Brain activation that reflects perceptual choices.

Thielscher and Pessoa (PDF here) have examined brain activation that reflects perceptual choices using fMRI during a two-choice perceptual discrimation task of fearful versus disgusted faces. From their abstract:

...Our analyses revealed that reporting a neutral face as "fearful" was associated with activation in a broad network of brain regions that process emotionally arousing stimuli, whereas reporting a neutral face as "disgusted" was associated with activation in a focused set of sites that included the putamen and anterior insula...fluctuations in fMRI amplitude for an individual participant could be used to reliably predict the perceptual choice of individual trials for that subject. In addition to the investigation of choice, we also isolated the neural correlates of decision making per se by using reaction time as an index of decision processes. Overall, our findings revealed that brain responses dynamically shifted according to perceptual choices. In addition, the neural correlates of decision making involved at least the anterior cingulate cortex, middle frontal gyrus, and inferior frontal gyrus/insula, consistent with recent proposals that decisions may emerge from distributed processes.

A review of this work by Tobler and Kalenscher (PDF here) provides a useful summary graphic:

Figure 1. Top, Model of decision process. Bottom, Selected decision-related activations. Regions in orange predict whether a fearful or a disgusted face has been presented. Regions in blue predict whether the participant will choose "fearful" or "disgusted," and regions in yellow correlate with decision as operationalized by trial-to-trial changes in reaction time.

Searching MindBlog - keywords (labels) and search function now added

I have now cruised through the 500+ posts of MindBlog since it started up in Feb. of 2006 and done a cursory job of adding keywords to each. Using the labels list to the left, you can pull up all the posts in the areas of greatest interest to me. While I was tempted to distinguish many more categories, I thought this would get unwieldy and run the list too far down the screen, so I've limited the labels or keywords to about 35 items. Here is a list of labels I was also tempted to
add as I went through the old posts:

affiliative neuroscience
empathy
altruism
alzheimers
computers
modeling
amygdala
group selection
pain
human evolution
pheromones
brain development
placebo
gender
gay
anthropology
folk psychology
intelligence
addiction/drugs
depression

BUT, entering any of these in the blog search box provided by Google in the left column also gets you there. The Google search function proves to be very powerful for more focused searches, as for specific brain structures (insula, amygdala, whatever....)., or experiments using MRI imaging, etc.

Musical intervals in speech

Ross, Choi and Purves (PDF here) offer a fascinating study how vocal tract anatomy and vocal language sounds might explain why humans, across cultures, have created music using pitch intervals that divide octaves into the 12 tones of the chromatic scale:

Throughout history and across cultures, humans have created music using pitch intervals that divide octaves into the 12 tones of the chromatic scale. Why these specific intervals in music are preferred, however, is not known. In the present study, we analyzed a database of individually spoken English vowel phones to examine the hypothesis that musical intervals arise from the relationships of the formants in speech spectra that determine the perceptions of distinct vowels. Expressed as ratios, the frequency relationships of the first two formants in vowel phones represent all 12 intervals of the chromatic scale. Were the formants to fall outside the ranges found in the human voice, their relationships would generate either a less complete or a more dilute representation of these specific intervals. These results imply that human preference for the intervals of the chromatic scale arises from experience with the way speech formants modulate laryngeal harmonics to create different phonemes.


The periodicity in speech sound stimuli is generated primarily by the repeating peaks of energy in the vocal air stream produced by oscillations of the vocal folds in the larynx. The intensity carried by the harmonic series produced in this way is altered, however, by the resonance frequencies of the rest of the vocal tract, which change dynamically in response to neurally controlled movements of the soft palate, tongue, lips and other articulators (see figure). These variable vocal tract resonances, called formants, modulate the harmonic series generated by the laryngeal oscillations by suppressing some harmonics more than others. When coupled with unvoiced speech sounds (consonants), this modulation by the formants creates the different voiced speech sounds that give rise to the semantic content in all human languages. With respect to vowel phones, only the first two formants have a major influence on the vowel perceived: artificially removing them from vowel phones makes vowel phonemes largely indistinguishable, whereas removing the higher formants has little effect on the perception of speech sounds. Indeed, the first and second formants of vowel sounds of all languages fall within well defined frequency ranges. The resonances of the first two formants are typically between approximately 200–1,000 Hz and approximately 800–3,000 Hz, respectively, their central values approximating the odd harmonics of the resonances of a tube approximately 17 cm in length open at one end, the usual physical model of the adult vocal tract in a relaxed state).

