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W Heiligenberg

Publications and source records attributed to W Heiligenberg.

51 records · Page 3Linked to original sources
PubMed1987

The optic tectum of the gymnotiform electric fish, Eigenmannia: labeling of physiologically identified cells.

A total of 47 tectal neurons of the weakly electric fish, Eigenmannia, were studied physiologically and labelled by intracellular injection of Lucifer Yellow. With the exception of two cell types, all cells could be classified in accordance with the Golgi studies of Sas and Maler. The dominant stimulus modality of neurons was correlated with their laminar location. Neurons of the stratum opticum only responded to visual stimuli, such as modulations of the light level or the motion of an object. They showed, however, no directional preferences for motion. Neurons of the stratum griseum centrale were predominantly driven by electrosensory stimuli, most often those associated with the movement of an object, and generally were very sensitive to the direction of motion. Integration of different sensory modalities was found in neurons with dendrites invading laminae with different sensory inputs. In addition, small axons of interneurons appear to relay information across laminae. Large multipolar neurons in the deep tectum responded to the motion of objects, often preferring a particular direction of motion. Some of these large multipolar neurons of the deep tectum also discriminated the sign of the frequency difference between a mimic of a neighbor's sinusoidal electric organ discharge and the animal's own signal. These neurons are potential candidates for the control of the jamming avoidance response. These neurons were morphologically indistinguishable from large multipolar neurons of the deep tectum that either responded to moving objects or to acoustical stimuli. Individual large cells of the deep tectum project to various targets (Fig. 1) and probably contribute to the control of different behavioral responses. This suggests that the nature of such responses would then depend upon the constitution of sets of neurons recruited by a given stimulus situation, and the role of individual tectal neurons would neither be particularly specific nor very significant.

Animals↗
PubMed1986

Limits of phase and amplitude sensitivity in the torus semicircularis of Eigenmannia.

Eigenmannia can detect modulations in the time disparity of signals received by different regions of the body surface as small as several hundred nanoseconds. This study presents recordings of single units in the torus semicircularis that are sensitive to time disparities (differential-phase) between a sinusoidal signal received by the head region and a similar signal received by the body surface caudal to the fish's pectoral fins. The sensitivity of units to differential phase, measured by the change in spike rate per unit change in time disparity, was greatest when small phase modulations, rather than stationary phase differences, were presented. Thresholds of differential-phase coders ranged from 6.5 microseconds to several hundred microseconds, with approximately 20% of the units having thresholds in the 5-10 microseconds range. For most cells, sensitivity to small modulations of differential-phase was relatively unaffected by time disparity 'offsets' within a range of several hundred microseconds. A threshold of 5-10 microseconds is still an order of magnitude higher than that measured in the Jamming Avoidance Response (JAR). Neurons that were sensitive to amplitude modulations (AMs) had thresholds as low as 0.05%. This value is comparable to that observed at the behavioral level.

Animals↗
PubMed1986

Neural coding of difference frequencies in the midbrain of the electric fish Eigenmannia: reading the sense of rotation in an amplitude-phase plane.

Eigenmannia is able to discriminate the sign of the difference, Df, between the frequency of a neighbor's electric organ discharge (EOD) and that of its own EOD. This discrimination can be demonstrated at the level of individual neurons of the midbrain. Intracellular and extracellular recordings of such sign-selective cells revealed the following: Units preferring positive Dfs and units preferring negative Dfs were found with equal frequency. The degree of selectivity was also similar for these two classes of neurons. All sign-selective units were sensitive to the magnitude of the frequency difference, i.e. the beat rate. Most units responded best to beat rates in the 4-8 Hz range. Sign-selectivity was observed only when the jamming signal (S2) was presented through electrodes other than those used to deliver the mimic (S1) of the fish's EOD, i.e. only when amplitude modulations were accompanied by modulations of differential phase. Intracellular studies suggest that most sign-selective neurons of the tectum are large, multipolar cells in the stratum album centrale. These cells send projections to the reticular formation, to lamina 9 of the torus semicircularis and to the N. electrosensorius.

Animals↗
PubMed1986

Gating of sensory information: joint computations of phase and amplitude data in the midbrain of the electric fish, Eigenmannia.

