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Wednesday, January 30, 2008

About Cochlear Implants & The Quality of Music

The cochlea is the receiver of sound in the inner ear. It is composed of three adjacent fluid-filled canals that coil in two and one-half windings encased in a bony shell. Sound waves set the tympanic membrane in the outer ear in vibration. The vibrations are conducted by three small bones in the middle ear to the oval window of the cochlea, stirring waves in the cochlear fluid. The waves move a membrane stretching from base to apex at the center of the cochlea. The membrane deflects hairs on sensory receptor cells nestled beneath in the organ of Corti. The hair deflections are transduced into nerve cell signals and conveyed to the brain through the auditory nerve. High pitch exerts the greatest membrane movements at the cochlea's base and low pitch at the apex. Because the auditory nerve fibers innervate the organ of Corti sequentially, each fiber is excited by a specific sound frequency.

Exposure to high volume noise may shear off sensory receptor hair. Exposure to high doses of antibiotics triggers hair cell death. The loss of sensory hair in as much as the loss of sensory receptor cells lead to early deafness. Hardening of the middle ear bones with advancing age is another common cause. Today, hearing can be restored with cochlear implants as long as the auditory nerve fibers in the cochlea remain intact. That is, wire electrodes are implanted into the cochlea. Ambient sound is recorded with a microphone. Computer algorithms transform the recording into electrical pulses that stimulate the auditory nerve fibers according to the pitch and the volume of the recorded sound. Intriguingly, the nerve cells in the brain can use the artificially generated input to interpret sound in a meaningful fashion. Through practice and optimization of the algorithms, hearing improves. The process constitutes a striking accomplishment of engineering and medicine. However, even greater achievement lies with the nerve cells in the auditory pathway. They must re-adjust their connections such that the novel sensory input can be successfully utilized.

In today's Morning Edition of National Public Radio (NPR), Robert Krulwich spoke with Oliver Sacks (pod cast) about the neurologist's latest book entitled Musicophilia: Tales of Music and the Brain. In the book, the author observes people who hear imaginary music that ensembles of nerve cells seem to generate in the auditory parts of their brains. Robert Krulwich interviews two persons described. One is a lady who lost her hearing with advancing age. Though she fell completely deaf, she reported frequently hearing pieces of music flawlessly performed loud and clear. She opted for a cochlear implant. Although she effectively regained hearing after implantation, the imaginary music persisted to emerge. The music does not bother her. In her judgment, the quality of the brain-generated pieces is far superior to the performances she hears with the implant. She must have had a keen sense of hearing and a great appreciation of music earlier in life, and the auditory inputs produced with the implant can not rival the quality of the memory trace. The great Ludwig van Beethoven managed to compose extraordinary music having fallen entirely deaf.


Addenda





Thursday, January 24, 2008

On the Value of Education

My son attends Meigs Magnet Middle School since last fall. The school is part of Metropolitan Nashville Public Schools. Acceptance is based on grades and a lottery. The other day, I had the chance to visit during class. I received my primary and secondary school education in Germany. The visit was my first at a US magnet school. Learning is project-oriented. The teachers were competent and involved. I saw children of a great variety of ethnic and racial backgrounds. Their diverse faces shared one striking feature: big, bright, and curious eyes. I was deeply impressed by their ubiquitous thirst for knowledge and cannot imagine a more profound demonstration of the essence of education. Its success cannot be bought. Rather, a successful education depends upon opportunities given and opportunities taken.

This principle also applies to higher education. Currently, graduating high school students and their parents are preparing college applications in this country. The New York Times ran an instructive article about the work of guidance councilors on January 4, 2008, accompanied by an illuminating Q&A section. Obviously the parties involved are deeply concerned with the wisdom of their decisions. Often, the equivalent value of a home may be spent.

I have studied and worked at four academic institutions, that is the Johann Wolfgang Goethe University Frankfurt a.M., Germany, the University of Tennessee, Knoxville, TN, USA, the University of Lausanne, Lausanne, Switzerland, and Vanderbilt University, Nashville, TN. The most demanding undergraduate class I took was a three-quarter course in Biochemistry for premedical students at UT. Regardless of private or public institution, only a select few students I met were eventually accepted by medical schools affiliated with the Ivy League. Besides impeccable grades, the most influential factor seemed the MCAT score. Everybody felt the need to take the Princeton Review.

Although higher education costs a lot in the US, it is a commodity without warranty. Education is not like a garment made to measure. Keeping with this analogy, the garment's fit depends on the ingenuity of the tailor and the wearer alike. The prospective student must decide in which environment her/his development may benefit the most. This may not necessarily be at the most expensive and prestigious school. A superb teaching environment does not depend on prime recreational facilities and posh accommodations. There may be value in simplicity. One of the most brilliant teacherswhose thoughts are still remembered after more than 2,400 years worked with very little overhead.


