The document discusses cerebral dominance and its pathophysiology. It notes that in most people, language functions are lateralized to the left hemisphere. The left hemisphere is specialized for sequential-analytic processes while the right hemisphere is specialized for visuospatial relations. Lesions in the left hemisphere can cause language disorders while lesions in the right hemisphere can cause agnosias like astereognosis. Overall, the hemispheres show complementary specialization rather than one being simply dominant or nondominant.

1. Cerebral dominance and its
pathophysiology
DR. ABONGA DANIEL AYEBE.
M.Med ortho I

2. • It is a well-established fact that human
language functions depend more on one
cerebral hemisphere than on the other. This
hemisphere is concerned with categorization
and symbolization and has often been called
the dominant hemisphere

3. • at birth, the area of the cortex that will
eventually become Wernicke’s area is 50
percent larger in the left hemisphere than
in the right in more than half of neonates.
• However, if for some reason this left side
area is damaged or removed in very early
childhood, the opposite side of the brain
will usually develop dominant
characteristics.

4. • The sensory area of the dominant
hemisphere for interpretation of language
is Wernicke’s area which is closely
associated with both the primary and
secondary hearing areas of the temporal
lobe.

5. • However, it is clear that the other hemisphere is
not simply less developed or "nondominant;"
instead, it is specialized in the area of
spatiotemporal relations. It is this hemisphere
that is concerned, for example, with the
identification of objects by their form and the
recognition of musical themes. It also plays a
primary role in the recognition of faces.
PROSOPAGNOSIA

6. • Thus, even though we speak of the
“dominant” hemisphere, this is primarily
for language-based intellectual
functions;
• the so-called nondominant hemisphere
might actually be dominant for some
other types of intelligence

7. • Consequently, the concept of "cerebral
dominance" and a dominant and
nondominant hemisphere has been replaced
by a concept of complementary specialization
of the hemispheres.
• one for sequential-analytic processes (the
categorical hemisphere) and one for
visuospatial relations (the representational
hemisphere).

8. The categorical hemisphere is concerned with
language functions

9. Lesions of Representational &
Categorical Hemispheres
• Lesions in the categorical hemisphere produce
language disorders, whereas extensive lesions
in the representational hemisphere does not.
Instead, lesions in the representational
hemisphere produce astereognosis—the
inability to identify objects by feeling them—
and other agnosias. Lesions producing these
defects are generally in the parietal lobe.

10. • when they are in the representational
hemisphere, lesions of the inferior parietal
lobule, a region in the posterior part of the
parietal lobe that is close to the occipital lobe,
cause unilateral inattention and neglect.
Individuals with such lesions do not have any
apparent primary visual, auditory, or
somatesthetic defects, but they ignore stimuli
from the contralateral portion of their bodies
or the space around these portions

11. • This leads to failure to care for half their
bodies and, in extreme cases, the individuals
shave half their faces, dress half their bodies,
or read half of each page.
• This inability to put together a picture of
visual space on one side is due to a shift in
visual attention to the side of the brain lesion
and can be improved, if not totally corrected,
by wearing eyeglasses that contain prisms.

12. Hemispheric specialisation vs
handedness
• Hemispheric specialization is related to
handedness.
• In 96% of right-handed individuals, who
constitute 91% of the human population, the left
hemisphere is the dominant or categorical
hemisphere, and in the remaining 4%, the right
hemisphere is dominant.
• In approximately 15% of left-handed individuals,
the right hemisphere is the categorical
hemisphere and in 15%, there is no clear
lateralization.

13. • However, in the remaining 70% of left-
handers, the left hemisphere is the categorical
hemisphere.
• It is interesting that learning disabilities such
as dyslexia , are 12 times as common in left-
handers as they are in right-handers, possibly
because some fundamental abnormality in
the left hemisphere led to a switch in
handedness early in development.

14. • However, the spatial talents of left-handers
may be well above average;
• A large number of artists, musicians, and
mathematicians are left-handed.
• For unknown reasons, left-handers have
slightly but significantly shorter life spans than
right-handers.

15. CONCLUSION
• Although the interpretative areas of the
temporal lobe and angular gyrus, as well
as many of the motor areas, are usually
highly developed in only the left
hemisphere, these areas receive sensory
information from both hemispheres and
are capable also of controlling motor
activities in both hemispheres

16. • For this purpose, they use mainly fiber
pathways in the corpus callosum for
communication between the two
hemispheres.
• This unitary, cross-feeding organization
prevents interference between the two sides
of the brain;
• such interference could create havoc with
both mental thoughts and motor
responses.

17. •ANY
QUESTION???

18. •THE END.