What are some examples of functional nodes ?

Explanation:

The human brain is a complex network of neurons. The problem is that there are about 10^12 of them with ~10^5 outgoing connections each; mapping out a network of this scale is not possible. Therefore, one needs to zoom out and look at the coarse-grained picture. This coarse-grained picture can be anatomical – a map of the large-scale wiring diagram between parts of the brain – or functional, indicating which parts of the brain tend to become active together under a given task.

But how should this coarse-graining be done in practice? How to define the nodes of a brain network –– what should brain nodes represent? In functional magnetic resonance imaging (fMRI), the highest level of detail is determined by the imaging technology. In a fMRI experiment, subjects are put inside a scanner that measures the dynamics of blood oxygenation in a 3D representation of the brain, divided into around 10,000 volume elements (voxels). Blood oxygenation is thought to correlate with the level of neural activity in the area. As each voxel contains about 5.5 million neurons, the network of voxels is significantly smaller than the network of neurons. However, it is still too large for many analysis tasks, and further coarse-graining is needed.

A typical way in the fMRI community is to group voxels into larger brain regions that are for historical reasons known as Regions of Interest (ROIs). This can be done in many ways, and there are many pre-defined maps (“brain atlases”) that define ROIs; these maps are based on anatomy, histology, or data-driven methods. It is common to use ROIs as the nodes of a brain functional network. The first step in constructing the brain network is to assign to each ROI a time series that is the average of the time series of its voxels measured in the imaging experiment. Then, to get the links, similarities between the ROI time series are calculated, usually with the Pearson correlation coefficient. The correlation between the two ROIs becomes their link weight. Often, only the strongest correlations are retained, and weak links are pruned from the network.

If the ROI approach is to work, the ROIs should be functionally homogeneous: their underlying voxels should behave approximately similarly. Otherwise, it is not clear what the brain network represents. Because this assumption hasn’t really been tested properly and because it is fundamentally important, we recently set out to explore whether it really holds.

We used resting-state data – data recorded with subjects who are just resting in the scanner, instructed to do nothing – to construct functional ROI-level networks based on some available atlases. We defined a measure of ROI consistency that has a value of one if all the voxels that make up the ROI have identical time series (making the ROI functionally homogeneous, which is good), and a value of zero if the voxels do not correlate at all (making that ROI a bad idea, in general).

land

explanation:

australia is the flattest continent, and it has vast plains.

hi there,

on december 11, 2001, china officially became the 143rd member of the

world trade organization (wto) in the culmination of a negotiation

process which began in 1986. economists have long been debating the

global effects of china's accession to the wto, and as china becomes

fully integrated into the organization over the next several years,

the accuracy of their predictions will be tested.

one of the biggest residual effects of china's entry to the wto,

according to economists, will be the relocation of manufacturing and

distribution centers to china. due to its cheap labor, cheap

industrial land, and educated workforce, china is an ideal production

centre for businesses based in outside countries. this will likely

result in a twofold impact – more jobs will be available in china,

while countries like india, which have historically offered cheap

labor, will suffer. taiwan and malaysia's technology industries are

already suffering as companies like dell computers move production to

china, and while foreign investment soars in china, other asian

countries suffer. in addition, mexico and the caribbean will lose

thousands of garment manufacturing jobs as the u.s. lifts restraints

on chinese textile imports.

while the impact on southeast asia may be negative, the western world

may benefit. while some suggest china's open borders will result in

increased competition and a decreased employment rate for the western

world, western countries will benefit from access to china's highly

developed electronics and industry sectors. with duties and quotas

slashed, and restrictions lifted, multinationals will benefit by

setting up distribution centers without the need for chinese

middlemen. in addition, it's expected that china will import massive

amounts of food products, machinery and vehicles from the u.s., japan,

hong kong, taiwan, singapore and south korea, thus providing

significant boosts to these countries' economies.

in conclusion, it seems that while western countries may benefit from

china's accession to the wto, there's the potential that asian and

south american countries may feel the pinch of free trade as china

moves to a global economy.