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Searching for the possible nature of this decrease in the response of A t cell with increasing intensity of the stimu- lus, we thought of some physiological phenomena that could account for it. One possibility was that non-linear me- chanical events could take place at the vibrating tympanic membrane, and so explain the At-cell response. However, the dynamic response of the A 2 cell, which in Noctuoidea is attached to the same point of the tympanic membrane as the A1 cell [7] (Coro, unpublished), showed a monotonic increase with the same stimulus intensity (Fig. 2). The recording method used implied the sec- tioning of the distal and proximal ends of both alar nerves - to which the tympanic nervelets adjoin before enter- ing the pterothoracic ganglion - so this sensory information never reaches the central nervous system and we also discard the possibility that some effer- ent control might be operating. Another explanation could be that at such intensities which evoke a decrease in the At-cell response, this receptor suffers some sort of fatigue because of the high frequency of response to which it is being forced. The fact that the A t cell shows a strong post-stimu- lus discharge (Fig. 1) indicates that at such intensities this receptor can still respond to the stimuli, and so we also discarded this possibility. The relationship between stimulus in- tensity and At-cell response could then

be explained by a lateral inhibition mechanism, because of the following facts: the rate of decrease in frequency and in the total number of spikes in the A i- cell response is almost the same as the rate of increase in these parameters in the A2-cell response (Fig. 2); there is a threshold for the inhibitory mechanism to decrease the response of the A 1 cell, that is, a certain value of the A2-cell discharge is needed for it to exert its inhibitory influence (Fig. 2); with long acoustic stimuli (5-10 s), the A2 cell adapts more rapidly than the At receptor and when its response de- creases below a certain threshold value,

the frequency of the A 1 cell increases, so the temporal pattern of discharge of these receptors is a "mirror image", as in the lateral eye of Limulus [8]; the post-stimulus discharge of the A 1 cell when the A2 cell has inhibited the At-cell response, may be considered as a post-inhibitory rebound, similar to that described in the lateral eye of Limulus [8]. All these facts point towards the ex- istence of a lateral inhibitory mecha- nism between the acoustic receptors of this moth. Further research is at pres- ent been carried out in our laboratory to elucidate this and other physiologi- cal features of the tympanic organ of E. pugione and other noctuoid moths.

Received September 2, 1982

1. Hartline, H.K.: Science 164, 270 (1969); Krischfeld, K., L.ntz, B. : Z. Naturforsch. 29c, 95 (1974)

2. Werblin, F.: J. Gen. Physiol. 63, 62 (1974); Spfith, M., Lehmann, B.: J. Comp. Physiol. i03, 69 (1975); Natur- wissenschaften 63, 435 (1976)

3. Roeder, K.K. : Nerve Cells and Insect Be- havior. Harvard Univ. Press 1967

4. Treat, A.E., Roeder, K.D.: J. Insect Physiol. 3, 262 (1959); Lechtenberg, R.: ibid. 17, 2395 (1971)

5. Suga, N.: Jap. J. Physiol. 11, 666 (1961) 6. Adams, W.B.: J. Gen. Physiol. 58, 562

(1971) 7. Eggers, F.: Zool. Jb. (Anat.) 41, 273

(1919); Ghiradella, H.: J. Morphol. 134, 21 (1971)

8. Hartline, H.K., Ratliff, F., Miller, W.H., in: Nervous Inhibition, p. 241 (ed. E. Florey). New York:Pergamon Press 1961

Relation between Activity of Tectal Neurons and Prey-catching Behavior in Toads Bufo bufo

A.L. Megela, H.-W. Botchers, and J.-P. Ewert

Arbeitsgruppe Neuroethologie und Biokybernetik, FB 19, der UniversitS.t (GhK), D-3500 Kassel

Single neurons in the optic tectum and thalamic-pretectal (TP) region of the common toad are sensitive to the ge- ometry of behaviorally relevant, moving visual stimuli [3]. Tectal class T5-2 neurons respond selectively to stimuli resembling possible prey objects (e.g.,"worm-like") over those resem-

bling non-prey objects (e.g., "anti- worm-like"). Tectal class T5-1 neurons exhibit sensitivity to these configura- tional stimuli. Neurons in the TP region (class TH-3) show selective re- sponses to "antiworm-like" stimuli. Results from neurophysiological and behavioral studies led Ewert [2] to

