Search our collection of 12.066 BOOKS

Author
Title
Publisher
Keywords
Booknr

Search our 2.818 News Items

INDEX AUTHORS


A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

We found 0 books

We found 3 news item(s)

SEJNOWSKI Terry, BARTOL Tom
Memory capacity of brain is 10 times more than previously thought - Data from the Salk Institute shows brain’s memory capacity is in the petabyte range, as much as entire Web
Edited: 201601200915
LA JOLLA—Salk researchers and collaborators have achieved critical insight into the size of neural connections, putting the memory capacity of the brain far higher than common estimates. The new work also answers a longstanding question as to how the brain is so energy efficient and could help engineers build computers that are incredibly powerful but also conserve energy.

“This is a real bombshell in the field of neuroscience,” says Terry Sejnowski, Salk professor and co-senior author of the paper, which was published in eLife. “We discovered the key to unlocking the design principle for how hippocampal neurons function with low energy but high computation power. Our new measurements of the brain’s memory capacity increase conservative estimates by a factor of 10 to at least a petabyte, in the same ballpark as the World Wide Web.”

Our memories and thoughts are the result of patterns of electrical and chemical activity in the brain. A key part of the activity happens when branches of neurons, much like electrical wire, interact at certain junctions, known as synapses. An output ‘wire’ (an axon) from one neuron connects to an input ‘wire’ (a dendrite) of a second neuron. Signals travel across the synapse as chemicals called neurotransmitters to tell the receiving neuron whether to convey an electrical signal to other neurons. Each neuron can have thousands of these synapses with thousands of other neurons.
“When we first reconstructed every dendrite, axon, glial process, and synapse from a volume of hippocampus the size of a single red blood cell, we were somewhat bewildered by the complexity and diversity amongst the synapses,” says Kristen Harris, co-senior author of the work and professor of neuroscience at the University of Texas, Austin. “While I had hoped to learn fundamental principles about how the brain is organized from these detailed reconstructions, I have been truly amazed at the precision obtained in the analyses of this report.”

Synapses are still a mystery, though their dysfunction can cause a range of neurological diseases. Larger synapses—with more surface area and vesicles of neurotransmitters—are stronger, making them more likely to activate their surrounding neurons than medium or small synapses.

The Salk team, while building a 3D reconstruction of rat hippocampus tissue (the memory center of the brain), noticed something unusual. In some cases, a single axon from one neuron formed two synapses reaching out to a single dendrite of a second neuron, signifying that the first neuron seemed to be sending a duplicate message to the receiving neuron.

At first, the researchers didn’t think much of this duplicity, which occurs about 10 percent of the time in the hippocampus. But Tom Bartol, a Salk staff scientist, had an idea: if they could measure the difference between two very similar synapses such as these, they might glean insight into synaptic sizes, which so far had only been classified in the field as small, medium and large.
To do this, researchers used advanced microscopy and computational algorithms they had developed to image rat brains and reconstruct the connectivity, shapes, volumes and surface area of the brain tissue down to a nanomolecular level.

The scientists expected the synapses would be roughly similar in size, but were surprised to discover the synapses were nearly identical.

“We were amazed to find that the difference in the sizes of the pairs of synapses were very small, on average, only about eight percent different in size. No one thought it would be such a small difference. This was a curveball from nature,” says Bartol.

Because the memory capacity of neurons is dependent upon synapse size, this eight percent difference turned out to be a key number the team could then plug into their algorithmic models of the brain to measure how much information could potentially be stored in synaptic connections.

It was known before that the range in sizes between the smallest and largest synapses was a factor of 60 and that most are small.

But armed with the knowledge that synapses of all sizes could vary in increments as little as eight percent between sizes within a factor of 60, the team determined there could be about 26 categories of sizes of synapses, rather than just a few.

“Our data suggests there are 10 times more discrete sizes of synapses than previously thought,” says Bartol. In computer terms, 26 sizes of synapses correspond to about 4.7 “bits” of information. Previously, it was thought that the brain was capable of just one to two bits for short and long memory storage in the hippocampus.

