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Biomedical subjects

F J Varela

Publications and source records attributed to F J Varela.

44 records · Page 3Linked to original sources
PubMed1977

Evidence for active role of cilia in sensory transduction.

Combined high-voltage electron-microscopic and electrophysiological studies strongly suggest that cilia play an active role in sensory transduction in the grasshopper proximal femoral chordotonal organ (FCO) a ciliated mechanoreceptor. The FCO of pro- and mesothoracic legs of Melanoplus bivittatus contains a group of several hundred chorodontal sensilla arranged in a near-parallel bundle and slung between the proximal femur and the knee joint. Both flexion and extension of the tibia stimulate the FCO, which appears to measure the femoro-tibial angle. The FCO's U-shaped response curve indicates that progressive flexion or extension from the resting joint angle of 90 degrees increases the response frequency of individual receptors and recruits additional units as well. Since the FCO is a purely tonic mechanoreceptor, it is possible to fix FCOs during maximum and minimum states of stimulation and electron-microscopically observed changes in the receptor's fine structure. The most conspicuous change is the production of a pronounced bend at the base of the sensory cilia in chordotonal sensilla of maximally stimulated femoral chordotonal organs.

Animals↗
PubMedDate not supplied

Self and non-sense: an organism-centered approach to immunology.

This paper provides a conceptual framework to accommodate important recent developments in immunology (genetic determination, cellular interactions, suppression). The basic idea is to look at the immune system as a closed network of interactions which self-determines its ongoing pattern of stability and its capacities of interaction with its environment. Thus, all immune events are understood as a form of self-recognition, and whatever falls outside this domain, shaped by genetics and ontogeny, is simply nonsensical. This paradigm, stemming from the ideas of Jerne, represents almost a logical inversion of the Burnetian idea of self-discrimination. A detailed discussion of the immunological evidence that substantiates this view is presented, together with some new concepts (eigenbehavior, cognitive domains). Although the paper is addressed to biologists and immunologists, we make extensive use of system-theoretic notions in a non-mathematical form (recursion, nets and trees, self-organization).

Animals↗
PubMedDate not supplied

Immune networks: getting on to the real thing.

After some ten years of faltering development, the network approach in immunology is finally heading toward steady ground. At a recent international workshop (*), experimentalists and theoreticians discussed some of the latest developments, including an impressive array of novel results and applications to fundamental properties of biological immune networks: connectivity, patterns of dynamic activity, ontogenesis, and tolerance.

Animals↗
PubMedDate not supplied

Synchronization of neuronal responses in the optic tectum of awake pigeons.

Multiunit activity was recorded in the optic tectum of awake pigeons with two electrodes at sites varying in depth and separated by 0.3 to 3.0 mm. Autocorrelation and cross-correlation functions were computed from the recorded spike trains to determine temporal relationships in the neuronal firing patterns. Cross-correlation analysis revealed that spatially separate groups of cells in the tectum show synchronous responses to a visual stimulus. Strong synchronization occurred in both superficial and deep layers of the tectum, in general with zero-phase shift. The response synchronization in the avian optic tectum resembles that observed in the mammalian cortex, suggesting that it may subserve common functions in visual processing.

Action Potentials↗
PubMedDate not supplied

A quantitative assessment of the dependency of the visual temporal frame upon the cortical rhythm.

This paper reports an attempt to measure the dependency of the visual temporal frame on cortical rhythms. As a probe, we used two short flashes of a point light source separated in time by a variable interstimulus interval (ISI). Subjects were asked to judge whether the two short flashes were perceived as simultaneous or as sequential. The onset of the light flashes was triggered at four chosen phases of the occipital alpha rhythm of the viewing subject, and the probabilities of perceived simultaneity at various ISI's were obtained. Data from three experimental subjects show that the triggering phase produced a significant shift along the ISI-axis, thus changing the probability of perceived simultaneity. The magnitude of this shift varied substantially across subjects. These results show that, although cortical rhythms correlate with perceptual framing as previously reported (Varela et al., 1981), the nature of this dependency is different than previously suggested: a visual temporal frame seems to be a local event at the cortex, and not a global coordination uniformly reflected in the alpha rhythm.

Adult↗