Limits...
Being critical of criticality in the brain.

Beggs JM, Timme N - Front Physiol (2012)

Bottom Line: The hypothesis that the electrical activity of neural networks in the brain is critical is potentially important, as many simulations suggest that information processing functions would be optimized at the critical point.This hypothesis, however, is still controversial.Points and counter points are presented in dialog form.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Indiana University Bloomington, IN, USA.

ABSTRACT
Relatively recent work has reported that networks of neurons can produce avalanches of activity whose sizes follow a power law distribution. This suggests that these networks may be operating near a critical point, poised between a phase where activity rapidly dies out and a phase where activity is amplified over time. The hypothesis that the electrical activity of neural networks in the brain is critical is potentially important, as many simulations suggest that information processing functions would be optimized at the critical point. This hypothesis, however, is still controversial. Here we will explain the concept of criticality and review the substantial objections to the criticality hypothesis raised by skeptics. Points and counter points are presented in dialog form.

No MeSH data available.


Related in: MedlinePlus

Hypothetical positions of two spins as a function of time. (Top) At high temperature, the spin orientations fluctuate greatly, but independently of one another, producing a low dynamic correlation value. (Middle) At the critical temperature, the spin orientations fluctuate somewhat and the fluctuations are coordinated, producing a high dynamic correlation value. (Bottom) At low temperature, the spin orientations do not fluctuate very much, yielding a low dynamic correlation value.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3369250&req=5

Figure 2: Hypothetical positions of two spins as a function of time. (Top) At high temperature, the spin orientations fluctuate greatly, but independently of one another, producing a low dynamic correlation value. (Middle) At the critical temperature, the spin orientations fluctuate somewhat and the fluctuations are coordinated, producing a high dynamic correlation value. (Bottom) At low temperature, the spin orientations do not fluctuate very much, yielding a low dynamic correlation value.

Mentions: Critio: Great, you get it! Now let’s take a look at what happens to the dynamic correlation for the three different cases we talked about: low T, high T, and critical T. In the low T case, the piece of iron is extremely ordered and all the spins are pointed in the same direction. The dynamic correlation is low because there are no fluctuations and the terms in parentheses are both nearly 0 all the time. In contrast, for the high T case, there are plenty of fluctuations, as the spins are constantly deviating from their averages, but there is no coordination between sites i and j. One term in parenthesis might be positive, while the other might be negative. On another occasion, they might both be positive. So on average the dynamic correlation is again low. But at critical T, there is enough heat to allow fluctuations, but not so much heat that it destroys coordination between spin sites. The spins deviate from their averages, and they often do so together because the nearest neighbor influence is not completely overwhelmed by the added heat. Here, there is both fluctuation and coordination. When one of those “amoeba-like” domains that you saw in Movie S3 in Supplementary Material crawls across the screen, it might cause nearby spins to flip one after the other, setting up a dynamic correlation. I could sketch the positions of the spins, either up or down or in between, over time for the three different cases. [Critio now pulls out red and green markers, grabs another napkin and sketches Figure 2.]


Being critical of criticality in the brain.

Beggs JM, Timme N - Front Physiol (2012)

Hypothetical positions of two spins as a function of time. (Top) At high temperature, the spin orientations fluctuate greatly, but independently of one another, producing a low dynamic correlation value. (Middle) At the critical temperature, the spin orientations fluctuate somewhat and the fluctuations are coordinated, producing a high dynamic correlation value. (Bottom) At low temperature, the spin orientations do not fluctuate very much, yielding a low dynamic correlation value.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3369250&req=5

Figure 2: Hypothetical positions of two spins as a function of time. (Top) At high temperature, the spin orientations fluctuate greatly, but independently of one another, producing a low dynamic correlation value. (Middle) At the critical temperature, the spin orientations fluctuate somewhat and the fluctuations are coordinated, producing a high dynamic correlation value. (Bottom) At low temperature, the spin orientations do not fluctuate very much, yielding a low dynamic correlation value.
Mentions: Critio: Great, you get it! Now let’s take a look at what happens to the dynamic correlation for the three different cases we talked about: low T, high T, and critical T. In the low T case, the piece of iron is extremely ordered and all the spins are pointed in the same direction. The dynamic correlation is low because there are no fluctuations and the terms in parentheses are both nearly 0 all the time. In contrast, for the high T case, there are plenty of fluctuations, as the spins are constantly deviating from their averages, but there is no coordination between sites i and j. One term in parenthesis might be positive, while the other might be negative. On another occasion, they might both be positive. So on average the dynamic correlation is again low. But at critical T, there is enough heat to allow fluctuations, but not so much heat that it destroys coordination between spin sites. The spins deviate from their averages, and they often do so together because the nearest neighbor influence is not completely overwhelmed by the added heat. Here, there is both fluctuation and coordination. When one of those “amoeba-like” domains that you saw in Movie S3 in Supplementary Material crawls across the screen, it might cause nearby spins to flip one after the other, setting up a dynamic correlation. I could sketch the positions of the spins, either up or down or in between, over time for the three different cases. [Critio now pulls out red and green markers, grabs another napkin and sketches Figure 2.]

Bottom Line: The hypothesis that the electrical activity of neural networks in the brain is critical is potentially important, as many simulations suggest that information processing functions would be optimized at the critical point.This hypothesis, however, is still controversial.Points and counter points are presented in dialog form.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Indiana University Bloomington, IN, USA.

ABSTRACT
Relatively recent work has reported that networks of neurons can produce avalanches of activity whose sizes follow a power law distribution. This suggests that these networks may be operating near a critical point, poised between a phase where activity rapidly dies out and a phase where activity is amplified over time. The hypothesis that the electrical activity of neural networks in the brain is critical is potentially important, as many simulations suggest that information processing functions would be optimized at the critical point. This hypothesis, however, is still controversial. Here we will explain the concept of criticality and review the substantial objections to the criticality hypothesis raised by skeptics. Points and counter points are presented in dialog form.

No MeSH data available.


Related in: MedlinePlus