(Left)
A coma-specific region in the left pontine tegmentum in the brainstem
(red). (Right) Multiple nuclei implicated in arousal surround the
coma-specific region, including the dorsal raphe (yellow dots), locus
coeruleus (black dots), and parabrachial nucleus (red dashed line).
(credit: David B. Fischer, MD et al./Neurology)
An international team of neurologists led by Beth Israel Deaconess
Medical Center (BIDMC) has identified three specific regions of the
brain that appear to be critical components of consciousness: one in the
brainstem, involved in arousal; and two cortical regions involved in
awareness.
To pinpoint the exact regions, the neurologists first analyzed 36
patients with brainstem lesions (injuries). They discovered that a
specific small area of the brainstem — the pontine tegmentum
(specifically, the rostral dorsolateral portion) — was significantly
associated with coma.* (The brainstem connects the brain with the spinal
cord and is responsible for the sleep/wake cycle and cardiac and
respiratory rates.)
Human connectome (credit: Human Connectome Project)
Once they had identified the area involved in arousal, they next
looked to see which cortical regions were connected to this arousal area
and also become disconnected in disorders of consciousness. To do that,
they used the Human Connectome — a sort of wiring diagram of the brain.
Thanks to the connectome, “we can look at not just the location of
lesions, but also their connectivity,” said Michael D. Fox, MD, PhD,
Director of the Laboratory for Brain Network Imaging and Modulation and
the Associate Director of the Berenson-Allen Center for Noninvasive Brain Stimulation at BIDMC.
The
coma-specific brainstem region is functionally connected to clusters in
the anterior insula (AI) and pregenual anterior cingulate cortex
(pACC). Voxels within these nodes were functionally connected to all 12
coma lesions, and were more functionally connected to coma lesions than
control lesions. (credit: David B. Fischer, MD et al./Neurology)
They discovered two connected cortical regions: the pregenual anterior cingulate cortex (pACC) and the left ventral anterior insula (AI). Both regions were previously implicated in both arousal and awareness.
“Over the past year, researchers in my lab have used this approach to
understand visual and auditory hallucinations, impaired speech, and
movement disorders,” said Fox. “A collaborative team of neuroscientists
and physicians had the insight and unique expertise needed to apply this
approach to consciousness.”
Consciousness network
Finally, the team investigated whether this brainstem-cortex network
was functioning in another subset of patients with disorders of
consciousness, including coma. Using a special type of MRI scan, the
scientists found that their newly identified “consciousness network” was
disrupted in patients with impaired consciousness.
Published recently in the journal Neurology, the findings —
bolstered by data from rodent studies — suggest that the network between
the brainstem and these two cortical regions plays a role in
maintaining human consciousness.
A next step, Fox notes, may be to investigate other data sets in
which patients lost consciousness to find out if the same, different, or
overlapping neural networks are involved.
“This is most relevant if we can use these networks as a target for
brain stimulation for people with disorders of consciousness,” said Fox.
“If we zero in on the regions and network involved, can we someday wake
someone up who is in a persistent vegetative state? That’s the ultimate
question.”
Researchers at the University of Iowa Carver College of Medicine, the
Brain and Spine Institute (Institut du Cerveau et de la Moelle
épinière-ICM) at Hôpital Pitié-Salpêtrière, University and University
Hospital of Liège, the Comparative Neuroanatomy Lab and the Centre for
Integrative Neuroscience in Tübingen, the Max Planck Institute for
Biological Cybernetics, and Massachusetts General Hospital were also
involved.
This work was supported by the Howard Hughes Medical Institute, the
Parkinson’s Disease Foundation, NIH, American Academy of
Neurology/American Brain Foundation, Sidney R. Baer, Jr. Foundation,
Harvard Catalyst, the Belgian National Funds for Scientific Research,
the European Commission, the James McDonnell Foundation, the European
Space Agency, Mind Science Foundation, the French Speaking Community
Concerted Research Action, the Public Utility Foundation “Université
Européenne du Travail,” Fondazione Europea di Ricerca Biomedica, the
University and University Hospital of Liège, the Center for Integrative
Neuroscience, and the Max Planck Society.
* 12 lesions led to coma and 24 (the control group) did not. Ten
out of the 12 coma-inducing brainstem lesions were involved in this
area, while just one of the 24 control lesions was.