Figure - Ranges of the peak harmonic in the first two formants (F1 and F2) for eight American English vowels uttered as single words in an emotionally neutral manner. (A) Diagram of the human larynx and vocal tract; see Introduction for explanation. (B) Distribution of the peak harmonics selected as the index for the first and second formant for the five male participants. (C) Distribution for the five female participants. The somewhat smaller harmonic ranges for females are due to the higher average fundamental frequency of female speech. The mean fundamental frequency for male speakers was 109 Hz (SD = 10) and for female speakers 171 Hz (SD = 20).

Cat meets Laptop

Laptop just like the one I'm using right now...

When Lots of Money Makes You Feel Rich

I'm passing on a curious (and not too surprising) short piece by Alex Mindlin in the New York Times with the same title this post:

Anyone who has ever thrown around a stack of liras or rupees knows that people are sometimes more extravagant with currencies that have high face values. A paper recently published in The Journal of Consumer Research explored that effect...In one study, students in Hong Kong, when asked to allocate spending from an imaginary paycheck of 9,000 Hong Kong dollars, devoted an average of 532.35 of those dollars to food spending...Two weeks later, the students were asked to imagine that they had moved to the fictional country of Tristania, where a Hong Kong dollar equaled 18 Tristanian dollars, and therefore their pay was 162,000 Tristanian dollars. The students splurged, spending 30 percent more on food in real terms...The opposite effect was seen among students sent to an alternate Tristania where their paychecks were worth only 500 Tristanian dollars...“You feel more rich if you have more units of currency,” said Dilip Soman, a professor of marketing at the University of Toronto, and one of the paper’s authors...Earlier studies have been taken to suggest the opposite — that consumers are wary of spending in “numerous” foreign currencies, because they are put off by the high numbers on price tags. But Mr. Soman said that those studies had not taken budgeting into account.

New cells in the brain require new experiences to live...

Leuner et al offer a nice review PDF here) of work by Tashiro et al. showing that survival of the thousands of new nerve cells that are born in the dentate gyrus of the hippocampus each day is enhanced if mice are exposed to new experiences during a critical window of time. Here is Tashiro et al.'s abstract, followed by a summary diagram from the Leuner review.

Neural circuits in the dentate gyrus are continuously modified by adult neurogenesis, whose level is affected by the animal's experience. However, it is not known whether this experience-dependent anatomical modification alters the functional properties of the dentate gyrus. Here, using the expression of immediate early gene products, c-fos and Zif268, as indicators of recently activated neurons, we show that previous exposure to an enriched environment increases the total number of new neurons and the number of new neurons responding to reexposure to the same environment. The increase in the density of activated new neurons occurred specifically in response to exposure to the same environment but not to a different experience. Furthermore, we found that these experience-specific modifications are affected exclusively by previous exposure around the second week after neuronal birth but not later than 3 weeks. Thus, the animal's experience within a critical period during an immature stage of new neurons determines the survival and population response of the new neurons and may affect later neural representation of the experience in the dentate gyrus. This experience-specific functional modification through adult neurogenesis could be a mechanism by which new neurons exert a long-term influence on the function of the dentate gyrus related to learning and memory.

Here is a summary figure of the results (NeuN+ is a marker for nerve cells; BrdU is a marker for new neurons; Zif268 is a marker for increased neural activation.
Figure legend: Simplified schematic diagram of the results presented by Tashiro et al. (2007). Exposure to environmental enrichment during a critical period (1–3 weeks after BrdU administration; bottom) increased the survival of new neurons in the dentate gyrus (BrdU+/NeuN+). In contrast, new neuron survival was not enhanced in mice exposed to an enriched environment after the critical period (top). The authors also demonstrated that reexposure to the same experience of environmental enrichment at a later time enhanced neuronal activation (BrdU+/NeuN+/Zif268+; bottom). Increased neuronal activation did not occur when mice were only given the initial exposure or were reexposed to a different experience of water maze training.

Gay animals II - from National Geographic

Gay animals I

El comportamiento homosexual en animales como el carnero, el búfalo y el bonobo...

More on the mirror "hearing-doing" system

Here is a more extended commentary on a paper I mentioned in my Jan. 30 post "The pianist in the mirror.." D'Ausilio (PDF here) discusses this work of Lahav et al. showing an auditory mirror area in the left inferior frontal gyrus for complex and newly acquired actions. In addition to rote auditory-motor mapping for learning and online execution control, this mirror mechanism might subserve other evolutionary critical functions like action recognition, and interindividual emotional resonance. This auditory mirror-like property seems indeed to be valid for a wide range of functions that in turn elicit very different behaviors.

