deadpopstar.com

I haven’t been posting a lot of neuroscience content lately, despite my aim to steer this blog in that direction. After spending 10 hours a day on neuroscience, writing about it isn’t usually the first thing that comes to mind upon returning home. But I’m going to try! And I’m going to cheat by writing about things that happen to be in my field.

So, without further ado: When hearing loss is caused by some fault of the machinery that converts sound energy into neural impulses within the cochlea, a spiral shaped structure within the inner ear, a cochlear implant (CI) is usually the only option in restoring hearing. It works by electrically activating remaining neurons, using an electrode array placed in the scala tympani, one of three fluid filled chambers of the cochlea (the coiled structure, below).

Now, the cochlea has what is known as a frequency-place code. Different regions of the cochlea are tuned to particular frequencies, with high frequency sounds down at the base, and low frequency sounds at the tip. So, by stimulating different regions, you can create the perception of different pitches. A CI, in essence, pulls out the dominant frequencies of the received auditory signal, and stimulates the corresponding region of the cochlea. In the very best patients, this gives near perfect speech perception — which is a fascinating phenomenon given how much information is stripped out by the CI.

There are a few limitations of the CI that researchers are trying to address. The most oft-stated are poor speech recognition in noisy environments (such as a busy restaurant), and poor music perception. It’s suggested that if you can deliver more detailed pitch information, it will allow the brain to filter out some noise, or recognize complex melodies.

Given what I’ve just said, you might imagine that if you can stimulate more regions of the cochlea, you can represent more pitches. Unfortunately, this is a difficult proposition. Unlike the normal mechanical fine tuning of the cochlea, the electrical stimulation from a CI spreads over a broad area, activating neurons that represent a range of frequencies. If you put electrodes too close together, there will be so much overlap in the groups of activated neurons that the brain won’t be able to tell the difference. In the case of speech perception, it’s been found that stimulating anything more than about eight electrodes yields no improvement (a typical human CI has about 22 electrodes to choose from).

Part of the problem is that the electrode array lies in the fluid of the scala tympani, often with a layers of protein and cell encapsulation, at some distance from the neurons it’s trying to stimulate. Therefore, you’re unlikely to get greater frequency selectivity with increased numbers of electrodes, unless you can somehow get the electrodes nice and close to those neurons.

Stained cochlea cross-section. The * shows where the electrode array was, with a tissue capsule left behind (black arrow). The blue arrow shows where the auditory neuron cell bodies are located, with their axons forming the auditory nerve down the centre (the modiolus).

There’s been a couple of approaches on that one. The first is trying to skewer the cochlea with an electrode array right down the middle of the cochlea, in the auditory nerve itself. Two problems with this are that it is (a) invasive, and (b) now difficult to determine which neurons correspond to which frequencies. But you do get lower thresholds (i.e. less power is required, which is very exciting to engineers like myself), and access to a broader frequency range (current clinical electrode arrays can’t reach the upper turns of the cochlea). Middlebrooks & Snyder (2008) recently provided a review of this approach. Another approach has been to insert an electrode array into the scala tympani, but get it to hug the wall against the modiolus, as close as possible to the neurons (there are also efforts afoot to get the neurons to grow onto the electrode array, but that’s another story).

Contour Electrode Array (Cochlear Ltd.)

The latter has been in clinical use for a while, but a clear benefit to auditory performance has yet to fully emerge, suggesting it isn’t the silver bullet some were hoping for. The means by which the curved electrode array is inserted is clever, but by no means advanced. During surgery, a stylette sits inside the electrode array, keeping it straight. As the array is inserted into the cochlea, the stylette is incrementally removed, allowing the tip to curl around the cochlea, eventually hugging the wall of the modiolus once fully removed. In short, it relies on the skill of the surgeon, knowing where the electrode tip is, and how it is situated. Pull the stylette out too slowly, and the electrode could bang against the wall of the cochlea instead of following the turns of the cochlea. Too quickly, and the tip could wrap back on itself.

I’m overstating the danger a bit; the array design has been optimized to reduce the risk of such hiccups. But wouldn’t it be nice to know where the electrode array is in the cochlea, how it is oriented, and if it is about the crash into something important, rather than just going by feel? That’s what Wise and colleagues (2008) set out to do at The University of Michigan. They built a pre-curved silicon electrode array with sensors along it’s length, and at its tip. Combined with some onboard processing, this permits the shape of the electrode array, and forces exerted upon it, to be monitored during insertion.

Photo showing the smart electrode array, with the inset showing a stimulation electrode (black circle) and position/contact sensors (the orange squiggly things).

The authors hope that this system will eventually be integrated with an automated insertion tool, allowing electrode arrays to be positioned with precision and repeatability. And, being silicon based, more electrode sites can be integrated than clinical (hand-made) electrode arrays, like the Contour. Though, as I’ve mentioned, it’s unclear whether this will provide added benefit to most patients. Lack of cochlear trauma, and preservation of any existing hearing, however, certainly provides benefit. In those with residual hearing, the best outcomes are achieved when a cochlear implant is combined with a hearing aid (usually used for low frequencies, where the electrode array can’t reach) — an approach called bimodal hearing.

