Biomedical Engineering Reference
In-Depth Information
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CHAPTER 4
Nanosensing the Brain
Understanding how the brain works is one of the greatest scientific challenges
of modern science. There is no general theory of brain function. The state-
of-the-art plan in neurobiology is to find neurons or subcircuits of inter-
connected neurons and the neural correlation of the rate and manner of firing
with behaviour and conscious experiences. Neuroscientists are still dreaming of
finding the neural code to discover if mean firing rates are associated with
experiences and to understand how the chemistry of neurotransmitters
influences behaviour. While the function of the brain and consciousness itself
are considered to be emerging from the complex, multi-hierarchical structure of
the brain, it seems to also be an intrinsic property of the brain. The brain is self-
wiring and then prunes the unwanted connections in the first years of life. The
same phenomenon can be observed directly in vitro in culture of neurons using
charge-coupled device (CCD) cameras. After establishing connections, some of
them are pruned, according to unknown rules. Inside the brain, the whole
process is a continuous and dynamic manifestation of brain's neuroplasticity,
and the connectivity matrix is perpetually rearranging as individual neurons are
making synaptic contacts and receiving synaptic contacts from thousands of
other neurons. Only after understanding how this extremely complicated
process unfolds can an attempt be made to restore the pattern of normal
activity and to remove the pathological manifestations of the injured or
diseased brain.
The latest discoveries using two-photon excitation techniques, fluorescent
imaging including voltage-based functional imaging, functional magnetic
resonance imaging (fMRI) and magnetoencephalography (MEG) capture
images of brain activity without having the spatial or temporal resolution to
detect the detailed patterns of neuronal firings. As such, new sensors with
better time resolution, better signal-to-noise ratio, less photodamage and
less invasive techniques are necessary. Newly discovered nanomaterials and the
miniaturization of electronic circuits to the present 22 nm (Intel) and
progressing to 14 nm and 10 nm (as Moore's law predicted, a size reduction of
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