Biomedical subjects

S du Lac

Publications and source records attributed to S du Lac.

7 recordsLinked to original sources

PubMed1992

Eye movements and brainstem neuronal responses evoked by cerebellar and vestibular stimulation in chicks.

The vestibulo-ocular reflex undergoes adaptive changes that require inputs from the cerebellar flocculus onto brainstem vestibular neurons. As a step toward developing an in vitro preparation in chicks for studying the synaptic basis of those changes, we have elucidated the organization of the pathways through which the flocculus influences vestibulo-ocular movements. Electrical stimulation of the vestibular ampulla evoked brief, contralaterally directed movements in both eyes. Although single current pulses to the flocculus elicited no response, conjunctive stimulation of the flocculus and the vestibular apparatus significantly reduced the vestibularly-evoked movement. Trains of current pulses applied to the flocculus and ampulla evoked eye movements directed toward and away from the side of stimulation, respectively. Recordings from the brainstem revealed neurons that were activated by ipsilateral vestibular stimulation and inhibited by ipsilateral floccular stimulation. Our sample included neurons in the lateral vestibular nucleus, the ventrolateral portion of the medial vestibular nucleus, and the superior vestibular nucleus. Similarities between these findings and those of similar studies in mammals indicate that the chick will provide a good model system for cellular studies of adaptive changes in the vestibulo-ocular reflex.

Animals↗

PubMed1991

Early visual deprivation results in a degraded motor map in the optic tectum of barn owls.

The optic tectum contains a precise map of orienting movements: the size and direction of movements of the eyes, head, and/or body vary systematically with the locus of neural activation within the tectum. In adult animals, this motor map aligns closely with the tectal map of visual space. This study addressed the question of whether the motor map develops entirely independently of visual experience. We found that in barn owls (Tyto alba) raised without vision, although a tectal map of head movement develops, its topography and alignment with the map of visual (and auditory) space are abnormal. The results demonstrate that during early life vision is necessary either to maintain or to guide the development of a normal tectal motor map.

Animals↗

PubMed1991

Stretched and upside-down maps of auditory space in the optic tectum of blind-reared owls; acoustic basis and behavioral correlates.

Vision during early life plays an important role in calibrating sound localization behavior. This study investigates the effects of visual deprivation on sound localization and on the neural representation of auditory space. Nine barn owls were raised with eyelids sutured closed; one owl was congenitally anophthalmic. Data from these birds were compared with data from owls raised with normal visual experience. Sound localization behavior was significantly less precise in blind-reared owls than in normal owls. The scatter of localization errors was particularly large in elevation, though it was abnormally large in both dimensions. However, there was no systematic bias to the localization errors measured over a range of source locations. This indicates that the representation of auditory space is degraded in some way for blind-reared owls, but on average is properly calibrated. The spatial tuning of auditory neurons in the optic tectum was studied in seven of the blind-reared owls to assess the effects of early visual deprivation on the neural representation of auditory space. In normal owls, units in the optic tectum are sharply tuned for sound source location and are organized systematically according to the locations of their receptive fields to form a map of auditory space. In blind-reared owls, the following auditory properties were abnormal: (1) auditory tuning for source elevation was abnormally broad, (2) the progression of the azimuths and elevations of auditory receptive fields across the tectum was erratic, and (3) in five of the seven owls, the auditory representation of elevation was systematically stretched, and in the two others large portions of the representation of elevation were flipped upside down. The following unit properties were apparently unaffected by blind rearing: (1) the sharpness of tuning for sound source azimuth, (2) the orientation of the auditory representation of azimuth, and (3) the mutual alignment of the auditory and visual receptive fields in the region of the tectum representing the area of space directly in front of the animal. The data demonstrate that the brain is capable of generating an auditory map of space without vision, but that the normal precision and topography of the map depend on visual experience. The space map results from the tuning of tectal units for interaural intensity differences (IIDs) and interaural time differences (ITDs; Olsen et al., 1989).(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗

PubMed1990

Neural maps of head movement vector and speed in the optic tectum of the barn owl.