So, the reason for the lack of updates lately has been the development and launch of the UROP Alumni Group website last month. UROP, the Undergraduate Research Opportunities Program, aims to give students of biology, maths, engineering and physics a chance to work in biomedical research. There are many such programs across the world, the earliest at MIT. This particular program is run by Bio21 Australia, for Victorian university students. I’m hoping this website will give past, present and prospective participants a chance to share their experiences, and learn about different opportunities across institutions

I would never have had the opportunity to undertake a PhD in hearing research if it weren’t for UROP, so I owe them greatly.

…after a disastrous upgrade to Wordpress 2.6. My old theme doesn’t work, so it will have to modified before everything is back to the way it was.

On March 29th this year, Velorock was held at the Brunswick Velodrome. It was easily the most fun music event I’d ever attended. The terrific bands. The bake sale. The people, young and old, but all thoroughly pleasant. The fact that everything — equipment and performers — were transported by bike and trailer. And it was free! That juggernaut festivals can get away with charging over $100, replete with corporate sponsorship, well, it kills me. It was a lovely day out. Hopefully the organizers broke even, and it will be back again next year.

Preparing for trailer races around the velodrome. Note Tali, of Lucksmiths fame, strapped securely in the toddler trailer.

Any injuries sustained didn’t seem to impede his subsequent performance.

More Flickr photos…

This is just too perfect.

(Via BB)

The problem with the Segway, as I see it, is that it screams “I’m a cashed-up dork.” The following is much cooler…

Link

The New York Times reports on a study published in Oikos, an Ecology journal, describing a correlation between increasing beer consumption in Czech avian ecologists and decreasing publication output and number of citations.

Though the public may tend to think of scientists as exceedingly sober, scientific schmoozing is often beer-tinged, famous for producing spectacular breakthroughs and productive collaborations, countless papers having begun as scrawls on cocktail napkins.

…
“It’s rather devastating to be told we should drink less beer in order to increase our scientific performance,” Dr. Symonds said.

I’m living in a horrible nightmare world! I have a brewery in my kitchen! There’s a beer tap in my fridge! My PhD advisor wears a Victoria Bitter t-shirt to the lab!

Thankfully, the usual caveats with respect to causation vs. correlation apply, as do the less usual concerns of generalizing Czech ornithologists to the general scientific population (though Shelley does have an African Grey…). Still, I’ll be needing a beer about now.

Link to Article: Grim (2008) A possible role of social activity to explain differences in publication output among ecolosgist. Oikos, 117(4), p.484.

(Stats for above figure: Shows pooled data, open circles are from 2002 survey, closed are from 2006 survey, with pooled r= -0.52, p= 0.0008.)

R2D2 Beanie…

And, the Utili-Kilt.

Maximum respect for anyone able to wear either (or both!) of these in public.

It is relatively common to experience auditory hallucinations following hearing loss. It has been suggested that these hallucinations are the result of a ‘release’ of inhibition, normally provided by auditory experience. This inhibition would act to balance the reciprocal activity between high- and low-level processing centers, which both transfer basic sensory information, as well as “fill in the gaps” to provide a cohesive auditory experience. When the former high-level centers are in overdrive, however, the effect may be to trigger complex auditory percepts, without a driving auditory stimulus.

Oliver Sacks describes this phenomenon, along with an (as usual) gorgeously written account of the “Power of music” in the journal Brain (Sacks, 2006 - free!), an excerpt of which is included below. An interesting aspect of the above hypothesis is that we may expect these hallucinations to disappear if afferent drive (auditory input) is restored, for instance, via a cochlear implant. This does not appear to be the case. This is described in more detail by Sacks in this NPR Story, and in his recent book, Musicophilia.

Our auditory systems, our nervous systems, are tuned for music. Perhaps we are a musical species no less than a linguistic one. But there seems to be in us a peculiar sensitivity to music, a sensitivity that can all too easily slip out of control, become excessive, become a susceptibility or a vulnerability. Too-muchness lies continually in wait, whether this takes the form of ‘earworms’, musical hallucinations, swoons and trances, or music-induced seizures. This is the other side of the otherwise wonderful power of music. How much this is due to the intrinsic characteristics of music itself—its complex sonic patterns woven in time, its logic, its momentum, its unbreakable sequences, its insistent rhythms and repetitions, the mysterious way in which it embodies emotion and ‘will’—and how much to special resonances, synchronizations, oscillations, mutual excitations, feedbacks, and so forth, in the immensely complex, multi-level neural circuitry that subserves musical perception and replay, we do not know. We do not even know why, for instance, simple stroboscopic light displays can excite hallucinations, myoclonus and seizures, and this is an infinitely simpler matter than the powers of music.

When Crichtley and Henson’s Music and the Brain was published in 1977, functional brain imaging still lay in the future, and neuroscience had yet to approach the neural correlates of musical perception, imagery and memory or their disorders. In the last 20 years, there have been huge advances here, but we have, as yet, scarcely touched the question of why music, for better or worse, has so much power. It is a question that goes to the heart of being human.

While on vacation recently, I had the pleasure of experiencing the discombobulating experience that is North American cable television. Amongst a sea of, well, crap, there are some absolute gems that haven’t yet made it to Australian shores. An example is Flight of the Conchords*. And then there is my favorite, Ace of Cakes. It concerns a cake shop in Baltimore, and it’s obscenely talented staff. The whole process - a deft mix of sugar & civil engineering - is fascinating. Duff Goldman and his staff at Charm City Cakes are thoroughly pleasant (in stark contrast to every other reality show, ever), and obviously enjoy what they do.

It’s nice to know that such a sincere television show can still be made.

*New Zealand’s fourth most popular digi-folk parodists