Abstract of A human brain network derived from coma-causing brainstem lesions
Objective: To characterize a brainstem location specific to coma-causing lesions, and its functional connectivity network.
Methods: We compared 12 coma-causing brainstem lesions to 24 control
brainstem lesions using voxel-based lesion-symptom mapping in a
case-control design to identify a site significantly associated with
coma. We next used resting-state functional connectivity from a healthy
cohort to identify a network of regions functionally connected to this
brainstem site. We further investigated the cortical regions of this
network by comparing their spatial topography to that of known networks
and by evaluating their functional connectivity in patients with
disorders of consciousness.
Results: A small region in the rostral dorsolateral pontine tegmentum
was significantly associated with coma-causing lesions. In healthy
adults, this brainstem site was functionally connected to the ventral
anterior insula (AI) and pregenual anterior cingulate cortex (pACC).
These cortical areas aligned poorly with previously defined
resting-state networks, better matching the distribution of von Economo
neurons. Finally, connectivity between the AI and pACC was disrupted in
patients with disorders of consciousness, and to a greater degree than
other brain networks.
Conclusions: Injury to a small region in the pontine tegmentum is
significantly associated with coma. This brainstem site is functionally
connected to 2 cortical regions, the AI and pACC, which become
disconnected in disorders of consciousness. This network of brain
regions may have a role in the maintenance of human consciousness.
Map showing the migration and expansion of the Austronesians.
Colorized photograph of a Tsou warrior wearing traditional clothing, pre-World War II
Archaeological evidence demonstrates a technological connection between the farming cultures of the "south", meaning Southeast Asia and Melanesia, and sites that are first known from mainland China;
whereas a combination of archaeological and linguistic evidence has
been interpreted as supporting a "northern" origin for the Austronesian language family in mainland southern China and Taiwan.
It is theoretically possible that a few thousand years before the Southward expansion of the Han dynasty and of Vietnam,
Austronesian speakers spread down the coast of southern China past
Taiwan as far as the (Gulf of Tonkin). In time, the spread of other
language groups such as Austroasiatic, Tai-Kadai, Hmong-Mien and Sino-Tibetan (such as Chinese) led to the assimilation and eventual sinicization of all (proto) Austronesian-speaking populations that remained on the mainland (a process which continues today in Taiwan).[16]
In a recent treatment, all Austronesian languages were classified into
10 subfamilies, with all the extra-Formosan languages grouped in one
subfamily and with representatives of the remaining nine known only in
Taiwan.[17]
It has been argued that these patterns are best explained by dispersal
of an agricultural people from Taiwan into insular Southeast Asia,
Melanesia, and, ultimately, the remote Pacific. This model has been termed the "express train to Polynesia"[18][19]— it is broadly consistent with available data [20], despite concerns that have been raised.[21]
Alternatives to this model posit an indigenous origin for the Austronesian languages in Southeast Asia or Melanesia.[22][23][24][25]
Genetic analyses suggest that the Southeast Asian Austronesians had spread over Sundaland (the land mass of Southeastern Asia before rising sea-level created the archipelago of Southeast Asia) and evolved in situ over the last 35,000 years.[26]
Nevertheless, in 2016, DNA analysis carried out found that one of the
genetic markers used in the study but not the others supports a
small-scale "out-of-Taiwan" hypothesis.[27]
The studies suggest that only a small fraction of the Taiwan genetic
lineages are found among the people of South East Asia, and it is argued
that these movements of people from Taiwan, while smaller in scale, had
a strong impact on the culture and language of the people.[28][29][30]
Migration and dispersion
Genomic analysis of cultivated coconut (Cocos nucifera)
has shed light on the movements of Austronesian peoples. By examining
10 microsatelite loci, researchers found that there are 2 genetically
distinct subpopulations of coconut – one originating in the Indian
Ocean, the other in the Pacific Ocean. However, there is evidence of admixture,
the transfer of genetic material, between the two populations. Given
that coconuts are ideally suited for ocean dispersal, it seems possible
that individuals from one population could have floated to the other.
However, the locations of the admixture events are limited to Madagascar and coastal east Africa and exclude the Seychelles and Mauritius.
