Author Archive

Neurons with similar tuning more likely to be connected

Friday, May 27th, 2011

From the abstract: … we determine synaptic connectivity between nearby layer 2/3 pyramidal neurons in vitro, the response properties of which were first characterized in mouse visual cortex in vivo. We found that connection probability was related to the similarity of visually driven neuronal activity. Neurons with the same preference for oriented stimuli connected at twice the rate of neurons with orthogonal orientation preferences. Neurons responding similarly to naturalistic stimuli formed connections at much higher rates than those with uncorrelated responses. Bidirectional synaptic connections were found more frequently between neuronal pairs with strongly correlated visual responses….

Ho Ko, Sonja B. Hofer, Bruno Pichler, Katherine A. Buchanan, P. Jesper Sjöström, Thomas D. Mrsic-Flogel. Functional specificity of local synaptic connections in neocortical networks. Nature. 2011 May 5;473(7345):87-91. Epub 2011 Apr 10.

Henry Markram and the Human Brain Project reported to be pursuing $1.4 billion grant

Friday, May 20th, 2011

This dailymail article claims that the Human Brain Project, directed by Henry Markram, is pursuing a 1 billion euro grant to simulate the human brain in 12 years.

By way of Nextbigfuture, by way of Hackernews.

Dopamine error

Wednesday, May 11th, 2011

(pun intended). I am embarrassed to say that earlier today I remarked to a colleague that dopamine only encodes unexpected reward, not unexpected lack of reward. This is (afaik) incorrect. It has a baseline level of firing that goes down when there is an unexpected lack of reward (see fig 1 in Wolfram Schultz, Peter Dayan, P. Read Montague. A Neural Substrate of Prediction and Reward)

However, because it can only go down so far, the negative signal is clipped, which might have consequences (see Yael Niv, Michael O Duff, Peter Dayan. Dopamine, uncertainty and TD learning).

The previous article mentions that some other people think that maybe dopamine is tracking uncertainty as well as reward. This one talks about a theory that acetylcholine is related to expected uncertainty, and norepinephrine is related to unexpected uncertainty:
Angela Yu, Peter Dayan. Expected and Unexpected Uncertainty: ACh and NE in the Neocortex (huh, all those papers had Peter Dayan as one of the authors) (btw I haven’t read all of the papers I’m posting here)

Since we’re on the subject of temporal difference learning, I’ll mention that in my opinion temporal difference learning may be a model of how futures/speculators in financial markets are supposed to propagate future price changes back in time to the present (if you think of the market as a cognitive system). I haven’t formalized this idea yet, though.

Local sleep in awake rats

Friday, April 29th, 2011

this experiment claims to show that

(1) when rats are sleep-deprived, small populations of rat brain neurons can fall asleep while the rest of the rat is awake, and
(2) this may correspond to performance degradation



i haven’t read the actual article yet…

Increasing adult hippocampal neurogenesis is sufficient to improve pattern separation.

Wednesday, April 6th, 2011

Sahay A, Scobie KN, Hill AS, O’Carroll CM, Kheirbek MA, Burghardt NS,
Fenton AA, Dranovsky A, Hen R. Increasing adult hippocampal neurogenesis is sufficient to improve
pattern separation. Nature. 2011 Apr 3

Abstract after the break.


Google Science Fair deadline tomorrow!

Wednesday, April 6th, 2011

“Google’s worldwide Science Fair competition …is calling for entries over the next few days. It gives kids the opportunity to join in a new kind of online science competition…offering them the chance to win … prizes including a 10-day trip to the Galapagos Islands or a $50,000 scholarship.”

They paid us to post this video of a Rube Goldberg machine (you don’t need sound, it’s just random music):

(you won’t be able to see it if you have AdBlock enabled)

Memory-oriented computing and “From Micro-processors to Nanostores: Rethinking Data-Centric Systems”

Wednesday, March 2nd, 2011

I’ve only skimmed this article by Ranganathan, but I find it notable because of the discussion of memory-oriented computing, in which processors are colocated with storage (he uses the word “nanostores”, which additionally implies that the memory is nonvolatile). One of the most important distinctions between neural architecture and present-day computing architecture is that brains appear to be built out of computing elements that do both processing and memory storage, whereas present-day computers have separate memory and CPU components (this separation is a key feature of what is called the “von Neumann” architecture).


Mobile phone increases brain glucose metabolism near phone antenna

Wednesday, February 23rd, 2011

This study claims that glucose metabolism in the brain goes up near a cellphone antenna. At first blush this may appear to conflict with other studies that claim that cellphones don’t cause cancer, but this can be resolved by supposing that cell phones don’t cause cancer, but affect the brain in other ways. As Volkow notes at the end of the Nytimes article, this may lead to the discovery of a mechanism for brain stimulation. Right now they don’t know what the mechanism is by which the electromagnetic field is causing the glucose metabolism. If neuronal firing is being altered, and if the bandwidth turns out to be sufficiently high (i.e. if the stimulation can be made sufficiently precise), this could eventually lead to a wireless brain-machine interface/neural prosthetic.

PET scans showing effect

Nora D. Volkow, Dardo Tomasi, Gene-Jack Wang, Paul Vaska, Joanna S. Fowler, Frank Telang, Dave Alexoff, Jean Logan, Christopher Wong. Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism. JAMA. 2011;305(8):808-813.

Summary in NYtimes: Cellphone Use Tied to Brain Changes

AI Mashup Challenge

Saturday, February 19th, 2011

A mashup is a lightweight (web) application that offers new functionality by combining, aggregating and transforming resources and services available on the web. The AI mashup challenge accepts and awards “intelligent” mashups that use AI technology

The deadline is April 1, 2011.


• € 1750 sponsored by Elsevier
• Speech outfit from Linguatec
• 10 O’Reilly e-books
• 2 x up to 5 mashup books from Addison-Wesley


Cognitive Atlas

Monday, January 31st, 2011

Cognitive Atlas, a machine-readable ontology and semantic database of assertions about cognitive studies, with bibliographic links and brain area localization.