Eigenmannia is able to determine whether the electric organ discharge (EOD) of a neighbor is of higher or lower frequency than its own EOD. For small frequency differences, Df, the fish avoids jamming by shifting its frequency away from that of its neighbor. This jamming avoidance response (JAR), therefore, requires that the fish discriminate the sign of Df. The interference pattern of two EODs of similar frequency is characterized by local modulations of the instantaneous amplitude and the spatial difference of the instantaneous phase, or 'differential phase', of the mixed signal. When amplitude and differential phase are plotted in a two-dimensional state plane, circular graphs are obtained with a sense of rotation that reflects the sign of Df. Behavioral studies have shown that both amplitude and differential phase modulations are required for the control of the JAR. Considering two regions of the body surface, A and B, that receive strong and weak contamination by the jamming signal, respectively, rises and falls of the signal amplitude in A will be accompanied by respective advances and delays of the signal in A relative to that in B if the jamming signal is of lower frequency, i.e. if Df is negative. A plot of amplitude versus different phase yields a clockwise sense of rotation in this case. The opposite relation between amplitude and phase modulations, resulting in a counterclockwise rotation, holds for a positive Df. For the less strongly contaminated area B, however, the relation between the sign of Df and the sense of rotation is reversed, so that for a negative Df, a rise of amplitude in B will coincide with a delay of the signal in B relative to that in A. By independent experimental control of amplitude and differential-phase modulations, we explored midbrain neurons that discriminate the sense of rotations in the amplitude-phase plane. We found that these neurons achieve this discrimination by gating amplitude inputs by differential-phase information, thus exploiting the particular combinations of amplitude and differential phase that characterize a given sense of rotation. Since the response properties of such neurons only reflect the sense of rotation, and since the same sense of rotation can be obtained for either sign of Df (depending upon the relative contamination of the receptive fields involved), individual neurons do not yet provide unambiguous information about the sign of Df.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1986

A time-comparison circuit in the electric fish midbrain. I. Behavior and physiology.

Behavioral experiments show that the weakly electric fish, Eigenmannia, detects differences in timing as small as 400 nsec between electric signals from different parts of its body surface. The neural basis of this remarkable temporal resolution was investigated by recording from elements of the phase-coding system, a chain of electrotonically connected neurons devoted to the processing of temporal information. Each element of this system fires a single action potential for every cycle of the electric signal (either the fish's own electric organ discharge or a sinusoidal signal of similar frequency). For phase-coding primary afferents and midbrain neurons, the temporal resolution was determined by measuring each unit's capacity to lock its spike to a particular phase of the stimulus cycle. The jitter of a neuron's response (measured as the standard deviation of the timing of the spikes with respect to the stimulus) decreases from the level of the primary afferent (mean = 30 microsec) to the midbrain torus (mean = 11 microsec); these results can be correlated with morphological measures of convergence. The temporal resolution of single neurons is still inferior to that displayed at the behavioral level.

Action Potentials↗
PubMed1985

Phase and amplitude computations in the midbrain of an electric fish: intracellular studies of neurons participating in the jamming avoidance response of Eigenmannia.

Electric fish monitor modulations in sensory feedback from their own electric organ discharges (EODs) to locate moving objects and to detect interfering EODs of their neighbors. The gymnotoid genus Eigenmannia minimizes detrimental effects of jamming by EODs of its neighbors by shifting its own EOD frequency away from a neighbor's EOD frequency that is too close to its own. Since the animal lowers its own frequency if its neighbor's frequency is higher and raises its frequency if its neighbor's frequency is lower, this jamming avoidance response (JAR) requires that the animal determine the sign of the difference frequency, Df, between the interfering EODs. Eigenmannia obtains this information by evaluating modulations in the amplitude and phase which its nearly sinusoidal EOD signal experiences due to the interference with the neighbor's EODs. The necessary logical operations are executed in the dorsal torus semicircularis, an analogue of the inferior colliculus of higher vertebrates, and are similar to operations underlying directional hearing. By intracellular labeling of physiologically identified cells we have identified the anatomy and functional characteristics of neurons involved in the processing of amplitude and phase information. The JAR is controlled by hierarchical and parallel processing of information in several laminae of somatotopically ordered neurons. Phase differences between signals received by electroreceptors in different parts of the body surface are computed in lamina 6. Information about differential phase is then relayed to multipolar cells in the deeper laminae 8, b and c, which also receive information about modulations in local signal amplitude. These cells are excited by a rise or fall of amplitude as well as by a lead or lag of phase. According to their responses to either of these two variables, these neurons can be divided into four classes. These classes encode all information necessary for the control of the JAR and project to the optic tectum. Dynamic properties and sensory specificities of the JAR are not found in individual, properly tuned neurons but rather emerge statistically from the joint effects of a large population of imprecisely tuned neurons. This system is characterized by a distributed pattern of organization and by the absence of a small number of key neurons whose malfunction would jeopardize the behavioral response. The complexity of this neural machinery appears unnecessary for the logically simple task of the JAR, and it suggests that this behavior was acquired later in evolution by being derived from more general motor responses to moving objects.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Structure and function of electrosensory neurons in the torus semicircularis of Eigenmannia: morphological correlates of phase and amplitude sensitivity.

