The development of lateral line placodes: Taking a broader view

The lateral line system of anamniote vertebrates enables the detection of local water movement and weak bioelectric fields. Ancestrally, it comprises neuromasts – small sense organs containing mechanosensory hair cells – distributed in characteristic lines over the head and trunk, flanked on the head by fields of electroreceptive ampullary organs, innervated by afferent neurons projecting respectively to the medial and dorsal octavolateral nuclei in the hindbrain. Given the independent loss of the electrosensory system in multiple lineages, the development and evolution of the mechanosensory and electrosensory components of the lateral line must be dissociable. Nevertheless, the entire system arises from a series of cranial lateral line placodes, which exhibit two modes of sensory organ formation: elongation to form sensory ridges that fragment (with neuromasts differentiating in the center of the ridge, and ampullary organs on the flanks), or migration as collectives of cells, depositing sense organs in their wake. Intensive study of the migrating posterior lateral line placode in zebrafish has yielded a wealth of information concerning the molecular control of migration and neuromast formation in this migrating placode, in this cypriniform teleost species. However, our mechanistic understanding of neuromast and ampullary organ formation by elongating lateral line placodes, and even of other zebrafish lateral line placodes, is sparse or non-existent. Here, we attempt to highlight the diversity of lateral line development and the limits of the current research focus on the zebrafish posterior lateral line placode. We hope this will stimulate a broader approach to this fascinating sensory system.     

Neural simulations of adaptive reafference suppression in the elasmobranch electrosensory system

The electrosensory system of elasmobranchs is extremely sensitive to weak electric fields, with behavioral thresholds having been reported at voltage gradients as low as 5 nV/cm. To achieve this amazing sensitivity, the electrosensory system must extract weak extrinsic signals from a relatively large reafferent background signal associated with the animal's own movements. Ventilatory movements, in particular, strongly modulate the firing rates of primary electrosensory afferent nerve fibers, but this modulation is greatly suppressed in the medullary electrosensory processing nucleus, the dorsal octavolateral nucleus. Experimental evidence suggests that the neural basis of reafference suppression involves a common-mode rejection mechanism supplemented by an adaptive filter that fine tunes the cancellation. We present a neural model and computer simulation results that support the hypothesis that the adaptive component may involve an anti-Hebbian form of synaptic plasticity at molecular layer synapses onto ascending efferent neurons, the principal output neurons of the nucleus. Parallel fibers in the molecular layer carry a wealth of proprioceptive, efference copy, and sensory signals related to the animal's own movements. The proposed adaptive mechanism acts by canceling out components of the electrosensory input signal that are consistently correlated with these internal reference signals.Abbreviations AEN ascending efferent neuron - AFF primary afferent nerve fiber - DGR dorsal granular ridge - DON dorsal octavolateral nucleus - ELL electrosensory lateral line lobe - GABA -aminobutyric acid - IN inhibitory interneuron - ISI interspike interval - ST stellate cell     

Central Lateral Line and Auditory Pathways: A Phylogenetic Perspective

The phylogenetic origins of the lateral line electrosensory,lateral line mechanosensory, and auditory components of theoctavolateralis system are unknown but each of these sensorymodalities appears to have evolved early in vertebrate history.The octavolateralis terminal field occupies a large area ofthe dorsolateral wall of the medulla and among agnathids, cartilaginousfishes, non-teleost bony fishes and, with modifications, urodeles,consists of a dorsal electrosensory nucleus, a medial mechanosensorynucleus and a ventral octaval nuclear complex. This arrangementof medullary octavolateral nuclei, which differs from that ofnon-electroreceptive and electroreceptive teleosts, is consideredthe primitive plan and is retained in that phyletic line leadingto tetrapods. Separate and parallel pathways are known, in elasmobranchsand a few teleosts, to ascend from each medullary lateral linecenter to the midbrain and presumably from midbrain to telencephaliclevels via thalamic relays. There is no evidence, with the lossof lateral line senses among some amphibians and all amniotes,that the central neural pathways and nuclei are retained andused to process information from other sensory modalities. Theanatomy of the central auditory system of fishes is unknownbut is required for an understanding of whether auditory nucleiand pathways are retained during the fishamphibian transition,or whether new ones arise, to process information from independentlyevolved peripheral receptors.     

The electric sense of the paddlefish: a passive system for the detection and capture of zooplankton prey.

