On Probabilities and Confirmation Holism

According to a theory of knowledge called confirmation holism, we believe facts on the basis of their being part of a larger body of knowledge that we believe in total. For example, my belief in Sweden is a part of my knowledge of geography and history as a whole. I would have to doubt much of what I know of the nations and history of the world to disbelieve in Sweden.

One problem that's been advanced against such confirmation holism is the idea that we must have to assign each fact we know a probability, and then, by the laws of probability, don't we calculate the odds of our entirety of holistic conjunction of facts just as the product of the individual probabilities? For example, if we believe each fact of a 500-fact conjunction with p = 0.95, does this make our degree of belief in the 500-conjunct equal to (0.95)^500, or just 0.0000000000073?

But, of course, we DON'T calculate the probabilities of the whole this way! The multiplication rule for the conjunct of two probabilities assumes that those probabilities are independent! . And, in the case of confirmation holism, that is exactly what we would deny.

Is the Human Body a Ship of Theseus? Comments on an Urban Legend in Identity

The Ship of Theseus is a classic thought experiment in Greek philosophy. As related by Plutarch the historian, Theseus' ship was kept as a famous artifact, and, over the years, as its wood decomposed the boards were replaced, until none of that ship was the same wood as the original.

Was that ship still the ship of Theseus after all those replacements? Heraclitus, who said all was change, would likely have said not the same ship, and Plato and Aristotle, with their emphasis on form as what makes things what they are, might have thought otherwise. In a materialistic society, there are direct implications of the story for questions of identity over time--including human identity.

In The God Delusion, Richard Dawkins quotes, with apparent approval:

Steve Grand points out that you and I are more like waves than permanent 'things'. He invites his reader to think . . . ... of an experience from your childhood. Something you remember clearly, something you can see, feel, maybe even smell, as if you were really there. After all, you really were there at the time, weren't you? How else would you remember it? But here is the bombshell: you weren't there. Not a single atom that is in your body today was there when that event took place . . . Matter flows from place to place and momentarily comes together to be you. Whatever you are, therefore, you are not the stuff of which you are made. If that doesn't make the hair stand up on the back of your neck, read it again until it does, because it is important.

This is a quote from Grand's book on supervenience in nature. Though I'm not disagreeing here with such a supervenience thesis, the assertion above that "Not a single atom that is in your body today was there" (when you, now an adult, experienced a past, childhood event) is, in fact, false.

What evidence do Grand and, via Grand, Dawkins, have for such an assertion?

Their outdated, incorrect claim is in fact a philosophical urban legend, where everyone vaguely quotes a paper written over 60 years ago by Dr. Paul Aebersold, then a physicist at Las Alamos with Ernest Lawrence, as part of a review of the then new technologies using radioisotopes made possible by peaceful nuclear technologies. Writing in 1953 in the Annual Report of the Smithsonian Instituion, Aebersold says,

Tracer studies show that the atomic turnover in our bodies is quite rapid and quite complete. For example, in a week or two half of the sodium atoms that are now in our bodies will be replaced by other sodium atoms. The case is similar for hydrogen and phosphorus. Even half of the carbon atoms will be replaced in a month or two. And so the story goes for nearly all the elements. Indeed, it has been shown that in a year approximately 98 percent of the atoms in us now will be replaced by other atoms that we take in in our air, food, and drink.

Aebersold's paper was later to be quoted in 1954 in Time Magazine, whence it passed into the "quoted by everyone facts" category. By the 1960's, it seems to have become embedded in the background notions of the philosophy of biology and identity, perhaps slowly taking on urban legend status over the next few decades.

Let's now update to the twenty-first century. Pulse-chase analysis is a technique used in biology to understand the changes in a cell or tissue over time. The cells are exposed to a labeled substance which it incorporates into cellular metabolism at the time of exposure. This "pulse" is followed by a further exposure of the same type substance, but without the label (the "chaser"). The cell or tissue can later be examined for the tracer at various times after the pulse of label, to see if and where in its metabolic flow the tracer can be located.