Structure-function relations in the electrosensory system of Eigenmannia were examined by labeling physiologically characterized neurons of the dorsal torus semicircularis. The sensitivity of cells to modulations in amplitude (AMs) and modulations in differential phase was determined. Approximately half of the 48 cell types defined by Golgi studies (Carr, C.E., and L. Maler (1985) J. Comp. Neurol. 235: 207-240) were identified in this manner. The majority of the neurons located in laminae (8a, b, c, and d, and 9 exhibited sensitivity to differential phase. In laminae 5 and 7, however, in addition to neurons which were sensitive to differential phase, many cells were found that were purely AM sensitive. Differential phase sensitivity originates in the small cells of lamina 6 (Heiligenberg, W., and G. Rose (1985) J. Neurosci. 5: 515-531), the exclusive termination site of phase-coding afferents from the electrosensory lateral line lobe. Cells that had dendritic extensions into the neuropil of lamina 6 exhibited sensitivity to differential phase, whereas neurons lacking dendrites in this lamina were only excited by AMs. These findings support the notion of a relationship between the morphology and laminar position of a neuron and its function.

Animals↗
PubMed1984

The electric sense of weakly electric fish.

Recent studies of electroreception have been particularly successful in three different areas: Electroreceptors are tuned to the dominant frequency of the animal's EOD, and their tuning follows natural and experimentally induced shifts in EOD frequency. Steroid hormones influence the electric organ pacemaker frequency in the genus Sternopygus, and the tuning of electroreceptors will follow hormone-induced frequency shifts only if the receptors experience the animal's EOD. The frequency tuning of electroreceptors reveals properties similar to those of cochlear hair cells, and electroreceptors may be suitable model systems for in vitro studies of cellular and molecular aspects of electrical filter mechanisms in hair cells. In contrast to the South American or gymnotoid electric fish, the African or mormyrid electric fish evaluate electroreceptive information with the help of corollary discharges of their electric-organ pacemaker. The corollary discharge inhibits input from knollenorgan receptors so that, in the context of social communication, the animal only perceives EODs of neighbors but not its own. The corollary discharge at the same time enhances input from most mormyromasts so that the animal, in the context of electrolocation, selectively receives feedback from its own EODs. Finally, responses of ampullary electroreceptors to the animal's own EODs are centrally nulled by an elaborate and modifiable efference copy so that the animal is only informed about "nontrivial", low-frequency events in its environment. Laminated and topographically organized structures in the hindbrain and midbrain of gymnotoid fish are being studied with regard to neuroanatomical fine structure and functional organization. Different laminae and cell types in the hindbrain are specialized for the extraction of specific stimulus features, such as modulations of phase or amplitude in a sinusoidal stimulus regime. This information is passed on to the midbrain for the computation of more complex stimulus variables, such as the difference in phase modulations reported from different parts of the body surface. The torus semicircularis of the midbrain is designed for parallel processing of information from different parts of the body surface and for parallel computation of different stimulus variables for the control of behavioral responses. Electrical and visual information converge in the tectum opticum, which harbors a multimodal representation of sensory space.

Afferent Pathways↗
PubMed1981

Laminar organization of the afferent and efferent systems of the torus semicircularis of gymnotiform fish: morphological substrates for parallel processing in the electrosensory system.

