Transcript of Daniel Amit 1938-2007 Systems of spin-like elements may dynamically relax governed by the...
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- Daniel Amit 1938-2007
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- Systems of spin-like elements may dynamically relax governed by
the Hamiltonian towards increasingly complex discrete attractor
states (Ising model)ferromagnetic (e.g., S.K. model)+ spin-glass
state (Hopfield model)+ memory states ABC D
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- Daniel Amit, Hanoch Gutfreund and Haim Sompolinsky showed how
to extend the mathematical analysis of spin-glasses into a new
statistical physics of Hopfield attractor networks No. Almost.
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- They derived the free-energy and the saddle-point equations
that describe the equilibrium reached by relaxational dynamics
yielding finally a phase-diagram storage load = p / N SG (spin
glass) DS (disordered state) +RS (retrieval memory state)
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- AT, J. Phys. A: Math. Gen. 24 (1991) 2645-2654. are spin-glass
effects really relevant to understanding realistic auto-associative
networks? binary threshold-linear: No. Almost. Threshold-linear
spin glass (SK) Threshold-linear neural network (Hopfield)
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- La reazione nera 1873 Camillo Golgi 1843-1926 Teoria reticolare
(il sincizio) Premio Nobel 1906 Santiago Ramn y Cajal 1852-1934
Teoria cellulare (i neuroni)
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- Arealization and Memory in the Cortex monkey Main perspectives:
a) Content-based b) Hierarchical c) Statistical/modular
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- The statistical/modular perspective The Braitenberg model N
pyramidal cells N compartments N cells each A pical synapses B asal
synapses
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- Cortical modules Local attractor states (=S) Global activity
patterns A simple semantic network (OKane & Treves, 1992)
Structured long-range connectivity 0 state included Sparse global
patterns updated to remove the memory glass problem (Fulvi Mari
& Treves, 1998) Potts units with dilute connectivity S+1 Potts
states Sparse Potts patterns Reduced to a Potts model (Kropff &
Treves, 2005)..but all cortical modules share the same organization
p c C S 2 !! p c S ?!?!
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- Cerebellar Networks
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- The numbers of expansion recoding Each MF terminates in several
hundreds rosettes Each rosette has the dendrites of 28 GCs Each GC
receives from 4 rosettes (MFs) There are 450 times more GCs than
MFs In humans, there are 3x10 10 GCs, each making about 300 PF
synapse, for a total 10 13 storage locations on some 5x10 7
Purkinje cells.
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- Nature 411, 189 - 193 (2001); doi:10.1038/35075564 Nature 411,
189 - 193 (2001) Scalable architecture in mammalian brains DAMON A.
CLARK*, PARTHA P. MITRA & SAMUEL S.-H. WANG* * Department of
Molecular Biology and Department of Physics, Princeton University,
Princeton, New Jersey 08544, USA Bell Laboratories, Lucent
Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974,
USA Correspondence and requests for materials should be addressed
to S.S.-H.W. (e-mail: samwang@molbio.princeton.edu). Comparison of
mammalian brain parts has often focused on differences in absolute
size, revealing only a general tendency for all parts to grow
together. Attempts to find size-independent effects using body
weight as a reference variable obscure size relationships owing to
independent variation of body size and give phylogenies of
questionable significance. Here we use the brain itself as a size
reference to define the cerebrotype, a species-by-species measure
of brain composition. With this measure, across many mammalian taxa
the cerebellum occupies a constant fraction of the total brain
volume (0.13 0.02), arguing against the hypothesis that the
cerebellum acts as a computational engine principally serving the
neocortex. Mammalian taxa can be well separated by cerebrotype,
thus allowing the use of quantitative neuroanatomical data to test
evolutionary relationships. Primate cerebrotypes have progressively
shifted and neocortical volume fractions have become successively
larger in lemurs and lorises, New World monkeys, Old World monkeys,
and hominoids, lending support to the idea that primate brain
architecture has been driven by directed selection pressure. At the
same time, absolute brain size can vary over 100-fold within a
taxon, while maintaining a relatively uniform cerebrotype. Brains
therefore constitute a scalable architecture.