Sailing west from Maritime Southeast Asia in the Indian Ocean, the
Austronesian peoples reached Madagascar by ca. 50–500 CE, and reached
other parts thereafter. This forms a pattern that coincides with the
known trade routes of Austronesian sailors. Additionally, there is a
genetically distinct sub-population of coconuts on the eastern coast of
South America which has undergone a genetic bottleneck resulting from a
founder effect; however, its ancestral population is the pacific
coconut, which suggests that Austronesian peoples may have sailed as far
east as the Americas.[31][32][33]
"Out of Taiwan" model
An Atayal tribal woman from Taiwan with tattoo on her face as a symbol of maturity, which was a tradition for both males and females.
An element in the ancestry of Austronesian-speaking peoples, the one
which carried their ancestral language, originated on the island of Taiwan. This occurred after the migration of pre-Austronesian-speaking peoples from continental Asia between approximately 10,000–6,000 BCE.[34][17]
Other research has suggested that, according to radiocarbon dates,
Austronesians may have migrated from mainland China to Taiwan as late as
4000 BC (Dapenkeng culture).[35] Before migrating to Taiwan, Austronesian speakers originated from the Neolithic cultures of Southeastern China, such as the Hemudu culture or the Liangzhu culture of the Yangtze River Delta.[36][37][38]
Based on recent archaeological evidence as well as linguistic evidence, Roger Blench (2014)[39] considers the Austronesians in Taiwan to have been a melting pot
of immigrants from various parts of the coast of eastern China that had
been migrating to Taiwan by 4,000 B.P. These immigrants included people
from the foxtail millet-cultivating Longshan culture of Shandong (with Longshan-type cultures found in southern Taiwan), the fishing-based Dapenkeng culture of coastal Fujian, and the Yuanshan culture of northernmost Taiwan which Blench suggests may have originated from the coast of Guangdong. Based on geography and cultural vocabulary, Blench believes that the Yuanshan people may have spoken Northeast Formosan languages. Thus, Blench believes that there is in fact no "apical" ancestor of Austronesian in the sense that there was no true single Proto-Austronesian language
that gave rise to present-day Austronesian languages. Instead, multiple
migrations of various pre-Austronesian peoples and languages from the
Chinese mainland that were related but distinct came together to form
what we now know as Austronesian in Taiwan. Hence, Blench considers the
single-migration model to be inconsistent with both the archaeological
and linguistic (lexical) evidence.
Tianlong Jiao (2007)[40]
notes that Neolithic peoples from the coast of southeastern China
migrated to Taiwan from 6,500-5,000 B.P. The Neolithic period in
southeastern China lasted from 6,500 B.P. until 3,500 B.P., and can be
divided into the early (ca, 6500-5000 B.P.), middle (ca. 5000-4300
B.P.), and late (ca. 4300-3500 B.P.) Neolithic periods. The Neolithic in
southeastern China started off with pottery, polished stone tools, and
bone tools, with technology continuing to progress over the years.
Neolithic peoples in Taiwan and mainland China continued to maintain
regular contact with each other until 3,500 B.P., which was when bronze
artefacts started to appear. Jiao (2013)[41]
notes the Neolithic appeared on the coast of Fujian around 6,000 B.P.
During the Neolithic, the coast of Fujian had a low population density,
with the population depending on mostly on fishing and hunting,
alongside with limited agriculture.
According to the mainstream "out-of-Taiwan model", a large-scale Austronesian expansion began around 3000–1500 BCE. Population growth primarily fuelled this migration. These first settlers may have landed in northern Luzon in the archipelago of the Philippines, intermingling with the earlier Australo-Melanesian
population who had inhabited the islands since about 23,000 years
earlier. Over the next thousand years, Austronesian peoples migrated
southeast to the rest of the Philippines, and into the islands of the Celebes Sea,
Borneo, and Indonesia. The Austronesian peoples of Maritime Southeast
Asia sailed eastward, and spread to the islands of Melanesia and
Micronesia between 1200 BCE and 500 CE, respectively. The Austronesian
inhabitants that spread westward through Maritime Southeast Asia had
reached some parts of mainland Southeast Asia, and later on Madagascar.[34][42]
Sailing to Micronesia and the previously uninhabited islands of
remote Oceania by 1000 BCE, the Austronesian peoples founded Polynesia.[43] These people settled most of the Pacific Islands. They had settled Rapa Nui (Easter Island) by AD 300, Hawaii by AD 400, and into New Zealand by about 1280 CE.
