john hawks weblog

paleoanthropology, genetics and evolution

brain function

  • Brain plasticity in adults and cognition

    Sun, 2013-06-16 20:48 -- John Hawks

    I ran across a study from a couple of years ago by Rachel Brans and colleagues, which has an interesting result showing a genetic correlation between plasticity of cortex thickness and performance on psychometric tests [1]. Plasticity is essential for brains to respond to pathological conditions like stroke; other studies have suggested that plasticity is likewise important to normal brain function. By means of conventional quantitative genetic analysis, Brans and colleagues suggest that plasticity is mechanistically related to the factors that underlie variation in cognitive performance:

    Our finding that intelligence and change in cortical thickness are partly associated through shared genes is consistent with the dependence of learning and memory formation on the plasticity of neural circuits (Escobar et al., 2008). The association between intelligence and structural brain changes may also reflect an association between intelligence and plasticity in structural (Chiang et al., 2009) and functional brain networks during the resting-state (van den Heuvel et al., 2009). Moreover, because functional brain activity during cognitive tasks was recently found to be heritable (Koten et al., 2009), genes for structural brain plasticity and intellectual ability may also be relevant for brain function while performing cognitive tasks.

    This is a classic twin study, examining the additive genetic variance of the change in cortical thickness measures in individuals sampled five years apart. As in almost all fMRI studies, the sample size is relatively small. But in comparison to previous studies that showed the relationship between psychometric test outcomes and the volumes of particular cortical areas, this one is much more functionally directed, looking at the change in cortical thickness across time.

    References

    1. Brans RGH, Kahn RS, Schnack HG, G van Baal CM, Posthuma D, van Haren NEM, Lepage C, Lerch JP, D Collins L, Evans AC, et al. Brain plasticity and intellectual ability are influenced by shared genes. J Neurosci. 2010;30(16):5519-24.
    Tags: 
    brain function
    heritability
    cognition
    psychology
    behavior genetics
    brain

  • Brains in a haystack

    Tue, 2013-04-30 09:45 -- John Hawks

    An essay by Gary Marcus, in the new online science magazine, Nautilus: "Where uniqueness lies".

    In short, humans may live very differently than chimpanzees, but the structural plans of our biology necessarily can represent only modest tinkerings to the genetic material that we inherited from our last common ancestors. Language, regardless of how it is instantiated in our brain, represents a comparatively tiny cognitive enhancement relative to the mental machinery we inherited from our last common ancestor. The same is true for the underlying biology of each of our cognitive innovations.

    If it seems like scientists trying to find the basis of human uniqueness in the brain are looking for a neural needle in a haystack, it’s because they are. Whatever makes us different is built on the bedrock of a billion years of common ancestry.

    A lot of what's interesting about humans is because we reuse the ancient systems of our brains in new ways. Technology and culture both help us to exploit systems shared much more broadly among animals. This greatly complicates our attempts to show what is really different about the biology of the human lineage, because shallow differences based on recent behavioral innovations abound.

    Tags: 
    brain
    brain evolution
    brain function
    language evolution

  • Thinking simply

    Mon, 2013-03-04 13:23 -- John Hawks

    Vaughan Bell has a nice piece in the Guardian on folk psychology -- how ordinary people tend to think about their own thinking: "Our brains, and how they're not as simple as we think". This is a very important concept in the study of the evolution of human cognition, because how we think about our brains today may have little to do with the reasons why they changed over time.

    For example, a great deal of psychology research has shown that we tend not to have a good insight into why we make certain choices. In one of the many studies in the area, Lars Hall and colleagues gave people a survey about their moral beliefs but used sleight of hand to change the choices they had originally made. When asked to justify the beliefs they hadn't endorsed, more than two-thirds of people didn't notice the switch and happily gave reasons for why they supported the opposite of their original position. Folk psychology tells us that we can accurately explain our actions and, consequently, many people think that these well-validated psychological effects never apply to them or simply don't exist. Suggesting that someone may not fully know their own actions and that their post-event justifications might be improvised simply won't wash in everyday conversation.

    This is a phenomenon where psychology affects how we do scientific reasoning. I was doing this with my graduate students this morning -- taking the opposite pattern of data and explaining it as a function of the same evolutionary hypothesis. It's all too easy to justify post hoc a pattern by explaining it in terms of well-understood assumptions.