In the past 15 years, studies done mostly at the Frisen lab at the Karolinska Intitute in Norway took advantage of a global carbon-14 pulse-chase experiment: the global atmospheric fallout exposure of the world's population alive or in utero at the time of atmospheric testing of atomic weapons by the United States, Russia, and Great Britain from 1945 through 1963 (note that France and China did a few more such tests through 1980). Here's one of the first abstracts:

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Cell. 2005 Jul 15;122(1):133-43.

Retrospective birth dating of cells in humans.

Spalding KL1, Bhardwaj RD, Buchholz BA, Druid H, Frisén J.

Abstract

The generation of cells in the human body has been difficult to study, and our understanding of cell turnover is limited. Testing of nuclear weapons resulted in a dramatic global increase in the levels of the isotope 14C in the atmosphere, followed by an exponential decrease after 1963. We show that the level of 14C in genomic DNA closely parallels atmospheric levels and can be used to establish the time point when the DNA was synthesized and cells were born. We use this strategy to determine the age of cells in the cortex of the adult human brain and show that whereas nonneuronal cells are exchanged, occipital neurons are as old as the individual, supporting the view that postnatal neurogenesis does not take place in this region. Retrospective birth dating is a generally applicable strategy that can be used to measure cell turnover in man under physiological and pathological conditions.

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So, here is a chart of the results of many such tests, courtesy of bionumbers.org:

What was wrong with the old urban legend? Note that Aebersold was mostly right (except for that word "complete") in what he wrote: it was extrapolation of what he said that was wrong!

Even in 1953, we knew that the body was not a uniform bag of tissue, and that cells were not mere bags of solute. It turns out that although it's true that over 98% of the body undergoes relatively rapid turnover during life, there are several tissues whose DNA does not turn over nearly as fast, or in some cases turn over at all.

Most of the human body is water, and this water flows in and through us like Heraclitus' river. However, bone turnover is far slower, and some tissues, such as tendons, turn over even less. Brain tissue contains some neurons which have not divided since we were born. DNA repair in those cells is not pervasive enough to turn over much of it during our lifespan.

So, not all the atoms of the human body turn over during life. Much of our DNA lingers.

Does it actually matter to philosophical conclusions about our identity that some small part of us (possibly an ounce) is completely unchanged during our lifetimes? Not if, like most of the world's population, you know that a ship is not just deadwood, and that matter is not all there is to living.

Gilles Deleuze on why the individual is not the species.

For Deleuze, perhaps to exist was not just to make a difference: it was to be a difference, to be uniquely configured by the effects of the singular flows within the configuration spaces by which a thing becomes what it individually is. One wonders what exactly Deleuze would now point to as the Source of difference in what exists? The vagueness of species is predicated on the difference of the individual.

Beneath the general operation of laws, however, there always remains the play of singularities. Cyclical generalities in nature are the masks of a singularity which appears through their interferences; and beneath the generalities of habit in moral life we rediscover singular processes of learning. The domain of laws must be understood, but always on the basis of a Nature and a Spirit superior to their own laws, which weave their repetitions in the depths of the earth and of the heart, where laws do not yet exist. The interior of repetition is always affected by an order of difference: it is only to the extent that something is linked to a repetition of an order other than its own that the repetition appears external and bare, and the thing itself subject to the categories of generality.

--Difference and Repetition (tr. Paul Patton, 1994), p. 25.

Too much of a good thing? Autism and Cortical Architecture

Brain microscopic anatomy in persons with autism shows an increase in the numbers of neuronal "dentritic spines" whuch conect neighboring cells in the brain. The dendritic spine density of the apical dendrites of pyramidal neurons are increased in several cortical layers (cortical layer 2 in frontal and parietal lobes and layers 2 and 5 in the temporal lobes). Spine density seems inversely correlated with cognitive function. Neurologists have hypothesized that the autism patient's brain is locally overconnected, so that the good connections are crowded out by poorly pruned, inefficient ones.

