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E I Knudsen

Publications and source records attributed to E I Knudsen.

At least 19 recordsLinked to original sources
PubMed1992

Anatomical pathways from the optic tectum to the spinal cord subserving orienting movements in the barn owl.

Electrical stimulation of the optic tectum in many vertebrate species elicits eye, head or body orienting movements in the direction of the receptive field location recorded at the site of stimulation; in the barn owl, tectal stimulation produces short latency saccadic head movements (du Lac and Knudsen 1990). However, the barn owl, like other avians, lacks a direct projection from the tectum to the spinal cord, implying that less direct connections underlie tectally mediated head movements. In order to determine the pathways by which the tectum gains access to spinal cord circuitry, we searched for overlap regions between tectal efferent projections and the locations of cells afferent to the spinal cord. Tectal efferent pathways and terminal fields were revealed by anterograde labeling using horseradish peroxidase (HRP) or tritiated amino acids injected into the optic tectum. Cells afferent to the spinal cord were identified by means of retrograde labeling using HRP, rhodamine, or rhodamine-coupled latex beads injected into the cervical spinal cord. A comparison of results from the anterograde and retrograde labeling experiments demonstrated several areas of overlap. All of the cell groups that both received heavy tectal input and contained a high proportion of cells projecting to the spinal cord were located in the medial half of the midbrain and rhombencephalic tegmentum, and included the red nucleus, the interstitial nucleus of Cajal, the medial reticular formation, the nucleus reticularis pontis giganto-cellularis, and the nucleus reticularis pontis oralis. All of these cell groups receive their tectal input from the medial efferent pathway, one of three major output pathways from the tectum. The other two output pathways (the rostral and the caudal) project to regions containing no more than a few scattered cells that are afferent to the spinal cord. Based on these data and on the functions of homologous cell groups in other vertebrates, we hypothesize that the medial efferent pathway and its brainstem target nuclei are primarily responsible for tectally mediated orienting head movements in the barn owl.

Animals↗
PubMed1992

Neural derivation of sound source location: resolution of spatial ambiguities in binaural cues.

Cues for sound localization are inherently spatially ambiguous. Nevertheless, most neurons in the barn owl's optic tectum (superior colliculus) have receptive fields for broadband noise stimuli that are restricted to a single region of space. This study characterizes the spatial ambiguities associated with two important sets of localization cues, interaural level differences (ILDs) and interaural phase differences (IPDs), and describes how information is integrated within and across frequencies to resolve these ambiguities. The auditory receptive fields of neurons in the optic tectum were measured with free-field sounds presented from a movable loudspeaker. In contrast to the single regions typical for broadband receptive fields, receptive fields for tonal stimuli usually included additional discrete regions of space (accessory fields). Based on acoustic measurements of ILD and IPD cues made in the external ear canals, it was shown that accessory fields corresponded to locations from which sound sources produced ILD and IPD values that were approximately the same as those arising from the broadband receptive field. In addition, accessory fields had inhibitory surrounds, corresponding to locations from which sound sources produced substantially different combinations of ILD and IPD values. Where an accessory field for one frequency overlapped with the inhibitory surround of a second frequency, an excitatory response to the first frequency could be reduced or eliminated by addition of the second frequency. Because tonal receptive fields for different frequencies always overlapped in the region of the broadband receptive field but tended not to overlap elsewhere, this integration of excitation and inhibition can account for the restriction of broadband receptive fields to a single region of space.

Animals↗
PubMed1992

Adaptive adjustment of unit tuning to sound localization cues in response to monaural occlusion in developing owl optic tectum.

