Developmental psychology.pdf

104 The Human Organism
After Archimedes allegedly stepped into the bath and discovered the principle
of specific gravity, some people thought, "How lucky he was to have noticed that!" But
consider how many others soaked in a full tub before his time and how many have
taken baths since without discovering the relationship between body mass and water
displacement. To say that Archimedes' discovery was one of chance is to underestimate
the preparedness of his mind and perhaps the relaxation induced by the warm water.
Throughout science there is confirmation for Pasteur's words: "In observation, chance
favors the well-prepared mind."
The bent needle prompts emphasis of one other point. Most findings in science
are not serendipitous but rather the result of a careful testing of hypotheses.
Reticular Formation
The investigator with the bent needle and well-prepared mind had planned to make
contact with the reticular formation, lying just below the hypothalamus. In fact, the
rear portion of the hypothalamus is sometimes considered part of the reticular formation,
another structure located between the end of the spinal cord and the upper
parts of the brain (Figure 4.13).
Waking Functions The reticular formation is so named because reticulai means
"netlike," and this delicate structure is an exquisitely crisscross pattern of nerve tissue.
It is also referred to by another name, more descriptive of its function than structure.
Part of this structure is called the reticular activating system, for it serves to influence
the arousal of the whole organism. Impulses arriving in this region can prompt diverse
reactions throughout the brain hierarchy, making the individual more alert and
responsive to the environment. With inordinately high arousal, the individual's activity
may even become disruptive rather than adaptive.
The reticular formation exerts this influence because some ascending neural
tracts, rather than going directly to the higher brain areas, have detours that connect
with the reticular system. Impulses from these detours prompt the reticular formation
to transmit signals of its own to the upper brain regions, thus increasing the general
arousal of the organism. When a sleeping animal is provided with mild electrical stimulation
in this area, it awakens slowly. When it receives stronger stimulation, the animal
wakes up much more alertly, apparently not from any increased pain but because
it is more prepared to be active (French, 1957).
Sleeping Functions When the reticular formation is damaged, the individual shows
a corresponding lack of responsiveness. A lesion separating the reticular formation
from the forward brain areas leads to inactivity or to prolonged sleep (Kalat, 1981).
Figure 4.13
Subcortical Structures. A cross
section of the brain is shown from the
left, indicating subcortical structures
involved in emotion and arousal.
Thalamus
Cerebrum
Hypothalamus
Reticular
formation