    Tags: 
    brain function
    psychology
    brain evolution

  • Micro-RNA 941

    Sun, 2012-11-25 19:39 -- John Hawks

    John Timmer covers the story of miR-941, a micro-RNA that may influence the expression of genes in human brains, and which appears to have taken on a novel role in our lineage compared to other primates:

    Looking at the region in the human genome that contains miR-941 showed it's an area with a series of repeats of the same sequence, arranged in tandem. Chimps and macaques have similar sequences, but the duplications aren't arranged in a way that allows the production of a hairpin structure. Somewhere after we split off from chimps 6 million years ago, a rearrangement in the area (an event that's common in areas with duplicated sequences) created the human form of miR-941. It was already in place a million years ago, when the Denisovan population branched off.

    But the rearrangements didn't end there, as there have been a series of duplications that created as many as 11 extra copies of miR-941 (the numbers vary in different populations, but average is about six or seven copies in most). The extra copies should help ensure it's expressed at higher levels than it would be otherwise.

    The research was carried out by Hai Yang Hu and colleagues [1] in an open access paper ("Evolution of the human-specific microRNA miR-941". It deserves a bit more attention than I can give it at the moment, as it is one of a series of recent papers demonstrating human-specific duplications that affect gene expression. It is one of the first cases in which RNA structure and function have been investigated in an ancient genome. The number of copies of miR-941 varies substantially both within and among human populations.

    This passage from the paper is provocative:

    Humans display both increased longevity and increased occurrence of certain forms of cancer compared with both chimpanzees and macaques39. It is, therefore, appealing to speculate that emergence of miR-941 enhanced the maintenance of adult stem cell populations, thus supporting longer human lifespan, but rendering human cells more prone to malignant transformation. The role of miR-941 in the regulation of insulin signaling adds support to this notion. The insulin-signaling pathway was consistently implicated in lifespan regulation in many species, including humans. Notably, experimentally verified targets of miR-941 within this pathway include genes directly shown to be involved in lifespan extension in model organisms: IRS1, PPARGC1A and FOXO140 (ref. 40). Furthermore, FOXO1 was linked to extended human longevity.

    Still, I am skeptical of the idea that this molecule had a strong effect on the human phenotype. The greater the network of genes influenced by this micro-RNA, the less likely a massive up-regulation or down-regulation will have a simple phenotypic effect. Most genes that were duplicated or deleted during our evolutionary history probably were free to change because of a lack of fitness effect. Maybe this micro-RNA is an exception -- with a new effect on the human lineage, and extensive variation in copy number within humans. But it seems more likely to me that the variation in miR-941 dosage leads to a minor phenotypic effect across the network of affected genes, not a major directional effect.

    References

    1. Hu H, He L, Fominykh K, Yan Z, Guo S, Zhang X, Taylor MS, Tang L, Li J, Liu J, et al. Evolution of the human-specific microRNA miR-941. Nat Commun. 2012;3:1145.
    Tags: 
    brain
    brain function
    gene regulation
    gene expression
    micro-RNA

  • Einstein and Taung: two brains collide

    Wed, 2012-11-21 13:03 -- John Hawks

    Dean Falk has a new article in the journal Brain, in which she and collaborators uncover the details within historical photographs of Albert Einstein's brain [1]. The brain was sectioned after Einstein's death and samples have been studied by several researchers over the years, including Falk. The research was recently covered by the TV program NOVA ScienceNOW, which is being rebroadcast this week.

    I wanted to point to the article by Falk and colleagues because it includes a brief discussion of the lunate sulcus -- one of the most persistently pernicious topics in paleoneurology.

    The terminology for sulci of the human occipital lobe, in particular, has been influenced by an erroneous historical claim that human brains manifest a so-called lunate sulcus that is homologous to the Affenspalte (‘ape sulcus’) that forms the rostral boundary of the primary visual cortex [Brodmann area (BA) 17] on the lateral surface of the brain in apes and some monkeys (Smith, 1904, 1925). However, BA 17 of humans may, or may not, extend onto the external surface of the occipital lobe. When it does, its rostral border is located far posterior to the normal position for ape brains and is rarely bordered by a sulcus (Allen et al., 2006). Despite the fact that recent gross morphological and cytoarchitectural studies refute the assertion that humans have a lunate sulcus that is homologous with the Affenspalte (Allen et al., 2006; see Falk, 2012 for a discussion of the evolutionary implications), contemporary authors continue to use a variety of criteria to identify different sulci as so-called lunate sulci in humans (Duvernoy et al., 1999; Iaria and Petrides, 2007). The classical terminology used by Connolly (1950) for the occipital lobe is also grounded on the mistaken notion that humans have lunate sulci that are homologous to those of apes. For example, Connolly (1950) identifies a prelunate sulcus, which we identify with its modern name of the lateral occipital sulcus (Table 1). For these reasons, we do not recognize a lunate sulcus in Einstein’s brain.