100 Naturwissenschaften 70 (1983) �9 Springer-Verlag 1983

propose a model of configurational prey/non-prey recognition in the toad's visual system, in which the response characteristics of tectal T5-2 neurons are determined by inhibitory input from the TP region. It has been proposed that T5-2 neurons are "command elements" of a system that releases prey-capture behaviors in toads [5]. Techniques have been developed re- cently which allow the simultaneous study of neuronal and behavioral re- sponses in freely moving toads [1, 4]. Thus, it is now possible to more closely investigate the question of coincidence between prey-catching behavior and neuronal activity in the visual system. We used these techniques to record neuronal and behavioral responses to moving configurational visual stimuli in toads with lesions of the TP region. Toads with TP lesions can no longer discriminate between prey and non- prey objects but, rather, readily exhibit prey-catching behaviors (turning, ori- enting, snapping) to any moving visual stimulus, regardless of its size or con- figuration [3]. These animals are "dis- inhibited", and since they show stereo- typed, predictable responses to all visu- al stimuli, provide an excellent oppor- tunity to examine the correspondence between neuronal activity and prey- catching behaviors. Female toads (Bufo bufo spinosus) were anesthetized with diethylether. A uni- lateral micro-knife cut was made sever- ing the connections between the postero-lateral nucleus of the thalamus and the optic tectum. After the animals recovered from the anesthesia, they were placed in a large black cylinder (diameter 45 cm, height 18 cm), and their responses to moving white stimuli of various sizes and shapes (discs, 10 and 30 mm diameter; squares, 30 x 30 or 60 x 60 mmZ; "worm-l ike" stripes, 2.5 x 30 mm 2 oriented parallel to the direction of movement; and "anti- worm-like" stripes, 2.5 x 30 mm 2 ori- ented perpendicular to the direction of movement) were observed. Descrip- tions of the techniques for recording the activity of single neurons in awake behaving animals have been presented previously [1, 4]. A video system was used to record the movements of the toad, the visual stimuli, and the neuro- nal activity. Frame-by-frame analyses of behavior and associated neuronal

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Fig. 1. Activity of single tectal neurons in the behaving toad Bufo bufo, representative examples. Each computer print-out shows the pattern of action potentials and the corre- sponding interspike frequency time (Dwell-) histogram. The horizontal lines indicate stimu- lus (s) and behavior events (m) calculated from a frame-by-frame analysis, a) Activity of a class T2-1 neuron during traverse of its excitatory receptive field with a moving visual stimulus (s); high discharge frequency did not necessarily coincide with a turning movement (m). b) Activity of a class T5 neuron; increased activity during stimulation (s) precedes a turning response (m). c) Spontaneously active class T8 neuron; the burst precedes a snapping response (s) toward a moving mealworm; note the subsequent silent period

events were made subsequently. A Nicolet Med 812 computer was used for off-line compiling and plotting of interspike frequency histograms [1]. Lesion and recording sites were verified histologically with Nissl stains using the Prussian-blue method.

Class R2 and R3 neurons: The re- sponses of ten retinal neurons (five class R2 and five class R3) located in superficial tectal layers were recorded. The response properties of these neurons were similar to those pre- viously described for both paralyzed

Naturwissenschaften 70 (1983) �9 Springer-Verlag 1983 101

and normal freely moving toads [3]. There was no strict correlation between neuronal activity and visually guided behavior, that is, bursts of activity from these neurons did not necessarily "predict" a subsequent behavioral re- sponse.

Class T2-1 neurons: Four T2-1 neurons were recorded from deep periventricu- lar tectal layers. As in the intact animal these neurons had frontal visual excit- atory receptive fields of about 70-90 ~ diameter, but could show in the TP- lesioned animal varying rates of ongoing spontaneous activity. T2-1 neurons exhibited no configurational selectivity to any of the stimuli pre- sented. These neurons did not fire dur- ing spontaneous non-visually guided movements of the animal. Moreover, there was no relationship between neu- ronal firing and prey-catching move- ments of the toad in response to a visu- al stimulus, i.e., high neuronal activity did not necessarily coincide with a motor response of the toad (Fig. I a). The activity of these neurons seemed to resemble the alertness of the toad which was fluctuating over time.

Class 7"4 neurons: Activity was re- corded from seven tectal class T4 neurons located in periventricular layers. The receptive fields of these neurons covered the entire contralater- al visual field. Some neurons were spontaneously active. These neurons fired during both active and passive movements of the toad; however, high- er rates of neuronal activity were seen

when the toad turned in response to a visual stimulus than during spontane- ous turning. In either case, neuronal activity did not necessarily precede turning or snapping movements.

Class T8 neurons." Five tectal class T8 neurons recorded were spontaneously active. They showed no direct visual input, although their firing rates seemed to be influenced by visual stim- ulation. The activity of these neurons coincided with any movements by the toad (e.g., turning, walking, snapping), whether the movement was elicited by a visual stimulus or occurred spontane- ously. But this kind o f "p re -moto r " ac- tivity showed no specificity with regard to a motor pattern [1]. In any case the neuron continued discharging bursts during the toad's movements, but after the movement the neurons showed clear postexcitatory inhibition (Fig. 1 c).

