Unit Responses from Commissural Fibers of Optic Lobes of Fish

A History of Corollary Discharge: Contributions of Mormyrid Weakly Electric Fish

Corollary discharge is an important brain function that allows animals to distinguish external from self-generated signals, which is critical to sensorimotor coordination. Since discovery of the concept of corollary discharge in 1950, neuroscientists have sought to elucidate underlying neural circuits and mechanisms. Here, we review a history of neurophysiological studies on corollary discharge and highlight significant contributions from studies using African mormyrid weakly electric fish. Mormyrid fish generate brief electric pulses to communicate with other fish and to sense their surroundings. In addition, mormyrids can passively locate weak, external electric signals. These three behaviors are mediated by different corollary discharge functions including inhibition, enhancement, and predictive “negative image” generation. Owing to several experimental advantages of mormyrids, investigations of these mechanisms have led to important general principles that have proven applicable to a wide diversity of animal species.

Measuring the amplification of attention

An ambiguous motion paradigm, in which the direction of apparent motion is determined by salience (i.e., the extent to which an area is perceived as figure versus ground), is used to assay the amplification of color by attention to color. In the red-green colored gratings used in these experiments, without attention instructions, salience depends on the chromaticity difference between colored stripes embedded in the motion sequence and the yellow background. Selective attention to red (or to green) alters the perceived direction of motion and is found to be equivalent to increasing the physical redness (or greenness) by 25-117%, depending on the observer and color. Whereas attention to a color drastically alters the salience of that color, it leaves color appearance unchanged. A computational model, which embodies separate, parallel pathways for object perception and for salience, accounts for 99% of the variance of the experimental data.

Functional anatomy of the tectum mesencephali of the goldfish. An explorative analysis of the functional implications of the laminar structural organization of the tectum

The present paper is aimed at an exploration of the possible functional significance of the laminar organization of the goldfish tectum at both the cellular and the synaptic level. For this purpose (1) the data concerning the structure of the teleostean tectum are surveyed, (2) a conceptual framework of the intratectal connectivity in the goldfish is proposed, (3) the electrophysiological data concerning the teleosteam tectum are surveyed and (4) the degree of correlation between the structural and physiological data available is discussed. Apart from the retina, tectal afferents originate from at least 10 other brain centers. At least 5 of these projections appear to be topographically organized. Tectal afferents, neurons as well as synapses reveal a characteristic intratectal lamination pattern. Tectal efferents project to at least 10 brain centers, and have until now been shown to arise from 6 cell types. The structural data surveyed allow the construction of a conceptual framework of tectal circuitry on the basis of 3 starting points. (1) The existence of at least 8 presynaptic zones or laminae, each containing a characteristic set of presynaptic structures (afferents and axons of interneurons). (2) The fact that the tectal postsynaptic structures (somata and dendrites of tectal neurons) each have a characteristic location, extension and synaptic density, which determines the relative importance of the different presynaptic zones for each cell type. (3) The laminar specificity hypothesis, which implies that presynaptic structures that coexist in a particular presynaptic zone terminate without preference on all types of postsynaptic structures within that zone. The conceptual framework of tectal circuitry is quantified in terms of connectivity index and connective importance. Analysis of the framework constructed leads to a detailed description of the intratectal pathways involved in the processing of the 4 main streams of tectal input (i.e. visual, toral, telencephalic and 'deep' input). It was concluded that the laminar organization of the tectum is primarily relevant for multimodal integration and that the tectal cell types each receive a characteristic sample out of the multimodal information available in the different tectal layers.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of extrinsic tectal connections in Goldfish (Caraccius auratus)

Nonretinal sources of tectal afferents, the laminar and regional organization of the inputs, and the relation of the tectum with primary and secondary visual and motor centers in goldfish were studied following HRP injections in the optic tectum, orbit of the eye, cerebellum, pretectal area, and dorsolateral mesencephalic tegmentum. Ipsilateral tectal afferents include the area dorsalis centralis of the forebrain, the nucleus dorsalis lateralis of the thalamus, the area pretectalis, the nucleus pretectalis, a nucleus in the rostral mesencephalic tegmentum, the torus longitudinales, the torus semicircularis, a dorsolateral tegmental nucleus, the nucleus isthmi, and a rostral cell group of the nucleus motorius tegmenti. Comparison of results in a series of tectal HRP injections which differed in depth, tangential extent, and location indicated that projections from the area pretectalis, nucleus pretectalis, and nucleus isthmi terminate in the stratum fibrosum et griseum superficiale of the tectum. Terminals of the forebrain and nucleus dorsolateralis and contralateral tectum are sparse and widely branching. Projections from the area and nucleus pretectalis tend to terminate in the rostral tectum, and those from the contralateral tectum, torus semicircularis, dorsolateral tegmental nucleus, and nucleus motorius tegmenti terminate preferentially in the caudal tectum. Cells of origin of extrinsic tectal efferents were also identified following HRP injections in the pretectal area and mesencephalic tegmentum. Proximal dendrites and axons of these cells were labeled sufficiently to allow comparison with morphological types characterized in Golgi studies. HRP injections in the cerebellum labeled cells bodies in the area pretectalis, nucleus pretectalis, and the nucleus of the posterior commissure. Double label experiments with intraocular injection of tritiated proline demonstrated direct retinal input to these three areas. No indications of direct connections between the tectum and cerebellum were found following tectal or cerebellar HRP injections.

Delayed plasticity of an instinct: recognition and avoidance of 2 facing eyes by the jewel fish

A model depicting 2 horizontally positioned black spots resembling facing eyes, as compared with models depicting other spot arrangements, elicits intense flight activity in young African jewel fish (Hemichromis bimaculatus) under 5 months of age and 7-month-old subadults reared apart from conspecifics with eyeless cave fish (Anoptichthys jordani). In contrast, subadults permitted to observe or interact fully with conspecifics during development exhibited attenuated discriminative flight activity. These findings suggest that visual experience with facing conspecifics, irrespective of physical contact, modifies the flight-eliciting properties of the innat mechanism subserving eye-schema recognition, but only during later maturation.

Electrophysiology of neural units in goldfish optic tectum

Axons of retinal ganglion cells showed responses not previously emphasized: (a) many tonic units discharged oscillations, 2--12 spikes per burst, interburst intervals 20--300 msec; (b) phasic units showed concentric or flanking ON and OFF fields, response frequency depended on balance of retinal excitation and inhibition; (c) directional sensitivity was maximal for retinal stimuli moving in naso-temporal direction; (d) in anterior tectum deep afferent layer (DAL) provides for deep electrical sink, fibers of DAL have small fields, mostly in front of fish; (e) color-opponent units are prevalent in the superficial terminal layers, color is spatially and temporally represented. Tectal cell responses were distinguished by large visual fields, spontaneity, multiple spikes and long latencies to optic nerve stimulation, failure to follow above 60 per sec, plasticity of response. Tectal neurons of three classes included (a) cells of one type in upper layers were inhibited in ongoing activity by visual input, receptive fields exceeded 100 degrees, were often oblong, responses did not habituate; (b) cells of second type were excited by visual stimuli, became unresponsive (habituated) or responsive only to stimuli in different position or direction (newness cells); lability precluded field mapping and dishabituation was produced by change in background, extraneous stimulation, and spontaneous firing; (c) pyriform cells in periventricular layer were abundant, difficult to isolate electrically, discharged spontaneously in bursts at intervals of several seconds and responded to visual input by interruption of firing. Some tectal cells responded to non-visual stimuli as well.