A Piazolla Tango

I'm working up the videos of the Sunday musical at Twin Valley mentioned in Monday's post. Here is Anton Piazolla's Invierno Porteno.

Why are musical chords cheerful or melancholy?

In the current issue of American Scientist, Cook and Hayashi offer a fascinating article on the psychoacoustics of harmony perception (PDF here). Major and minor chords entered Western music during the Renaissance, when two-part harmonies were supplanted by three-tone chords. The authors argue that human responses to these chords have a biological basis, rather than being learned (the opinion of most musical theorists). Their acoustical model explains harmony in terms of the relative positions of the three notes in a triad and how their complex higher harmonics, or upper partials, interact with them. Those of you interested in science and music should check out the special Nature series of essays on this topic.

Jean-Philippe Rameau, a French composer and author, wrote his Treatise on Harmony in 1722, one of the first and most influential studies of harmony in Western music. His book noted the profound emotional difference between major and minor chords: “The major mode is suitable for songs of mirth and rejoicing,” he wrote, while the minor mode was suitable for “plaints, and mournful songs.”

From their conclusions, after the analysis section of the paper:

Now that we have a model of how listeners identify a chord as major or minor, we may take the final step and speculate as to why the acoustical valence carries an emotional valence as well. We contend that the emotional symbolism of major and minor chords has a biological basis. Across the animal kingdom, vocalizations with a descending pitch are used to signal social strength, aggression or dominance. Similarly, vocalizations with a rising pitch connote social weakness, defeat or submission. Of course, animals convey these messages in other ways as well, with facial expressions, body posture and so on—but all else being equal, changes in the fundamental frequency of the voice have intrinsic meaning.

This same frequency code has been absorbed, though attenuated, in human speech patterns: A rising inflection is commonly used to denote questions, politeness or deference, whereas a falling inflection signals commands, statements or dominance. How might this translate to a musical context? If we start with a tense, ambiguous chord—for example, the augmented chord containing two 4-semitone intervals— and decrease any one of the three fundamentals by one semitone, the chord will resolve into a major key. It will then have a 5–4, 3–5, or 4–3 semitone structure. Conversely, if we resolve the ambiguous chord by raising any one of the three fundamentals by a semitone, we will obtain a minor chord. The universal emotional response to these chords stems, we believe, directly from an instinctive, preverbal understanding of the frequency code in nature. One of us (Cook) has explored this in more detail (see the bibliography).

Individual tastes and musical styles vary widely. In the West, music has changed over the centuries from styles that employed predominantly the resolved major and minor chords to styles that include more and more dissonant intervals and unresolved chords. Inevitably, some composers have taken this historical trend to its logical extreme, and produced music that fanatically avoids all indications of consonance or harmonic resolution. Such surprisingly colorless “chromatic” music is intellectually interesting, but notably lacking in the ebb and flow of tension and resolution that most popular music employs, and that most listeners crave. Whatever one’s own personal preferences may be for dissonance and unresolved harmonies, some kind of balance between consonance and dissonance, and between harmonic tension and resolution, seems to be essential—genre by genre, and individual by individual—to assure the emotional ups and downs that make music satisfying.

Making Memories, Again

Lasry et al. , in a letter to Science, offer an interesting interpretation of work reported in a previous post, showing that testing of already learned words enhances long-term recall when assessed 1 week later, whereas repeated studying had no beneficial effects. Here are their comments:

In their Report, "The critical importance of retrieval for learning" (15 February, p. 966), J. D. Karpicke and H. L. Roediger III show that delayed recall is optimized, not with repeated studying sessions, but with repeated testing sessions. The authors conclude that "retrieval during tests produces more learning than additional encoding."

