April 2, 2005

Error! Reference Source not found

"Error! Reference Source not found" has caused me much stress today. Every so often, virtually all my cross-references turn into this error message. It is absolutely aggravating. It's really sucking the life out of me. Microsoft is of no help and I'm not sure how to repair my document. For the record, I am using Endnote, Mathtype 5.1 and Microsoft Word 2003. Arrrrrrgggggghhhhhhhhhh!

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February 18, 2005

Assure, ensure or insure?

The Hutchinson Encyclopedia has the skinny.

To assure something is to make certain it will happen: Victory is assured for the younger, fitter boxer as he has the advantage. To ensure something is to take steps to make sure that something happens: Seat belts should ensure that you will be unhurt in an accident. To insure something is to take precautions against something undesirable happening: The concertgoers insured against disappointment by buying their tickets early.

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December 18, 2004

Traditional Chinese Unicode Fonts

I located my Chinese font (see previous post) at David McCreedy's most excellent Gallery of Unicode Fonts. Incidentally, it is also a good place to (1) start learning about Unicode, and (2) learn some travel phrases.

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Changing the default chinese font in Word from SimSun to something else

I found a nice traditional Chinese font today. I had been using it in Microsoft Word when I started noticing some funny behavior. Somehow placing the Chinese text by certain styles would revert the font back to SimSun, the default (and not-so-pretty) Asian text font. This, not being consistently replicable, frustrated me enough to do a search for a solution on Google. The fix is easy. Go to Format, then Font and then select the new Asian text font, in my case, AR PL KaitiM Big 5. Click on Default.... That's it!

defaultasianfont.PNG

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November 28, 2004

Writing well

Sonja and I are reading "On Writing Well" by William Zinsser. It is remarkably well-written.

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November 26, 2004

The power of the pen

Skimming through Google News this morning I spotted a headline from Wired News which read "US Still Has Half of Falluja to Clear of Weapons". Pretty dismal huh? The fact is that "US Marines have cleared over 50 percent of Falluja's houses of weapons caches". Think of how much more optimistic the article could have been had it read "US Has Cleared a Majority of Falluja of Weapons". Ahh, the power of the media.

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May 5, 2004

Obsessive writing - the midnight disease

At lunch today, Peter introduced us to Alice Flaherty's The Midnight Disease : The Drive to Write, Writer's Block, and the Creative Brain. Flaherty explores obsessive writing. hypergraphia, from a neurological perspective. Excerpts here. As you might have expected, Ken and I were immediately facinated and interested in how we too could get this wonderful disease.

The Harvard Gazette has a nice profile on Ms. Flaherty and her book.

How about helping the brain along with some sort of electric stimulation, finding the best brain patterns to excite the muse and feeding them into the brain from outside? It's been done, although accidentally. Flaherty describes one of her patients, a well-educated 37-year-old woman who had wires surgically implanted in her frontal lobes to control the tics of Tourette's syndrome. At certain current settings, the woman reported increased creativity and productivity in both her professional and personal activities. Her boss asked her what they had put in her head, and how he could get one.
In Telling a tale with too many words, Chantal Martineau credits psychiatrist Elim Kraepelin of indentifying temporal lobe epilepsy with which hypergraphia is most commonly associated. Innterestingly,
Fyodor Dostoyevsky was probably a temporal lobe epileptic, as was Vincent van Gogh, who at his peak produced a canvas every 36 hours, writing his brother Theo up to three evocatively detailed six-page letters daily.
NPR interviewed Ms. Flaherty on Morning Edition (Real | Windows Media). The term "midnight disease" came from Edgar Allan Poe.

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December 11, 2003

Generators of EEG

I left off yesterday wondering about sources of EEG - actually, I read a few papers. I'll try to summarize what I found. Essentially, the accepted description is that the EEG is a result of extracellular currents, i.e., the ions which flow following neuronal discharge.

To be precise, let me quote from Ebersole and Pedley's "Current Practice of Clinical Electroencephalography". In the first chapter, Buzsáki, Traub and Pedley write:

Membrane currents generated by neurons pass through the extracellular space. These currents can be measured by electrodes placed outside the neurons. The field potential (i.e., local mean field), recorded at any given site, reflects the linear sum of numerous overlapping fields generated by current sources (current from the intracellular space to the extracellular space) and sinks (current from the extracellular space to the intracellular space) distributed along multiple cells. This macroscopic state variable can be recorded with electrodes as a field potential or EEG or with magnetosensors (superconducting interference devices [SQUIDs] ) as a MEG. These local field patterns therefore provide experimental access to the spatiotemporal activity of afferent, associational, and local operations in a given neural structure. To date, field potential measurements provide the best experimental and clinical tool for assessing cooperative neuronal activity at high temporal resolution. However, without a mechanistic description of the underlying neuronal processes, scalp or depth EEG is simply a gross correlate of brain activity rather than a predictive descriptor of the specific funcional and anatomical events. The essential experimental tools for the exploration of EEG generation have yet to be developed. [1, p. 1]