The torus semicircularis of Gymnotiform fish is an enlarged laminated midbrain structure which receives lemniscal input from electrosensory, mechanoreceptive lateral line, and auditory systems. The electrosensory input in confined to the dorsal torus, while the auditory and mechanoreceptive systems project to the ventral torus. Anterograde and retrograde techniques were used were used to determine the connections of the dorsal torus in Apteronotus and Eigenmannia. The dorsal torus can be divided into nine major laminae, each of which has distinct afferent and efferent connections. The dorsal torus receives five afferent inputs: (1) A contralateral topographic input from the posterior lateral line lobe (PLLL) projects to laminae III, V, VI, VII, VIIIB, and VIIID. (2) Eurydendroid cells of the caudal lobe of the cerebellum project contralaterally to lamina VIIIB. (3) A portion of the descending nucleus of V projects to laminae VIIIA, VIIIC, and IX. (4) Lamina I is a cap of fine myelinated fibers which may originate in the torus longitudinalis. They project to laminae II and III. (5) The ipsilateral optic tectum projects to the dorsal torus. The dorsal torus projects to six major targets: (1) Laminae VII, VIII, and IX project bilaterally to a lateral region of the diencephalon above n. preglomerulosus, herein named n. electrosensorius. An area below the dorsal thalamus receives a smaller ipsilateral projection. (2) Laminae II, V, VIvn, VII, VIII, and IX project topographically to the deeper laminae of the ipsilateral optic tectum. This projection is in spatial register with the visual map in the superficial layers of the tectum. (3) Lamina VIIID projects ipsilaterally to the lateral reticular formation. (4) All laminae other than I, VI, and VIIIB project topographically to ahe ipsilateral n. praeeminentialis, which provides a powerful descending projection to the PLLL. (5) Lamina IX projects to a dorsal pretectal area. (6) The ipsilateral inferior olive receives a projection from the dorsal torus.

Afferent Pathways↗
PubMed1981

Input to the medullary pacemaker nucleus in the weakly electric fish, Eigenmannia (sternopygidae, gymnotiformes).

In order to identify which brain centers are involved in the control of electric organ discharge in electric fish, HRP was injected into the medullary electromotor (pacemaker) nucleus in the gymnotoid Eigenmannia. Neurons were retrogradely labeled in only a small nucleus of the mesencephalic tegmentum, herein called the prepacemaker nucleus. The prepacemaker nucleus lies just caudal and ventral to the posterior commissure and comprises at least two types of neurons.

Afferent Pathways↗
PubMed1980

Phase-sensitive midbrain neurons in Eigenmannia: neural correlates of the jamming avoidance response.

Neurons in the torus semicircularis of the weakly electric fish Eigenmannia encode phase differences between sinusoidal electrical stimuli received in different body regions. These fish normally experience time-varying phase differences when the electric organ discharge fields of two or more individuals overlap. These phase differences supply information necessary for the animal's jamming avoidance behavior.

Animals↗
PubMed1980

The jamming avoidance response in the weakly electric fish Eigenmannia. A behavior controlled by distributed evaluation of electroreceptive afferences.

This study analyzes the algorithm by which the animal's nervous system evaluates spatially distributed temporal patterns of electroreceptive information. The outcome of this evaluation controls the jamming avoidance response, which is a shift in the animal's electric organ discharge frequency away from similar foreign frequencies. The encoding of "behaviorally relevant" stimulus variables by electroreceptors and the central computation of their messages are investigated by combined behavioral and neurophysiological strategies.

Animals↗
PubMed1978

Phase sensitivity in electroreception.

The gymnotoid electric fish Hypopomus artedi discriminates between electric stimulus pulses with identical spectral amplitudes but different spectral phase functions. Behavioral results can be explained on the assumption that electroreception is based on a linear filter, approximately matched to the species' electric organ discharge. The impulse response of the appropriate matched filter, in fact, resembles the known impulse response of the electroreceptors involved.

Animals↗
PubMedDate not supplied

Temporal hyperacuity in the electric sense of fish.

It has recently become evident that sensory thresholds for certain tasks are lower than those expected from the properties of individual receptors. This perceptual capacity, termed hyperacuity, reveals the impressive information-processing abilities of the central nervous system. Although much is known about spatial hyperacuity, temporal hyperacuity has received little attention. Here we demonstrate that an electric fish, Eigenmannia, can detect modulations in the timing (phase) of an electrical signal at least as small as 400 ns. Such sensitivity exceeds the temporal resolution of individual phase-coding afferents. This hyperacuity results from a nonlinear convergence of parallel afferent inputs to the central nervous system; subthreshold inputs from particular areas of the body surface accumulate to permit the detection of these extremely small temporal modulations.

Animals↗