Behavioral and electrophysiological experiments have shown that the elongated paddlefish rostrum, with its extensive population of ampullae of Lorenzini, constitutes a passive electrosensory antenna of great sensitivity and spatial resolution. As demonstrated in juvenile paddlefish, the passive electrosense serves a novel function in feeding serving as the primary, if not exclusive sensory modality for the detection and capture of zooplanktonic prey. Ampullary receptors are sensitive to the weak electrical fields of plankton from distances up to 9 cm, and juvenile paddlefish capture plankton individually with great swimming dexterity in the absence of vision or other stimulus signals. Paddlefish also detect and avoid metal obstacles, the electrical signatures of which are a potential hindrance to their feeding and reproductive migrations. The ampullary receptors, their peripheral innervation and central targets in the dorsal octavolateral nucleus, are described. We also describe the ascending and descending neuronal circuitry of the electrosensory system in the brain based on tracer studies using dextran amines.     

Response properties of electrosensory neurons in the lateral mesencephalic nucleus of the paddlefish

Many fishes and amphibians are able to sense weak electric fields from prey animals or other sources. The response properties of primary afferent fibers innervating the electroreceptors and information processing at the level of the hindbrain is well investigated in a number of taxa. However, there are only a few studies in higher brain areas. We recorded from electrosensory neurons in the lateral mesencephalic nucleus (LMN) and from neurons in the dorsal octavolateral nucleus (DON) of the paddlefish. We stimulated with sine wave stimuli of different amplitudes and frequencies and with moving DC stimuli. During sinusoidal stimulation, DON units increased their firing rate during the negative cycle of the sine wave and decreased their firing rate to the positive cycle. Lateral mesencephalic nucleus units increased their rate for both half cycles of the sine wave. Lateral mesencephalic nucleus units are more sensitive than DON units, especially to small moving dipoles. Dorsal octavolateral nucleus units respond to a moving DC dipole with an increase followed by a decrease in spike rate or vice versa, depending on movement direction and dipole orientation. Lateral mesencephalic nucleus units, in contrast, increased their discharge rate for all stimuli. Any change in discharge rate of DON units is converted in the LMN to a discharge rate increase. Lateral mesencephalic nucleus units therefore appear to code the presence of a stimulus regardless of orientation and motion direction.     

Receptive field organization of electrosensory neurons in the paddlefish (Polyodon spathula)

Paddlefish use their electrosense to locate small water fleas (daphnia), their primary prey, in three-dimensional space. High sensitivity and a representation of object location are essential for this task. High sensitivity can be achieved by convergence of information from a large number of receptors and object location is usually represented in the nervous system by topographic maps. However the first electrosensory center in the brain, the dorsal octavolateral nucleus in the hindbrain, is neither topographically organized nor does it show a higher sensitivity than primary afferent fibers. Here, we investigated the response properties of electrosensory neurons in the dorsal octavolateral nucleus (DON), the lateral mesencephalic nucleus (LMN) and the tectum mesencephali (TM). LMN units are characterized by large receptive fields, which suggest a high degree of convergence. TM units have small receptive fields and are topographically arranged, at least in the rostro-caudal axis, the only dimension we could test. Well-defined receptive fields, however, could only be detected in the TM with a moving DC stimulus. The receptive fields of TM units, as determined by slowly scanning the rostrum and head with a 5 Hz stimulus, were very large and frequently two or more receptive fields were present. The receptive fields for LMN units were located in the anterior half of the rostrum whereas TM units had receptive fields predominantly on the head and at the base of the rostrum. A detailed analysis of the prey catching behavior revealed that it consists of two phases that coincide with the location of the receptive fields in LMN and TM, respectively. This suggests that LMN units are responsible for the initial orienting response that occurs when the prey is alongside the anterior first half of the rostrum. TM units, in contrast, had receptive fields at locations where the prey is located when the fish opens its mouth and attempts the final strike.     

Anatomy of the mechanosensory lateral line canal system and electrosensory ampullae of Lorenzini in two species of sawshark (fam. Pristiophoridae)

It has long been assumed that the elongated rostra (the saws) of sawsharks (family: Pristiophoridae) and sawfish (family: Pristidae) serve a similar function. Recent behavioural and anatomical studies have shed light on the dual function of the pristid rostrum in mechanosensory and electrosensory prey detection and prey manipulation. Here, the authors examine the distributions of the mechanosensory lateral line canals and electrosensory ampullae of Lorenzini in the southern sawshark, Pristiophorus nudipinnis and the longnose sawshark, Pristiophorus cirratus. In both species, the receptive fields of the mechano- and electrosensory systems extend the full length of the rostrum indicating that the sawshark rostrum serves a sensory function. Interestingly, despite recent findings suggesting they feed at different trophic levels, minimal interspecific variation between the two species was recorded. Nonetheless, compared to pristids, the pristiophorid rostrum possesses a reduced mechanosensory sampling field but higher electrosensory resolution, which suggests that pristiophorids may not use their rostrums to disable large prey like pristids do.     