Shrimp on a treadmill....

Remix tricks....

Who watches the watcher?

I recommend reading Adami's review (PDF here) of Douglas Hofstadter's recent book on consciousness "I am a Strange Loop," Basic Books, New York, 2007. A few excerpts:

Hofstadter's explanation of human consciousness is disarmingly simple...the main idea is simply that our feeling of a conscious "I" is but an illusion created by our neuronal circuitry: an illusion that is only apparent at the level of symbols and thoughts, in much the same way as the concepts of pressure and temperature are only apparent at the level of 10^23 molecules but not the level of single molecules. In other words, Hofstadter denies consciousness an element of ontological reality, without denying that our thoughts and feelings, pains and longings have an "inner reality" when we have them.

Hofstadter's book and Koch's recent "The Quest for Consciousness" make for an interesting juxtaposition. Each addresses the same problem but entirely on different levels. Yet both authors reach some of the same conclusions, sometimes using precisely the same metaphor (as when they compare the activity of "making up one's mind" in terms of a voting process). In the end, both authors could have profited from peeking at each other's arsenal: Hofstadter would probably be delighted to see some of the putative neural underpinnings of consciousness, to peer underneath the strange loop as it were, at the inordinately complex firework and the neuroanatomy that supports it. For his part, Koch would no doubt appreciate the computational trick that Gödel incompleteness plays on us, as well as the developmental aspect of consciousness that Hofstadter advocates.

The Accidental Mind

Geory Striedter writes a review of David Linden's new book "The Accidental Mind: How Brain Evolution Has Given Us Love, Memory, Dreams, and God" ..Harvard University Press: 2007. (PDF of the review is here) Some clips:

The human brain, and hence the human mind, is not an optimal, designed-from-scratch apparatus. Rather, it is an imperfect amalgam of shoddy components. That is the central thesis of David Linden's new book The Accidental Mind. Neurons are slow, leaky, and unreliable — hardly ideal computing elements. The whole brain, too, is not designed to the plan of some omnipotent engineer. Instead, evolution has endowed it with plenty of 'anachronistic junk'. Which is why, according to Linden, our minds often distort reality and can lead us to act foolishly. For example, when you reach out to touch something, your brain filters out what it expects. This selective neglect of expected input allows us to focus on unexpected stimuli, but it can be counterproductive. It may explain, for instance, why pushing and shoving confrontations tend to escalate. When someone pushes you, you feel it more than when you push the other with the same force, because the sensation caused by your own push is largely, though unconsciously, expected by your brain.

Linden tells his story well, in an engaging style, with plenty of erudition and a refreshing honesty about how much remains unknown. The book should easily hold the attention of readers with little background in biology and no prior knowledge of brains. It would make an excellent present for curious non-scientists and a good book for undergraduates who are just entering into the brain's magic menagerie. Even readers trained in neuroscience are likely to enjoy the many tidbits of rarely taught information — on love, sex, gender, sleep and dreams — that spice up Linden's main argument.

Our prefrontal control system is altered by unconscious stimuli.

Lau et al. (PDF here) used fMRI to test

..whether unconscious information can influence the cognitive control system in the human prefrontal cortex. Volunteers had to prepare to perform either a phonological judgment (whether the word is bisyllabic) or a semantic judgment (whether the word refers to concrete objects) on an upcoming word, based on the instruction given at the beginning of each trial. However, in some trials they were visually primed to prepare for the alternative (i.e., "wrong") task, and this impaired their performance. This priming effect is taken to depend on unconscious processes because the effect was present even when the volunteers could only discriminate the identity of the primes at chance level. Furthermore, the effect was stronger when the visibility of the prime was near zero than when the visibility of the prime was significantly higher. When volunteers were unconsciously primed to perform the alternative task, there was also decreased neural activity in the brain areas relevant to the instructed task and increased neural activity in the brain areas relevant to the alternative task, which shows that the volunteers were actually engaged in the wrong task, instead of simply being distracted. Activity in the mid-dorsolateral prefrontal cortex was also found to be associated with this unconscious priming effect. These results suggest that the cognitive control system in the prefrontal cortex is not exclusively driven by conscious information, as has been believed previously.