Class T5 neurons: In the toads with TP lesions, tectal T5 neurons lose their normal configurational selectivity, and habituation properties [3]. Therefore, distinctions between T5-1 and T5-2 classes can no longer be made in these animals. Thirteen T5-type neurons in the freely moving disinhibited toad were identified by receptive-field size (3040~ and location within the central tectal layers. These neurons were activated both by moving visual stimuli and during the subsequent movements of the animal, suggesting some kind of feedback which keeps the neuron active during the period of

turning behavior. When a stimulus was moved through the receptive field and the toad responded with a prey- catching movement, the frequency of neuronal firing was greater than that observed when the toad did not beha- viorally respond to the same stimulus (Fig. 1 b). Thus, relatively high neuro- nal activity coincided with behavioral responding. The activity preceded and, so to speak, "predicted" a subsequent turning movement. These data suggest that a clear corre- spondence exists between the frequency of firing of T5 neurons in response to a moving visual stimulus and subse- quent orienting (turning) movements of the toad. Therefore, the activity of T5 neurons may play a crucial role in the behavioral events of prey recogni- tion and prey capture [3, 5].

Received September 6 and November 3, 1982

1. Borchers, H.-W., in: Progress in Cyber- netics and Systems Research, Vol. 9, p. 109 (R. Trappl, G. Pask, L. Ricciardi, eds.). Washington-New York-London: Hemisphere Publ. Co. 1982

2. Ewert, J.-P., in: Recent Progress in Per- ception (R. Held, ed.). San Francisco: Freeman 1974

3. Ewert, J.-P., in: Neurology of the Optic Tectum (H. Vanegas, ed.). New York: Plenum Press 1983

4. Ewert, J.-P., Borchers, H.-W.: J. Comp. Physiol. 92, 117 (1974)

5. Ewert, J.-P., Burghagen, H., Schiirg- Pfeiffer, E., in: Advances in Vertebrate Neuroethology, p. 413 (J.-P. Ewert, R.R. Capranica, D.J. Ingle, eds.). New York: Plenum Press 1983

Buchbesprechungen Galaxien. Von T. Ferris. Basel-Boston- Stuttgart: Birkh~iuser 1981. 183 S., 137 Abb., DM 128,-. Das Buch ist eine ausgezeichnete popul/ire Darstellung der Ergebnisse der modernen Astronomie. Der ansprechend tibersetzte Text des bekannten Wissenschaftsjournali- sten Ferris ist anschaulich und lebendig, oft sogar mitreiBend; er bringt eine riesige Fiille yon Fakten und gibt einen guten ljberblick fiber den Stand der Forschung. Die Darstellung ist ausgewogen, und delia Rezensenten sind keine Fehler aufgefallen. Geradezu umwerfend sind Anzahl und Qualit/it der gr6Btenteils farbigen Aufnah-

men. Das Buch ist ein Kompendium der sch6nsten astronomischen Photographien, die es auch fiir den Fachmann attraktiv machen. Auf jeden Fall ist es eine hervor- ragende Einftihrung ftir interessierte Laien. Will man jemand ftir die Astronomie be- geistern, so gebe man ibm dieses Buch in die Hand. M. Reinhardt (Bochum)

Handbuch der gef'dhrliehen Giiter. Von G. Hommel. Berlin-Heidelberg-New York: Springer 1980. Preis des Gesamtwerkes derzeit DM 371,-. Der ,,Hommel" ist nicht neu. Der ,,alte Hommel" steht in meinem Schrank. Seit

1974. Viel gebraucht und deshalb schon ein wenig abgegriffen. Den ,,neuen Horn- reel" erhielt ich gestern. Ich habe gebl~ittert und verglichen. Er ist tats~ichlich ,,neu". Vieles hat sich ge~indert in den letzten Jah- ren, vieles wurde deshalb erg/inzt in diesem Nachschlagewerk, das sich in zwei Plastik- ordnern DIN A 4 pr/isentiert. Ober 600 Merkbl/itter und zus~itzlich mehr als 300 Seiten wichtiger Text - all das macht den ,,Hommel" zu einem wichtigen Werk ftir alle, die mit der Sicherheit konfrontiert werden. Oder mit der Unsicherheit, die im Umgang mit gef~ihrlichen Giitern so ge- f~hrlich ist. Die Polizei bei einern Unfall,

102 Naturwissenschaffen 70 (1983) �9 Springer-Verlag 1981