Nico A. M. Schellart

Temporal and spatial congruence of components of motion-onset evoked responses investigated by whole-head magneto-electroencephalography

Motion-onset related components in averaged whole head co-recorded MEG and EEG responses of 24 adults to a low-contrast checkerboard pattern were studied. The aims were to identify these components, to characterize quantitatively their maps and to localize the underlying sources by equivalent-current-dipole (ECD) analyses with a spherical head model.After a weak P1, a large start-elicited negativity arises, comprising the novel N2a (occipital positive and parieto-central negative, peak-latency 141 ms) and the N2 like N2b (bilateral parieto-temporal, 175 ms) component. It is followed by a large positive stop-related component, P2 (156 ms after motion-offset). The corresponding MEG components N2am and N2bm showed bilateral dipole fields with considerable overlap. P1m has a single dipole field around the midline. N2a(m) and N2b(m) can be modelled with two bilateral ECDs with significant different locations. The study shows that accurate mapping and ECD analyses can distinguish two neighbouring areas of the visual cortex, 21+/-4 (SE) mm separated, which activities are reflected in both spatio-temporally closely related N2(m) components. N2a(m) and N2b(m) originate in the extrastriate cortex, possibly close to or in V3/V3A and MT/V5 respectively. Motion-evoked activity in (near) V3/V3A is novel on the basis of EEG data.

Acousticolateral and visual processing and their interaction in the torus semicircularis of the trout, Salmo gairdneri

In the torus semicircularis of the trout, visual, auditory, visual-auditory, acousticolateral broadband, lateral line, visual-acousticolateral broadband and visual-lateral line units have been found, listed in decreasing frequency of occurrence. In contrast to the acousticolateral characteristics, the visual characteristics of toral units are poor; only sudden changes in the visual field seem to be of importance. When bimodal units are stimulated simultaneously with light and sound the responses of most units behave in a basically additive fashion. The activity of some units which responded to only one of the modalities could be modulated by the other modality.

Center-surround organisation and interactions in receptive fields of goldfish tectal units.

Abstract Small spot mapping of the receptive fields (RFs) of tectal units never revealed a truly annular surround. In contrast, a surround enclosing receptive field center (RFC) often appeared if the RFC was illuminated by a small spot of light. The so-called induced surround was found for 21 on units ( N = 36). With flickering spot at a fixed position outside the RFC, the strength of the response to the flickering spot was a function of the position of the adapting spot in the RF and appeared to be proportional to the RFC response profile. The RFC behaved predominantly as an adaptation pool. Electrical stimulation established that ganglion cells as well as tectal neurons can have an induced surround.

Shapes of receptive field centers in optic tectum of goldfish

In fish the lobes of the optic tectum receiv-e visual information directly from the retinal ganglion cells. Tectal units of goldfish and carp are generally reported to have receptive Iiefd centers with shapes varying from circular to elliptical, and sizes ranging from a few to tens of degrees of visual angle (Jacobson and Gaze, 1964: Guthrie and Banks. 1974; Niida and Sato. 1975; Sutterlin and Prosser. 1970: Wartzock and Marks. 1973). On the other hand. in the isolated retina of goldfish the receptive field centers of ganglion cell responses appear to be mainly circular and measure about 10’ in diameter (Easter, _1963: Spekreijse. Wagner and Wolbarsht. 1972). It cannot be excluded that this discrepancy may be due to differences in experimental conditions (isolated retina vs anaesthetized animal). For example directional selectivity has been found in optic nerve recordings in sitrt, but not for ganglion cell recordings in isolated retina (Daw and Beauchamp, 1972; Scheilart, 1973). Furthermore, shape and size of receptive field centers of tectal units of goldfish have never been determined in a quantitative way. In general only the sign of the response was plotted to obtain an indication of receptive field extension. In the present paper a constant response criterion is used to define a receptive field center. The origin of single unit activity recorded extra-cellularly from the optic tectum is frequently uncertain. Some authors claim to record both from tectal somata and from optic nerve fibre endings (Sutteriin and Prosser. 1970; Guthrie and Banks. 1974), others consider they record exclusively the latter (Jacobson and Gaze, 1964; Wartzock and Marks, 1973). Criteria like depth of recording, spike waveform and spike duration are used to establish the origin of tectal recordings. One of the purposes of the present paper is to investigate whether shape and size of receptive fieId centers determined from tectal and optic nerve recordings can be used as criteria to distinguish between recordings of nerve fibre endings and tectal neurons.