“This is roughly an order of magnitude of precision more than anyone has ever imagined,” says Sejnowski.

What makes this precision puzzling is that hippocampal synapses are notoriously unreliable. When a signal travels from one neuron to another, it typically activates that second neuron only 10 to 20 percent of the time.

“We had often wondered how the remarkable precision of the brain can come out of such unreliable synapses,” says Bartol. One answer, it seems, is in the constant adjustment of synapses, averaging out their success and failure rates over time. The team used their new data and a statistical model to find out how many signals it would take a pair of synapses to get to that eight percent difference.

The researchers calculated that for the smallest synapses, about 1,500 events cause a change in their size/ability (20 minutes) and for the largest synapses, only a couple hundred signaling events (1 to 2 minutes) cause a change.

“This means that every 2 or 20 minutes, your synapses are going up or down to the next size. The synapses are adjusting themselves according to the signals they receive,” says Bartol.

link to Salk Institute




half a brain ...
Statistica
Twitter: 307 miljoen actieve twitteraars in het 3de kwartaal van 2015 - Turkije zeer actief in censuur
Edited: 201512201202
Dat betekent een vertienvoudiging op 5 jaar tijd.

bron: lees meer


In the first half of 2015, there were 1,003 requests from courts and government agencies to remove content from Twitter. Out of this, 72 percent came from the Turkish authorities. Twitter removal requests leads to tweets no longer being displayed in individual countries rather than being deleted altogether. In the United States, there only 25 requests in the first six months of the year. The number of content removal requests is soaring. In the second half of 2014, 13 percent of these requests were successful; between January and June, it was higher - 42 percent of requests were granted.


Infographic: Turkey Dominates Global Twitter Censorship | Statista
CINGANO Federico
OECD SOCIAL, EMPLOYMENT AND MIGRATION WORKING PAPERS No. 163 - TRENDS IN INCOME INEQUALITY AND ITS IMPACT ON ECONOMIC GROWTH
Edited: 201412090905
20141209 - ABSTRACT

1. In most OECD countries, the gap between rich and poor is at its highest level since 30 years.
Today, the richest 10 per cent of the population in the OECD area earn 9.5 times the income of the poorest
10 per cent; in the 1980s this ratio stood at 7:1 and has been rising continuously ever since. However, the
rise in overall income inequality is not (only) about surging top income shares: often, incomes at the
bottom grew much slower during the prosperous years and fell during downturns, putting relative (and in
some countries, absolute) income poverty on the radar of policy concerns. This paper explores whether
such developments may have an impact on economic performance.

2. Drawing on harmonised data covering the OECD countries over the past 30 years, the
econometric analysis suggests that income inequality has a negative and statistically significant impact on
subsequent growth. In particular, what matters most is the gap between low income households and the rest
of the population. In contrast, no evidence is found that those with high incomes pulling away from the rest
of the population harms growth. The paper also evaluates the “human capital accumulation theory” finding
evidence for human capital as a channel through which inequality may affect growth. Analysis based on
micro data from the Adult Skills Survey (PIAAC) shows that increased income disparities depress skills
development among individuals with poorer parental education background, both in terms of the quantity
of education attained (e.g. years of schooling), and in terms of its quality (i.e. skill proficiency).
Educational outcomes of individuals from richer backgrounds, however, are not affected by inequality.

3. It follows that policies to reduce income inequalities should not only be pursued to improve
social outcomes but also to sustain long-term growth. Redistribution policies via taxes and transfers are a
key tool to ensure the benefits of growth are more broadly distributed and the results suggest they need not
be expected to undermine growth. But it is also important to promote equality of opportunity in access to
and quality of education. This implies a focus on families with children and youths – as this is when
decisions about human capital accumulation are made -- promoting employment for disadvantaged groups
through active labour market policies, childcare supports and in-work benefits.

Note LT: the famous book of Piketty (Capital) is not mentioned in the bibliography of this report!; Methodology: measurement of inequality with the use of Gini.
Read the report in PDF here ...