DISCRIMINATORY APPROACH TO AUDITORY STIMULI IN GUINEA FOWL (NUMIDA MELEAGRIS) AFTER HYPERSTRIATAL∕HIPPOCAMP- AL BRAIN DAMAGE



229

chickens (Oades, 1976a). Indeed Oades (1976b) did find that birds with dam-
age to the parahippocampal area posterior to the anterior commissure show-
ed a stability and persistence in their selection of food colour like those with
more anterior damage and unlike those with lateral damage.

(3) Recent neurophysiological findings (review, Scheich, 1977) using spe-
cies-specific vocalisations as stimuli in birds and mammals supports a hierarch-
ical concept for central auditory analysis. Can this hierarchy be extended in
anatomical terms from the primary auditory forebrain field (Field L of the
neostriatum), that connects to the
posterior parahippocampus and the anter-
ior hyperstriatum∕hippocampus?

Such an anatomical sequence may represent a hierarchy in terms of func-
tional specialisation. Behavioural measures were taken to investigate whether
brain damage to two separate but connected areas could result in two separ-
able but related deficits. Such a result is not without precedent. For example
Sahgal and Iversen (1978) showed that damage to the posterior and anterior
inferior temporal cortex of monkeys interfered with their ability to categorise
and to retrieve information, respectively, on a colour match-to-sample task.
The current analysis of the behaviour of the Guinea fowl also leads to the
hypothesis that separate processes have been affected by the two areas of le-
sion damage.

The Guinea fowl is the subject of these experiments because of an exten-
sive background of experience with this bird in auditory analysis research in
this laboratory. The task consisted of a time-limited, motivated approach
(food reward) and withdrawal (punishment) from a species-specific call (food-
trill). Natural variations of the trill-call and other sounds were used as test
stimuli. An ethogram is shown to be a potentially useful tool in the analysis
of an attentional situation where overt behaviour has formerly been over-
looked.

MATERIALS AND METHODS

Preparation of animals

Results are reported from 17 adult Guinea fowl. All birds were trained
and tested in their home chambers (48 × 130 × 120 cm high). They were
maintained on a 12:12 h light:dark cycle at 23 ± 20C at about 75% normal
body weight. Water was continuously available.

The animals were prepared for operation under hypnodil anaesthesia (Jans-
sen). The drug was injected into the pectoral muscle, 25 mg initially, follow-
ed by 10 mg every 0.5 h. The head was held between two ear bars of a stereo-
taxic apparatus with the bite bar 23 mm anterior and 23 mm below. The skin
and bony horn were removed from the dorsal surface of the skull. Bilateral
aspiration lesions were performed 1.2—3.7 mm (posterior) and 4.5—7.0 mm
(anterior) with respect to a null point of the depression between forebrain
and cerebellum over the blood sinus. Lesion depth were judged at 1.5 and



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