Neural activity associated with priming. (Click to enlarge). Data were extracted from the brain areas that were previously found to be associated with the Phonological task (left ventral premotor area) and the Semantic task (left inferior frontal cortex and middle temporal gyrus). The location of these is schematically illustrated on the brain above. Here, task relevant means activity from the Semantic areas when the volunteers were instructed to perform the Semantic task, and activity from the Phonological areas when they were instructed to perform the Phonological task. Task irrelevant means the activity was extracted from the alternative areas, which was more important for the primed task than the instructed task. When the visibility of the primes was low (LoVis), which means the priming effect was strongest, activity in task-relevant areas was significantly reduced (p = 0.019), and activity in task-irrelevant areas was significantly increased (p = 0.045). This suggests that the volunteers were actually engaged in exercising the wrong neural circuits when they were primed to perform the wrong task. This effect is not present when the visibility of the primes was high (HiVis), suggesting that this effect could not be attributable to the degree of conscious perception of the prime. This is reflected by a three-way interaction between Task Relevance (i.e., activity in task relevant areas vs activity in task irrelevant areas), Congruency (Con; between prime and instruction), and Visibility (of the prime) (p = 0.040). InCon, Incongruency; n.s., not significant.

Mid-DLPFC and unconscious priming. (Click to enlarge) Lau et al. looked for activity in the brain that was associated with the unconscious priming effect in general, regardless of which task was explicitly cued, by testing for the interaction between Congruency (Con; between prime and instruction) and Visibility (of the prime). This test revealed activity in the mid-DLPFC (right; x = –38). This effect was specific to the Low-Visibility condition, in which volunteers did not consciously perceive the primes. InCon, Incongruency; n.s., not significant; HiVis, high visibility; LoVis, low visibility.

Octopus tricks....

Need help opening that jar?

Use Viagra to recover from jet lag?

I always perk up when I see reports of new side effects of sildenafil (Viagra), because it is an inhibitor of one form of an enzyme, cyclic GMP phosphodiesterase, that my earlier research showed to be central to changing light into a nerve signal in the rod and cone cells of our retinas (check here if you are curious about this previous life..). One of the interesting side effects of viagra is on color vision. Here is another interesting bit from Agostino et al. in PNAS:

Mammalian circadian rhythms are generated by a master clock located in the suprachiasmatic nuclei and entrained by light-activated signaling pathways. In hamsters, the mechanism responsible for light-induced phase advances involves the activation of guanylyl cyclase, cGMP and its related kinase (PKG). It is not completely known whether interference with this pathway affects entrainment of the clock, including adaptation to changing light schedules. Here we report that cGMP-specific phosphodiesterase 5 is present in the hamster suprachiasmatic nuclei, and administration of the inhibitor sildenafil (3.5 mg/kg, i.p.) enhances circadian responses to light and decreases the amount of time necessary for reentrainment after phase advances of the light–dark cycle. These results suggest that sildenafil may be useful for treatment of circadian adaptation to environmental changes, including transmeridian eastbound flight schedules.

Possible RSS feed errors

If you are seeing old posts in your feed, go directly to the blog. During this next period when I am adding labels (keywords) to old posts, the RSS feed may be presenting the old posts as new posts. I'll try to get around this by usually reposting the last five or so most recent posts when I have finished a session of labeling. Also, the previous posts shown in the adjacent right column are in the right sequence.

Synesthesia - evidence for increased cortical connectivity

Synesthesia, in which letters or numbers elicit color perception, could be due to increased brain connectivity between relevant regions, or due to failure to inhibit feedback in cortical circuits. Diffusion tensor imaging now provides evidence for increased connectivity in word processing and binding regions of the brain. Hubbard comments (PDF here) on the article by Rouw and Scholte (PDE here):

If looking at this page of text causes you to see a cascade of colors, you have grapheme-color synesthesia, in which viewing letters and numbers in black and white elicits the experience of seeing colors... grapheme-color synesthesia occurs in as many as 2 out of every 100 people...

To study this:

...the authors used diffusion tensor imaging (DTI), a neuroimaging technique that measures the diffusion of water molecules in the living human brain. Water molecules diffuse more easily parallel than perpendicular to the direction of white-matter fibers, because of the myelin sheaths and axonal membranes. By measuring relative differences in how easily water diffuses along different axes (termed fractional anisotropy), it is possible to infer the size, orientation and degree of myelination of white matter tracts in vivo... this technique demonstrated increased structural connectivity in synesthetes compared with controls in three brain regions: the right fusiform gyrus, which is near regions involved in word and color processing, and the left intraparietal sulcus (IPS) and frontal cortex, both of which are part of a network of regions involved in binding and consciousness

Figure - The outer cortical surface with relevant brain regions indicated.
The color-selective hV4 is indicated in red, and the visual word form area is indicated in green. Cross-activation between these regions, mediated by increased anatomical connectivity, correlates with the generation of the additional experiences of grapheme-color synesthesia, and the degree of connectivity determines their strength. The posterior IPS, thought to be involved in binding, is in blue. Additional anatomical connectivity in this region may be critical for synesthetic binding, which must operate on the colors generated by the cross-activation between grapheme regions and hV4. These regions have been projected to the left hemisphere for simplicity.