Something along those lines seems to fit the report below. Perhaps even in the first year of life, the brains of those who are to more obviously develop autism in the second year of life grow in a way that causes an unusual increase in cortical surface area. That means that their outer brain cortex is actually expanding faster than that of normal infants. Unfortunately, not all such brain size increases are desirable ones.

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ABSTRACT

Early brain development in infants at high risk for autism spectrum disorder

Heather Cody Hazlett, Hongbin Gu, Brent C. Munsell, Sun Hyung Kim, Martin Styner, Jason J. Wolff, Jed T. Elison, Meghan R. Swanson, Hongtu Zhu, Kelly N. Botteron, D. Louis Collins, John N. Constantino, Stephen R. Dager, Annette M. Estes, Alan C. Evans, Vladimir S. Fonov, Guido Gerig, Penelope Kostopoulos, Robert C. McKinstry, Juhi Pandey, Sarah Paterson, John R. Pruett, Robert T. Schultz, Dennis W. Shaw, Lonnie Zwaigenbaum, et al.

Nature 542, 348–351 (16 February 2017) doi:10.1038/nature21369

Received 15 April 2016 Accepted 06 January 2017 Published online 15 February 2017

Brain enlargement has been observed in children with autism spectrum disorder (ASD), but the timing of this phenomenon, and the relationship between ASD and the appearance of behavioural symptoms, are unknown. Retrospective head circumference and longitudinal brain volume studies of two-year olds followed up at four years of age have provided evidence that increased brain volume may emerge early in development. Studies of infants at high familial risk of autism can provide insight into the early development of autism and have shown that characteristic social deficits in ASD emerge during the latter part of the first and in the second year of life. These observations suggest that prospective brain-imaging studies of infants at high familial risk of ASD might identify early postnatal changes in brain volume that occur before an ASD diagnosis. In this prospective neuroimaging study of 106 infants at high familial risk of ASD and 42 low-risk infants, we show that hyperexpansion of the cortical surface area between 6 and 12 months of age precedes brain volume overgrowth observed between 12 and 24 months in 15 high-risk infants who were diagnosed with autism at 24 months. Brain volume overgrowth was linked to the emergence and severity of autistic social deficits. A deep-learning algorithm that primarily uses surface area information from magnetic resonance imaging of the brain of 6–12-month-old individuals predicted the diagnosis of autism in individual high-risk children at 24 months (with a positive predictive value of 81% and a sensitivity of 88%). These findings demonstrate that early brain changes occur during the period in which autistic behaviours are first emerging.

This is your Brain on E-Cigarettes

From the bioRxiv.org preprint site, some evidence that e-smoking is potentially habit-forming. Like ordinary smoking as well as several other habit forming drugs, e-cigarette smoking causes increased posterior striatal metabolism, which often correlates with addictive craving and behavior.

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ABSTRACT

The effect of smoking on the brain revealed by using electronic cigarettes with concurrent fMRI

Matthew B Wall, Alexander Mentink, Georgina Lyons, Oliwia S Kowalczyk, Lysia Demetriou, Rexford D Newbould

doi: https://doi.org/10.1101/107771

Cigarette addiction is driven partly by the physiological effects of nicotine, but also by the distinctive sensory and behavioural aspects of smoking, and understanding the neural effects of such processes is vital. There are many practical difficulties associated with subjects smoking in the modern neuroscientific laboratory environment, however electronic cigarettes obviate many of these issues, and provide a close simulation of smoking tobacco cigarettes. We have examined the neural effects of 'smoking' electronic cigarettes with concurrent functional Magnetic Resonance Imaging (fMRI). The results demonstrate the feasibility of using these devices in the MRI environment, and show brain activation in a network of cortical (motor cortex, insula, cingulate, amygdala) and sub-cortical (putamen, thalamus, globus pallidus, cerebellum) regions. Concomitant relative deactivations were seen in the ventral striatum and orbitofrontal cortex. These results reveal the brain processes involved in (simulated) smoking for the first time, and validate a novel approach to the study of smoking, and addiction more generally.