We suggest a complementary interpretation. Classically, encoded information becomes consolidated and can later be retrieved. The tacit assumption is that retrieval of a consolidated memory is a read-only mechanism, which does not affect the memory. Recent studies have shown that elicited memories are in fact labile and become reconsolidated following each retrieval. Labile elicited memories require de novo protein synthesis to be maintained, similar to that of newly acquired memories. Neurobiological differences between consolidation and reconsolidation processes were recently described in Science. On the psychological level, reconsolidation is useful for explaining false and biased memories. Reconsolidation also leads to a memory model called multiple-trace theory: Every time a memory is reactivated, a new version of it is reconsolidated, leaving multiple traces of the same memory.

With respect to Karpicke and Roediger's study, we hypothesize that repeated testing (retrieval) should lead to multiple traces (due to repeated reconsolidation), which facilitate recall. Reinterpreting Karpicke and Roediger's results from a multiple-trace reconsolidation perspective supports this hypothesis and provides a new framework for explaining the effectiveness of frequent in-class assessments in pedagogies such as Peer Instruction.

The Toronto Village

A vacation picture...sidewalk cafe lunch at Maitland and Church streets.

Discontinuity between human and nonhuman minds?

In a recent issue of Brain and Behavioral Science (BBS) Penn, Holyoak and Povinelli argue for a profound difference in kind, not degree, between human and animal minds. Their suggestions elicit mainly vigorous opposition as well as some support from an array of commentators. Several of the commentators point out evidence for flexible relational capabilities within a physical symbol system exhibited by dolphins and birds. As I read through the debate and its mind-numbing detail I give up on trying to convey a succinct summary, but here is their abstract. (You might compare this with the work of Hauser et al, that I mentioned in a previous post.):

Over the last quarter century, the dominant tendency in comparative cognitive psychology has been to emphasize the similarities between human and nonhuman minds and to downplay the differences as “one of degree and not of kind” (Darwin 1871). In the present target article, we argue that Darwin was mistaken: the profound biological continuity between human and nonhuman animals masks an equally profound discontinuity between human and nonhuman minds. To wit, there is a significant discontinuity in the degree to which human and nonhuman animals are able to approximate the higher-order, systematic, relational capabilities of a physical symbol system (PSS) (Newell 1980). We show that this symbolic-relational discontinuity pervades nearly every domain of cognition and runs much deeper than even the spectacular scaffolding provided by language or culture alone can explain. We propose a representational-level specification as to where human and nonhuman animals' abilities to approximate a PSS are similar and where they differ. We conclude by suggesting that recent symbolic-connectionist models of cognition shed new light on the mechanisms that underlie the gap between human and nonhuman minds.

Most popular consciousness papers...

For April 2008, from the ASSC archive:

1. Destrebecqz, Arnaud and Peigneux, Philippe (2005) Methods for studying
unconscious learning. In: Progress in Brain Research. Elsevier, pp. 69-80.
1968 downloads from 26 countries. http://eprints.assc.caltech.edu/170/
2. Koriat, A. (2006) Metacognition and Consciousness. In: Cambridge handbook
of consciousness. Cambridge University Press, New York, USA. 1799 downloads
from 29 countries. http://eprints.assc.caltech.edu/175/
3. Sagiv, Noam and Ward, Jamie (2006) Crossmodal interactions: lessons from
synesthesia. In: Visual Perception, Part 2 - Fundamentals of Awareness:
Multi-Sensory Integration and High-Order Perception. Progress in Brain
Research, Volume 155. Elsevier, pp. 259-271. 1089 downloads from 18
countries. http://eprints.assc.caltech.edu/224/
4. Chalmers, David J. (2004) How can we construct a science of
consciousness? In: The Cognitive Neurosciences III. MIT Press, Cambridge,
MA. 1009 downloads from 9 countries. http://eprints.assc.caltech.edu/28/
5. Dehaene, Stanislas and Changeux, Jean-Pierre and Naccache, Lionel and
Sackur, Jérôme and Sergent, Claire (2006) Conscious, preconscious, and
subliminal processing: a testable taxonomy. Trends in Cognitive Science, 10
(5). pp. 204-211. 900 downloads from 13 countries.
http://eprints.assc.caltech.edu/20/

MindBlog on the road

This week, I'm starting a seven day vacation in Toronto with my partner Len. It is our 19th anniversary. The mindblog posts that appear will be using Blogger's neat new feature that permits the specification of a date in the future for a prepared posting to actually appear on the website.

