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{\LARGE Communication in the Brain: 
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When Lines Go Down}
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{\Large 9.00 Paper I}
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{\large Juliet C. Bourne 
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October 5, 1989}
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{\narrower\sspace\noindent\it ``It is assumed that the brain is a
decision system which works along line prescribed by the analogy with
a telecommunications network. Information entering the brain is coded
and transduced, distributed and employed for the purposes of the
individual.''  (Dimond~3) \par}
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The many functions of the brain are carried out in many different
parts of it. The part of the brain collecting information from the
eyes must be able to send some of this information to the area of the
brain coordinating motor functions, so that a person can easily reach
out and grab an apple that he sees before him. Research has shown that
the brain is modular, in that relatively distinct regions of the brain
are dedicated to certain functions. For example, the occipital region
of the brain is also known as the visual cortex, for it is the region
of the brain that receives and processes the visual input from the
eyes. In order to perform integrated functions, such as visual-motor
coordination or recognition of an object (visual-memory coordination),
the different regions of the brain must be able to send information to
one another. This communication is achieved through ``pathways'' in
the brain which connect the different regions. When a pathway between
two regions is disrupted, those two regions can no longer communicate.
In the case of the pathway between the visual cortex and the motor
area, when that pathway is disrupted there is no longer any
visual-motor coordination and thus a person is unable to simply reach
out and grab the apple because his visual system cannot tell his motor
controller where to grab for the apple. However, it is usually the
case that disrupting one pathway disrupts several connections between
regions of the brain. Thus, many ``lack of communication'' problems
will develop, not just one simple one. In some cases the disruption is
permanent. However, in others, it is temporary and the functions
previously impaired return to almost normal. There are several
theories explaining this recovery of function, all of which are still
being heavily researched. Thus, since the brain is modular,
communication between the different ``modules'' of the brain is vital
for the more complex and integrated functions of the brain.

Studies have shown that there projection areas for the different
senses. Projection areas ``serve as receiving stations for sensory
information or as dispatching centers for the motor commands''
(Gleitman~36). Thus, the sensory projection area, known as the
somatosensory area, which is located along the parietal side of the
frontal-parietal border, receives the input from the skin. Different
parts of the body are projected onto different parts of this area.
There is also the visual sensory projection area, located in the
occipital lobe, and the auditory sensory area located in the temporal
lobe. The motor projection area, which sends all of the commands to
the muscles, is located on the frontal side of the frontal-parietal
border. In the case of both the sensory and motor projection areas,
these areas are located in both hemispheres of the brain, receiving
input from or sending commands to the opposite side of the body. For
example, the visual projection area in the right hemisphere of the
brain receives input from the left eye. The different sensory and
motor projection areas provide the clearest example of the modularity
of the brain. Each of the senses has its own distinct area of the
brain in which to process raw input. The modularity here is clear
because the senses themselves are distinct and require different and
separate processing. However, as the processing involved in particular
functions becomes more complex and integrated, distinct areas for
these higher functions cannot be defined as easily.  The majority of
the regions in the brain are traditionally called association areas,
``a term that grew out of an earlier notion that these areas somehow
link events arising in different projection zones, whether motor or
sensory.'' (Gleitman~38) Indication of the function of different
association areas has come mostly from studying people who have
damage, or lesions, to association areas. By studying the impairment
of functions due to lesions in certain areas, the basic functions of
those association areas can be extrapolated. Since ``lesions in the
association areas seem to impair the organization of messages that
come from the sensory projection areas or that go to the motor
areas,'' (Gleitman~38) it can be surmised through studying patients
with lesions which regions of the brain organize which types of
messages. Thus, again, the modularity of the brain is evident, if not
as clear. For example, agnosia is a disorder which ``is
characterized by a disorganization of various aspects of the sensory
world.'' (Gleitman~39) Visual agnosia, therefore, is ``usually
produced by lesions of the association areas surrounding the visual
projection zone, for it is not implausible to believe that the
elaboration and organization of messages from a given projection area
is the primary business of neighboring association areas.''
(Gleitman~39) Although it is the basic assumption that most processing
associated with vision occurs around the visual cortex, the
distinction between association areas is not as simple and clear as it
is for the sensory and motor projection areas. Thus, a number of
theories have been proposed and studies done to try to explain the
reason for disorders such visual agnosia.

