Brain Research on Lizards 
9 
increase the apparent size of the lizard. Be- 
cause the optic nerves are almost entirely 
crossed, we can injure the striatal complex in 
one hemisphere and then test the animal’s 
display with either eye covered. Although 
capable of seeing, the animal shows no inter- 
est in the rival lizard when looking with the 
eye projecting to the injured hemisphere. 
But allow him to see his rival with the intact 
hemisphere and the challenge display re- 
turns in full force (Greenberg, 1977&). To- 
gether with the experiments on monkeys, 
the findings indicate that in animals as 
widely separated as reptiles and primates, 
the R-complex is basically implicated in 
conspecific recognition and the organized 
expression of prosematic behavior. 
CONCLUDING COMMENTS 
With respect to the striatal complex, there 
are two other areas of research that are of 
timely interest. As mentioned earlier, the 
pineal opening disappeared with the evolu- 
tion of the more advanced mammal-like rep- 
tiles. As is well known, in reptiles with a 
parietal eye there is a close functional rela- 
tionship of this structure with the habenular 
nucleus and the pineal gland. The habenular- 
peduncular system of structures is strongly 
developed in terrestrial vertebrates. It not 
only ties in with the hypothalamus and the 
accessory optic system, but also receives 
strong projections from the pallidal part of 
the striatal complex and from the midbrain. 
In view of this extensive neural network, it 
is curious that so few symptoms have been 
detected in mammals after injury to any 
part of it. Such results suggest that the sys- 
tem may be so fundamental that, just as a 
flow of traffic in Paris is assured by many 
bridges across the Seine, so too the redun- 
dant connections of the habenula insure 
preservation of function in case of injury. 
As one would be led to expect in view of 
its evolutionary development, a variety of 
evidence is accumulating that the habenular 
system may be involved in thermoregulation 
and functions of the organism such as repro- 
duction subject to photic influences. Apropos 
of research on prosematic communication, it 
should be noted that many of the physical 
manifestations of thermoregulation also find 
expression in social communication and in 
the show of emotion. 
The habenular system has also been shown 
to be under the influence of serotonin- and 
norepinepherine-containing neurons located 
in the midbrain, pons, and medulla. As was 
noted earlier, parts of the striatal complex 
are rich in serotonin and dopamine. Parent 
has found that in the turtle the three recog- 
nized monoaminergic systems have essen- 
tially the same pattern of organization as in 
the rat (Parent, in press). In a similar study 
on monkeys, Jacobowitz and I found that the 
prototypical pattern of organization of mono- 
aminergic systems has been preserved with 
remarkable fidelity in the evolution of pri- 
mates (Jacobowitz and MacLean, 1978). 
Hopefully, the developing work on lizards 
will not only help to give some insight into 
the enigmatic functions of the striatal com- 
plex, but also of the monoaminergic systems 
and of the extensive habenular network. 
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