Bimodal units in the barn owl's optic tectum are tuned to the location of auditory and visual stimuli, and are systematically organized according to their spatial tuning to form mutually aligned maps of auditory and visual space. Map alignment results from the fact that, normally, units are tuned to the values of interaural level difference (ILD) and interaural time difference (ITD) produced by a sound source at the location of their visual receptive fields (VRFs). Monaural occlusion alters the correspondence of ILD and ITD values with locations in space. We investigated the effect that raising owls with a chronic monaural occlusion has on the tuning of tectal units to ILD and ITD. Owls were monaurally occluded beginning at 1 month of age. The effects of monaural occlusion were assessed 2-4 months later by comparing the ILD and ITD tuning of units in monaurally occluded owls with the ILD and ITD tuning of units with equivalent VRFs in normal owls. ILD and ITD tuning was shifted substantially and in the direction of the unoccluded ear (the adaptive direction) in owls raised with a monaural occlusion. In most tecta, the mapped representations of ILD and ITD were shifted systematically. In addition, in some tecta, monaural occlusion induced a change in the topography of the ILD map such that ILD tuning remained essentially constant at values near 0 dB over abnormally large portions of the tectum. Across all recording sites, the average shift in ILD tuning was 9 dB (n = 396) and the average shift in ITD tuning was 40 microseconds (n = 414). In four of five animals, the magnitude of the effect was not equivalent on the two sides of the brain, the adjustments being significantly larger and more systematic on the side ipsilateral to the occlusion. Such differences in the altered ILD and ITD maps on the two sides of the brain in individual animals indicate that, although a component of the adaptive adjustment might be due to regulation of the gain and phase response of the monaural signals early in the auditory pathway, a major component of the adjustment must occur at or beyond the level where the encoding of ILDs and ITDs for left and right space separates.

Adaptation, Physiological↗
PubMed1992

Vision-independent adjustment of unit tuning to sound localization cues in response to monaural occlusion in developing owl optic tectum.

Neurons in the developing optic tectum adjust their tuning to auditory localization cues in response to chronic monaural occlusion so that auditory spatial fields align with visual receptive fields (VRFs). We tested whether this adaptive adjustment of auditory tuning requires visual instruction. Both eyelids were sutured closed at the same time that one ear was occluded in two barn owls that were 1 month old. After 70 and 100 d, respectively, the tuning of units to interaural level difference (ILD) and to interaural time difference (ITD) was measured. These data were compared with equivalent data from 15 normal owls. Unit tuning to ITD was shifted from normal in both of the monaurally occluded owls. In one owl, ILD tuning was also clearly shifted. In the other owl, the map of ILD was flipped upside down and adaptive adjustments in ILD tuning could not be assessed. Instead, adjustments in ILD tuning were observed following removal of the earplug with the eyelids kept closed. Unit tuning was monitored at several sites in the tectum for 1 month after earplug removal using chronically implanted electrodes. Then, ILD tuning was resampled across the entire tectum. Both measures indicated shifts in ILD tuning in response to removal of the earplug in the second blind owl. In both animals, the magnitude of the shifts in ILD tuning and ITD tuning was smaller than has been observed previously in monaurally occluded but sighted owls. The results demonstrate that the brain can make adaptive adjustments in ILD and ITD tuning in response to early monaural occlusion even without the guiding influence of vision.

Adaptation, Physiological↗
PubMed1991

Visual instruction of the neural map of auditory space in the developing optic tectum.

Neural maps of visual and auditory space are aligned in the adult optic tectum. In barn owls, this alignment of sensory maps was found to be controlled during ontogeny by visual instruction of the auditory spatial tuning of neurons. Large adaptive changes in auditory spatial tuning were induced by raising owls with displacing prisms mounted in spectacle frames in front of the eyes; neurons became tuned to sound source locations corresponding to their optically displaced, rather than their normal, visual receptive field locations. The results demonstrate that visual experience during development calibrates the tectal auditory space map in a site-specific manner, dictating its topography and alignment with the visual space map.

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

Dynamic space codes in the superior colliculus.

Space coding in the superior colliculus has traditionally been viewed as a static representation by multiple, aligned, sensory and motor maps. Recent evidence has revealed that the maps are dynamic, shaped by sensory experience in developing animals, and by eye and head position signals in adults. The superior colliculus thus provides an ideal model for studying the neural mechanisms underlying developmental and real-time modifications of information representation in the brain.

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

Horizontal and vertical components of head movement are controlled by distinct neural circuits in the barn owl.