    The long-running argument over the possible location of the lunate sulcus in the endocast of the Taung fossil hominin was a heated debate for more than 20 years in paleoanthropology. For Falk, the end of the story is that the sulcal patterns in human and other primate brains in this region are not homologous -- making it problematic to recognize either in the fossil endocasts of early hominins. I'm sure it isn't over, but I find it inspiring to see the evolutionary record make an appearance in this consideration of the brain of a very famous scientist.

    References

    1. Falk D, Lepore FE, Noe A. The cerebral cortex of Albert Einstein: a description and preliminary analysis of unpublished photographs. Brain. 2012.
    Tags: 
    Taung
    brain
    brain function
    Albert Einstein

  • Keep still for your brain picture

    Thu, 2012-11-01 22:52 -- John Hawks

    Ben Deen and Kevin Pelphrey in Nature: "Perspective: Brain scans need a rethink" .

    Recent studies, however, have found that when a person moves their head while undergoing functional magnetic resonance imaging (fMRI) -- a method that maps how different neuroanatomical structures of the brain interact in real time, its functional connectivity -- it looks like the neural activity observed in autism. That's a sobering discovery: it means that a major source of evidence for a leading hypothesis on autism, and one that several research teams have pursued for years, may arise from an artifact.

    Remember the "dead salmon" study, in which inert tissue placed in the scanner produced results? The statistical methods underlying comparisons of fMRI between cases and controls rely on averaging a multidimensional space across many individuals. A bias doesn't have to be very large to lead to a significant difference between groups:

    [A]s one of the new studies showed, even a difference as small as 0.004 millimetre in average head motion across groups of patients can lead to significant differences in correlation strengths.

    That's four microns! That is, of course, an average across a large sample, each child has his or her own motion. Imagine trying to get them to average out so that the average motto is precisely equal across a few dozen individuals. And then, as the article discusses ways that might correct for linear biases, you are still left with the possibility that head motion has a nonlinear effect on result, so that the bias survives your attempt to correct for it.

    How remarkable, the very complex approaches necessary to deal with a relatively simple phenomenon.

    Tags: 
    fMRI
    brain
    autism
    brain function

  • Building bigger dolphin brains

    Tue, 2012-09-11 18:14 -- John Hawks

    Ed Yong reports on a new study demonstrating a history of positive selection on the gene ASPM in cetaceans. Bruce Lahn's group previously showed that this gene has been positively selected in primate lineages, including recent humans: "Same gene involved in bigger brains of dolphins and primates".

    Now, Shixia Xu from Nanjing Normal University has found that a gene called ASPM played an important role in the evolution of cetacean brains. The gene shows clear signatures of adaptive change at two points in history, when the brains of some cetaceans ballooned in size. But ASPM has also been linked to the evolution of bigger brains in another branch of the mammal family tree – ours. It went through similar bursts of accelerated evolution in the great apes, and especially in our own ancestors after they split away from chimpanzees.

    It seems likely that both primates and cetaceans—the intellectual heavyweights of the animal world—both owe our bulging brains to changes in the same gene. “It’s a significant result,” says Michael McGowen, who studies the genetic evolution of whales at Wayne State University. “The work on ASPM shows clear evidence of adaptive evolution, and adds to the growing evidence of convergence between primates and cetaceans from a molecular perspective.”

    Molecular mechanisms of convergence have proved to be very common in the evolution of different mammalian orders. Mechanistically, evolution seems to select the same pathways when the same general functional requirements are adaptive. It is interesting that cetaceans and primates have broadly similar social and communication constraints, but very different ecological constraints in other respects, such as diet, thermoregulation navigation and home range.

    Tags: 
    brain
    convergence
    brain function
    development
    non-primate
    positive selection

  • Mouse brain mapping

    Tue, 2012-06-05 12:39 -- John Hawks

    This merits some attention: "Neuroscientists reach major milestone in whole-brain circuit mapping project".