Yesterday, Sunday, June 29, we hosted a social/musical at our home on Twin Valley road in the Town of Middleton, Wisconsin. Len does the food and I do the music. Over the next period of time, I will post here and on YouTube the music we played. Here is the invitation to the event, followed by a photo taken just before the music, and one during it:

Please join Deric and Len at the Twin Valley schoolhouse sunday afternoon, June 29, from 3 to 6 p.m. for conversation, wine, and Len's appetizers & h'orderves. If you like, bring a wine or other liquid to share.

Music at 4:00 p.m. (~45 min duration)
Two tangoes by Astor Piazzolla
Four movements from the two Mendelssohn piano trios.

Deric (piano), Daphne Tsao (violin) and Sonny Enslen (Cello)

Young and old brains differ in encoding positive information

A number of studies have revealed a "positivity shift" with aging; whereas young adults are more likely to remember negative information than positive or neutral information, older adults may be at least as likely (or even more likely) to remember positive information compared with negative information. It has been proposed that this "positivity shift" may occur because older adults put more emphasis on emotion regulation goals than do young adults, with older adults having a greater motivation to derive emotional meaning from life and to maintain positive affect. In the service of these goals, older adults may focus their attention on things that will elicit pleasant feelings and may process positive information in a more self-referential fashion. Thus this work (slightly edited) from Kensinger and Schacter probing the issue is of interest:

Young and older adults are more likely to remember emotional information than neutral information. The authors performed a magnetic resonance imaging study examining the neural processes supporting young (ages 18–35) and older (ages 62–79) adults' successful encoding of positive, negative, and neutral objects (e.g., a sundae, a grenade, a canoe). The results revealed general preservation of the emotional memory network across the age groups. Both groups recruited the amygdala and the orbito-frontal cortex during the successful encoding of positive and negative information. Both ages also showed valence-specific recruitment: right fusiform activity was greatest during the successful encoding of negative information, whereas left prefrontal and temporal activity was greatest during the successful encoding of positive information. These valence-specific processes are consistent with behavioral evidence that negative information is processed with perceptual detail, whereas positive information is processed at a conceptual or schematic level. The only age differences in emotional memory emerged during the successful encoding of positive items: Older adults showed more activity in the medial prefrontal cortex and along the cingulate gyrus than young adults. Because these regions often are associated with self-referential processing, these results suggest that older adults' mnemonic boost for positive information may stem from an increased tendency to process this information in relation to themselves.

Figure - Regions that showed a stronger correspondence to subsequent general recognition (i.e., subsequently recognized > subsequently forgotten) for the positive items than for the neutral or negative items. Red regions showed this correspondence for both young and older adults. Green regions showed this correspondence for the older adults but not for the young adults. No regions showed this correspondence for the young adults but not the older adults, consistent with the behavioral finding that only older adults showed mnemonic enhancement for the positive items.

ScienceHack - monkey brain moving robotic arm

I stumbled across this site with interesting science videos from a number of areas (biology, psychology, robotics, etc.). They are mainly at a superficial 'gee whiz' level, but quite engaging. Here is the Monkey moving a robotic arm. This is work from the Pittsburgh group, described in Nature, which promises to lead to effective therapy for human patients paralyzed by strokes, spinal-cord injuries and degenerative neuromuscular disease.

Best visual illusion of the year

Check out the Best Visual Illusion of the Year contest.....