There is evidence, based in the spreading of the sweet potato, that they reached South America where they traded with the Native Americans.[44][45]
In the Indian Ocean they sailed west from Maritime Southeast Asia; the Austronesian peoples reached Madagascar by ca. 50–500 CE.[32][33]
"Southeast Asian origin" model
This "out of Taiwan model" has been challenged by a 2008 study. Examination of mitochondrial DNA
lineages shows that they have been evolving within Island Southeast
Asia (ISEA) for a longer period than previously believed. Population
dispersals occurred at the same time as sea levels rose, which may have
resulted in migrations to the Philippines as far north as Taiwan within
the last 10,000 years.[26]
The migrations were likely driven by climate change — the effects of the drowning the Sundaland
subcontinent (which had extended the Asian landmass as far as Borneo
and Java). This happened during the period 15,000 to 7,000 years ago
following the Last Glacial Maximum. Rising sea levels in three massive
pulses caused flooding and the partial submergence of the Sunda
subcontinent, creating the Java and South China Seas and the thousands
of islands that make up Indonesia and the Philippines today.[24]
Genetic evidence found in 2016 indicates that movements of people from
Taiwan to the islands of South East Asia did occur, albeit smaller in
scale, which nevertheless may have brought about linguistic and
cultural changes.[27]
Findings from HUGO (Human Genome Organization)
in 2009 also show that Asia was populated primarily through a single
migration event out of Africa whereby an early population first entered
South East Asia before they moved northwards to East Asia.[46][47][48]
They found genetic similarities between populations throughout Asia and
an increase in genetic diversity from northern to southern latitudes.
Although the Chinese population is very large, it has less variation
than the smaller number of individuals living in South East Asia,
because the Chinese expansion occurred very recently, following the
development of rice agriculture — within only the last 10,000 years.[citation needed]
Formation of tribes and kingdoms
A TagalogMaginoo (noble class) couple, both wearing blue-coloured clothing (blue being the distinctive colour of their class).
Muslim traders from the Arabian peninsula were thought to have brought Islam by the 10th century. Islam was established as the dominant religion in the Indonesian archipelago
by the 16th century. The Austronesian inhabitants of Polynesia were
unaffected by this cultural trade, and retained their indigenous culture
in the Pacific region.[49]
Western Europeans in search of spices and gold later colonized
most of the Austronesian-speaking countries of the Asia-Pacific region,
beginning from the 16th century with the Portuguese and Spanish
colonization of some parts of Indonesia (present day East Timor), the Philippines, Palau, Guam, and the Mariana Islands; the Dutch colonization of the Indonesian archipelago; the British colonization of Malaysia and Oceania; the French colonization of French Polynesia; and later, the American governance of the Pacific.
Meanwhile, the British, Germans, French, Americans, and Japanese
began establishing spheres of influence within the Pacific Islands
during the 19th and early 20th centuries. The Japanese later invaded
most of Southeast Asia and some parts of the Pacific during World War II.
The latter half of the 20th century initiated independence of
modern-day Indonesia, Malaysia, East Timor and many of the Pacific
Island nations, as well as the re-independence of the Philippines.
Geographic distribution
Map
showing the distribution of the Austronesian language family (light
rose pink). It roughly corresponds to the distribution of the
Austronesian people.
According to a recent studies by Stanford University,
there is wide variety of paternal ancestry among the Austronesian
people, aside from European introgression found in Maritime Southeast
Asia, Oceania, and Madagascar. They constitute the dominant ethnic group
in the Malay Peninsula, Maritime Southeast Asia, Melanesia, Micronesia,
Polynesia and Madagascar. An estimated 380,000,000 people living in
these regions are of Austronesian descent.
The peoples constitute the dominant ethnic groups in Malaysia, Indonesia, Brunei, the Philippines, the southernmost part of Thailand and East Timor, together with Singapore.
Outside this area, they inhabit Palau, Guam and the Northern Marianas,
most of Madagascar, the Cham areas of Vietnam and Cambodia (the remnants
of the Champa kingdom which covered central and southern Vietnam), and
all countries in the Micronesian and Polynesian sphere of influence.