    The data consist of gigapixel images (each close to 1 billion pixels) of whole-brain sections that can be zoomed to show individual neurons and their processes, providing a “virtual microscope.” The images are integrated with other data sources from the web, and are being made fully accessible to neuroscientists as well as interested members of the general public (http://mouse.brainarchitecture.org). The data are being released pre-publication in the spirit of open science initiatives that have become familiar in digital astronomy (e.g., Sloan Digital Sky Survey) but are not yet as widespread in neurobiology.

    It's a press release from Cold Spring Harbor Labs, giving some background on the project and its use of a "shotgun" mapping approach for neuronal connections. For me, the most exciting aspect of the open access data is the potential of running analyses across different datasets, such as the gene expression element of the Allen Brain Atlas. Drawing conclusions may require a sample more representative of different stages of ontogeny than is now available, but these will be the next logical step -- understanding brain structure really requires us to understand how it develops.

    Tags: 
    brain
    open access
    data access
    open science
    brain function

  • Neuron theory

    Wed, 2012-05-16 20:49 -- John Hawks

    Ferris Jabr has begun a series called "Know your neurons", which will be a tour of the types of neurons. The first installment ("Know Your Neurons: The Discovery and Naming of the Neuron") covers the science that established the existence of neurons, in the late nineteenth century, when Santiago Ramón y Cajal used the staining technique developed by Camillo Golgi to visualize and draw detailed pictures of the microscopic cells. At issue was whether all the nerve fibers ultimately merged into a connected network, or reticulum:

    Golgi’s “black reaction,” combined with the painstaking work of Karl Deiters and others, clearly distinguished two kinds of projections from cell bodies in nervous tissue: a long slender cable that did not seem to branch much and a cluster of shorter branching fibers. Even though Golgi saw that one cell body’s branching fibers did not fuse with another’s, he did not reject Gerlach’s idea of the reticulum—instead, he decided that the long slender cables probably connected to form one continuous network.

    Ramón y Cajal showed that the fibers did not merge into a continuous reticulum, the essential data supporting the neuron theory. I'll look forward to more in the series.

    Tags: 
    brain
    brain function
    history of psychology
    anatomy

  • Culture in the brain

    Sun, 2012-04-29 17:47 -- John Hawks

    The Guardian has a dialogue between David Eagleman and Raymond Tallis in which the two authors debate the importance of culture as a constraint on behavior. This paragraph is from Eagleman:

    Nonetheless, culture does leave its signature in the circuitry of the individual brain. If you were to examine an acorn by itself, it could tell you a great deal about its surroundings – from moisture to microbes to the sunlight conditions of the larger forest. By analogy, an individual brain reflects its culture. Our opinions on normality, custom, dress codes and local superstitions are absorbed into our neural circuitry from the social forest around us. To a surprising extent, one can glimpse a culture by studying a brain. Moral attitudes toward cows, pigs, crosses and burkas can be read from the physiological responses of brains in different cultures.

    I've just returned from the Consilience Conference organized by Joseph Carroll, a founder of the Darwinian school of literary analysis. I had some very interesting conversations about the way that culture may have come to influence the brains of ancient humans, and how gene-culture coevolution may have influenced a wide array of behavioral and cognitive traits of present humans. Over the next few weeks I'll be pointing to current research by some of the participants and some other useful lines of inquiry.

    Meanwhile, I have some catching-up to do here. Several recent papers have important consequences for how we think about the variation and population movements of the last 10,000 years. We can now dispense with 100-year-old speculation about migrations and movements because we have direct data from ancient populations. Razib Khan comments on last week's papers about the Neolithic population of Scandinavia ("Facing the ocean").

    Tags: 
    culture
    consilience
    brain function

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Neandertals

For years, I've worked on their bones. Now I'm working on their genes. Read more about the science studying these ancient people.

Denisova

From a finger bone of an ancient human came the record of a completely unexpected population. My lab is working on the science of the Denisova genome.

Acceleration

The advent of agriculture caused natural selection to speed up greatly in humans. We're uncovering some of the ways that populations have rapidly changed during the last 10,000 years.

Malapa

Just outside Johannesburg, the Malapa site is producing some of the most exciting finds in human evolution. This site is the headquarters of the Malapa Soft Tissue Project.