neurodudes

Neuron : Uncertainty, Neuromodulation, and Attention

Haven’t read this article from Peter Dayan’s lab yet but some interesting Bayesian modeling implicating acetylcholine as a signal of expected uncertainty and norepinephrine as a signal of unexpected uncertainty.

Abstract:

Uncertainty in various forms plagues our interactions with the environment. In a Bayesian statistical framework, optimal inference and prediction, based on unreliable observations in changing contexts, require the representation and manipulation of different forms of uncertainty. We propose that the neuromodulators acetylcholine and norepinephrine play a major role in the brain’s implementation of these uncertainty computations. Acetylcholine signals expected uncertainty, coming from known unreliability of predictive cues within a context. Norepinephrine signals unexpected uncertainty, as when unsignaled context switches produce strongly unexpected observations. These uncertainty signals interact to enable optimal inference and learning in noisy and changeable environments. This formulation is consistent with a wealth of physiological, pharmacological, and behavioral data implicating acetylcholine and norepinephrine in specific aspects of a range of cognitive processes. Moreover, the model suggests a class of attentional cueing tasks that involve both neuromodulators and shows how their interactions may be part-antagonistic, part-synergistic.

Weak pairwise correlations imply strongly correlated network states in a neural population : Nature

Very few MEA studies make it into Nature, so this definitely got my attention.

Often in neuroscience we are confronted with a small sample measurement of a few neurons from a large population. Although many have assumed, few have actually asked: What are we missing here? What does recording a few neurons really tell you about the entire network?

Using an elegant prep (retina on a MEA viewing defined scenes/stimuli), Segev, Bialek, and students show that statistical physics models that assume pairwise correlations (but disregard any higher order phenomena) perform very well in modeling the data. This indicates a certain redundancy exists in the neural code. The results are also replicated with cultured cortical neurons on a MEA.

Some key ideas from the paper are presented after the jump. (more…)

Soon machines will obtain higher IQ’s than humans in intelligence tests.
Traditionally the intelligence quotient has been considered the best indicator for scientifically evaluating natural intelligence.
Is this indeed the best way to measure this human capacity? Could a machine emulate a human being solving traditional intelligence tests? If so, could we affirm that a machine possesses an intelligence equivalent to that of a human?
KITBIT explores some of these possibilities.
The ability of KITBIT in symbolic logic problems, in those which verbal intelligence does not come into play, is comparable to that of humans.
On our web-page, TheIQChallenge.com, we challenge our visitors to put KITBIT to the test in solving numerical and logical problems which have the exact same format as traditional intelligence tests used by psychologists.
The KITBIT project develops research in diverse areas of artificial intelligence such as image recognition, creation of models, predictions and data mining.
KITBIT has been designed by a small team of engineers, mathematicians and programmers. Currently we hope to substantially enlarge this team to carry out our ongoing projects.
www.theIQChallenge.com
www.kitbit.com

[This sounds interesting... although it is fine to promote your personal projects here, we'd at least like to know a little bit about how your project is achieving its goal or how your specific algorithms make this different from similar AI endeavors. And please, please always put your name at the bottom of the post! -Neville]

PLoS Biology: Attenuation of Self-Generated Tactile Sensations Is Predictive, not Postdictive [open access]

I haven’t gotten a chance to fully digest this article (What is the attenuation phenomena that happens when the taps are delayed?), but it seems like a deep result from a relatively simple haptics experiment. Just thought I’d share it with the crowd.

Also, Happy Birthday to fellow Neurodude Bayle! Congrats, man.

A Resilient, Low-Frequency, Small-World Human Brain Functional Network with Highly Connected Association Cortical Hubs (Achard et al., 2006)

A study on network properties of the whole brain (functional connectivity data from fMRI)… interesting to see this type of work published in J. Neurosci. Building on previous fMRI/whole brain connectivity studies, the authors use a set of wavelet basis functions to estimate the correlations between different anatomical regions.

Also includes some analyses on resiliency of the system (via a metric like “largest connected cluster”) to random and targeted attack (ie. node deletion). It would be neat if they also did some analysis of common stroke damage. I would think that a stroke probably doesn’t qualify as a “targeted attack”, in the traditional sense, but, due to the predefined structure of the major circulatory structures (eg. circle of Willis), there are likely regions that are near the most commonly blocked arteries, etc. Perhaps someone with some medical qualifications could weigh in here?

There is also a nice discussion of why the human brain does not appear to be a scale-free network: That nodes do not seem to follow the “rich-get-richer” rule of preferential attachment. Evolutionarily recent structures like prefrontal seem to be among the hubs of the system and older structures like limbic regions do not dominate. Here’s a picture of the connectivity map from the paper:

Full abstract after the jump.
(more…)

Some folks have created NeuroTree to document the advisor-advisee relationships (i.e., “so-and-so was a grad student of that guy, and that guy postdoc’d with someone else”) of neuroscience. With this information, one can draw “family trees” like this.

Here is the FAQ.

Importantly, this is a collaborative effort, so add your name if it’s not there already.

-John O’Leary

This project was announced several months ago, but I didn’t see a post here so I thought I would add it.

The project, dubbed “Blue Brain“, represents a team up between Henry Markram, (who co-authored the chapter on the neocortex in the acclaimed reference The Synaptic Organization of the Brain), and IBM’s Blue Gene super computer.

From the New Scientist article: For over a decade Markram and his colleagues have been building a database of the neural architecture of the neocortex, the largest and most complex part of mammalian brains.

Very thin slices of mouse brain were kept alive under a microscope and probed electrically before being stained to reveal the synaptic, or nerve, connections. “We have the largest database in the world of single neurons that have been recorded and stained,” says Markram.

–Stephen

The Guardian has posted a very well written and entertaining profile of Robert Trivers, an evolutionary biologist who proposed controversial but influential ideas concerning the emergence of concepts such as altruism and justice as a natural consequence of Darwinian evolution. As with all evolutionary {biology, psychology, computation}, you may readily disagree with the strength of the theories, but it is fun to consider their logical structure. Not to mention Trivers is a guy with an amusing biography and quotes.

Bacterial speech bubbles : Nature

Bacteria secrete signals to other bacteria of the same species through vesicle packets.

Mashburn and Whiteley describe the unexpected convergence of two seemingly unrelated areas of microbiological research: how bacteria talk to their friends, and how they attack their enemies. The authors studied the bacterial pathogen Pseudomonas aeruginosa, which releases a hydrophobic molecule called the ‘pseudomonas quinolone signal’ (PQS) to send messages to other bacteria of the same species. The surprise is that, rather than being secreted as single molecules, PQS is released in bubble-like ‘vesicles’ that also contain antibacterial agents and probably toxins aimed at host tissue cells as well.

I wonder if this is evolutionarily connected to synaptic vesicles or if this is a case of something like convergent evolution…

For those who contemplate the day when we can say the workings of the brain are fully understood and solved, this article (Building a Virtual Microbe, Gene by Gene by Gene – New York Times) about the consortium trying to do the same for the simple bacterium E. Coli is humbling.

Click more for some interesting excerpts. (more…)