Culture
The
native culture of Austronesia varies from region to region. The early
Austronesian peoples considered the sea as the basic feature of their
life.[citation needed] Following their diaspora to Southeast Asia and Oceania,
they migrated by boat to other islands. Boats of different sizes and
shapes have been found in every Austronesian culture, from Madagascar,
Maritime Southeast Asia, to Polynesia, and have different names.
In Southeast Asia, head-hunting was restricted to the highlands as a
result of warfare. Mummification is only found among the highland
Austronesian Filipinos, and in some Indonesian groups in Celebes and
Borneo.
Writing
Left: Petroglyph on the western coast of Hawaii. Petroglyphs were symbolic, but could not encode language. Right: An Austronesian abugida known as Baybayin from the Philippines.
With the possible exception of rongorongo
on Easter Island, writing among pre-modern Austronesians was limited to
the Indianized states and the sultanates of Maritime Southeast Asia.
These systems included abugidas from the Brahmic family, such as Baybayin, the Javanese script, and Old Kawi, and abjads derived from the Arabic script such as Jawi.
Left: A young Bontoc man from the Philippines (c. 1908) with tattoos on the chest and arms (chaklag). These indicated that the man was a warrior who had taken heads during battle.[57] Right: A young Māori woman with traditional tattoos (moko) on the lips and chin (c. 1860–1879). These were symbols of status and rank, as well as being considered marks of beauty.
Body art among Austronesian peoples is common, especially elaborate tattooing which has ancient origins.[58] It is particularly prominent in Polynesian cultures, from where the word "tattoo" derives. But tattooing is also prominent among Austronesian groups in Taiwan, the Philippines, Indonesia, and Malaysia.[59]
Among the Māori of New Zealand, tattoos (moko) were originally carved into the skin using bone chisels (uhi) rather than through puncturing as in usual practice.[60] In addition to being pigmented, the skin was also left raised into ridges of swirling patterns.[61]
In the Philippines, the Spanish called the Filipinos they first encountered in the Visayas as the Pintados, ("the painted ones" or "the tattooed ones")[62] due to their practice of tattooing their entire bodies.[63]
Tattooing traditions were mostly lost as the natives of the islands
converted to Christianity and Islam, though they were still practised in
isolated groups in the highlands of Luzon and Mindanao. Philippine tattoos were usually geometric patterns or stylized depictions of animals, plants, and human figures.[64][65][66] Some of the few remaining traditional tattoos in the Philippines are from elders of the Igorot peoples. Most of these were records of war exploits against the Japanese during World War II.[67]
Decorated jars and other forms of pottery are also common, with
patterns often resembling those used in tattoos. Austronesian peoples
living close to mainland Asia were also influenced by Chinese, Indian, and Arabic art forms.
Architecture
Austronesian
Vernacular Stilt house is the native cultural houses of Austronesian
people. Every Austronesian country has their own name and style for
their own Austronesian houses. In the Philippines these are called Bahay kubo with many styles and variants, in Indonesia these are called Rumah adat also with many variants, and in Malaysia these are called Rumah Melayu which are also found in Indonesia and part of the Rumah Adat family.
Religion
Left: A troupe of BahauDayak performers during the Hudoq festival (Harvest festival) in Kalimantan, Indonesia). (c. 1898–1900) Right: Balinese small familial house shrines to honor the households' ancestor in Bali island, Indonesia.
Indigenous religions were initially predominant. Mythologies vary by
culture and geographical location, but are generally bound by the belief
in an all-powerful divinity. Other beliefs such as ancestor worship, animism, and shamanism are also practiced. Currently, many of these beliefs have gradually been replaced. Examples of native religions include: Anito, Gabâ, Sunda Wiwitan, Kejawen, and the Māori religion. The moai of the Rapa Nui is another example since they are built to represent deceased ancestors.
