Call for Volunteers (no longer active) INTRODUCTION Abstract of preliminary results (Society for Neuroscience
Abstracts, 2002)
Links to BIPOLAR DISORDER
INTRODUCTION
BACKGROUND
PURPOSE FOR STUDY
SPECIFIC GOALS FOR PROJECT
PROCEDURE
The procedures to be followed in this study have been reviewed and approved by the SIU Human Subjects Committee.
This research project is supported by an Independent Investigator
Award from NARSAD, the National Alliance
for Research on Schizophrenia and Depression.
Comments and questions: dgking@siu.edu
An abstract of preliminary results is available here.
BACKGROUND
Visual Perception
Brain Disorder
Binocular Rivalry
Heritability and Genetic Anticipation
PURPOSE
GOALS
PROCEDURE
Informed Consent Form
Links to NEUROSCIENCE
The phenomenon called binocular
rivalry might provide an unexpected connection between two seemingly
disparate topics in neuroscience, visual perception
(sight) and brain disorder (mental illness).
A recent publication by Pettigrew
and Miller at the University of Queensland has indicated that certain variations
in binocular rivalry measurement are correlated with bipolar disorder
(also called manic depression). Preliminary data by White and colleagues
at the University of Florida have also suggested a correlation with schizophrenia.
The current investigation is planned to explore these associations, which
might lead to new diagnostic tests for these two disorders. This research
project will also assess the heritability
of variation in binocular rivalry measurements, to explore whether such variation
shows genetic anticipation like that
associated with both bipolar disorder and schizophrenia (as well as with several
other neurological diseases). If a genetic link can be found between these
diseases and normal perception, then future research in either area may advance
our understanding of both.
Visual perception. Understanding
how the mind achieves a conscious perception of the visual world remains one
of the most challenging problems for philosophy. Science has learned much
about the initial steps in the process by which we see, from the focussing of
an image in each eyeball to the complex encoding of qualities such as contour,
color, and motion by nerve cells in the cerebral cortex. Our firmest understanding
concerns preliminary aspects of information processing which occur automatically
and proceed even under anesthesia. In contrast, mechanisms underlying
conscious awareness remain largely unknown. [Lots
more about vision.]
Brain disorder. The
concept of brain disorder encompasses a wide range of diseases that involve
disturbance of normal brain function, including those afflictions of thought,
emotion, or motivation which are commonly called "mental illness". The
conditions addressed by this study, bipolar
disorder and schizophrenia,
are severe diseases which impose a substantial burden on our society, including
not only suffering by patients and their families but also considerable risk
of premature death from suicide and high economic costs (tens of billions of
dollars) for medical care, criminal justice intervention, and lost productivity.
The biological or medical basis for many brain disorders is demonstrated
both by their responsiveness to chemical therapy (i.e., "drugs") and by their
heritability (i.e., their tendency to "run in families"). Yet in spite
of the importance of these diseases, their underlying biological mechanisms
remain as mysterious as do those of consciousness itself. [Outside link
to NAMI, the National Alliance for
the Mentally Ill, with many more links.]
Binocular rivalry. Normally,
anyone can "pay attention" to input from one sense (concentrating, for example,
on sight or sound or taste or touch) while other sensations fade from awareness.
But one cannot voluntarily choose to see with just one eye, except by
the rather crude expedient of closing or covering the other eye. Normally,
images from both eyes are automatically combined into a single stereoscopic
view of the world. (Stereoscopic vision depends on small differences between
the two images, which arise because the two eyes have slightly different points
of view.) When the two eyes receive markedly different images, as for
example when a nearby object blocks the view of one eye, this integration can
no longer occur. Attention is then given to the more striking image--the
one which has greater brightness, sharper edges, more intense color, or faster
motion. (As a do-it-yourself demonstration, if you try looking with one
eye through a cardboard tube from a paper-towel roll while holding up a hand
in front of the other eye, you may perceive a "hole" in the palm of
your hand.) If, however, the two eyes are experimentally presented with
conflicting images that have been carefully matched for average quality, the
two images then seem to compete with each other for conscious perception by
the "mind's eye". This situation is called binocular rivalry.
During an experience with binocular rivalry, images from
the two eyes may momentarily blend together. More commonly, however, the
perceived image alternates back and forth between the two. Science does
not yet know what mechanism underlies this alternating choice of one image over
the other. Although both eyes remain continually active (as do the corresponding
regions in the primary visual cortex), the input from one eye is somehow suppressed
while the other eye's image is consciously "seen". Since the rhythmic
alternation between conflicting images appears to be largely involuntary, the
phenomenon of binocular rivalry may lie near the mysterious boundary between
automatic information processing and conscious awareness. (For additional
information about binocular rivalry, see further reading.)