EVOLUSHARK

Here is Evolushark (spelling evolution) - to intimidate the conservation Christian mascot Ichthys.

Memory depends on how well you can forget...

Benedict Carey reviews (PDF here) new work on memory (PDF here) by a Stanford group that is the first to record visual images of people’s brains as they suppress distracting memories:

Blocking out a distracting memory is something like ignoring an old (and perhaps distracting) acquaintance... it that much harder to reconnect the next time around...recent studies suggest that the brain plays favorites with memories in exactly this way, snubbing some to better capture others. A lightning memory... is not so much a matter of capacity as it is of ruthless pruning

The experiments:

...had 20 young men and women, mostly Stanford students, view in quick succession a list of 240 word pairs. These included 40 capitalized words, each paired with six related, lower-case words: For example, “ATTIC-dust,” “ATTIC-junk,” and so on....After studying the pairs, the participants were instructed to memorize three selected pairs from each of 20 capitalized words. In effect, this forced them to flag individual pairs, like ATTIC-dust, while trying to tune out very similar, distracting ones, like ATTIC-junk, for half of the total list of pairs they saw...They were told not to memorize any pairs from the other half of the list.....while participants were having their brains scanned by an M.R.I. machine, each person’s memory was tested several times, and scores ranged from about 30 percent accuracy to 80 percent. ...how well each person suppressed the distracting word pairs was also measured by comparing recall of those pairs with recall of the half of the list that was studied at first but later ignored.

from Kulh et al.'s abstract:

Functional magnetic resonance imaging during selective retrieval showed that repeated retrieval of target memories was accompanied by dynamic reductions in the engagement of functionally coupled cognitive control mechanisms that detect (anterior cingulate cortex) and resolve (dorsolateral and ventrolateral prefrontal cortex) mnemonic competition. Strikingly, regression analyses revealed that this prefrontal disengagement tracked the extent to which competing memories were forgotten; greater forgetting of competing memories was associated with a greater decline in demands on prefrontal cortex during target remembering. These findings indicate that, although forgetting can be frustrating, memory might be adaptive because forgetting confers neural processing benefits.

Figure Legend: A whole-brain regression analysis showed that memory suppression at test was predicted by repetition-related activation decreases in (a) left dorsal ACC (anterior cingulate) (b) right anterior VLPFC (ventrolateral prefrontal cortex) In the ACC and right VLPFC, high suppressors showed reliable decreases in activation from first to third retrieval practice trials, whereas low suppressors did not. High suppressors showed greater initial ACC activation than low suppressors, but comparable initial right VLPFC activation. (c) A whole-brain regression analysis showed that the repetition-related activation decline in the right DLPFC covaried with that in the ACC, showing a functional coupling between ACC and right DLPFC that specifically relates to changes in demands on cognitive control across retrieval repetitions.

Learning after movement error, a memory trace.

Huang and Shadmehr report an interesting study in J. Neurophysiol. "Evolution of Motor Memory During the Seconds After Observation of Motor Error." Here is their abstract:

When a movement results in error, the nervous system amends the motor commands that generate the subsequent movement. Here we show that this adaptation depends not just on error, but also on passage of time between the two movements. We observed that subjects learned a reaching task faster, i.e., with fewer trials, when the intertrial time intervals (ITIs) were lengthened. We hypothesized two computational mechanisms that could have accounted for this. First, learning could have been driven by a Bayesian process where the learner assumed that errors are the result of perturbations that have multiple timescales. In theory, longer ITIs can produce faster learning because passage of time might increase uncertainty, which in turn increases sensitivity to error. Second, error in a trial may result in a trace that decays with time. If the learner continued to sample from the trace during the ITI, then adaptation would increase with increased ITIs. The two models made separate predictions: The Bayesian model predicted that when movements are separated by random ITIs, the learner would learn most from a trial that followed a long time interval. In contrast, the trace model predicted that the learner would learn most from a trial that preceded a long time interval. We performed two experiments to test for these predictions and in both experiments found evidence for the trace model. We suggest that motor error produces an error memory trace that decays with a time constant of about 4 s, continuously promoting adaptation until the next movement.