Summary.Recent research has demonstrated that ipsilaterally visually evoked potentials (VEPs) can be measured within the ectostriatum, the telencephalic target area of the tectofugal visual pathway in birds. In this paper we systematically measured contra-and ipsilateral VEPs within the ectostriatal complex to obtain more detailed information on the processing of contra-and ipsilateral stimuli. The similarity of neighbouring VEPs at equal depth and a comparison of a one dimensional and a three dimensional analysis of current source-densities (CSDs) for identical coordinates suggested that a one dimensional current source-density analysis might be applicable. The one dimensional current source-density analysis demonstrated largely corresponding patterns in the sinksource sequences of the current source-density depth profiles for the contra-and ipsilateral stimulus responses. The occurrence of a large sink in the centre of the ectostriatal core, together with the results of multiunit recordings, shows that the ectostriatal core is the location of the generators for both the contra-and the ipsilaterally evoked responses. The occurrence of macroscopic sinks and sources and the fact that VEPs can be recorded from the ectostriatum shows that there is a higher degree of order in the ectostriatum than has been previously demonstrated by anatomical methods. The time coincidence between the maximum spike rate of multiunit responses, the negative peak of the evoked potential, and the large central sink demonstrates that the influence of ipsi-as well as of contralateral stimuli is predominantly excitatory.

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Key words': zebra finch visually evoked potentials hyperstnatum ventrale pars caudaleThe song of the zebra finch is facilitated and altered bv the presence ol a female. Thus. visual information should affect the song system of the bird. Visually evoked potentials can be recorded from n. hyperstriatum ventrale pars caudale [HVc). The long latency ot this potential and its variability indicate several processing steps between primary sensory areas of the telencephalon and HVC. Within HVc, under these experimental conditions no interaction between acoustic and visual input could be demonstrated. However. at the dorsal border and within the shelf below HVc. visual information seems to enhance acoustically evoked potentialsThe song of oscine birds is controlled bv a well-defined system of concatenated brain nuclei, the socalled song system L3. As feedback control is necessary for development and for performance of song in many of these birds s, connections from the auditory system to the song control system have been proposed and could be demonstrated bv several authors 5 7.1o, i],14. According to their results, the nucleus hyperstriatum ventrale pars caudale (HVc) receives input from field L, the telencephalic nucleus of the auditory pathway in the bird's brain.The song of the male is, at least in the zebra finch. facilitated by the presence of a female. II could be demonstrated that quality and quantity of the male's song is altered by presentation of a living female as well as by a female dummy or even a picture of a female 1-4. With increasing similarity of the stimulus to a living female the song of the male becomes more stereotyped and frequent and has more introductory elements and motifs. Based on these song features. two different song types can be detected under natural conditions: the so-called 'undirected" song which is uttered in situations not dearly assoctated with a definite function; and the 'directed' song, which is directed towards the female and combined with courtship display 4-12,15. Solely acoustic contact with a female is not sufficient to elicit courtship behavior and directed song (Bischof, unpublished results).From these behavioral studies it is likely that the song control system is in some way affected by visual information. However. there are no data available concerning connections between the visual system and song control nuclei. Thus we decided to examine directly whether the song system receives visual input. For this purpose, we tried to record visually evoked potentials (VEPs) from HVc. while one of the bird's eyes was stimulated with flashes. HVc. a higher order nucleus of the song control system, was chosen, because it receives acoustic input (see aboveJ. We proposed that most likely acoustic and visual influences should interact for the control of song elicitation. Evoked potentials were recorded with glass electrodes (K-citrate 10-40 MQ) from the HVc of 20 adult male zebra finches. The birds were anesthetized with Urethane (20% w~v. U.1 mlJ. Visual stimuli were provided by a s...

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Anatomical data suggest that visual information from the thalamofugal pathway contributes to visual processing in the tectofugal pathway. We addressed the question of the functionality of anatomically described connections to the visual system of a laterally eyed bird, the zebra finch. The study shows the contribution of visual wulst efferents to visual processing in the ectostriatum by recordings of visually evoked slow field potentials. Suppression of visual wulst activity resulted in a selective reduction of distinct potential components in contralaterally evoked slow field potentials. A clear reduction was observed in the maximum amplitude of short latency components in the negative wave. Long latency components of the negative wave and the entire positive wave of the contralaterally flash evoked potentials were almost abolished. Ipsilateral visual evoked potentials (VEPs) were not significantly affected. Cooling and spreading depression of the optic tectum resulted in a uniform amplitude reduction of the negative wave. The positive wave was almost abolished. Ipsilateral VEPs disappeared completely during suppression of optic tectum activity. The results showed that the visual wulst has a significant, most likely facilitatory, influence on the processing of contralateral visual information in the ectostriatum. Ipsilateral stimulus processing was partly independent from visual wulst activity. A model for thalamo-and tectofugal connectivity in the ectostriatum is suggested.