Two modes of information processing in the electrosensory system of the paddlefish (Polyodon spathula)

Paddlefish are uniquely adapted for the detection of their prey, small water fleas, by primarily using their passive electrosensory system. In a recent anatomical study, we found two populations of secondary neurons in the electrosensory hind brain area (dorsal octavolateral nucleus, DON). Cells in the anterior DON project to the contralateral tectum, whereas cells in the posterior DON project bilaterally to the torus semicircularis and lateral mesencephalic nucleus. In this study, we investigated the properties of both populations and found that they form two physiologically different populations. Cells in the posterior DON are about one order of magnitude more sensitive and respond better to stimuli with lower frequency content than anterior cells. The posterior cells are, therefore, better suited to detect distant prey represented by low-amplitude signals at the receptors, along with a lower frequency spectrum, whereas cells in the anterior DON may only be able to sense nearby prey. This suggests the existence of two distinct channels for electrosensory information processing: one for proximal signals via the anterior DON and one for distant stimuli via the posterior DON with the sensory input fed into the appropriate ascending channels based on the relative sensitivity of both cell populations.     

Adaptive processing in electrosensory systems: Links to cerebellar plasticity and learning

The first central stage of electrosensory processing in fish takes place in structures with local circuitry that resembles the cerebellum. Cerebellum-like structures and the cerebellum itself share common patterns of gene expression and may also share developmental and evolutionary origins. Given these similarities it is natural to ask whether insights gleaned from the study of cerebellum-like structures might be useful for understanding aspects of cerebellar function and vice versa. Work from electrosensory systems has shown that cerebellum-like circuitry acts to generate learned predictions about the sensory consequences of the animals’ own behavior through a process of associative plasticity at parallel fiber synapses. Subtraction of these predictions from the actual sensory input serves to highlight unexpected and hence behaviorally relevant features. Learning and prediction are also central to many current ideas regarding the function of the cerebellum itself. The present review draws comparisons between cerebellum-like structures and the cerebellum focusing on the properties and sites of synaptic plasticity in these structures and on connections between plasticity and learning. Examples are drawn mainly from the electrosensory lobe (ELL) of mormyrid fish and from extensive work characterizing the role of the cerebellum in Pavlovian eyelid conditioning and vestibulo-ocular reflex (VOR) modification. Parallels with other cerebellum-like structures, including the gymnotid ELL, the elasmobranch dorsal octavolateral nucleus (DON), and the mammalian dorsal cochlear nucleus (DCN) are also discussed.     

Are mushroom bodies cerebellum-like structures?

The mushroom bodies are distinctive neuropils in the protocerebral brain segments of many protostomes. A defining feature of mushroom bodies is their intrinsic neurons, masses of cytoplasm-poor globuli cells that form a system of lobes with their densely-packed, parallel-projecting axon-like processes. In insects, the role of the mushroom bodies in olfactory processing and associative learning and memory has been studied in depth, but several lines of evidence suggest that the function of these higher brain centers cannot be restricted to these roles. The present account considers whether insight into an underlying function of mushroom bodies may be provided by cerebellum-like structures in vertebrates, which are similarly defined by the presence of masses of tiny granule cells that emit thin parallel fibers forming a dense molecular layer. In vertebrates, the shared neuroarchitecture of cerebellum-like structures has been suggested to underlie a common functional role as adaptive filters for the removal of predictable sensory elements, such as those arising from reafference, from the total sensory input. Cerebellum-like structures include the vertebrate cerebellum, the electrosensory lateral line lobe, dorsal and medial octavolateral nuclei of fish, and the dorsal cochlear nucleus of mammals. The many architectural and physiological features that the insect mushroom bodies share with cerebellum-like structures suggest that it might be fruitful to consider mushroom body function in light of a possible role as adaptive sensory filters. The present account thus presents a detailed comparison of the insect mushroom bodies with vertebrate cerebellum-like structures.     