Southeast Asian contact with India and China allowed the
introduction of Hinduism and Buddhism. Later, Muslim traders introduced
the Islamic faith between the periods of the 10th, and 13th century. The
European Age of Discovery, brought Christianity to various parts of the region, including both New Zealand and Australia. Currently, the dominant religions are Christianity
in the Philippines, much of eastern Indonesia, some parts of Indonesian
Sumatra and Borneo, East Timor, Papua New Guinea, Singapore, most of
the Pacific Islands, and Madagascar; Islam found in Singapore, Indonesia, Malaysia, southern Thailand, the southern Philippines and Brunei; Hinduism in Singapore, Bali, and some parts of Indonesia, Malaysia and Philippines. There is also a tiny population in Manado on the island of Sulawesi who professed Judaism, most of whom either have Jewish ancestry who later mixed with the indigenous Minahasans or are converts.
The Austronesian music in Maritime Southeast Asia had a mixture of
Chinese, Indian, and Arabic musical styles and sounds that had fused
together with the indigenous Austronesian culture and music. In
Indonesia, Gamelan,
a type of orchestra that incorporates Xylophone and Metallophone
elements, is widely used in its Hindu, Buddhist, and Islamic cultural
tradition. In some parts of the southern, and northern Philippines, an
Arabic gong-drum known as Kulintang, and a gong-chime known as Gangsa, is also used. The Austronesian music of Oceania have retained their indigenous Austronesian sounds. The Slit drums
is an indigenous Austronesian musical instrument that were invented and
used by the Southeast Asian-Austronesian, and Oceanic-Austronesian
ethnic groups.
Genetic studies
Genetic studies have been done on the people and related groups.[68] The Haplogroup O1 (Y-DNA)a-M119 genetic marker
is frequently detected in Native Taiwanese, northern Philippines and
Polynesians, as well as some people in Indonesia, Malaysia and
non-Austronesian populations in southern China.[69]
A 2007 analysis of the DNA recovered from human remains in archeological sites of prehistoric peoples along the Yangtze River in China also shows high frequencies of Haplogroup O1 in the NeolithicLiangzhu culture, linking them to Austronesian and Tai-Kadai peoples. The Liangzhu culture existed in coastal areas around the mouth of the Yangtze.
Haplogroup O1 was absent in other archeological sites inland. The
authors of the study suggest that this may be evidence of two different
human migration routes during the peopling of Eastern Asia; one coastal
and the other inland, with little genetic flow between them.[70]
Mitochondrial DNA (mtDNA) analysis in 2008 suggests that the populations in the islands of South East Asia may have evolved in situ over the last 35,000 years, that they had already established themselves in the region before the Neolithic period, long before the Taiwanese people were proposed to have moved out of Taiwan into the region.[26]
Nevertheless, in 2016, DNA analysis carried out found that one of the
genetic markers used in the study, haplogroup M7c3c, supports the
"out-of-Taiwan" hypothesis, although not from the other genetic markers.
Results from these studies suggest that there were movements of
Neolithic people from Taiwan to the islands of South East Asia around
4,000 years ago, but they were small-scale affairs, with greater impact
in the Philippines.[27] The fractions of Taiwanese Neolithic lineages present in the people of
the islands of South East Asia today are estimated to range from 28% in
the Philippines to 13.6% in Western Indonesia and 10.3% in Kalimantan.[71]
The authors argue that the cultural impact on the people was due to
small-scale interactions and waves of acculturation, and that the
Taiwanese migrants despite being smaller in numbers had a strong
influence on the culture and language of the people as they were seen as
an elite or associated with a new religion or philosophy.[28][30]
Some researchers have proposed a more complex pattern of settlement and
dispersal, where the Austronesians were dispersed from mainland South
East Asia via two routes: a northern route through Taiwan before they
moved further down to the South East Asian islands, and a southern route
through western Indonesia.[72] Others have also found genetic links between the ancestors of Austronesians and people of North and South China.[73][74]
The Austronesian speaking people can now be grouped into two genetically close groups:[citation needed]
Stanford
post-doctoral scholar Peter McMahon, left, and visiting researcher
Alireza Marandi examine a prototype of a new type of light-based
computer. (credit: L.A. Cicero)
Stanford researchers have designed a new type of computer that combines optical and electronic technology to solve combinatorial optimization problems, which are challenging for traditional computers, even for supercomputers.
An optimal traveling salesman route through some U.S. capital cities (credit: SAS)
An example is the “traveling salesman”
problem, in which a salesman has to visit a specific set of cities,
each only once, and return to the first city, taking the most efficient
route possible. The number of possible routes increases extremely
rapidly as cities are added, and this underlies why the problem is
difficult to solve.