The brain's default network - a review

Buckner et al. offer a review of work what our brains are doing when we are not focused on the external environment. This is an open access article in a new annual volume, "The Year in Cognitive Neuroscience," being initiated by the New York Academy of Sciences. (Table of contents of this first issue is here. ) I am passing on the abstract and one central figure and legend from the article:

Thirty years of brain imaging research has converged to define the brain's default network—a novel and only recently appreciated brain system that participates in internal modes of cognition. Here we synthesize past observations to provide strong evidence that the default network is a specific, anatomically defined brain system preferentially active when individuals are not focused on the external environment. Analysis of connectional anatomy in the monkey supports the presence of an interconnected brain system. Providing insight into function, the default network is active when individuals are engaged in internally focused tasks including autobiographical memory retrieval, envisioning the future, and conceiving the perspectives of others. Probing the functional anatomy of the network in detail reveals that it is best understood as multiple interacting subsystems. The medial temporal lobe subsystem provides information from prior experiences in the form of memories and associations that are the building blocks of mental simulation. The medial prefrontal subsystem facilitates the flexible use of this information during the construction of self-relevant mental simulations. These two subsystems converge on important nodes of integration including the posterior cingulate cortex. The implications of these functional and anatomical observations are discussed in relation to possible adaptive roles of the default network for using past experiences to plan for the future, navigate social interactions, and maximize the utility of moments when we are not otherwise engaged by the external world. We conclude by discussing the relevance of the default network for understanding mental disorders including autism, schizophrenia, and Alzheimer's disease.


The default network is activated by diverse forms of tasks that require mental simulation of alternative perspectives or imagined scenes. Four such examples from the literature illustrate the generality. (A) Autobiographical memory: subjects recount a specific, past event from memory. (B) Envisioning the future: cued with an item (e.g., dress), subjects imagine a specific future event involving that item. (C) Theory of mind: subjects answer questions that require them to conceive of the perspective (belief) of another person. (D) Moral decision making: subjects decide upon a personal moral dilemma. Note that all the studies activate strongly PCC/Rsp and dMPFC. Active regions also include those close to IPL and LTC, although further research will be required to determine the exact degree of anatomic overlap. It seems likely that these maps represent multiple, interacting subsystems.

More from the great curmudgeon...

To follow up my June 15 post, here is an Esquire Magazine "What I have learned" offering from Gore Vidal that my colleague Jim Steakley alterted me to. A few selections:

God has been expelled. I think he knows when he’s on a losing wicket.
I went into a line of work in which jealousy is the principle emotion between practitioners. I don’t think I ever suffered from it, because there was no need. But I was aware of it in others, and I found it a regrettable fault.
There was more of a flow to my output of writing in the past, certainly. Having no contemporaries left means you cannot say, “Well, so-and-so will like this,” which you do when you’re younger. You realize there is no so-and-so anymore. You are your own so-and-so. There is a bleak side to it.
You hear all this whining going on, “Where are our great writers?” The thing I might feel doleful about is: Where are the readers?
Some of my father’s fellow West Pointers once asked him why I turned out so well, his secret in raising me. And he said, “I never gave him any advice, and he never asked for any.” We agreed on nothing, but we never quarreled once.
Every fool I knew had gone to university. I didn’t think it necessary. I’d seen some of the results, you know?
When I was young, I was bored shitless with being desired by others. I don’t look in the mirror anymore.
I lived with Howard for fifty years, but what we had was certainly not romantic love, not passionate love. And it certainly was nonsexual. Try and explain that to the fags.
Nonprofit status is what created the Bible Belt. The tax code brought religion back to this country.
When she was running for the Senate, Hillary’s psephologists discovered that the one group that really hated her was white, middle-aged men of property. She got the whole thing immediately -- I heard she said, “I remind them of their first wife.”
“You got to meet everyone -- Jackie Kennedy, William Burroughs.” People always put that sentence the wrong way around. I mean, why not put it the true way, that these people got to meet me, and wanted to? Otherwise it sounds like I spent my life hustling around trying to meet people: “Oh, look, there’s the governor.“
For a writer, memory is everything. But then you have to test it; how good is it, really? Whether it’s wrong or not, I’m beyond caring. It is what it is. As Norman Mailer would say, “It’s existential.” He went to his grave without knowing what that word meant.
We’re the most captive nation of slaves that ever came along. The moral timidity of the average American is quite noticeable. Everybody’s afraid to be thought in any way different from everyone else.
Get rid of religion. It’ll do you no good.
As the Greeks sensibly believed, should you get to know yourself, you will have penetrated as much of the human mystery as anyone need ever know.
I wasn’t like everyone, you know. What everyone did, I was sure not to do.

