The Cerebrum

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    The hypothalamus functions as a principal             language that makes exchange of ideas possible.        Different animal species
regulating center for the autonomic nervous sys-          This combination has provided humans with the          probably possess varying
tem, and controls and coordinates the activity of         ability to perform intellectual and artistic activi-   levels of consciousness
the autonomic reflex centers in the pons and me-          ties. We also have direct, voluntary control over
dulla. The hypothalamus also plays a key role in          the muscles of our hands, which are effective
the regulation of body temperature (p. 672) and           implements for manipulating our environment.
the osmolarity of body fluids (p. 492). Sensations        These innate abilities of humans have enabled
such as thirst, hunger, and sex drive are associ-         us to develop tools and technology, complicated
ated with specific regions of the hypothalamus,           social structures, and the patterns of living that
as is the feeling of wellbeing when these drives          we call culture.
have been satisfied. The hypothalamus and the                 It is not clear to what extent consciousness
brain stem are the brain regions that are the most        is present in other mammals. However, as is the
important for regulation of homeostasis.                  case for other physiological functions, it is likely
                                                          that this characteristic differs between mamma-
TheCerebrum                                             lian species more in terms of degree than by its
In comparison with other vertebrates, the abil-           absence or presence.                                   The unique analytical
ity of the most advanced mammals to choose                    The unique analytical abilities of mammals         abilities of mammals are
between alternative behavioral patterns in given          are tied to the cerebrum, which, because of the        tied to the cerebrum
situations is highly evolved. This flexibility is due     considerable growth of the neocortex, represents
to the ability of the brain to evaluate the pres-         the largest part of the brain in most mammals.
ent situation on the basis of prior experience be-        There is large inter-species variation in the rela-    The neocortex is the
fore making decisions. This analytical capacity           tive size of the neocortex (Fig. 4.36). In insec-      largest part of the ce-
provides advanced mammals with a significant              tivores, the neocortex comprises 8–20 % of the         rebrum in advanced
competitive advantage over animals exhibiting             brain weight, while the corresponding figure for       mammals
more automatic behavior. However, this type of            humans is 76 %. In large ruminants and preda-
adaptable behavior is only possible if the brain          tors, the relative size of the neocortex is about 70
has access to information about the surround-             %, while in sperm whales, it constitutes 87 % of
ings and the state of the animal, via the sensory         the brain weight.
organs, as well as stored information about prior             In fish, amphibians, reptiles, and the most
experience. When the available information                primitive mammals, the most important func-
has been analyzed, the brain must also be able            tion of the cerebrum is to receive and process
to control the animal’s behavior. In humans, the          olfactory information. In mammals, this task is
term “consciousness” is used to describe the close        performed by the ventral part of the cerebrum,
connection between sensory input, stored infor-           the rhinencephalon. The cerebral cortex in mam-
mation, and behavior. In humans, the ability to           mals also receives, via the thalamus, all other
think analytically is combined with an abstract           types of sensory information about the envi-

                                                                                                                 Figure 4.36 The size of
     Pigeon           Hedgehog                 Rat                   Cat                     Dog                 the rhinencephalon
                                                                                                                 (olfactory brain) rela-
                                                                                                                 tive to the rest of the
                                                                                                                 cerebrum in birds and
                                                                                                                 selected mammals. The
                                                                                                                 formation of gyri by
                                                                                                                 convolution of the ce-
                                                                                                                 rebral cortex increases
        Cow/horse                                Man                             Fin whale                       with brain size. Modi-
                                                                                                                 fied from Nieuwenhuys
    Neocortex             Rhinencephalon                Mesencephalon             Cerebellum and brain stem      et al., 1998.

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