Distribution of Kv1-like potassium channels in the electromotor and electrosensory systems of the weakly electric fish Apteronotus leptorhynchus

The electromotor and electrosensory systems of the weakly electric fish Apteronotus leptorhynchus are model systems for studying mechanisms of high-frequency motor pattern generation and sensory processing. Voltage-dependent ionic currents, including low-threshold potassium currents, influence excitability of neurons in these circuits and thereby regulate motor output and sensory filtering. Although Kv1-like potassium channels are likely to carry low-threshold potassium currents in electromotor and electrosensory neurons, the distribution of Kv1 alpha subunits in A. leptorhynchus is unknown. In this study, we used immunohistochemistry with six different antibodies raised against specific mammalian Kv1 alpha subunits (Kv1.1-Kv1.6) to characterize the distribution of Kv1-like channels in electromotor and electrosensory structures. Each Kv1 antibody labeled a distinct subset of neurons, fibers, and/or dendrites in electromotor and electrosensory nuclei. Kv1-like immunoreactivity in the electrosensory lateral line lobe (ELL) and pacemaker nucleus are particularly relevant in light of previous studies suggesting that potassium currents carried by Kv1 channels regulate neuronal excitability in these regions. Immunoreactivity of pyramidal cells in the ELL with several Kv1 antibodies is consistent with Kv1 channels carrying low-threshold outward currents that regulate spike waveform in these cells (Fernandez et al., J Neurosci 2005;25:363-371). Similarly, Kv1-like immunoreactivity in the pacemaker nucleus is consistent with a role of Kv1 channels in spontaneous high-frequency firing in pacemaker neurons. Robust Kv1-like immunoreactivity in several other structures, including the dorsal torus semicircularis, tuberous electroreceptors, and the electric organ, indicates that Kv1 channels are broadly expressed and are likely to contribute significantly to generating the electric organ discharge and processing electrosensory inputs.     

Design principles of sensory processing in cerebellum-like structures

Cerebellum-like structures are compared for two sensory systems: electrosensory and auditory. The electrosensory lateral line lobe of mormyrid electric fish is reviewed and the neural representation of electrosensory objects in this structure is modeled and discussed. The dorsal cochlear nucleus in the auditory brainstem of mammals is reviewed and new data are presented that characterize the responses of neurons in this structure in the mouse. Similarities between the electrosensory and auditory cerebellum-like structures are shown, in particular adaptive processes that may reduce responses to predictable stimuli. We suggest that the differences in the types of sensory objects may drive the differences in the anatomical and physiological characteristics of these two cerebellum-like structures.     

Some introductory notes on the organization of the forebrain in tetrapods.

As an introduction to the main theme of this conference an overview of the organization of the tetrapod forebrain is presented with emphasis on the telencephalic representation of sensory and motor functions. In all classes of tetrapods, olfactory, visual, octavolateral, somatosensory and gustatory information reaches the telencephalon. Major differences exist in the telencephalic targets of sensory information between amphibians and amniotes. In amphibians, three targets are found: the lateral pallium for olfactory input, the medial pallium for visual and multisensory input, and the lateral subpallium for visual, octavolateral and somatosensory information. The forebrains of reptiles and mammals are similar in that the dorsal surface of their cerebral hemisphere is formed by a pallium with three major segments: (a) an olfactory, lateral cortex; (b) a 'limbic' cortex that forms the dorsomedial wall of the hemisphere, and (c) an intermediate cortex that is composed entirely of isocortex in mammals, but in reptiles (and birds) consists of at least part of the dorsal cortex (in birds the Wulst) and a large intraventricular protrusion, i.e. the dorsal ventricular ridge. In birds, the entire lateral wall of the hemisphere is involved in this expansion. The intermediate pallial segment receives sensory projections from the thalamus and contains modality-specific sensory areas in reptiles, birds and mammals. The most important differences between the intermediate pallial segment of amniotes concern motor systems.     