Earlier Noncontact Exercise May Decrease Risk of PostConcussive Syndrome in Youth

The best practice estimates regarding the timing of return to high levels of physical activity in sports after concussion keeps changing in recent years. The study below suggests that early return to exercise type, non-contact sports practice may be beneficial after concussion. The best protocol then might be early reintegration into non-contact practice but only later restart of physical contact practice and games after concussion in sports, at least at the junior high and high school levels, contingent at least until further study is done.

ABSTRACT

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Association Between Early Participation in Physical Activity Following Acute Concussion and Persistent Postconcussive Symptoms in Children and Adolescents

Anne M. Grool, MD, PhD1; Mary Aglipay, MSc1; Franco Momoli, PhD1; et al William P. Meehan III, MD2; Stephen B. Freedman, MDCM, MSc3; Keith Owen Yeates, PhD4; Jocelyn Gravel, MD5; Isabelle Gagnon, PhD6; Kathy Boutis, MD7; Willem Meeuwisse, MD, PhD8; Nick Barrowman, PhD1; Andrée-Anne Ledoux, PhD1; Martin H. Osmond, MDCM9; Roger Zemek, MD9; for the Pediatric Emergency Research Canada (PERC) Concussion Team

JAMA. 2016;316(23):2504-2514. doi:10.1001/jama.2016.17396

Key Points

Question

Is participation in physical activity within 7 days following acute concussion associated with lower rates of persistent postconcussive symptoms in children and adolescents compared with conservative rest?

Findings

In this prospective, multicenter cohort study of 3063 children and adolescents aged 5.00 to 17.99 years after propensity matching, the proportion with postconcussive symptoms at 28 days was 28.7% with participation in early physical activity vs 40.1% with conservative rest, a significant difference.

Meaning

Participation in physical activity within 1 week after injury may benefit symptom recovery following acute concussion in children and adolescents.

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Importance

Although concussion treatment guidelines advocate rest in the immediate postinjury period until symptoms resolve, no clear evidence has determined that avoiding physical activity expedites recovery.

Objective

To investigate the association between participation in physical activity within 7 days postinjury and incidence of persistent postconcussive symptoms (PPCS).

Design, Setting, and Participants

Prospective, multicenter cohort study (August 2013-June 2015) of 3063 children and adolescents aged 5.00-17.99 years with acute concussion from 9 Pediatric Emergency Research Canada network emergency departments (EDs).

Exposures

Early physical activity participation within 7 days postinjury.

Main Outcomes and Measures

Physical activity participation and postconcussive symptom severity were rated using standardized questionnaires in the ED and at days 7 and 28 postinjury. PPCS (≥3 new or worsening symptoms on the Post-Concussion Symptom Inventory) was assessed at 28 days postenrollment. Early physical activity and PPCS relationships were examined by unadjusted analysis, 1:1 propensity score matching, and inverse probability of treatment weighting (IPTW). Sensitivity analyses examined patients (≥3 symptoms) at day 7.

