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26 Oct 09

PLoS Biology: Towards a Mathematical Theory of Cortical Micro-circuits (about Hawkins' HTM)

Hawkins' new document explaining biological basis of his HTM

www.ploscompbiol.org/...10.1371%2Fjournal.pcbi.1000532 - Preview

neuroinformatics neuroscience HTM cortex PLoS hawkins bayesian theory of the brain

Th
e theoretical setting of hierarchical Bayesian inference is gaining acceptance as a framework for understanding cortical computation.
Friston recently expanded on this to suggest an inversion method for hierarchical Bayesian dynamic models and to point out that the brain, in principle, has the infrastructure needed to invert hierarchical dynamic models [6].
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- In a recent review, Hegde and Felleman pointed out that the “Bayesian framework is not yet a neural model. [The Bayesian] framework currently helps explain the computations that underlie various brain functions, but not how the brain implements these computations” [2]. This paper is an attempt to fill this gap by deriving a computational model for cortical circuits based on the mathematics of Bayesian belief propagation in the context of a particular Bayesian framework called Hierarchical Temporal Memory (HTM).
- This paper's other author, George, recognized that the Memory-Prediction framework could be formulated in Bayesian terms and given a proper mathematical foundation [8],[9].
- Several researchers have proposed detailed models for cortical circuits [10]–[12].
- Other researchers [4],[13] have proposed detailed mechanisms by which Bayesian belief propagation techniques can be implemented in neurons.

23 Oct 09

PLoS Computational Biology: Subbarrel Patterns in Somatosensory Cortical Barrels Can Emerge from Local Dynamic Instabilities

Complex spatial patterning, common in the brain as well as in other biological systems, can emerge as a result of dynamic interactions that occur locally within developing structures. In the rodent somatosensory cortex, groups of neurons called “barrels” correspond to individual whiskers on the contralateral face. Barrels themselves often contain subbarrels organized into one of a few characteristic patterns. Here we demonstrate that similar patterns can be simulated by means of local growth-promoting and growth-retarding interactions within the circular domains of single barrels. The model correctly predicts that larger barrels contain more spatially complex subbarrel patterns, suggesting that the development of barrels and of the patterns within them may be understood in terms of some relatively simple dynamic processes. We also simulate the full nonlinear equations to demonstrate the predictive value of our linear analysis. Finally, we show that the pattern formation is robust with respect to the geometry of the barrel by simulating patterns on a realistically shaped barrel domain. This work shows how simple pattern forming mechanisms can explain neural wiring both qualitatively and quantitatively even in complex and irregular domains.

www.ploscompbiol.org/...10.1371%2Fjournal.pcbi.1000537 - Preview

cortex brain neuroscience PLoS

Can We 'Learn To See?': Study Shows Perception Of Invisible Stimuli Improves With Training

www.sciencedaily.com/...091021172659.htm - Preview

cortex neuroscience news

A Harvard Medical School study last year found that one blindsight patient could maneuver down a hallway filled with obstacles, even though the subject could not actually see.

Schwiedrzik said the new research may help blindsight patients gain conscious awareness of what their minds can see, and he suggested that new research should address whether the brains in blindsight patients and people with normal vision process the information the same way.

22 Oct 09

Cortical memory (Fuster) - Scholarpedia

www.scholarpedia.org/...Cortical_memory - Preview

Fuster brain neuroscience cortex memory

Hebb (1949) postulated that two cells or systems of cells that are repeatedly activated in the cortex at the same time will become associated, so that activity in one facilitates activity in the other.
Temporally coincident experiences of one or more sense modalities will modulate synapses between cells in those areas, leading to the formation of wider networks representing assorted items of individual memory, and, at higher cortical levels, of knowledge, which is the conceptual or semantic form of memory.
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- It is appropriate, therefore, to view the structure of primary sensory and motor cortices as a form of memory at the foundation of individual memory: phyletic memory. In accord with this view, phyletic memory is constituted by the structure of primary sensory and motor cortex at birth, which is common to all organisms of the same species. Phyletic memory would be the most basic of all memories, the genetic memory that the organism has formed in the course of evolution by interactions with the surrounding world. The genetically defined structures of primary cortex dedicated to analyzing elementary sensory features and to integrating elementary primitives of movement would form the basic template on which the memory of the individual would develop. On that foundation of phyletic memory, all the memory of the individual is formed according to Hebbian principles and hierarchically organized in cortex of association. Perceptual memories organize themselves in posterior (parietal-temporal) cortex and executive or motor memories in frontal cortex.
  - Cant catch his logic. Earliest development of primary areas could be perfectly explaind by assuming that brain at first learning elemetrarly sensory and motor "pixels", right? - on 2009-10-22
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- Working memory is the temporary active retention of information for prospective action. It is a kind of sustained attention focused on an internal representation to be used in the near term.

11 Oct 09

Prefrontal cortex - Wikipedia, the free encyclopedia

en.wikipedia.org/...Prefrontal_cortex - Preview

brain cortex prefrontal cortex wiki neuroscience

Miller and Cohen propose an Integrative Theory of Prefrontal Cortex Function. The two theorize that “cognitive control stems from the active maintenance of patterns of activity in the prefrontal cortex that represents goals and means to achieve them. They provide bias signals to other brain structures whose net effect is to guide the flow of activity along neural pathways that establish the proper mappings between inputs, internal states, and outputs needed to perform a given task” (Miller & Cohen, 2001). Essentially the two theorize that the prefrontal cortex guides the inputs and connections which allows for cognitive control of our actions.

26 Aug 09