Spatiotemporal burst coding for extracting features of spatiotemporally varying stimuli

Encoding features of spatiotemporally varying stimuli is quite important for understanding the neural mechanisms of various sensory coding. Temporal coding can encode features of time-varying stimulus, and population coding with temporal coding is adequate for encoding spatiotemporal correlation of stimulus features into spatiotemporal activity of neurons. However, little is known about how spatiotemporal features of stimulus are encoded by spatiotemporal property of neural activity. To address this issue, we propose here a population coding with burst spikes, called here spatiotemporal burst (STB) coding. In STB coding, the temporal variation of stimuli is encoded by the precise onset timing of burst spike, and the spatiotemporal correlation of stimuli is emphasized by one specific aspect of burst firing, or spike packet followed by silent interval. To show concretely the role of STB coding, we study the electrosensory system of a weakly electric fish. Weakly electric fish must perceive the information about an object nearby by analyzing spatiotemporal modulations of electric field around it. On the basis of well-characterized circuitry, we constructed a neural network model of the electrosensory system. Here we show that STB coding encodes well the information of object distance and size by extracting the spatiotemporal correlation of the distorted electric field. The burst activity of electrosensory neurons is also affected by feedback signals through synaptic plasticity. We show that the control of burst activity caused by the synaptic plasticity leads to extracting the stimulus features depending on the stimulus context. Our results suggest that sensory systems use burst spikes as a unit of sensory coding in order to extract spatiotemporal features of stimuli from spatially distributed stimuli.     

Nature as a model for technical sensors

Nature has developed a stunning diversity of sensory systems. Humans and many animals mainly rely on visual information. In addition, they may use acoustic, olfactory, and tactile cues for object detection and spatial orientation. Beyond these sensory systems a large variety of highly specialized sensors have evolved. For instance, some buprestid beetles use infrared organs for the detection of forest fires. The infrared sensors of boid and crotalid snakes are used for prey detection at night. For object detection and spatial orientation many species of nocturnal fish employ active electrolocation. This review describes certain aspects of the detection and processing of infrared and electrosensory information. We show that the study of natural exotic sensory systems can lead to discoveries that are useful for the construction of technical sensors and artificial control systems. Comparative studies of animal sensory systems have the power to uncover at least a small fraction of the gigantic untapped reservoir of natural solutions for perceptive problems.     

食蚊鱼的生物电场特征

文章采用活体记录的方法测量了食蚊鱼(Gambusia affinis)的生物电场。实验分单尾鱼、两尾鱼同向和两尾鱼反向三组测量, 每组10 个重复。结果表明:单尾鱼的生物电场表现为头负、尾正的偶极子直流电场,头部相对电势为(242.4) V, 尾部为(211.6) V, 且头部附近产生1-3 Hz 与呼吸频率对应的交流呼吸电场, 大小为(4.20.8) V。两尾鱼生物电场测量表明, 其直流电场均大于单尾鱼(P0.05); 两尾鱼同向靠近时产生的交流呼吸电场显著大于单尾鱼(P0.01), 而反向靠近时产生的呼吸电场显著小于单尾鱼(P0.001)。这表明两条鱼不同方向靠近时, 可通过呼吸作用改变交流呼吸电场的大小。此种现象对于依靠感知交流呼吸电场来摄食的被动电感受鱼类是不利的。       

Sensory control of behavior in electric fish

The electrosensory system is ideally suited for the integration of behavioral and cellular approaches and, therefore, has led to the most detailed explanations of natural behaviors at the single-cell level. The electric sense shares basic principles in the coding of sensory information with more advanced sensory modalities and thus provides a convenient model system for studying neuronal mechanisms of information processing in general.     

Phantoms in the brain: Ambiguous representations of stimulus amplitude and timing in weakly electric fish

In wave-type weakly electric fish, two distinct types of primary afferent fibers are specialized for separately encoding modulations in the amplitude and phase (timing) of electrosensory stimuli. Time-coding afferents phase lock to periodic stimuli and respond to changes in stimulus phase with shifts in spike timing. Amplitude-coding afferents fire sporadically to periodic stimuli. Their probability of firing in a given cycle, and therefore their firing rate, is proportional to stimulus amplitude. However, the spike times of time-coding afferents are also affected by changes in amplitude; similarly, the firing rates of amplitude-coding afferents are also affected by changes in phase. Because identical changes in the activity of an individual primary afferent can be caused by modulations in either the amplitude or phase of stimuli, there is ambiguity regarding the information content of primary afferent responses that can result in ‘phantom’ modulations not present in an actual stimulus. Central electrosensory neurons in the hindbrain and midbrain respond to these phantom modulations. Phantom modulations can also elicit behavioral responses, indicating that ambiguity in the encoding of amplitude and timing information ultimately distorts electrosensory perception. A lack of independence in the encoding of multiple stimulus attributes can therefore result in perceptual illusions. Similar effects may occur in other sensory systems as well. In particular, the vertebrate auditory system is thought to be phylogenetically related to the electrosensory system and it encodes information about amplitude and timing in similar ways. It has been well established that pitch perception and loudness perception are both affected by the frequency and intensity of sounds, raising the intriguing possibility that auditory perception may also be affected by ambiguity in the encoding of sound amplitude and timing.     