Addenda
  • Unigo is the most informative college survey site, if you do not know which direction to turn (added 09/21/08).
  • You may wish to read on the unfolding financial crunch gripping U.S. colleges and universities in my posts dated Oct. 30 and Dec. 9, 2008.
  • The other day, I paid my first visit to an American mega-university. More than 63,000 students toil at Ohio State University (OSU) in Columbus, Ohio. Total cost in this academic year for in-state students may come to a third of private college cost. Its a huge campus. The shear size may be startling. But I was deeply impressed with the faculty. All professors I met had attended highly reputed universities and spent their earlier careers at top-ten research universities. I took my visit to show that many institutions of higher learning in this country may offer an excellent education at affordable cost. If we are willing to take the front seat, crowds pose no obstacle. We were a thousand students in my Introduction to Biology lectures. Yet, even an auditorium for a thousand students offers seats up front. You could easily read the slides and enjoy the action still from the tenth row. The lectures were highly instructive. The demonstrations were fascinating. These crowded lectures sowed the seeds for many posts on this blog (10/31/09).
  • Last weekend, Nashville made the national headlines with the news of a catastrophic historical flood. According to NashvilleWX Channel2, some areas received more than 18 inches of rain. Last Monday evening, the Cumberland River crested just under 52 feet, 4 feet below the highest level recorded in history. Mayor Karl Dean estimates that the damage may exceed $1.5 billion. The Tennessean covers the events extensively. The impact of the horrific deluge depends on location. We live on a hill. Though our basement is unfinished, it only turned damp. No tornado struck our home. We were spared one more time. By contrast, homes and businesses near the Cumberland River and its tributaries were totally flooded. To date, we know that ten people lost their lives in Metropolitan Davidson County. About 2,000 residences took water. Countless families lost their homes. Public schools have been closed all week. My son's school, Meigs Magnet Middle School, provided outstanding leadership in these extraordinary times. On the day of the worst flooding, May 2, the school's principal inquired in phone and e-mail messages about the status of the students and their families. Based on the school's initiative, we know now that flooding severely affected at least 20 Meigs families, and the PTO is organizing help and relief. My son could not attend a better school (05/06/10).
  • People begin to listen (05/24/10)!
  • Based on a student survey conducted by ratemyprofessors.com, Robert Franek, Laura Braswell and the staff of The Princeton Review compiled a list of the 300 best professors at US institutions of higher learning along with professor and school profiles. The list was published in softcover by Random House this year and is quite informative. For example, Harvard University (private; annual tuition: $34,976.-) contributes two professors to the list. By contrast, The College of William and Mary (public; in-state tuition: $13,132.-; out-of-state tuition: $35,409.-) is home to ten such professors. According to William and Mary's Faculty Compensation Board Report 2009-10, full professors at the college earned on average roughly $112,000.- in that academic year (most recent data available), whereas at Harvard University they earned $198,400.- in the academic year 2011-12 (AAUP's Annual Report on The Economic Status of The Profession 2011-2012 with the title "A Very Slow Recovery"). Passion for teaching need not necessarily correlate with pay (05/23/12)!
Related Posts



Wednesday, January 23, 2008

(Wo)Man & Machine

I once was privileged to witness a controlled wrecking on a college campus. The goal of the project was not to destroy the whole structure, a three-story laboratory building, but only the two-storied annex. This "surgical cut" was executed using a hulky excavator armed with a oversized pneumatic jackhammer. The hammer was shaped like a giant tooth with which the operator probed the structures' beams. The operator gingerly moved the tooth about the building, gently probing here and there, constantly searching for the critical junctions that, once the jackhammer was unleashed, would only let the annex collapse. The operator approached the job with extreme diligence. The pneumatic hammer was activated with utmost nimbleness, leaving the observer with the impression that the person at the controls was able to sense the softening of the structure through the machine's tooth. Although the procedure was carried out with urgency, progress was excruciatingly slow. No mistakes were allowed. Blows were dealt with a sensitive touch. Despite the formidable challenge, the annex eventually turned into a pile of rubble while the main building remained unharmed. In the end, a lady with a big happy grin stepped from the cab to the ovations of a small crowd of academic onlookers that had gathered.