1. This study investigates the contribution of the optic tectum in encoding the metric and kinetic properties of saccadic head movements. We describe the dependence of head movement components (size, direction, and speed) on parameters of focal electrical stimulation of the barn owl's optic tectum. The results demonstrate that both the site and the amount of activity can influence head saccade metrics and kinetics. 2. Electrical stimulation of the owl's optic tectum elicited rapid head movements that closely resembled natural head movements made in response to auditory and visual stimuli. The kinetics of these movements were similar to those of saccadic eye movements in primates. 3. The metrics and kinetics of head movements evoked from any given site depended strongly on stimulus parameters. Movement duration increased with stimulus duration, as did movement size. Both the size and the maximum speed of the movement increased to a plateau value with current strength and pulse rate. Movement direction was independent of stimulus parameters. 4. The initial position of the head influenced the size, direction, and speed of movements evoked from any given site: when the owl initially faced away from the direction of the induced saccade, the movement was larger and faster than when the owl initially faced toward the direction of the induced movement. 5. A characteristic movement of particular size, direction, and speed could be defined for each site by the use of stimulation parameters that elicited plateau movements with normal kinetic profiles and by having the head initially centered on the body. The size, direction, and speed of these characteristic movements varied systematically with the site of stimulation across the tectum. The map of head movement vector (size and direction) was aligned with the sensory representations of visual and auditory space, such that the movement elicited from a given site when the owl initially faced straight ahead brought the owl to face that region of space represented by the sensory responses of the neurons at the site of stimulation. 6. The results imply that both the site and the amount of neural activity in the optic tectum contribute to encoding the metrics and kinetics of saccadic movements. A comparison of the present findings with previous studies on saccadic eye movements in primates and combined eye and head movements in cats suggests striking similarities in the ways in which tectal activity specifies a redirection in gaze to such dissimilar motor effectors as the eyes and head.

Animals↗

PubMed1987

Computational maps in the brain.

The nervous system performs computations to process information that is biologically important. Some of these computations occur in maps--arrays of neurons in which the tuning of neighboring neurons for a particular parameter value varies systematically. Computational maps transform the representation of information into a place-coded probability distribution that represents the computed values of parameters by sites of maximum relative activity. Numerous computational maps have been discovered, including visual maps of line orientation and direction of motion, auditory maps of amplitude spectrum and time interval, and motor maps of orienting movements. The construction of the auditory map of space is the most thoroughly understood: information about interaural delays and interaural intensity differences is processed in parallel by separate computational maps, and the outputs of these maps feed into a higher order processor that integrates sets of cues corresponding to sound source locations and creates a map of auditory space. Computational maps represent ranges of parameter values that are relevant to the animal, and may differentially magnify the representation of values that are of particular importance. The tuning of individual neurons for values of a mapped parameter is broad relative to the range of the map. Consequently, neurons throughout a large portion of a computational map are activated by any given stimulus, and precise information about the mapped parameter is coded by the locations of peak activity. There are a number of advantages of performing computations in maps. First, information is processed rapidly because the computations are preset and are executed in parallel. Second, maps simplify the schemes of connectivity required for processing and utilizing the information. Third, a common, mapped representation of the results of different kinds of computations allows the nervous system to employ a single strategy for reading the information. Finally, maps enable several classes of neuronal mechanisms to sharpen tuning in a manner not possible for information that is represented in a non-topographic code.

Animals↗

PubMed1986

Guidance of neuronal growth cones in the grasshopper embryo. I. Recognition of a specific axonal pathway by the pCC neuron.

The selective affinities that growth cones display for specific axonal surfaces give rise to stereotyped patterns of selective fasciculation. Previous studies on cell recognition by neuronal growth cones in the grasshopper embryo led to the proposal and initial experimental testing of the labeled-pathways hypothesis. Here we report on a further experimental analysis of this hypothesis, using the first 3 longitudinal axon fascicles, which initially contain only the axons of 7 identified neurons. We describe and experimentally test the selective affinity of the pCC growth cone for the MP1 and dMP2 axons in the MP1/dMP2 fascicle. The pCC growth cone appears to demonstrate an absolute, rather than hierarchical, preference for the MP1/dMP2 fascicle, as compared with other longitudinal axon fascicles, which supports the notion that the surfaces of the MP1 and dMP2 axons have some special distinguishing label that guides the pCC growth cone onto and along them.

Animals↗

PubMed1986

Guidance of neuronal growth cones in the grasshopper embryo. II. Recognition of a specific axonal pathway by the aCC neuron.

In the previous paper, we experimentally analyzed the selective affinity of the pCC growth cone for the MP1/dMP2 fascicle in the grasshopper embryo. Here we describe a similar experimental analysis demonstrating the selective affinity of the aCC growth cone for the U fascicle. These results support the labeled-pathways hypothesis. The 2 sets of cell ablation experiments argue against the simple location of axons, the simple timing of axon outgrowth, and/or simple quantitative differences in the expression of a common surface label being the major determinant in pathway selection by neuronal growth cones. Rather, these 2 examples of growth-cone specificity, together with previous studies on the G growth cone, suggest that neuronal recognition molecules are differentially expressed on the surfaces of different embryonic axonal pathways and tracts and are used to guide growth cones through a series of choice points to their targets.

Animals↗