Hmm, what do they mean when they say that "EEG is simply a gross correlate... rather than a predictive descriptor." I think they want to be able to say if I see such and such a pattern then it has to do with this part of the brain doing this thing.
A straightforward approach to decomose the surface (scalp) recorded event is to study electrical activity simultaneously on the surface and at the sites of the extraccellular current generation. Electrical recording from deep brain structures by means of wire electrodes is one of the oldest recording methods in neuroscience. Local field potential measurements, or "micro-EEG", combined with recording of neuronal discharges is the best experimental tool available for studying the influence of cytoarchitectural properties, such as cortical lamination, distribution, size, and netowkr connectivity of neural elements on electrogenesis. However, a large number of observation points combined with decreased distance between the recording sites are required for high spaital resolution and for enabling interpretation of the underlying cellular events. Progress in this field should be accelerated by the availability of micromachine silicon-based probes with numerous recording sites. Information obtained from the depths of the brain will then help clinicians interpret the surface-recorded events.
...
In principle, every event associated with membrane potential changes of individual cells (neurons and glia) should contribute to the perpetual voltage variability of the extracellular space. Until recently, synaptic activity was viewed as the exclusive source of extracellular current flow or EEG potential. Progress during the 1990s revealed numerous sources of relatively slow membrane potential fluctuations, not directly associated with synaptic activity. Such non-synaptic events may also contribute significantly to the generation of local field potentials. These events include calcium spikes, voltage-dependent oscillations, and spike afterpotentials observed in various neurons. [1]
Buzsáki et al. go on to describe various sources of extracellular current flow. What seems to be missing is some discussion on how the fields then affect all these other things. They list the following sources:
  • Fast (Na+) Action Potentials - by far the largest amplitude intracellular event, also known as the sodium-potassium spike, usually not considered to contribute significantly to scalp-recorded EEG potentials because of their short duration (<2 ms) and the low-pass frequency filtering property of the extracellular medium (Buzsáki et al. wrote "high-pass", but I'm sure they meant "low-pass"), they do however, give room for population spikes to be detected
  • Synaptic Activity - "clearly the most significant source of the extracellular current flow that produces EEG potentials," they cite here Humprehy's "Re-analysis of the antidromic cortical response. I. Potentials evoked by simulation of the isolated pyramidal tract."
  • Calcium spikes
  • Voltage-Dependent Intrinsic Oscillation

References
[1] G. Buzáki, R.D. Traub and T.A. Pedley, "The Cellular Basis of EEG Activity," in Current Practice of Clinical Electroencephalography, 3rd ed., J.S. Ebersole and T.A. Pedley Eds. Philadelphia: Lippincott Williams & Wilkins, 2003, pp. 1-11.

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December 10, 2003

Sources of EEG

In non-invasive EEG, we measure tiny fluctuations in electrical potential at the scalp. What causes these fluctuations?

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MEG strength

I found some information on the strength of MEG in The Encyclopaedia of Medical Imaging Vol 1: Physics, Techniques and Procedures by Gustav K. Von Schulthness. I'll need to get the reference when it shows up on the Library of Congress database. Here is the useful quote:

Neuromagnetic fields have amplitudes in the order of a few picotesla ( 10 12 MathType@MTEF@5@5@+=feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaaicdadaahaaWcbeqaaiabgkHiTiaaigdacaaIYaaaaaaa@39F2@  tesla) and very sensitive instruments are needed to detect these extremely weak fields.

Ahh, here's a better one, from Jasper Daube's "Clinical Neurophysiology" [1].

Magnetoencephalography (MEG) is the recording of the small magnetic fields produced by the electric activity of neurons in the brain. These magnetic fields are generated by current flowing in neurons, with a small contribution from extracellular current flow in the volume conducting medium around the brain (generally less than the contribution of intracellular currents). These magnetic fields are extremely small, typically in the femptotesla or picotesla range ( 10 15 MathType@MTEF@5@5@+=feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaaicdadaahaaWcbeqaaiabgkHiTiaaigdacaaI1aaaaaaa@39F5@  to 10 12 MathType@MTEF@5@5@+=feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLnhiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=xfr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaaGymaiaaicdadaahaaWcbeqaaiabgkHiTiaaigdacaaIYaaaaaaa@39F2@  T). They must be detected by a magnetic gradiometer connected to a special type of extremely sensitive amplifier called a superconducting quantum interference device (SQUID), which must be cooled by liquid helium. To eliminate noise signals caused by the much larger magnetic fields associated with electrical equipment, power lines, and the earth's magnetic field, a special magnetically shielded room is required. For all these reasons, MEG is a very expensive tool. Another disadvantage of MEG, compared with EEG, is that it cannot be used readily for the long-term recordings needed to capture and to localize an epileptic seizure, because the subject's head must be kept immobilized near the magnetic gradiometer array during the entire recording...

...Because magnetic fields created by a current source are always oriented along a tangent to a circle around the line of current flow, MEG is insensitive to radially oriented currents in cerebral cortex and is sensitive only to tangential currents, in contrast to EEG, which is sensitive to both (although more sensitive to radial than to tangential currents). Thus, in practice, MEG recordings are often combined with simultaneous conventional EEG recordings.

Hmm, the comment about extracellular flow versus current flowing in the neurons is interesting. I thought the typical claim is that EEG is mostly due to the extracellular current flow.

References
[1] J.R. Daube, Clinical neurophysiology, Oxford ; New York: Oxford University Press, 2002, p. 144.

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June 5, 2003

How to Cite Patents

I often find myself avoiding writing for the stupidest reasons. Today I made the excuse that (1) I did not have Endnote or Microsoft Word on my room 28 computer, and that (2) without Endnote I couldn't properly cite stuff. That's baloney, so that I don't lose it, UIUC has 16 examples of how to cite, IEEE style. My thought now is to blog my thesis out. One entry at a time, and then someday I'll put it back together.

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