A memorial for our president...

I simply can't resist passing this on - an article on a proposal, naturally hatched in a bar, to change the name of a prize-winning water treatment plant on the shoreline of San Francisco to the George W. Bush Sewage Plant. This is a memorial you can contribute to from your bathroom. The proposal has enough signatures to qualify it as an initiative on the November ballot.

Retaliation for unfairness - depends on serotonin

Nature highlights an article by Crockett et al. showing that serotonin modulates our reaction to unfairness. The experimenters:

...temporarily lowered serotonin (5-HT) levels in 20 volunteers and had them play the part of responder in the 'ultimatum game'. The responder can either accept the division of a sum of money offered by the game's proposer, in which case they both get their share, or reject it and deprive both players of the amounts proposed.

Although mood, fairness judgments, basic reward processing, or response inhibition, remained unchanged when players' serotonin levels were lowered, they were more likely to reject unfair and very unfair offers, defined as 30% and 20% of the stake, respectively.

Trust in oxytocin.

I pass on a brief news review by Leonie Welberg from Nature Neuroscience:

The neuropeptide oxytocin is released during childbirth, suckling, touch and orgasm, suggesting that it might have a 'pro-social' function. This idea was strengthened by a recent study in Nature (see my 2/13/06 post, or enter oxytocin inthe search box in the left column of this blog), which showed that an oxytocin nasal spray caused people playing a 'trust' game to retain their trust in a stranger who was looking after their money, even though this trust was violated on many occasions. At the same time, the oxytocin spray decreased activity in the amygdala and the caudate nucleus, brain areas that are involved in the regulation of fear and decision making, respectively.

"We now know ... what exactly is going on in the brain when oxytocin increases trust," says lead researcher Thomas Baumgartner of the University of Zürich, Switzerland. "It seems to diminish our fears." (BBC News, 21 May 2008.) As humans are typically averse to taking social risks, "...a little bit of oxytocin may facilitate carrying on relationships with others," according to Mauricio Delgado, a neuroscientist at Rutgers University in Newark, New Jersey. (ScienceNOW, 21 May 2008.)

How people in real-life situations develop and retain trust in others is another question, however. "They certainly don't do it by spraying stuff up each other's noses," says Paul Zak of the Center for Neuroeconomics Studies at Claremont Graduate University in California. (Science News, 21 May 2008.)

Nevertheless, the findings have implications for understanding mental disorders in which deficits in social behaviour are observed and "...could provide a bridge for potential clinical applications," thinks Delgado (BBC News). An oxytocin spray might help people with a social phobia or autism. "Autistic people also have a fear of social situations and have problems interacting, so it is very likely that oxytocin could help," says Baumgartner. "This hormone seems to play a very specific role in social situations so might be able to improve autism." (BBC News.)

Are the religionists lightening up?

The graphic is from Banerjee's NYTimes summary of the Pew Forum report. The good news is that while the vast majority of Americans (many more than Western Europeans) believe in "God" and eternal life, more accept that there are varieties of Pearly Gates, and how you might get to them. Better yet, fewer get anthropomorphic about it, citing 'an impersonal force' as closer to their idea of God, and thus might be more friendly to the sort of emergence models mentioned in the previous post.

Can 'emergence' put spirituality back into nature?

