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  • 1
    Electronic Resource
    Electronic Resource
    Temporal discharge patterns of tectal and medullary neurons chronically recorded during snapping toward prey in toads Bufo bufo spinosus (1993)
    Springer
    Journal of comparative physiology 173 (1993), S. 363-376 
    Details
    ISSN: 1432-1351
    Keywords: Snapping ; Chronic single cell recording ; Optic tectum ; Medulla oblongata ; Toad
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In freely moving toads, the temporal discharge patterns of tectal and medullary neurons were observed during prey-catching. 1. Tectal T5.2 and T8.1 neurons displayed a premotor warming up firing that in the former was addressed specifically to prey orienting or snapping and in the latter generally to almost any kind of body movement. 2. The temporal discharge patterns of T5.2 neurons during snapping were different from those during orienting toward prey. Snapping started in the peak phase of warming up; firing was immediately terminated during the snap; thereafter some rebound activity was observed. Orienting started after the premotor warming up in the declining phase whilst the neuron kept on firing during orienting and then settled when the orienting movement was completed. 3. In toads which were not motivated to catch prey — comparabl to immobilized ones — the discharge frequency of T5.2 neurons toward a prey stimulus revealed no such warming up. 4. Because it is known that prey-selective T5.2 neurons are controlled by pretectal inhibitory influences, the following experiment was conducted: during recording a T5.2 neuron a pretectal lesion was applied ipsilaterally to the recording site. After a few seconds, the neuron showed a strong premotor wanning up in response to any kind of moving object, followed by prey-catching. 5. In the medulla oblongata, different H-type neurons of the hypoglossal nucleus displayed specific discharge patterns which resembled the tongue protractor and retractor muscle activities; a third type resembled the activity of the genio/sterno-hyoid muscle, which are suggested to stabilize the hyoid bone during snapping. 6. There were medullary M8-type neurons with properties similar to T8.1. 7. Snapping could be triggered by electrical stimulation of the optic tectum in the representation of the frontal visual field, but not by stimulation in the hypoglossal nucleus or the adjacent medial reticular formation. 8. A concept of a neuronal circuit for the coordination of tongue muscle contractions in response to prey is proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00212701
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  • 2
    Electronic Resource
    Electronic Resource
    Responses of medullary neurons to moving visual stimuli in the common toad (1990)
    Springer
    Journal of comparative physiology 167 (1990), S. 495-508 
    Details
    ISSN: 1432-1351
    Keywords: Command releasing systems ; Pre-motor visual integration ; Medulla oblongata ; Extracellular recording ; Toad
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The concept of coded ‘command releasing systems’ proposes that visually specialized descending tectal (and pretectal) neurons converge on motor pattern generating medullary circuits and release — in goal-specific combination — specific action patterns. Extracellular recordings from medullary neurons of the medial reticular formation of the awake immobilized toad in response to moving visual stimuli revealed the following main results. (i) Properties of medullary neurons were distinguished by location, shape, and size of visual receptive fields (ranging from relatively small to wide), by trigger features of various moving configural stimulus objects (including preyand predator-selective properties), by tactile sensitivity, and by firing pattern characteristics (sluggish, tonic, warming-up, and cyclic). (ii) Visual receptive fields of medullary neurons and their responses to moving configural objects suggest converging inputs of tectal (and pretectal) descending neurons. (iii) In contrast to tectal monocular ‘small-field’ neurons, the excitatory visual receptive fields of comparable medullary neurons were larger, ellipsoidally shaped, mostly oriented horizontally, and not topographically mapped in an obvious fashion. Furthermore, configural feature discrimination was sharper. (iv) The observation of multiple properties in most medullary neurons (partly showing combined visual and cutaneous sensitivities) suggests integration of various inputs by these cells, and this is in principle consistent with the concept of command releasing systems. (v) There is evidence for reciprocal tectal/medullary excitatory pathways suitable for premotor warming-up. (vi) Cyclic bursting of many neurons, spontaneously or as a post-stimulus sustaining event, points to a medullary premotor/motor property.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190820
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