Results

Among 2413 participants who completed the primary outcome and exposure, (mean [SD] age, 11.77 [3.35] years; 1205 [39.3%] females), PPCS at 28 days occurred in 733 (30.4%); 1677 (69.5%) participated in early physical activity including light aerobic exercise (n = 795 [32.9%]), sport-specific exercise (n = 214 [8.9%]), noncontact drills (n = 143 [5.9%]), full-contact practice (n = 106 [4.4%]), or full competition (n = 419 [17.4%]), whereas 736 (30.5%) had no physical activity. On unadjusted analysis, early physical activity participants had lower risk of PPCS than those with no physical activity (24.6% vs 43.5%; Absolute risk difference [ARD], 18.9% [95% CI,14.7%-23.0%]). Early physical activity was associated with lower PPCS risk on propensity score matching (n = 1108 [28.7% for early physical activity vs 40.1% for no physical activity]; ARD, 11.4% [95% CI, 5.8%-16.9%]) and on inverse probability of treatment weighting analysis (n = 2099; relative risk [RR], 0.74 [95% CI, 0.65-0.84]; ARD, 9.7% [95% CI, 5.7%-13.7%]). Among only patients symptomatic at day 7 (n = 803) compared with those who reported no physical activity (n = 584; PPCS, 52.9%), PPCS rates were lower for participants of light aerobic activity (n = 494 [46.4%]; ARD, 6.5% [95% CI, 5.7%-12.5%]), moderate activity (n = 176 [38.6%]; ARD, 14.3% [95% CI, 5.9%-22.2%]), and full-contact activity (n = 133 [36.1%]; ARD, 16.8% [95% CI, 7.5%-25.5%]). No significant group difference was observed on propensity-matched analysis of this subgroup (n = 776 [47.2% vs 51.5%]; ARD, 4.4% [95% CI, −2.6% to 11.3%]).

Conclusions and Relevance

Among participants aged 5 to 18 years with acute concussion, physical activity within 7 days of acute injury compared with no physical activity was associated with reduced risk of PPCS at 28 days. A well-designed randomized clinical trial is needed to determine the benefits of early physical activity following concussion.

Split Brain Research Fails to Replicate Different Hemisphere Awareness After Corpus Callosotomy

According to the Nobel-prize-winning work in the 1960's by Sperry and Gazzaniga, after the two cerebral hemisphere are cut by callosotomy (a surgery sometimes done for intractable epilepsy), a person seeing an object in one visual field can signal seeing it with the hand on that side, but not with the hand on the other side, which will respond as if no object was seen.

I'd heard several tales in more recent years from neuropsychologists just out of university training of how researchers at their institutions were failing to replicate those classic results. This was usually attributed to variations in the surgery performed, as well as the fact the posterior commissure was usually left intact.

However, in a recent issue of Brain, Pinto and colleagues below report they have systematically re-studied many of the patients from these surgeries and are showing that a single awareness persists in such subjects-- exactly as the persons who had the surgery (I've seen three since the 1990's) themselves will tell you, if you ask them :).

What improved over the decades? Perhaps they got better at re-routing the interrupted communications. Did the subjects ever have more than one center of consciousness? Probably no more than we do when we split our attention between simultaneous tasks.

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ABSTRACT

Split brain: divided perception but undivided consciousness

Yair Pinto David A. Neville Marte Otten Paul M. Corballis Victor A. F. Lamme Edward H. F de Haan Nicoletta Foschi Mara Fabri

Brain (2017) aww358. DOI: https://doi.org/10.1093/brain/aww358

Published: 24 January 2017

In extensive studies with two split-brain patients we replicate the standard finding that stimuli cannot be compared across visual half-fields, indicating that each hemisphere processes information independently of the other. Yet, crucially, we show that the canonical textbook findings that a split-brain patient can only respond to stimuli in the left visual half-field with the left hand, and to stimuli in the right visual half-field with the right hand and verbally, are not universally true. Across a wide variety of tasks, split-brain patients with a complete and radiologically confirmed transection of the corpus callosum showed full awareness of presence, and well above chance-level recognition of location, orientation and identity of stimuli throughout the entire visual field, irrespective of response type (left hand, right hand, or verbally). Crucially, we used confidence ratings to assess conscious awareness. This revealed that also on high confidence trials, indicative of conscious perception, response type did not affect performance. These findings suggest that severing the cortical connections between hemispheres splits visual perception, but does not create two independent conscious perceivers within one brain.