneration of ganglion cells caused by unilateral section of the optic nerve the alternating grating ERG disappears while the ERG in response to flashes is unaffected. All these findings indicate that the various electrical retinal sources contribute in a different way to the pattern ERG and flash ERG and suggest that the main source of the pattern ERG is at the ganglion cell level.

Animals↗
PubMed1982

Role of extraocular proprioception in the orienting behaviour of cats.

We investigated the effects of unilateral deafferentation of extraocular proprioception on the orienting behaviour of cats. The ophthalmic branch of the Vth cranial nerve, in which most of the extraocular proprioceptive fibers are known to run, was cut unilaterally in adult cats. The animals had been previously trained to jump from a start box to a luminous target at various possible locations in the right or left visual hemifield. The postsurgical orienting performance of the animals, evaluated from the difference between landing position and position of the target, differed from the presurgical performance. The postsurgical errors were typically: (1) ipsiversive to the side of the section, (2) usually of a larger magnitude in the hemifield contralateral to the section, (3) present in binocular as well as in monocular viewing conditions and approximately of the same magnitude for jumps guided by either eye. These findings indicate that extraocular proprioception plays a role in the orienting behaviour of cats.

Afferent Pathways↗
PubMed1982

Correlation between the preferred orientation and spatial frequency of neurones in visual areas 17 and 18 of the cat.

1. In seventy-six penetrations through areas 17 and 18 of the cat, neurones were regularly sampled at intervals of 100 micrometers and preferred orientation, optimal spatial frequency and resolving power were determined for each neurone in response to drifting sinusoidal gratings. 2. As already shown for area 17, in tangential penetrations through area 18, whenever the preferred orientation rotates progressively from cell to cell, the optimal spatial frequency tends to remain constant. 3. A statistical analysis on 1574 cells in areas 17 and 18 showed that for pairs of cells separated 200-300 micrometers along a track the difference in preferred orientation delta alpha and the difference in optimal spatial frequency delta f are not randomly distributed: cell pairs with small delta alpha are most likely to have large delta f and vice versa. 4. These findings indicate that in areas 17 and 18 neurones with the same optimal frequency are aligned along a direction orthogonal to the orientation columns. 5. The optimal spatial frequency, resolving power and the velocity cut-off were averaged for cells from different penetrations located in the same cortical layer or sublayer of area 18: mean optimal spatial frequency and acuity are highest in layer IV and lowest in layers II and V, while the velocity cut-off is highest in layers II and V and lowest in layer IV. 6. Our data suggest that the layering of cells according to optimal spatial frequency is a more subtle subdivision than the six histological layers.

Action Potentials↗
PubMed1982

On the application of systems analysis to neurophysiological problems.

In this essay we have presented some personal viewpoints on the application of Systems. Analysis to suitable neurophysiological problems and provided reasoned reviews on selected topics (receptor and nerve cell physiology, motor control, vestibular and visual systems) in which new data and ideas were brought about in the past several years by the use of Systems Analysis. Since the nature of the paper precludes the possibility of writing a summary, we simply thank those readers who have endured up to this point. As for those prudent persons who are beginning from this summary, before deciding as to the advisability of taking-up the task, we have a simple advice which runs contrary to the rule stated by the King to Alice in Wonderland (and accepted by one of us; see p. 60): begin from the topic that you like most and eventually go on, using the same criteria, till you are tired: then stop.

Animals↗
PubMed1981

Patterns in the discharge of simple and complex visual cortical cells.

The activity of visual cortical neurons (area 17) was recorded in anaesthetized cats in response to sinusoidal drifting gratings. The statistical structure of the discharge of simple and complex cells has been studied as a function of the various parameters of a drifting grating: spatial frequency, orientation, drifting velocity and contrast. For simple cells it has been found that the interspike interval distributions in response to drifting gratings of various spatial frequencies differ only by a time scale factor. They can be reduced to a unique distribution by a linear time transformation. Variations in the spatial frequency of the grating induce variations in the mean firing rate of the cell but leave unchanged the statistical structure of the discharge. On the contrary, the statistical structure of the simple cell activity changes when the contrast or the velocity of the stimulus is varied. For complex cells it has been found that the invariance property described above for simple cells is not valid. Complex cells present in their activity in response to visual stimuli two different firing patterns: spikes organized in clusters and spikes that do not show this organization ('isolated spikes'). The clustered component is the only component of the complex cell discharge that is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.

Action Potentials↗
PubMed1981

Intra-cortical inhibition prevents simple cells from responding to textured visual patterns.

Evidence is presented that simple cells in the cat striate cortex (area 17) fail to respond to two dimensional random patterns but respond vigorously to one dimensional patterns with identical power at the preferred orientation of the cell. Further observations suggest that complex cells inhibit simple cells so as to permit them to respond selectively to one-dimensional stimuli. Implications for the role of this inhibition in visual analysis are discussed.

Animals↗
PubMed1981

Two firing patterns in the discharge of complex cells encoding different attributes of the visual stimulus.

The activity of complex neurones of area 17 was recorded in anaesthetized cats in response to sinusoidal drifting gratings of various orientations, spatial frequencies and contrasts. The responses of complex cells present two different firing patterns: spikes organized in clusters and spikes which do not show this organization ("isolated spikes"). The clustered component is the only one in the complex cell discharge which is tuned for spatial frequency and orientation, while the isolated spike component is correlated with the contrast of the stimulus.

Animals↗
PubMed1981

The ERG in response to alternating gratings in patients with diseases of the peripheral visual pathway.

Electroretinogram (ERG) responses to alternating gratings have been recorded in patients with temporary occlusion of the retinal artery, retrobulbar optic neuritis, and other ganglion cell diseases. The ERG responses to alternating gratings were absent in first case and dramatically depressed in the others, whereas the ERG responses to light flashes or to homogeneous flickering light were normal. These findings corroborate recent evidence from studies on the cat, showing that the ERG in response to alternating gratings is correlated with ganglion cell activity.

Animals↗