neurodudes

A few places on the internet are talking about a study conducted on Amazon tribespeople which demonstrates that basic concepts about geometry are independant of culture and level of education.

Here’s the story from Science News and here’s the story from Slashdot.

If this is the case, it suggests that there might be something special about geometry that made it evolutionarily advantageous to hard-wire into the brain. Or, from another perspective, some evolutionary adaptation makes geometry easy for our brains to understand. After all, a triangle is just the combination of three bars, which V1 is very good at responding to. As vision research continues to study the brain’s representation of increasingly complex objects, it may shed light on how this works from a systems neuroscience perspective.

–Stephen

This is really weird!

Somebody debunk this before it blows my mind.

–Stephen

This Is Your Brain Under Hypnosis - New York Times

Very interesting stuff. Subjects were hypnotized and told that days later they would see “gibberish” symbols printed in particular colors. They needed to report back the color that the word appeared in. (For those unfamiliar, the Stroop test presents color words, like “red”, in a different color, such as the word “red” written with green ink. People have difficulty reporting the color of the word because we have a strong need to “read” the written word.)

The highly hypnotizable subjects (grouped according to a predetermined measure) essentially showed no Stroop effect (ie. no reaction time difference with conflicting word and color). And, with fMRI, they saw that normally activated visual-reading areas were not activated in these subjects.

I skimmed this paper very briefly and it looks cool. Of course, I’m not a computer vision expert so I can’t really tell how state-of-the-art the results are.

Murphy-Chutorian, E., Aboutalib, S., Triesch, J.(2005). Analysis of a Biologically-Inspired System for Real-time Object Recognition. Cognitive Science Online, 3.2, pp. 1-14. http://cogsci-online.ucsd.edu/3/3-3.pdf

“We present a biologically-inspired system for real-time, feed-forward object recognition in cluttered scenes. Our system utilizes a vocabulary of very sparse features that are shared between and within different object models. To detect objects in a novel scene, these features are located in the image, and each detected feature votes for all objects that are consistent with its presence. Due to the sharing of features between object models our approach is more scalable to large object databases than traditional methods. To demonstrate the utility of this approach, we train our system to recognize any of 50 objects in everyday cluttered scenes with substantial occlusion. Without further optimization we also demonstrate near-perfect recognition on a standard 3-D recognition problem. Our system has an interpretation as a sparsely connected feed-forward neural network, making it a viable model for fast, feed-forward object recognition in the primate visual system.”

This post has much the same content as this NeuroWiki page; you may wish to read and comment on it there.

I’ve only skimmed this interesting article, so beware that I may not correctly understand it.

This article proposes that recurrent excitation in cortex leads to amplification, and analyzes this using the mathematics of basic amplifiers (taught in introductory electrical engineering courses; i.e. open-loop gain and closed loop gain).

They construct a simulation based on this principal that agrees with some electrophysiological and pharmacological results from neurobiology experiments in layer IV of V1.

At the end, they conjecture that a sensory network could use this principal for noise reduction and possibly pattern recognition.

Douglas, Rodney J.; Koch, Christof; Mahowald, Misha; Martin, Kevan A. C.; Suarez, Humbert H. Recurrent Excitation in Neocortical Circuits. Science, Volume 269, Issue 5226, pp. 981-985.

In the September Nature Neuroscience, we have a promising new technique: Millisecond-timescale, genetically targeted optical control of neural activity.

I think several people have suggested doing something like this before but no one has actually done it. What they’ve done is genetically modified (by lentivirus, for those curious) ordinary hippocampal neurons in culture, adding the same photo-electric transducing protein — rhodopsin – found in photoreceptors. Yup. You heard me right. They’ve expressed a cation-channel-gating rhodopsin in ordinary hippocampal neurons. With an standard fluorescence microscope (Xenon lamp + Chroma GFP cube), they can photostimulate single action potentials (and sub-threshold depolarizations) in single neurons.

Now here’s my idea for bioengineers to take this to the next level: Add a second photosensitive protein tied to an inhibitory channel. Ideally, we would want total separation between the stimulating wavelengths for the two different (excitatory, inhibitory) channels. Now, you have a system where all neurons can be directly excited or inhibited with different laser lines. In other words, a network of neurons where all voltages can be fully controlled. Sweet!

This seems like a great tool to add to the existing arsenal of photostimulation techniques (like photoelectric effect-based light-on-silicon stimulation that was pioneered by Goda lab.) Here’s a question: Is this the end of multi-electrode arrays? In slice, we already have single spike detection with Ca-sensitive dyes from Yuste’s lab. Now, we have optical single spike stimulation. Perhaps MEAs will be relegated to the domain implantable devices. Regardless, I’m proud to see several of the authors are from Stanford! Read on for the full abstract. (more…)

The Aug 4 issue of Neuron has an interesting article (news & views) on fMRI of the ventral (”what”/perception) and dorsal (”where”/motor) visual pathways.

Subjects in the fMRI were either shown images of objects alone or hands grasping these objects. Reliably, the object-only stimuli activated the contralateral ventral visual pathway. In the case of grasping stimuli where the hand was presented in the opposite visual hemifield from the object, contralateral activation of the dorsal and ventral visual pathways was seen. When subjects were asked to focus their attention on either object or grasping hand, activation was pronounced in the ventral or dorsal visual streams, respectively.

Most importantly, the study affirms that there really isn’t a single fundamental visual representation in the brain — the representation used to recognize an object is not the same as the representation used to pick up that object. Because of the different functions of these tasks, this probably doesn’t sound too surprising but, to me, it is surprising! What we consciously see is neurally separate from what our motor system is “seeing” and the break between the two pathways happens quite early in visual processing.

Like the mirror neuron work, this provides further evidence in the “seeing is believing/doing” vein. As the author of the news and views summary points out, this work

remind[s] us once more that (ultimately) the brain did not evolve to enable us to think; it evolved to enable us to act.

Lastly, this type of idea is the basis of Rodolfo Llinas’s elegant book i of the vortex, which I’ve been reading recently. So far, it’s great and I recommend it highly!