The anti-reductionist view of emergence undergoes cycles of popularity as a philosophical topic. Valerie Hardcastle gives a rather critical review (in Jour. Consciousness Studies, Vol. 14, No. 11, pp.119-122) of a recent collection "The Re-Emergence of Emergence - The Emergentist Hypothesis from Science to Religion" edited by Clayton and Davies (Oxford Univ. Press, 2006). This emergentism is 'feel good' stuff. I think most of us get a bit frightened and a bit dried and shriveled up at the implications of strong reductionism in which all the explanatory arrows point down. Reversing the reductionist’s causal arrow with a comprehensive theory of emergence and self-organization that breaks no laws of physics and yet cannot be explained by them is a laudable project, but as Hardcastle wryly notes, one that continues to fail the "where's the beef" test.

Michael Shermer offers a very appealing gloss in his "Skeptic" column in the Scientific American, with the title: Sacred Science - Can emergence break the spell of reductionism and put spirituality back into nature? He specifically reviews a new book by Stuart Kauffman, Reinventing the Sacred (Basic Books, 2008). Denis Noble also reviews Kauffman's book in Science Magazine. Here are some clips from Shermer's column:
Kaufman:

...reverses the reductionist’s causal arrow with a comprehensive theory of emergence and self-organization that Kaufman says “breaks no laws of physics” and yet cannot be explained by them. God “is our chosen name for the ceaseless creativity in the natural universe, biosphere and human cultures.” In Kauffman’s emergent universe, reductionism is not wrong so much as incomplete. It has done much of the heavy lifting in the history of science, but reductionism cannot explain a host of as yet unsolved mysteries, such as the origin of life, the biosphere, consciousness, evolution, ethics and economics... How would a reductionist explain the biosphere, for example? “One approach would be, following Newton, to write down the equations for the evolution of the biosphere and solve them. This cannot be done,” Kauffman avers. “We cannot say ahead of time what novel functionalities will arise in the biosphere. Thus we do not know what variables—lungs, wings, etc.—to put into our equations. The Newtonian scientific framework where we can prestate the variables, the laws among the variables, and the initial and boundary conditions, and then compute the forward behavior of the system, cannot help us predict future states of the biosphere.”... This problem is not merely an epistemological matter of computing power, Kauffman cautions; it is an ontological problem of different causes at different levels. Something wholly new emerges at these higher levels of complexity.

Similar ontological differences exist in the self-organized emergence of consciousness, morality and the economy...economics and evolution are complex adaptive systems that learn and grow as they evolve from simple to complex...they are autocatalytic, containing self-driving feedback loops...such phenomena “cannot be deduced from physics, have causal powers of their own, and therefore are emergent real entities in the universe.” This creative process of emergence, Kauffman contends, “is so stunning, so overwhelming, so worthy of awe, gratitude and respect, that it is God enough for many of us. God, a fully natural God, is the very creativity in the universe.”

Shermer ends noting that Kaufman's:

God 2.0 is a deity worthy of worship. But I am skeptical that it will displace God 1.0, Yahweh, whose Bronze Age program has been running for 6,000 years on the software of our brains and culture.

Brain exercise/fitness links...

Tom Hanson, the Editor of OpenEducation.net, asks me to pass on these two separate posts on brain exercise/fitness, noting some firms that I have mentioned previously, and so I do this as a professional courtesy.

Strengths and Limits of fMRI studies on the brain

Nikos Logothetis offers a long and detailed discussion of what we can and cannot learn from brain imaging approaches. I'm giving a few clips from his discussion:

fMRI is not and will never be a mind reader, as some of the proponents of decoding-based methods suggest, nor is it a worthless and non-informative 'neophrenology' that is condemned to fail, as has been occasionally argued.

The principal advantages of fMRI lie in its noninvasive nature, ever-increasing availability, relatively high spatiotemporal resolution, and its capacity to demonstrate the entire network of brain areas engaged when subjects undertake particular tasks. One disadvantage is that, like all haemodynamic-based modalities, it measures a surrogate signal whose spatial specificity and temporal response are subject to both physical and biological constraints. A more important shortcoming is that this surrogate signal reflects neuronal mass activity.