Heritability and genetic
anticipation. Individual people differ from one another in many measurements
such as height, hair color, facial shape, etc. When variation in measurable
traits is correlated from generation to generation, the variation is said to
be heritable. Such correlation provides indirect evidence of genetic influence,
although environmental influences can also yield similar results. Preliminary
research has shown that individuals vary in their experience of binocular rivalry,
for example in the frequency of alternation and in the proportion of time spent
perceiving one eye's image or the other's, or some blended image. Although
nothing is currently known about the heritability of such variation in binocular
rivalry measurements, preliminary research has indicated that certain variations
in binocular rivalry may be correlated with bipolar disorder and others with
schizophrenia. And the etiology (causal mechanism) of both bipolar disorder
and schizophrenia is already known to involve a significant genetic contribution.
Furthermore, both bipolar disorder and schizophrenia display
a curious phenomenon called genetic anticipation. That is, the disorder
seems to grow more severe or occur at an earlier age as it is passed from one
generation to the next. Several other neurological diseases which show
genetic anticipation are known to be caused by a peculiar pattern of DNA in
which a few base pairs (the "letters" of the genetic code) are repeated like
a genetic "stutter". Such repetitive patterns are especially susceptible
to mutations which increase the number of repetitions. When the number
of repetitions grows too large, disease occurs. If the number of repetitions
continues to increase, the disease may worsen in later generations. Identification
of a repetitive DNA pattern associated with bipolar disorder or schizophrenia
would not only help explain the genetic anticipation shown by these diseases,
but might also provide the basis for deeper understanding (and hence treatment)
of the underlying disease mechanism.
If confirmed, the discovery of a correlation between binocular rivalry measurements and bipolar disorder or schizophrenia would have several implications.
(1) First, measurement of binocular rivalry might permit more reliable and objective diagnosis of these particular diseases. Conceivably, such measurement might even enable screening tests to identify persons at special risk for developing the disorders, and thereby facilitate earlier recognition and more effective treatment if the disease does develop.
(2) Second, binocular rivalry measurement might provide the basis for more effective analysis of underlying genetic mechanisms. Working out the genetics of bipolar disorder and schizophrenia has proven to be extraordinarily difficult, partly because of difficulty in diagnosing these disorders and partly because of variability in disease development. Because variation in binocular rivalry can be measured objectively and quantitatively, inheritance patterns might be more readily determined. Such a result might, in turn, facilitate identification of genetic loci responsible for variation in the associated brain disorders.
(3) Finally, discovery of a relationship between binocular rivalry and brain disorders might provide insight into normal as well as abnormal brain function. If there is a causal mechanism underlying both brain disorder and visual perception (or any other aspect of normal cognitive information processing), then any progress toward understanding either one might also help to illuminate the other.
At the present time, correlations between binocular rivalry measurement and certain brain disorders have been reported only from preliminary studies. Assessing whether such correlations can be replicated, and if so how reliable the correlation may be, is a primary goal of the present study. Such assessment will require statistical analysis of measurements from many subjects, including numerous individuals of normal mental health status.
This study will also assess the correlation of binocular rivalry measurements between close relatives (parent-child and sibling pairs), investigating the extent to which this variation may be inherited.
This study will not test any form of medical treatment or therapy, nor is any such treatment expected to be a direct byproduct of this study.
The present study is designed to measure perceptual responses during binocular rivalry. Participants in this study will experience binocular rivalry in a setting where the images seen by each eye are carefully controlled and varied. The research apparatus consists of a computer display coordinated with stereoscopic glasses. Liquid crystal shutters within the glasses open and close in alternation, so that while one eye sees the computer screen, the other eye is covered. While the shutters switch the view from one eye to the other, the computer screen also displays alternating images. This apparatus permits one image to be presented to the left eye while a different image is presented to the right eye.
While the subject gazes at a spot on the computer screen, the shutters "blink" rapidly, 60 times per second. This blinking is too fast to notice, like the rapid blinking of images on a television or movie screen. Under such circumstances, the image which is actually perceived may be that presented to the left eye or to the right eye, some combination of the two images, or something altogether different. The subject reports which image is seen by pressing buttons on a computer mouse. The computer records each button press. When analyzed, this record provides a measurement of binocular rivalry.
The results of individual measurements from this study cannot be reliably interpreted at the present time. Therefore, personal measurements will normally not be shared with research participants.
Department of Zoology e-mail: zoology@zoology.siu.edu
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SIUC / College of Science / Zoology / Faculty / David King
URL: http://www.science.siu.edu/zoology/king/oldbplr.htm
Last updated: 30 March 2005 / dgk