by Denis Larrivee
Growing up in an era of rapid scientific advance it
is possible to see the currents and ebbs that mark preferred ways of thinking
in a way that cannot be captured post-hoc about older eras. Yet it is also a
characteristic of this kind of personal intimacy that the dominance of its principal
tenets makes the masking of idea rivulets barely perceptible. Cases in point
are themes now emerging from the neuroscientific groundswell that has reached
decibels not heard since the Concorde’s sonic booms. Cellular levels of nerve understanding
that were its first love now comprise but a small fraction of the knowledge
since accumulated, which has grown to include global state interactions,
tasking networks, dynamical activity patterns, and large-scale circuits, just to
name several. For one of these themes, the working out of underlying mechanisms
of brain diseases, the newly accumulated knowledge has assisted not only in
sketching a panorama of the brain’s geographical terrain, but it has also acted
as a springboard for investigative strategies intended to unravel the complexities
of its operation gone awry. A leading premise that underpins much of this latter
work, and frequently expressed by former director of NIMH Tom Insel, is that of
disease modified circuit architectures. In this manner of thinking normal brain
operation is structured by information flow along defined paths of transmission
analogous to electrical circuits; hence, brain diseases, as seen by this model,
are as the result of inexact, incorrect, or deficient manners of forming these
routes. For example, OCD behaviors are thought to be the result of circuit
rewiring in striatal - as you may guess - nerve circuits
Influenced by this conception, and
developing in parallel with strategies for approaching circuit based, disease
models, is an extensive and expanding research domain that is devoted to
characterizing neural network operation. Networks, by way of explanation, are
the background frameworks on which the individual circuits are situated. The evolution of the network and circuit
based research enterprise that is directed to disease study is illustrative for
the way in which a battery of widely differing experimental technologies can be
entrained to focus on a single, powerful, conceptual image to elucidate the details
that structure the concept. However, it is also illustrative of how the power
of a single image of brain operation can so entrain the process of hypothesis
construction that avenues to other explanatory visions may be shielded from
discovery. Thus, it is also a testimony to the ever-receding geographical
horizon of brain complexity, or in the cosmic metaphors of the director of
Paris’s Brain and Spine Institute, Yves Agid, more like that of galactic
intervals, that needs to become amenable to characterization in order to yield
fruitful forms of neurological intervention for brain disease therapy.
Something of this discrepancy between the knowledge gleaned in early stages of
neuroscience with its limited relevance to medical intervention, and the
receding horizon of therapeutic goal setting, is now seen in treatments
intended to minister to the patient who exhibits some form of conscious
impairment. Conscious impairment is increasing in prevalence, and it is,
therefore, highly desirable to have treatment options. Among other factors
affecting this situation, improved emergency room care and life-saving
technologies have increased the survival rate of patients who experienced an
incident of brain damage. Such patients may and often do become comatose, a
condition predisposed by stroke. Coupled with population demographics that are
trending grayward, the improved medical scenario thus portends a distinct
upward swing in the incidence of this type of brain disease.
It is at this level of assessment,
however, where the current methodological and technological approaches not only
show the great amount of knowledge that has been accumulated, with its improved
understanding that may be used to better patient oversight, but where also the
sort of information provided offers still just a little glimmer of the physical
features that contribute to patient status; hence, where the challenge to the
prevailing, politically correct science, arises. It thus reveals a horizon yet
to be reached at a conceptual level with regard to patient physiology, and at a
clinical level with regard to determining the salient features needed in order
to therapeutically intervene. These current methods now largely used for
consciousness assessments, for example, no longer rely predominantly on
behavioral monitoring, instead turning to imaging technologies that make it
possible to make objective inferences that may complement behavioral
assessments. Their objective reliability thus offers to the physician the
opportunity for a presumed closer correspondence to patient status than might
be availed from a patient either incapable of knowing, communicating, or of
reliably assessing – and perhaps even being liminally influenced by – physician
monitoring. Yet their improved insight into status also metaphorically
replicates the consciousness paradigm that is awaiting the next upward stage in
its trajectory.
Despite significant advances in
the ability to assess consciously impaired patients, however, the parameters
actually monitored by these technologies do not directly reveal information
that is salient with regard to consciousness, particularly the patient’s sense
of awareness. This latter remains a distant horizon for objective inferences
diagnostically and prognostically. It is with the intention of managing the
semantic content to be inferred from brain activity, as opposed to simple
inferences about brain state activation, that even more qualitatively new ground
has been explored to elucidate what brain states actually mean. These additional
approaches have yet to see entry into the medical setting as viable medical
devices or device/approaches. Nonetheless they afford the prospectus for
revealing distinguishing features of brain activity patterns that can be
correlated with objective features of the world. For the consciously impaired
patient these new technologies begin to offer the promise of communication at a
level more closely approximating the sorts of symbolical representations that
humans use to convey conceptual content to others. The answers to the questions
of what the patient may be thinking, how well or poorly he is doing so, and
what may be affecting this are, therefore, made more tractable than in the
solely qualitative answers obtained from the current medical imaging analysis
alone. These latter reveal a capacity for consciousness, while not
quantitatively indicating the level at which that capacity may be used.
On the other hand, while these new
technologies may offer significant qualitative advances to the physician in the
type of knowledge acquired, they do relatively little to explain either the
mechanism that generates the particular form of brain activity that is being
classified or what information, if any, is internally activated by the patient.
This gap in understanding is revealing for again opening the spectrum of
explanatory possibilities to a wider and, to date, largely unidentified
property scope than is encompassed by strictly neuronal features. It is likely
that representations are not, for example, the exclusive province of
connectivity architectures; thus, they reveal the insufficiency of the circuit
model as a conceptual device for brain operation. While it is clear that
connectivity organization plays a very significant role in structuring
representational activity it is much less clear that such activity is
structured either solely by circuits, or confined only to circuits. Existing
emphases on circuit based operation, that have the effect of entraining
hypothesis building around it, therefore, like limit cycle attractors, leave
research impoverished with regard to insights that may be better used to
charting the terrain ahead. Importantly, they reveal that there are as yet many
unknown features about how the brain functions to engage our subjective sense.
It is this revelation, perhaps, that is most promissory – more so even than the
possibility of ever new therapies helpful for treatment of tragic personal
scourges – that the human person is a special mystery always awaiting new
discovery.
No comments:
Post a Comment