The operator's performance impressed so profoundly, because she appeared to control the excavator as if it were part of her body. In support of this idea, the machine mediates impact and vibration, providing meaningful tactile and proprioceptive feedback to the operator. Combined with visual and auditory cues, this feedback may produce an accurate perception of the machine's precise dimensions and forces of engagement can be gauged with the necessary accuracy. Reinforced by the continued use of successful strategies, connections between nerve cells strengthen, forming new networks that ultimately represent the machine in the mind as an extended part of the body.

Such plasticity of nerve cell networks is fundamental to the demonstration reported by Sandra Blakeslee in her article entitled "Monkey’s Thoughts Propel Robot, a Step That May Help Humans" in The New York Times on Jan. 15, 2008, that a monkey in the U.S. could steer a robot's walk in Japan with neuronal action potentials, that is electric nerve cell signals, recorded from her brain. The work was carried out in Miguel Nicolelis' laboratory at Duke University. The monkey was trained to walk on a treadmill while watching on a video screen the back of the robot walking on a similar mill, seemingly ahead of her. Microwire electrodes were implanted through an opening in the skull into the monkey's somatic sensory and motor cortex to record nerve cell signals. Signals that control leg movements were transmitted to Japan via the internet and fed to the robot's computer controlling its walk. The monkey was rewarded with treats for keeping the robot walking on the belt. Eventually, she managed to keep the robot on the move, while giving herself a rest.

The computer monitor shown in the Reuters video at 0:18 minutes:seconds displays electrical nerve cell activity in the monkey's cortex acquired with a Plexon's multichannel acquisition processor. The large window on the right side depicts recordings from 128 electrodes arrayed in a matrix of 16 x 8 channels. Each electrode picks up electrical spikes from a number of cells. However, particularities in spike shape can be used to identify individual cells. The sorting of nerve cells by wave form is displayed in the windows on the left. The upper window depicts the spikes recorded from one electrode. The red, green, yellow and blue traces identify the spikes of four nerve cells. The isolated spike wave forms are shown separately in the window below. The upper window is shown enlarged at 0:23. The electrode channel from which the recordings were taken is framed in red on the left border of the enlarged matrix window at 0:28. Only the nerve cell signals essential to the control of the monkey's legs were used to control the robot's walk.

The success of this demonstration doubtlessly constitutes a formidable achievement of science and engineering. Yet, the greatest accomplishment resides in the monkey's brain. Similar to the big machine operator, the monkey experienced positive reinforcement when the robot walked successfully. During training, nerve cells in the monkey's motor cortex must have modified their connections such that their signals could be correctly interpreted by the robot's computer to keep the machine on the treadmill. As Eugen Herrigel so befittingly described in Zen in the Art of Archery the arrow, i.e. the nerve cell signals, and the bull's-eye, i.e. the robot, must fuse into one to get the job done.

The technology of controlling computers with nerve cell signals has been already applied to humans. Kennedy and Bakay (1998) demonstrated that a paralyzed patient could intentionally move a cursor on a computer monitor with nerve cell signals recorded from an electrode implanted into motor cortex. Eliminating the need for an opening in the skull, Birbaumer and others (2006) showed that recordings of small electrical currents on the scalp can be used to work a word processor. Nerve cells may even be able to control computers directly one day. Peter Fromherz and colleagues successfully grew endings of nerve cells onto silicon wafers in tissue culture and provided evidence that the nerve cell signals influenced the flow of electrons in the semiconductor (Fromherz and others, 1991). The implementation of this idea in vivo is not entirely utopian. Damaged peripheral nerve cell fibers are known to regenerate and may establish functional connections (Melzer and Smith, 1995).

Addenda
  • Richard Allen Greene reports in his post entitled "Brain-Twitter project offers hope to paralyzed patients" on CNN today on exciting progress that Adam Wilson and Justin Williams at the University of Wisconsin have made in developing a method with which electrical signals of nerve cells in the brain recorded from the scalp can be used to compose a message on Twitter, opening up a new avenue for paralyzed people to communicate (04/23/09).
  • On National Public Radio's All Things Considered today, Michele Norris anchored a segment entitled "Your Brain On Twitter: No Hands Necessary" on brain wave-controlled Twitter messages (04/24/09).
  • This short, but impressive video clip below superbly corroborates my observation. Bionic legs will assist us on our first steps into a very useful direction (07/18/10).
  • Today, Diane Rehm interviewed Miguel Nicolelis on her show with the title "Miguel Nicolelis: 'Beyond Boundaries'". Dr. Nicolelis is a lead investigator in this research and discusses his fascinating insights (03/16/11).
  • Nicolelis and others (2011) published the proof of concept for nerve cell activity-controlled movements of a virtual limb combined with feedback through electrical microstimulation of nerve cells in somatic sensory cortex in this week's issue of Nature (10/06/11).

References