Consciousness and how it got to be that way

Monday, May 31, 2010

The Loneliness of the Seminal Computer Scientist

(Granted, Sillitoe's story has a better ring to it than the title of this post.) Probably already well-known among modern mathematicians and computer scientists, Alan Turing was quite an accomplished distance runner. When I first saw his 1947 Lecestershire marathon time of 2:46, I thought there might be some confusion; Europeans use the term "marathon" much more loosely than North Americans. On this side of the Atlantic, a marathon is 26.2 miles, period. So I looked it up and there's even a newspaper clipping image which specifies that yes, this is a real marathon time. 2:46 would be a damn good time in 2010, let alone in 1947 with bad running gear and probably bad nutrition and training. My own PR is 3:13 and I will likely never approach Turing's time regardless how much EPO and 'roids I consume.

Sunday, May 23, 2010

Hemineglect and Delusions

Hemineglect is among the more bizarre neurological conditions (which is also to say, devastating to the patient). In brief, the patient ignores one or the other half of space, right or left, up to and including his or her own body. They won't register stimuli on the neglected side and will even ignore their own bodies on that side, sometimes claiming that their limbs aren't their own: if you hold their arm up in front of them and ask them whose arm it is, they'll often insist it's a family member who's hiding nearby. (Yes, really.) A neurologist related to me that these patients will even sometimes request to be moved to a new bed in the hospital because there's someone else laying in bed with them (as in, the neglected half of their own body. Yes, really.) To these patients, a circle has only 180 degrees. The neglected half of space might as well be the fourth dimension.

Needless to say, natural experiments like these cases are a rich substrate for neurophilosophy. One aspect of neglect syndromes that I find interesting is that some of this behavior apparently amounts to a delusion, in the strict sense of a steadfast false belief. Neglect patients will sometimes complain that the hospital isn't feeding them enough, and of course when the nurse or physician comes into the room, they see a plate of food that's exactly half-eaten. So they turn the plate 180 degrees - and the patient grumbles "Good," and continues eating. See the disconnect here? If I were at dinner and said "Wow that green curry was good but I wish there were more," and my dining companion was able to magically produce more curry out of the fourth dimension before my eyes like some kind of a 3D chef visiting Flatland, of course I would be utterly amazed - but I haven't heard of such a reaction in the anecdotal reports I've heard from neurologists so far (I have not yet interacted with a neglect patient).

I'll do my best to put myself in the neglect patient's place again. Most of us believe that we have exactly 2 arms and 2 legs, and would react incredulously if a researcher told us that no, in fact we had four arms and four legs, but we were only using two of each. The researcher says to me "Fine, I can prove it." In an empty room with just her and me, she holds up an arm in front of me that looks just like me other two arms - skin color, size, etc. - and says it's my arm. I can't feel it or move it, and somehow I'm unable to see what it connects to, and it seemed to appear out of thin air (just like the green curry). But having four arms is ridiculous! Yet I trust this researcher; she seems incredibly earnest, she can reproduce this trick any time I ask with no preparation, and as I soon discover, so can anyone else I ask, including people with no possible connection to the researcher. All of them can hold up in front of me one or two arms that look like my own arms.

In such a position, I would be forced to conclude, as bizarre as it seems, that the evidence points to some kind of a perceptual defect on my part. As strange as it is, and as much as I absolutely cannot understand where this arm is coming from or how it connects to me, I eventually have to accept the incredible truth (after many, many trials) that I and everybody else has four arms, and that there's something strange about my perception that keeps me from seeing them. And even if I remain incredulous, certainly I would at least want to know how they were doing this amazing trick. But severe neglect patients not only avoid curiosity about things that could disturb their limited perception of space, they make up impossible stories about where their limb is coming from if it's presented to them. Clearly the deficit that produces their inability to fully represent space is neurological, rather than psychogenic. But isn't this part of the behavior arguably delusional?

Saturday, May 15, 2010

Ultrasound, Neuronal Excitability, and Hallucinations

A few years ago it was announced that a U.S. patent had been filed by Thomas Dawson on behalf of Sony for direct neural input of sensory information. There are a few: the most recent related patent by the same inventor here, but the one that I believe attracted media attention is here).

The patents describe a method of stimulating multi-modality sensory experience through the use of sound energy. The basic idea is that neuronal excitability can be increased with ultrasound (review here) although to date it seems that all the work has been either with CNS neurons in culture, or PNS neurons, rather than CNS neurons inside a spine or skull. Obviously if these patents represent functioning technology the implications are profound. For that reason I scrutinized 6,536,440 for evidence that the concept had in fact been reduced to practice, which (naively I'm told) I had thought was still a requirement for the issue of a patent. There's precious little in the document to suggest anyone is ready to build a transducer capable of producing any sensory experience in subjects, let alone a coherent one.

Of course ultrasound is already used in medical imaging all the time, in a similar range to that reported in the review (optimal transcranial transmission of ultrasound at 7 x 10^5 Hz, but in vitro studies showed neuronal excitability changes at higher frequencies around 2-7 x 10^6 Hz. Medical imaging ultrasounds use frequencies up to 10^7 Hz, but the intensity range is 1-10 W/cm^2, and the imaging device is rarely applied to the skull (useless for imaging, because bone blocks commercial ultrasound). That said, I'm unaware of anecdotal reports of patients hallucinating by any modality during ultrasound imaging, a very common outpatient procedure, and quick search of Pubmed reveals no such cases among the first 30 articles.

Sunday, May 9, 2010

A Possible Mechanistic Answer to Penrose et al

Paper here, "Informal Concepts in Machines", Kurt Ammon. Argues that algorithms exist which can perform computations beyond the limits of Turing machines. This is one answer to the problem of how, if humans are machines, we can definitively decide non-computability (one of Penrose's challenges).

Sunday, May 2, 2010

Junk DNA and Cancer

In Nature Lamprecht et al provide evidence that the presence of long terminal repeats (LTRs, a form of junk DNA) increases the risk of humans' developing certain cancers, especially lymphomas. [Added later: in 2007 the ENCODE study was supposed to show evidence that intragenic regions are pervasively transcribed but there's a large segment that believes this to be an artifact.]

Initially the discovery that our genomes were to a first approximation entirely composed of non-coding garbage characters was a surprise. But on further evolutionary reflection, it made sense: DNA is about copying itself, and it sometimes codes for proteins in networks with other pieces of DNA as a replication strategy. Consequently we should expect that most DNA is passively or selfishly just along for the ride, except in highly fecundity-dependent species where the extra time and energy make a fitness difference (like bacteria). Before you make the effort to back-of-the-envelope calculate the daily cost of replicating the 97% extra noncoding portion of our genome, realize that I have doubtless expended more calories typing this blog post than I will expend from all the DNA replication and proofreading I do during the entire day.

But even if the energy expended is not a problem, this paper revives the debate, because it shows that there still is a fitness cost for junk DNA in multicellular organisms - but it's paid in terms of cancer risk rather than energy cost. It's a little harder to write this off as fitness noise. We're back to the old question of what the advantage is for multicellular organisms to carry so much junk DNA.