To generate behaviour, the brain must transform sensory information into signals that are appropriate to control movement. Sensory and motor coordinate frames are fundamentally different, however: sensory coordinates are based on the spatiotemporal patterns of activity arising from the various sense organs, whereas motor coordinates are based on the pulling directions of muscles or groups of muscles. Results from psychophysical experiments suggest that in the process of transforming sensory information into motor control signals, the brain encodes movements in abstract or extrinsic coordinate frames, that is ones not closely related to the geometry of the sensory apparatus or of the skeletomusculature. Here we show that an abstract code underlies movements of the head by the barn owl. Specifically, the data show that subsequent to the retinotopic code for space in the optic tectum yet before the motor neuron code for muscle tensions there exists a code for head movement in which upward, downward, leftward and rightward components of movement are controlled by four functionally distinct neural circuits. Such independent coding of orthogonal components of movement may be a common intermediate step in the transformation of sensation into behaviour.

Animals↗
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↗
PubMed1990

Sensitive and critical periods for visual calibration of sound localization by barn owls.

This study describes developmental changes in the capacity of owls to adjust sound localization in response to chronic prismatic displacement of the visual field and to recover accurate sound localization following the restoration of normal vision. Matched, binocular displacing prisms were mounted over the eyes of 19 barn owls (Tyto alba) beginning at ages ranging from 10 to 272 d. In nearly all cases, the visual field was shifted 23 degrees to the right. Sound localization was assessed on the basis of head orientations to sound sources, measured in a darkened sound chamber with a search coil system. Chronic exposure to a displaced visual field caused the owls to alter sound localization in the direction of the visual field displacement, thereby inducing a sound-localization error. The size of the sound-localization error that resulted depended on the age of the animal when prism experience began. Maximal errors of about 20 degrees were induced only when prism experience began by 21 d of age. As prism experience began at later ages, the magnitude of induced errors decreased. A bird that wore prisms beginning at 102 d of age, altered sound localization by only 6 degrees. An adult owl, when exposed chronically to a displaced visual field, altered sound localization by about 3 degrees. We refer to the early period in life when displaced vision induces exceptionally large sound-localization errors (relative to those induced in the adult) as a sensitive period. The capacity to recover accurate sound localization following restoration of normal vision was tested in 7 owls that had been raised wearing prisms. Four owls that had prisms removed by 182 d of age recovered accurate localization rapidly (over a period of weeks), whereas 3 owls that were older when the prisms were removed did not recover accurate localization when tested for up to 7 months after prism removal. Adjustment of sound localization slowed greatly or ceased at about 200 days of age, referred to here as the critical period for visual calibration of sound localization. Three owls were subjected repetitively to displacement of the visual field. An owl that adjusted sound localization to the left of normal during the sensitive period retained the capacity to adjust again to the left, but not to the right of normal, later in the critical period. The converse was true for an owl that adjusted sound localization to the right of normal during the sensitive period.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1979

The oilbird: hearing and echolocation.

Oilbirds can navigate in total darkness by echolocation. The sound energy in their sonar cries is unevenly distributed over the range from about 1 to 15 kilohertz, with a dominant frequency range of 1.5 to 2.5 kilohertz. This corresponds to the most sensitive range of their hearing as determined by neurophysiological methods. Behavioral tests in their home cave indicate that the smallest object avoided by this is a disk 20 centimeters in diameter.

Animals↗
PubMed1978

Center-surround organization of auditory receptive fields in the owl.

The spinal receptive fields of specialized auditory units in the midbrain of the barn owl (Tyto abla) contain two functionally antagonistic areas: an excitatory center and an inhibitory surround. The response of these units represents the balance of acoustic activation of the two areas, which in turn depends upon the location, intensity, and spectral content of the sound stimulus.

Animals↗
PubMed1978

A neural map of auditory space in the owl.

Auditory units that responded to sound only when it originated from a limited area of space were found in the lateral and anterior portions of the midbrain auditory nucleus of the owl (Tyto alba). The areas of space to which these units responded (their receptive fields) were largely independent of the nature and intensity of the sound stimulus. The units were arranged systematically within the midbrain auditory nucleus according to the relative locations of their receptive fields, thus creating a physiological map of auditory space.

Action Potentials↗
PubMed1978

Space and frequency are represented separately in auditory midbrain of the owl.