Influence of temperature on retinal ganglion cell response and e.r.g. of goldfish

1. Extracellular recordings were made from the colour and spatial coded ganglion cells in the isolated goldfish retina.

Octavolateral projections to the torus semicircularis of the trout, Salmo Gairdneri

Microiontophoretic delivery of horseradish peroxidase in the torus semicircularis of the trout resulted in heavy labeling of somata in the rhombencephalic nucleus intermedius octavolateralis and nucleus octavus magnocellularis. In addition some labeled somata were found closely to the fasciculus longitudinalis lateralis and in the diencephalon. Efferents leave the torus to the diencephalon, the tegmentum and the tectum and, via the fasciculus longitudinalis lateralis, to the rhombencephalon and the spinal cord. It is concluded that in the trout the torus receives octaval and lateral line input mainly directly from the octavolateral area in the hindbrain, without involvement of a superior olive.

Mapping of sound direction in the trout lower midbrain

In the trout lower midbrain 35% of the auditory neurons are directionally selective (DS). Most of these neurons have a higher directional selectivity than the sensory hair cells. DS units and non-DS units occur in vertical clusters, with the former more dorsally. The direction of preference is topographically mapped. Apparently, auditory space mapping is a common feature in the midbrain of vertebrates.

Origin of the stochastic nature of ganglion cell activity in isolated goldfish retina

Abstract In goldfish retina, like in that of other vertebrates, the receptive fields of the ganglion cells are so large that the stochastic nature of the spike response cannot be explained by the quantum nature of the arrival and absorption of light quanta. This indicates that “noise” is added somewhere in the retinal chain of transformations converging to the ganglion cell responses. Four arguments are advanced that noise feeds in after spatial summation and that the most likely site of the noise is the ganglion cell itself.

Interrelations Between the Auditory, the Visual and the Lateral Line Systems of Teleosts; a Mini-Review of Modelling Sensory Capabilities

Models are proposed, which allow the quality of performance of the auditory, visual and mechanosensory lateral line systems of 63 teleost species to be calculated. These systems are particularly suitable for remote detection of objects. The general capability of each system is expressed as an index, which is evaluated in relation to habitat and behaviour. The index of the lateral line canal system, LI, is mainly based on anatomical characteristics. Species with many superficial neuromasts generally have low LIs and appear to prefer quiet waters. The hearing index, HI, is based on the audiogram, the intensity discrimination threshold and the psychophysical tuning curve. It expresses the number of distinguishable pure tone-intensity combinations. Highest HIS are found among species living in shallow, mostly fresh waters with soft bottoms. Low and moderate HIS are related to noisy habitats. Excellent hearing is found only in species with Weberian ossicles or other structures to improve the swimbladder-ear coupling. The visual index, VI, is based upon the focal length of the eye and characteristics of the two principal retinorecipient tectal layers. The volume of these layers is proportional to the retinal surface area, irrespective of species and size. VI is in broad agreement with published data on the psychophysical minimum resolvable angle. High VIs are found among pelagic, diurnal species living in clear waters and vice versa. Well-developed canal lateral line organs seldom go together with very good hearing, but a high HI is often accompanied by large numbers of superficial neuromasts. Poor hearing is often compensated for by good vision, and vice versa. Species with a high VI are mostly predators.

Evoked potentials and spike responses to moving stimuli in the optic tectum of goldfish

Summary1.Tectal evoked responses (TERs) to periodically moving stimuli recorded from common goldfish (Carassius auratus) are a mixture of luminance and directionally selective components, reflecting the activity of the various kinds of tectal cells.2.To separate the directionally selective components from the luminance components the TERs to moving stimuli were recorded at a flat part of the TER sensitivity profile and Fourier analysed. The profiles were plotted automatically with flickering light by application of the equal response method.3.Fourier analysis showed that only a small part (ca. 18%) of the power of the response to horizontal movements can be attributed to directional selectivity.4.Electrical stimulation of the optic nerve helps to identify ganglion cell terminals from post-synaptic tectal neurons. The units identified in this manner as tectal neurons can be directionally selective.5.It was found that a very small part of the retinal ganglion cells but a considerable part of the tectal cells are directionally selective.6.The small excess of the tectal cells with a temporo-nasal preferred direction makes the generally weak directional selectivity of the TER plausible.