247
Conclusions
The results reported here support and extend the concept of a hierarchy
for anatomical and functional specialisation for central auditory analysis
(Scheich, 1977) that progresses from the sensory projections to Field L into
the neighbouring hyperstriatum∕parahippocampus for selection. This may ex-
tend to more anterior hyperstriatum for matching.
It may be significant that the posterior group received damage both to
part of the auditory projection field and to the closely connected hyperstria-
tum. Units in the neostriatum bordering the hyperstriatum respond to species-
specific calls (Bonke et al., 1979). This lesion will also have disrupted the in-
fundibular connection to the parahippocampus (Benowitz and Karten, 1976).
Kelley and Nottebohm (1978) have shown with autoradiographic methods
that in the canary there may be connection from Field L to the overlying
parahippocampus that projects forward to the anterior hyperstriatum. Al-
though they thought that this labelling may have been due to isotope leakage,
injections into the parahippocampus confirmed the postero-anterior connec-
tions. However, Field L does project to the hyperstriatum ventrale and a
superficial dorsal area at the edge of the hyperstriatum (Zaretsky, 1978;
Bonke et al., 1979).
The present study extends earlier work on the role of avian forebrain le-
sions in attention-related processes. It shows that areas potentially analogous
to mammalian limbic structures are involved with the use of visual and audi-
tory inputs. Having been trained to respond to one specific stimulus, birds
with damage to the hyperstriatum∕hippocampus anterior and posterior to the
anterior commissure showed more search-related behaviour than controls
after stimuli that varied from the trained stimulus. The anterior and posterior
groups differed from each other in two principle respects. The anterior group
reacted positively to the new stimulus and then disengaged rapidly (more
low tension). The posterior group continued to approach more stimuli and
after searching remained aroused (more high tension).
The finding of two neighbouring and connected brain regions with com-
plementary functions in an attention system is not unique. Anterior and post-
erior Inferotemporal lesions in monkeys impair the processes of retrieval and
categorisation of information, respectively (Sahgal and Iversen, 1978). Also
the closely bound hippocampus and septum of the rat mirror each other in
some situations. Lesion of the hippocampus appears to impair the exclusion
of redundant information in a conditioned association paradigm (Rickert et
al., 1978), whereas septal lesions (Donovick et al., 1978) impair the ability
to use redundant information provided to solve a maze problem (cf. discus-
sion, Oades, 1979).
I should emphasise that the analysis of the observed behaviour of the
Guinea fowl has led to the proposal of an hypothesis for the functional com-
ponents of an avian attention system, but these components have received no
direct test. Direct testing should involve interruption of input channels (e.g.