Development of the jamming avoidance response and its morphological correlates in the gymnotiform electric fish,Eigenmannia

The electric fish, Eigenmannia, will smoothly shift the frequency of its electric organ discharge away from an interfering electric signal. This shift in frequency is called the jamming avoidance response (JAR). In this article, we analyze the behavioral development of the JAR and the anatomical development of structures critical for the performance of the JAR. The JAR first appears when juvenile Eigenmannia are approximately 1 month old, at a total length of 13–18 mm. We have found that the establishment of much of the sensory periphery and of central connections precedes the onset of the JAR. We describe three aspects of the behavioral development of the JAR: (a) the onset and development of the behavior is closely correlated with size, not age; (b) the magnitude (in Hz) of the JAR increases with size until the juveniles display values within the adult range (10–20 Hz) at a total length of 25–30 mm; and (3) the JAR does not require prior experience or exposure to electrical signals. Raised in total electrical isolation from the egg stage, animals tested at a total length of 25 mm performed a correct JAR when first exposed to the stimulus. We examine the development of anatomical areas important for the performance of the JAR: the peripheral electrosensory system (mechano- and electroreceptors and peripheral nerves); and central electrosensory pathways and nuclei [the electrosensory lateral line lobe (ELL), the lateral lemniscus, the torus semicircularis, and the pacemaker nucleus]. The first recognizable structures in the developing electrosensory system are the peripheral neurites of the anterior lateral line nerve. The afferent nerves are established by day 2, which is prior to the formation of receptors in the epidermis. Thus, the neurites wait for their targets. This sequence of events suggests that receptor formation may be induced by innervation of primordial cells within the epidermis. Mechanoreceptors are first formed between day 3 and 4, while electroreceptors are first formed on day 7. Electroreceptor multiplication is observed for the first time at an age of 25 days and correlates with the onset of the JAR. The somata of the anterior lateral line nerve ganglion project afferents out to peripheral electroreceptors and also send axons centrally into the ELL. The first electroreceptive axons invade the ELL by day 6, and presumably a rough somatotopic organization and segmentation within the ELL may arise as early as day 7. Axonal projections from the ELL to the torus develop after day 18. Within the torus semicircularis, giant cells are necessary for the performance of the JAR. Giant cell numbers increase exponentially during development and the onset of the JAR coincides with a minimum of at least 150 giant cells and the attainment of a total length of at least 15 mm and at least 150 giant cells. Pacemaker and relay cells comprise the adult Eigenmannia pacemaker nucleus. The growth and differentiation of these cell types also correlates with the onset of the JAR in developing animals. We describe a gradual improvement of sensory abilities, as opposed to an explosive onset of the mature JAR. We further suggest that this may be a rule common in most developing behavioral systems. © 1992 John Wiley & Sons, Inc.     

Responses of neurons in the electrosensory lateral line lobe of the weakly electric fish <Emphasis Type="Italic">Gnathonemus petersii</Emphasis> to simple and complex electrosensory stimuli

Mormyrid fish use active electrolocation to detect and analyze objects. The electrosensory lateral line lobe in the brain receives input from electroreceptors and an efference copy of the command to discharge the electric organ. In curarized fish, we recorded extracellularly from neurons of the electrosensory lateral line lobe while stimulating in the periphery with either a local point stimulus or with a more natural whole-body stimulus. Two classes of neurons were found: (1) three types of E-cells, which were excited by a point stimulus; and (2) two types of I-cells, which were inhibited by point stimulus and responded with excitation to the electric organ corollary discharge. While all neurons responded to a point stimulus, only one out of two types of I-units and two of the three types of E-units changed their firing behavior to a whole-body stimulus or when an object was present. In most units, the responses to whole-body stimuli and to point stimuli differed substantially. Many electrosensory lateral line lobe units showed neural plasticity after prolonged sensory stimulation. However, plastic effects during whole body stimulation were often unlike those occurring during point stimuli, suggesting that under natural conditions electrosensory lateral line lobe network effects play an important role in shaping neural plasticity.