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At least 847 records · Page 47Linked to original sources
PubMed2006

Representation of behaviourally relevant information by blowfly motion-sensitive visual interneurons requires precise compensatory head movements.

Flying blowflies shift their gaze by saccadic turns of body and head, keeping their gaze basically fixed between saccades. For the head, this results in almost pure translational optic flow between saccades, enabling visual interneurons in the fly motion pathway to extract information about translation of the animal and thereby about the spatial layout of the environment. There are noticeable differences between head and body movements during flight. Head saccades are faster and shorter than body saccades, and the head orientation is more stable between saccades than the body orientation. Here, we analyse the functional importance of these differences by probing visual interneurons of the blowfly motion pathway with optic flow based on either head movements or body movements, as recorded accurately with a magnetic search coil technique. We find that the precise head-body coordination is essential for the visual system to separate the translational from the rotational optic flow. If the head were tightly coupled to the body, the resulting optic flow would not contain the behaviourally important information on translation. Since it is difficult to resolve head orientation in many experimental paradigms, even when employing state-of-the-art digital video techniques, we introduce a 'headifying algorithm', which transforms the time-dependent body orientation in free flight into an estimate of head orientation. We show that application of this algorithm leads to an estimated head orientation between saccades that is sufficiently stable to enable recovering information on translation. The algorithm may therefore be of practical use when head orientation is needed but cannot be measured.

Algorithms↗
PubMed2005

Polarization-sensitive and light-sensitive neurons in two parallel pathways passing through the anterior optic tubercle in the locust brain.

Many migrating animals use a sun compass for long-range navigation. One of the guiding cues used by insects is the polarization pattern of the blue sky. In the desert locust Schistocerca gregaria, neurons of the central complex, a neuropil in the center of the brain, are sensitive to polarized light and might serve a key role in compass navigation. Visual pathways to the central complex include signal processing in the upper and lower units of the anterior optic tubercle. To determine whether these pathways carry polarization-vision signals, we have recorded the responses of interneurons of the optic tubercle of the locust to visual stimuli including polarized light. All neurons of the lower unit but only one of five recorded neurons of the upper unit of the tubercle were sensitive to linearly polarized light presented in the dorsal visual field. These neurons showed polarization opponency, or a sinusoidal modulation of activity, during stimulation through a rotating polarizer. Two types of bilateral interneurons preferred particular e-vector orientations, reflecting the presence of bilateral pairs of these neurons in the brain. We show here for the first time neurons with projections to the lateral accessory lobe that are suited to provide polarization input to the central complex. All neurons of the tubercle, furthermore, responded to unpolarized light, mostly with tonic activity changes. These responses strongly depended on stimulus position and might reflect navigation-relevant signals such as direct sunlight or visual landmarks that are integrated with polarization responses in neurons of the lower unit.

Action Potentials↗
PubMed1975

Polarity of structure and of ordered nerve connections in the developing amphibian brain.

Tectal polarity for retinal connections remains reversible long after the anatomical pattern of neural structures has been determined. Cells in the diencephalon seem to control this polarity. Following certain embryonic operations, the diencephalon developed behind the tectum. In such cases, the polarity of the retino-tectal projection was reversed.

Animals↗
PubMed2002

Optically and thermally induced electron transfer pathways in hexakis[4-(N,N-diarylamino)phenyl]benzene derivatives.

The optically and thermally induced electron transfer pathways of highly symmetrical (D(3)) hexaarylbenzene systems with six triarylamine redox sites have been investigated. Owing to slightly different local redox potentials, the radical trication could be selectively generated by electrochemical methods. This trication shows a strong intervalence charge-transfer band in the near infrared (NIR) that was measured by spectroelectrochemistry and analysed using multi-dimensional Mulliken-Hush theory. Quantum chemical AM1 CI calculations indicate that there is no optically induced concerted three-electron transfer that transforms the ground state into a state in which all three positively charged triarylamine moieties change place with their neutral neighbours. The potential energy surface of the ground state was constructed by using quadratic potentials. From this potential surface it is apparent that there is also no thermally allowed concerted three-electron transfer pathway. Instead, three consecutive one-electron transfer steps are necessary for this process.

Benzene Derivatives↗
PubMed1998

MRI of optic nerve and postchiasmal visual pathways and visual evoked potentials in secondary progressive multiple sclerosis.