1. The influence of sound location and sound frequency on the responses of single units in the midbrain auditory area (MLD) of the owl (Tyto alba) were studied using a movable sound source under free-field conditions. With this technique, two functionally distinct regions in MLD have been identified: a tonotopic region and a space-mapped region. 2. MLD units were classified according to their receptive-field properties: 1) limited-field units responded only to sound from a small, discrete area of space; 2) complex-field units exhibited two to four different excitatory areas separated by areas of reduced response or inhibition: 3) space-preferring units responded best to a certain area of space, but their fields expanded considerably with increasing sound intensities; 4) Space-independent units responded similarly to a sound stimulus regardless of its location in space. 3. Limited-field units were located exclusively along the lateral and anterior borders of MLD. These units were tuned to sound frequencies at the high end of the owl's audible range (5-8.7 kHz). They usually responded only at the onset of a tonal stimulus; but most importantly, the units were systematically arranged in this region according to the azimuths and elevations of their receptive fields, thus creating a physiological map of auditory space. Because of this latter, dominant aspect of its functional organization, this region is named the space-mapped region of MLD. 4. The receptive fields of units in the larger, medial portion of MLD were of the space-independent, space-preferring, or complex-field types. These units tended to respond in a sustained fashion to tone and noise bursts, and these units were arranged in a strict frequency-dependent order. Based on this last property, this region is named the tonotopic region of MLD. 5. Because of the salient differences in the response properties of their constituent units, it is argued that the space-mapped region and the tonotopic region are involved in different aspects of sound analysis.

Acoustic Stimulation↗
PubMed1977

Receptive fields of auditory neurons in the owl.

The influence of sound location on the responses of auditory neurons in the forebrain of the owl (Tyto alba) was studied directly by using a remotely controlled, movable sound source under free-field, anechoic conditions. Some auditory neurons demonstrated well-defined receptive fields that were (i) restricted both in elevation and in azimuth and (ii) relatively independent of the intensity and the nature of the sound stimulus. The majority of the fields were located frontally and contralateral to the recording site.

Action Potentials↗
PubMed1977

Distinct auditory and lateral line nuclei in the midbrain catfishes.

The catfish torus semicircularis (TS) comprises two major nuclei, which are specialized to process separately inputs of three acousticolateral modalities: VIII nerve acoustic input in one, and lateral line mechanoreceptive and electroreceptive input in the other. Electrophysiological recording and mapping experiments demonstrate a medial auditory region, a lateral electroreceptive region, and an intercalated mechanoreceptive region in the TS Nissl and Golgi-Cox preparations distinguished two rostrocaudally elongate, nuclear divisions, which correlate, one with the auditory and the other with the mechano- and electroreceptive regions. The medially positioned auditory nucleus is here called the nucleus centralis. The nucleus centralis appears as a rostrally flattened cylinder of uniformly packed cells, covered dorsally and laterally by a fiber rind. Cells within this nucleus conform to one of three general cell types based upon somatic and dendritic morphology: type 1 cells, which are the most abundant" have a single major primary dendrite and an axon typically arising from the same somatic pole; type 2 cells have two major primary dendrites and an axon, which issues from a third distinct somatic pole; and type 3 cells have several major primary dendrites and their axons are associated with one of the major somatic poles. No systematic orientation of dendrites could be found in the nucleus centralis. The laterally positioned lateral line nucleus, to be called the nucleus lateralis, includes two subdivisions: a large pars lateralis containing predominantly electroreceptive units, and a smaller, ventromedial pars medialis encompassing predominantly mechanoreceptive units. Each subdivision is found to be somatotopically organized, inputs from the head projecting to rostral areas and inputs from the tail to caudal areas. Although the cell types resemble those described for the nucleus centralis, a greater degree of cytoarchitectural orderliness is discernible: (a) cells in the nucleus lateralis group into four, alternating cell-poor cell-rich, layers; and (b) the dendritic fields of many type 1 and type 2 cells located in layer II tend to orient in a rostrodorsal-caudoventral attitude, perpendicular to the laminar planes. Fink-Heimer preparations of brains with unilateral, lateral line lobe lesions demonstrate heavy fiber and terminal degeneration confined to the nucleus lateralis on both sides. Lateral line fibers ascend bilaterally in the lateral halves of the lateral lemnisci. At the level of the dorsal oculomotor nucleus the lemniscal fibers in this portion split into two fascicles, one proceeding rostrally to innervate the rostral portion of the nucleus lateralis, and the other arching back dorsolaterally to innervate the caudal portions of the nucleus.

Animals↗