Although the disorders caused by damage to different parts of the
brain are numerous and varied, examining the disorders associated with
damage to certain regions of the brain should serve as a good example
of why disorders occur. For example, damage or lesions in the
occipital and occipitoparietal regions of the brain causes disorders
involving vision. The discovery in 1855 that lesions in the occipital
region cause blindness, termed ``central blindness,'' (Luria~124)
began numerous investigations into disorders caused by lesions in the
occipital cortex. In 1881, Munk ``observed that destruction of the
occipital divisions of the cerebral hemispheres of the dog leads to a
characteristic phenomenon: The dog retains its ability to see and to
avoid objects but it ceases to `recognize' them.'' (Luria~124) In
1891, Freud applied the term ``agnosia'' to this ``disturbance of the
optical perception of an object although all the elementary processes
of visual sensation are preserved.'' (Luria~125) Agnosia has also been
described as ``a disturbance of the secondary analysis of intact
visual perceptions.'' (Luria~125) Back to the phenomenon of central
blindness, Luria states that lesions to the primary visual cortex,
meaning the sensory projection area for vision, result in scotomas, or
``localized manifestations of central blindness,'' (Luria~135) and not
in visual agnosia.  Thus, from the evidence it would seem that damage
to the association areas around the visual cortex results in visual
agnosia. This makes sense, since damage in the association area for
vision would result in the inability to process visual input into a
recognizable whole.  However, there is another possible explanation
for visual agnosia.  Although the association areas for vision may be
able to assemble a ``correct'' whole, that processed information may
not be able to reach whatever part of the brain has the stored
``visual memories'' of objects. If visual memories of common objects
are stored in the frontal lobe, for example, and the neural pathway
form the occipital lobe to the frontal lobe is disrupted, then
processed visual input could not be compared with stored visual memory
to achieve recognition of common objects. This could also explain the
inability to recognize common objects, along with the theory of the
disruption of the association areas.

Either (or neither) of these theories on visual agnosia could be
correct; the problem could be in processing input or in communicating
the processed input to another part of the brain. In the case of the
impairment of visual-motor coordination, however, the problem is more
likely to be one of communication. The impairment of visual-motor
coordination is usually associated with lesions in the
occipitoparietal region. (Eysenck~39) Based on that observation, it is
likely that the occipitoparietal area is devoted, at least in part, to
visual-motor coordination. Visual input gets processed near the visual
cortex in the main occipital lobe. Commands to move muscles and so on
are issued by the motor projection area along the frontal-parietal
border. Thus it seems likely that that lesions in the occipitoparietal
region interfere with communication between the visual association
areas and the motor projection area, so that the visual system cannot
tell the motor system where objects are spatially. Indeed, Luria
states: 
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{\narrower\sspace\noindent ``The posterior parts of the inferoparietal
region, directly continuous with the occipital divisions, constitute
one of the newest cortical formations connecting the central
apparatuses of the kinesthetic, vestibular, and visual analyzers. They
play a dominant part in the integration of all of these various
stimuli, and a lesion of these areas is inevitably followed by some
degree of disturbance of the more complex forms of visual-spatial
synthesis. This type of disturbance leads to a breakdown of spatial
orientation and to the phenomena of spatial apraxia.'' (Luria~148) \par}

\noindent
Thus, lesions in areas involved which connect different processing
centers of the brain, or in areas in which different regions
communicate with one another, cause disorders of functions which rely
on the disrupted communication.

The study of disorders resulting from lesions, such as visual agnosia,
can be approached as a study of broken communication lines. Since the
brain is basically modular, with different parts of the brain
responsible for different functions, a disorder of a certain function
can usually be traced to damage in a specific area or the pathway
between two or more specific areas. Of course, in the earlier days of
neuropsychology, this process was done the other way around; the
locations of the lesions were known and the resulting disorders were
observed. From such observations, it could be surmised that the
damaged area was involved in some way in the impaired functions.  How
the brain eventually recovers most of the functions affected by
lesions in different areas of the brain is still very much a mystery.
A major theory is that somehow other parts of the brain take over the
function of the damaged part of the brain, or the ``spontaneous
reorganization or substitution of an intact brain zone for the damaged
area.'' (Stuss~219) Another theory is ``supersensitivity, a state
following injury where remaining neurons become more efficient.''
(Stuss~219) The general observation of recovery is that a ``patient
may spontaneously, or through therapy, learn strategies of
compensation leading to entirely different ways to achieve the desired
goal.'' (Stuss~219)
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{\narrower\sspace\noindent\it ``Finally, we have to face the
difficulty of explaining the fact that the brain has a remarkable
capacity to compensate for any changes within its structure which may
ten to impair performance. After insult, a reordering occurs perhaps
over months but often over days or hours, which enables the patient
with a damaged brain, often totally without awareness, to make the
best use of what capacities remain. This ability of the brain,
although damaged, to organise behaviour strategically is, at the same
time, a puzzling phenomenon, and also a factor with confounds
results.'' (Dimond~5) \par}

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\underline{BIBLIOGRAPHY}
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\noindent
Dimond, Stuart J., and J. Graham Beaumont. \underline{Hemisphere
Function in the} \ 
\underline{Human Brain}. Halstead Press, New York: 1974.
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\noindent
Eysenck. \underline{Encyclopedia of Psychology}.
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\noindent
Gleitman, Henry. \underline{Psychology}, second edition. W. W. Norton
and Company, New York: 1986.
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\noindent
Stuss, Donald T., and D. Frank Benson. \underline{The Frontal Lobes}.
Raven Press, New York: 1986.
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\noindent
Luria, Aleksandr R. \underline{Higher Cortical Functions in Man}.
Translated by Basil Haigh. Basic Books, Inc., New York: 1966.
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