We studied the relationship between abnormalities shown by MRI and functional disturbances in the visual pathway as assessed by the visual evoked potential (VEP) in 25 patients with established multiple sclerosis (MS); only 4 of whom had a history of acute optic neuritis. Optic nerve MRI was abnormal in 19 (76%) and is thus useful in detecting subclinical disease. Optic nerve total lesion length and area on the STIR sequence was found to correlate significantly with prolongation of the VEP latency. This may reflect a predominantly demyelinating rather than inflammatory origin for the signal change in the optic nerve.

Adult↗
PubMed1995

Comparative distribution of 2[125I]iodomelatonin binding in the brains of diurnal birds: outgroup analysis with turtles.

The roles that the pineal gland and its hormone melatonin play in the regulation of circadian rhythmicity and photoperiodism vary among vertebrate species. Recently, putative sites of melatonin action have been elucidated in several avian and mammalian species by application of in vitro binding of a radioiodinated melatonin agonist, 2[125I]iodomelatonin (IMEL) and autoradioradiography. These studies in mammals, birds and reptiles have indicated profound differences in the distribution of IMEL binding between these diverse groups, suggesting that these large differences in binding may reflect differences in melatonin function. The present study was performed to determine systematically whether the variance in IMEL binding among avian species corresponds to changes in circadian organization and/or phylogenetic relationships. The distribution of specific IMEL binding was determined in the brains from birds belonging to 14 different species in 5 Orders (Psittaciformes, Passeriformes, Columbiformes, Galliformes and Anseriformes) using in vitro binding, autoradiography and computer-assisted image analysis. The distribution was compared to a similar study in 3 species of turtles as an outgroup. The data indicated IMEL binding in retinorecipient structures of the circadian, tectofugal, thalamofugal and accessory optic visual pathways in all avian species. Relay nuclei and integrative structures of the tectofugal, thalamofugal, accessory optic, and limbic systems, however, bound the hormone to varying degrees. In turtles, binding was observed in retinorecipient structures of the thalamofugal visual pathway and in retinorecipient and integrative areas of the tectofugal visual pathway. No binding was observed in the pineal gland, tuberal hypothalamus or adenohypophysis in any avian or testudine species. This distribution is drastically different from that observed in mammals, where binding predominates in the pars tuberalis of the adenohypophysis and in the suprachiasmatic nucleus, suggesting that the circadian system may influence a wide array of sensory and integrative functions in birds and reptiles through the circadian secretion of melatonin, but that this capacity has been lost in mammals.

Animals↗
PubMed1982

Localization of neurons afferent to the optic tectum in longnose gars.

Afferent pathways to the optic tectum in the longnose gar were determined by unilateral tectal injections of HRP. Retrogradely labeled cells were observed in the ipsilateral caudal portion of the rostral entopeduncular nucleus and bilaterally in the rostral half of the lateral zone of area dorsalis of the telencephalon. The following diencephalic cell groups were also labeled following tectal injections: the ipsilateral anterior, ventrolateral, and ventromedial thalamic nuclei, the periventricular pretectal nucleus, and the central pretectal nucleus (bilaterally); the ventromedial thalamic and central pretectal nuclei revealed the largest number of labeled cells. At midbrain levels, retrogradely labeled cells were seen in the ipsilateral torus longitudinalis, nucleus isthmi, and accessory optic nucleus; cells were labeled bilaterally in the torus semicircularis and a rostral tegmental nucleus. Only a few cells were labeled in the contralateral optic tectum, suggesting that few of the fibers of the intertectal commissure are actually commissural to the tectum. At hindbrain levels, retrogradely labeled cells were seen bilaterally in the locus coeruleus, the superior, medial, and inferior reticular formations, the eurydendroid cells of the cerebellum, and the nucleus of the descending trigeminal tract; the contralateral dorsal funicular nucleus also exhibited labeling. Clearly, the tectum in gars receives a substantial number of nonvisual afferents from all major brain areas, most of which have been reported in other vertebrates. The functional significance of these afferent sources and their probable homologues in other vertebrate groups are discussed.

Afferent Pathways↗
PubMed1994

Magno- and parvocellular pathways are segregated in the human optic tract.

There is abundant psychophysical evidence in humans suggesting the existence of parallel pathways subserving different aspects of vision. However, there is little direct proof of the neural structures underlying the two pathways. We present direct anatomical evidence that in the normal human optic tract fibres are segregated according to size. Large axons, likely to correspond to the magnocellular pathway of non-human primates, take a more ventral and superficial course than the smaller axons belonging to the parvocellular pathway. This anatomical segregation not only reinforces the hypothesis of parallel pathways but, more importantly, offers a unique opportunity for studying the psychophysical effects of selective damage to one or the other fibre contingent.

Aged↗