Figure - Two slices of GE-EPI demonstrating the high functional signal-to-noise ratio (SNR) of the images, but also the strong contribution of macrovessels. The yellow areas (indicated with the green arrows) are pia vessels, an example of which is shown in the inset scanning electron microscopy image (total width of inset, 2 mm). For the functional images red indicates low and yellow indicates high.

MRI may soon provide us with images of a fraction of a millimetre (for example, 300 x 300 m² with a couple of millimetres slice thickness or 500 x 500 x 500 m³ isotropic), which amount to voxel volumes of about two–three orders of magnitude smaller than those currently used in human imaging. With an increasing number of acquisition channels such resolution may ultimately be attained in whole-head imaging protocols, yielding unparalleled maps of distributed brain activity in great regional detail and with reasonable—a couple of seconds—temporal resolution. Would that be enough for using fMRI to understand brain function?

The answer obviously depends on the scientific question and the spatial scale at which this question could be addressed—"it makes no sense to read a newspaper with a microscope", as neuroanatomist Valentino Braitenberg once pointed out. To understand the functioning of the microcircuits in cortical columns or of the cell assemblies in the striosomes of basal ganglia, one must know a great deal about synapses, neurons and their interconnections. To understand the functioning of a distributed large-scale system, such as that underlying our memory or linguistic capacities, one must first know the architectural units that organize neural populations of similar properties, and the interconnections of such units. With 10¹⁰ neurons and 10¹⁴ connections in the cortex alone, attempting to study dynamic interactions between subsystems at the level of single neurons would probably make little sense, even if it were technically feasible. It is probably much more important to understand better the differential activity of functional subunits—whether subcortical nuclei, or cortical columns, blobs and laminae—and the instances of their joint or conditional activation. If so, whole-head imaging with a spatial resolution, say, of 0.7 0.7 mm² in slices of 1-mm thickness, and a sampling time of a couple of seconds, might prove optimal for the vast majority of questions in basic and clinical research. More so, because of the great sensitivity of the fMRI signal to neuromodulation. Neuromodulatory effects, such as those effected by arousal, attention, memory, and so on, are slow and have reduced spatiotemporal resolution and specificity.

Logothesis offers a concluding perspective.

The limitations of fMRI are not related to physics or poor engineering, and are unlikely to be resolved by increasing the sophistication and power of the scanners; they are instead due to the circuitry and functional organization of the brain, as well as to inappropriate experimental protocols that ignore this organization. The fMRI signal cannot easily differentiate between function-specific processing and neuromodulation, between bottom-up and top-down signals, and it may potentially confuse excitation and inhibition. The magnitude of the fMRI signal cannot be quantified to reflect accurately differences between brain regions, or between tasks within the same region. The origin of the latter problem is not due to our current inability to estimate accurately cerebral metabolic rate of oxygen (CMRO2) from the BOLD signal, but to the fact that haemodynamic responses are sensitive to the size of the activated population, which may change as the sparsity of neural representations varies spatially and temporally. In cortical regions in which stimulus- or task-related perceptual or cognitive capacities are sparsely represented (for example, instantiated in the activity of a very small number of neurons), volume transmission (see Supplementary Information)—which probably underlies the altered states of motivation, attention, learning and memory—may dominate haemodynamic responses and make it impossible to deduce the exact role of the area in the task at hand. Neuromodulation is also likely to affect the ultimate spatiotemporal resolution of the signal.

This having been said, and despite its shortcomings, fMRI is currently the best tool we have for gaining insights into brain function and formulating interesting and eventually testable hypotheses, even though the plausibility of these hypotheses critically depends on used magnetic resonance technology, experimental protocol, statistical analysis and insightful modelling. Theories on the brain's functional organization (not just modelling of data) will probably be the best strategy for optimizing all of the above. Hypotheses formulated on the basis of fMRI experiments are unlikely to be analytically tested with fMRI itself in terms of neural mechanisms, and this is unlikely to change any time in the near future.

Neuro-puffs and neuropundits...

Check out this debunking of neuroimaging research on things like political partisanship and superbowl commercials.