Dear List Members,
I would like to submit the following paper I have written for general
discussion and feedback. Due to its length (about 9 pages of text) Barba=
ra
Patterson suggested that I submit it in three installments. The paper is=
entitled "Gait and Parkinson's Disease - A Conceptual Model" and is deriv=
ed
from my empirically based exploration of this topic over the past 5 years=
=2E =
I apologize for the lack of formatting that results when a text document =
is
converted to e-mail and also for the loss of diagrams. However, I feel t=
he
basic concepts will get through and I look forward to any critical
feedback.
regards, =
Tom Riess
Gait and Parkinson's Disease - A Conceptual Model: Part 1 of 3
My name is Tom Riess. I consider myself to be an independent researcher i=
n
the area of Parkinson's Disease. I am 49 years old and have had Parkinson=
's
Disease (PD) myself for 16 years. For the past 5 years I have been
working to develop vision based therapeutic devices intended to overcome
some of the more debilitating aspects of this disease. The scientific
basis for this work is the well known phenomenon known as Kinesia Paradox=
a,
whereby in the presence of certain so-called visual cues a PD subject can=
be transformed from a totally immobile, helpless victim of this disease
into a near normal walking individual. I have in fact built several
effective prototype devices, which evoke the same response by generating =
on
demand the virtual equivalent of real visual cues. These devices augment=
reality by superimposing data (visual cues) onto the real world without
impairing the subject's ability to see the real world.
In the course of this project I have found it useful to construct a
conceptual model to try and explain the effects of visual cues and identi=
fy
the fundamental underlying parameters. The model is constantly undergoin=
g
revision and while it remains essentially unproven speculation it has bee=
n
very useful as a predictive tool for how a PD subject would respond to
novel situations. More importantly it has enabled me to conceive of and
build new and effective devices, which are very different from the origin=
al
object, based cues (real or virtual).
What follows is an abbreviated version of the aforementioned conceptual
model and principles on which some of these therapeutic devices are based=
=2E =
A General Model of Gait
Gait can be thought of as learned motor activity of the lower extremities=
which when performed results in movement of the subject in the environmen=
t.
By varying the various parameters of gait, (stride length, velocity, heel=
and toe strike timing etc.) one can perform an infinite variety of gaits.=
Like any other learned information (motor or sensory or cognitive) a
particular gait can be newly learned or overlearned. A newly learned gai=
t
exists in short term memory. Characteristics of a given environment
determine the particular characteristics of a newly learned gait. Once t=
he
environment changes, the newly learned gait is no longer needed and like
short-term memory is quickly forgotten and replaced by a different newly
learned gait tailored to new environmental conditions. While the
environment does vary, there are a few environmental conditions that recu=
r
repeatedly and are present most of the time. This results in repeated
learning of a select few newly learned gaits until the learned informatio=
n
is transformed in the brain into what is termed overlearned information. =
Overlearned information differs from newly learned information in several=
important ways. The most important distinction is that once initiated, a=
n
overlearned motor package can be performed unconsciously or automatically=
=2E =
This allows our conscious attention to be directed to another task and is=
the basis for efficient simultaneous task performance. I would suggest
that this is mediated by the basal ganglia and can be thought of as its
evolutionary purpose. =
Newly learned gait is defined or cued by the external environment (for
example, fording a stream by stepping on randomly protruding stones) and =
is
ephemeral whereas the overlearned motor package is predefined and
permanently stored in the brain. An internal cue prompts the performance=
of the entire overlearned motor program as a unit but I would suggest tha=
t
the essential parameter, which triggers this internal cue, is what I call=
minimal threshold stride length. For example, if one physically moves th=
e
lower extremity of a totally akinetic PD person beyond the minimal
threshold stride length he will be able to complete at least one step. Th=
e
following concepts of stride length are, I believe, part of normal gait
function.
1. Initiating Stride: a consciously taken stride, which always follows a
position where the feet are separated by less than a threshold stride
length stride. The length of the stride is defined by environmental
conditions but the stride itself is under conscious control. It is possib=
le
to have a series of initiating steps or it is possible to have a single
initiating step followed by unconscious automatic gait. In the absence o=
f
pathology the environment determines which option occurs.
2. Threshold Stride Length: the minimal inter-pedal distance required to
access automatic gait. When this minimum is reached the stride serves as=
a
template for access and performance of automatic gait, which will occur i=
f
the environment is compatible with automatic gait.
3. Sub Threshold Stride Length: a stride where the inter-pedal distance i=
s
less than that of a Threshold Stride Length. A sub-threshold stride leng=
th
can be as little as no stridelength whatsoever (for example, when one is
standing still with feet side by side) to just slightly less than the
threshold stridelength. In normal people environmental conditions, which
result in stride lengths, which fall below this minimal threshold, result=
in externally cued, consciously controlled gait. A conscious, initiating=
stride will always follow a sub threshold stride length stride.
To summarize, gait can be performed in two different modes; conscious mod=
e
and unconscious (automatic) mode. Conscious, newly learned gait is
externally cued and its parameters change constantly to adapt to the
changing conditions of the environment. Automatic gait is prerecorded or=
=
predefined. An externally cued stride serves as a template and when
certain critical parameters match an automatic (overlearned) motor packag=
e
that package is accessed.
=
Whenever the environment permits we function in the automatic mode (it ca=
n
be thought of as the default mode). This allows us to perform more compl=
ex
tasks by assembling overlearned motor packages. When the environment is
incompatible with the automatic mode we function in the conscious mode an=
d
then revert to the automatic mode when the environment allows it.
Sensory information is required to evaluate the environment and make the
determination that a specific program can be performed under the current
environmental conditions. The appropriate mode (overlearned versus
externally cued) is selected as a result of a dynamic interaction between=
the environment and the brain. This interaction is mediated via sensory
information, which is perceived primarily (but not exclusively) through t=
he
sensory organ known as the eye. =
The function of sensory information derived from subject - environment
interactions is to acquire information about the external environment
(environment based sensory information) and to acquire information about
how the environment responds as we interact with it (subject induced
sensory information). The stimuli resulting in the former originate in t=
he
environment while the latter are dependent on the subject for their
existence. In regards to motor function environment based sensory
information is required to monitor the environment to assess its
compatibility with specific motor activity i.e. it defines the motor
activity. Subject induced sensory information directly influences the
characteristics of the motor activity being performed (if possible, what
you see is what you get). Thus, the processing of visual data can be
functionally organized into two distinct categories, which have evolved i=
n
response to two types of visually perceived sensory information.
1. conscious vision (seeing): visually sensed data plus conscious=
processing. The data perceived through conscious vision only becomes
meaningful after it has been analyzed on a higher cognitive level -
filtered through the eye of experience. For example identifying an objec=
t
in a room as a chair or recognizing a face.
2. unconscious vision: visually sensed data which does not requi=
re
conscious interpretation, it is processed without conscious awareness. =
Unconscious vision takes place in the presence of visual data, which is
consistent with the motor activity of which it is a consequence (e.g. the=
apparent motion of the environment as a subject walks through it). =
Non-conforming visual data is the prompt, which results in a shift from
unconscious to conscious vision and results in the subject's consciously
altering his motor function to adapt to a perceived change in the
environment.
End of part 1...