Other examples of such problems include finding the optimal path for
delivery trucks, minimizing interference in wireless networks, and
determining how proteins fold. Even small improvements in some of these
areas could result in massive monetary savings.
Quantum computers are also being explored to solve such problems, but
“providing dense connectivity between qubits remains a major
challenge,” the authors note in a paper published Oct. 20 in the
journal Science.
The Stanford team has built an “Ising machine,”
named for a mathematical model of magnetism. But instead of using
magnetism, the team built an entirely new type of computer that blends
optical and electrical processing.*
Experimental schematic of a measurement-feedback-based coherent Ising machine.
A
time-division-multiplexed pulsed degenerate optical parametric
oscillator is formed by a nonlinear crystal (PPLN) in a fiber ring
cavity containing 160 pulses. A fraction of each pulse is measured and
used to compute a feedback signal that effectively couples the otherwise-independent pulses in the cavity. IM: intensity modulator; PM: phase
modulator; LO: local oscillator; SHG: second-harmonic generation; FPGA:
field-programmable gate array. (credit: Peter L. McMahon et
al./Science)
The team used a special kind of laser system, known as a “degenerate
optical parametric oscillator.” When turned on, it will represent an
upward- or downward-pointing “spin” in the classic Ising machine. Pulses
of the laser represent a city’s position in a path the salesman could
take.
Scaling up
If it can be scaled up, this non-traditional computer could save
costs by finding more optimal solutions to problems that have an
incredibly high number of possible solutions, the researchers suggest.
Nearly all of the materials used to make this machine are
off-the-shelf elements that are already used for telecommunications.
That, in combination with the simplicity of the programming, makes it
easy to scale up, the researchers say. Stanford’s machine is currently
able to solve 100-variable problems with any arbitrary set of
connections between variables, and it has been tested on thousands of
scenarios.
A group at NTT in Japan that consulted with Stanford’s team has also
created an independent version of the machine; its study has been published alongside Stanford’s by Science.
For now, the Ising machine-based system still falls short of beating
the processing power of traditional digital computers when it comes to
combinatorial optimization.
Researchers from the National Institute of Informatics (Japan),
University of Tokyo, NTT Basic Research Laboratories, and the ImPACT
Program were also co-authors. This research was funded by the Impulsing
Paradigm Change through Disruptive Technologies (ImPACT) Program of the
Council of Science, Technology and Innovation (Cabinet Office, Government
of Japan).
* A theoretical Ising machine acts like a reprogrammable network
of artificial magnets, where each magnet only points up or down and,
like a real magnetic system, it is expected to tend toward operating at
low energy.
The theory is that, if the connections among a network of magnets
can be programmed to represent the problem at hand, once they settle on
the optimal, low-energy directions they should face, the solution can
be derived from their final state. In the case of the traveling
salesman, each artificial magnet in the Ising machine represents the
position of a city in a particular path.
In an earlier version of this machine (published two years ago),
the team members extracted a small portion of each pulse, delayed it
and added a controlled amount of that portion to the subsequent pulses.
In traveling salesman terms, this is how they program the machine with
the connections and distances between the cities. The pulse-to-pulse
couplings constitute the programming of the problem. Then the machine is
turned on to try to find a solution, which can be obtained by measuring
the final output phases of the pulses.
The problem in this previous approach was connecting large
numbers of pulses in arbitrarily complex ways. It was doable but
required an added controllable optical delay for each pulse, which was
costly and difficult to implement.
The new Stanford Ising machine shows that a more affordable and
practical version could be made by replacing the controllable optical
delays with a digital electronic circuit, which emulates the optical
connections among the pulses to program the problem.
Abstract of A fully-programmable 100-spin coherent Ising machine with all-to-all connections
Unconventional, special-purpose machines may aid in accelerating the
solution of some of the hardest problems in computing, such as
large-scale combinatorial optimizations, by exploiting different
operating mechanisms than standard digital computers. We present a
scalable optical processor with electronic feedback that can be realized
at large scale with room-temperature technology. Our prototype machine
is able to find exact solutions of, or to sample good approximate
solutions to, a variety of hard instances of Ising problems with up to
100 spins and 10,000 spin-spin connections.
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