George Levy wrote:
[quoting Stathis Papaioannou]
>I believe the level of detail required and the complexity of the
required models is grossly underestimated.
>Simply getting a 3D image of a brain down to electron microscopic
detail, including all the synaptic
>connections, would be an enormous task, and it probabaly wouldn't
tell us any more about the mind
>of the brain's owner than a picture of the books on a library
shelf would tell us about the book contents.
>I would bet more on mediaeval monks decoding the data on a DVD
sent back in time than I would
>bet on scientists decoding the contents of a human mind from
cryopreserved brain sections.
Let's cut through all this complexity and look at the functional equivalent
of a neuron or a group of neuron. I want to distinguish between general
architecture and particular architecture: general architecture will provide
the framework within which any human brain could fit. Particular
architecture is the architecture of a particular brain.
1) General Architecture
The general architecture of the brain is a hot research project of the
scale and importance of the Genome Project and is currently being worked on
by major laboratories. We could speed up the functional identification of
neuronal groups or modules by using general architecture apriori knowledge
we have about these modules. For example the architecture of the visual
cortex is well defined. We could treat it as a module with minor variations
from individual to individuals due to genetic differences such as Single
Nucleotide Polymorphism SNP. SNPs. Very soon we shall have the genetic map
of all the human SNPs. We shall also have the general architecture of the
brain and all its nominal variations.
2) Particular Architecture
Imagine using an advanced version of a functional Magnetic Resonance
Imaging (fMRI) device operating at the microscopic level on a slice of
brain tissue. Without knowing exaclty what is in the brain tissue black
box, it may be possible to identify their functional property and recreate
these in silicon or any other convenient substrate. By the way, microscopic
functional Magnetic Resonance Imaging is an existing technology that is
currently being used. This is what I got using Google.
Scholarly articles for functional magnetic resonance imaging microscop$
The primate neocortex in comparative perspective using ...
- by Insel - 40 citations
Neuroimaging and neuropathology in epilepsy: With ...
- by Nishio - 1 citations
Evaluation by Contrast-Enhanced MR Imaging of the ...
- by Jeong - 2 citations
3) Combining General and Particular Architectures
Fusing information to combine apriori knowledge of general architecture
brain functions, and particular architecture data obtained from in situ
functional measurements (e.g. fMRI), neurological and psychological
measurements, as well as self-analysis, it may be possible to reconstruct a
functional copy of the brain close enough as to be indinstinguishable from
the original by the owner. How does the owner knows it is
indistinguishable? This is a whole topic. He could for example do a series
of partial substitutions to find out if it feels the same or not. For
example, he could substitute in sequence the visual cortex, the auditory
cortex, some of the motor functions....
We may be closer to this goal than you think.
OK, I agree it is possible, and I'm glad nobody is insisting that just the
arrangement of neurons and their connections, such as could in theory have
been determined by a 19th century histologist, is enough information to
emulate a brain. I think we would need to have scanning resolution close to
the atomic level, and very detailed modelling of the behaviour of cellular
subsystems and components down to the same level. I don't know how long it
would take to achieve this, but I know that we are nowhere near it now. For
example, consider our understanding of schizophrenia, an illness which
drastically changes almost every aspect of cognition. For half a century we
have had drugs which ameliorate the psychotic symptoms patients with this
illness experience, and we have been able to determine which receptors these
drugs target. But despite decades of research, we still have no idea what
the basic defect in schizophrenia is, how the drugs work, or any clinically
useful investigation which helps with diagnosis. Although fMRI and PET scans
can show differences in cerebral blood flow compared to control subjects,
this is a secondary effect. The brains of schizophrenia sufferers, looked at
with any tools available to us, are essentially the same as normal brains.
In other words, a very subtle, at present undetectable, change in the brains
of these patients can cause gross cognitive and behavioural changes.
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