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- Striatal Networks
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- paleocortex (olfactory) archicortex (hippocampus) neocortex
(the rest)
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- Brain Behav Evol. 1997;49(4):179-213. The telencephalon of
tetrapods in evolution. Striedter GF. Department of Psychobiology,
University of California, Irvine 92697-4550, USA. Numerous
scientists have sought a homologue of mammalian isocortex in
sauropsids (reptiles and birds) and a homologue of sauropsid dorsal
ventricular ridge in mammals. Although some of the proposed
theories were enormously influential, alternative theories
continued to coexist, primarily because the striking differences in
pallial organization between adult mammals, sauropsids, and
amphibians enabled different authors to enlist different subsets of
similarity data in support of different hypotheses of putative
homology. A phylogenetic analysis based on parsimony cannot
discriminate between such alternative hypotheses of putative
homology, because sauropsids and mammals are sister groups. One
solution to this dilemma is to include embryological patterns of
telencephalic organization in the comparative analysis. Because
early developmental stages in different taxa tend to resemble each
other more than the adults do, the embryological data may reveal
intermediate patterns of organization that provide unambiguous
support for a single hypothesis of putative homology. The validity
of this putative homology may then be supported by means of a
phylogenetic analysis based on parsimony. A comparative analysis of
pallial organization that includes embryological data suggests the
following set of homologies. The lateral cortex in reptiles is
homologous to the piriform cortex in birds and mammals. The
anterior dorsal ventricular ridge in reptiles is probably
homologous to the neostriatum and ventral hyperstriatum in birds
and to the endopiriform nucleus in mammals. The posterior dorsal
ventricular ridge in reptiles is most likely homologous to the
archistriatum in birds and to the pallial amygdala in mammals. The
pallial thickening in reptiles is probably homologous to the dorsal
and intercalated portions of the hyperstriatum in birds and to the
claustrum proper in mammals. Finally, the dorsal cortex in reptiles
is probably homologous to the accessory hyperstriatum and
parahippocampal area in birds and to the isocortex in mammals.
These hypotheses of homology imply relatively minor evolutionary
changes in development but major changes in neuronal connections.
Most significantly, they imply the independent elaboration of
thalamic sensory projections to derivatives of the lateral and
dorsal pallia in sauropsids and mammals, respectively. They also
imply the independent evolution of lamination in the pallium of
birds and mammals.
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- Biochem Cell Biol. 1997;75(6):651-67. The brain in evolution
and involution. Parent A. Laboratoire de neurobiologie, Universite
Laval Robert-Giffard, Beauport, QC, Canada. This paper provides an
overview of the phylogenetic evolution and structural organization
of the basal ganglia. These large subcortical structures that form
the core of the cerebral hemispheres directly participate in the
control of psychomotor behavior. Neuroanatomical methods combined
with transmitter localization procedures were used to study the
chemical organization of the forebrain in each major group of
vertebrates. The various components of the basal ganglia appear
well developed in amniote vertebrates, but remain rudimentary in
anamniote vertebrates. For example, a typical substantia nigra
composed of numerous dopaminergic neurons that project to the
striatum already exists in the brain of reptiles. Other studies in
mammals show that glutamatergic cortical inputs establish distinct
functional territories within the basal ganglia, and that neurons
in each of these territories act upon other brain neuronal systems
principally via a GABAergic disinhibitory output mechanism. The
functional status of the various basal ganglia chemospecific
systems was examined in animal models of neurodegenerative
diseases, as well as in postmortem material from Parkinson's and
Huntington's disease patients. The neurodegenerative processes at
play in such conditions specifically target the most
phylogenetically ancient components of the brain, including the
substantia nigra and the striatum, and the marked involution of
these brain structures is accompanied by severe motor and cognitive
deficits. Studies of neural mechanisms involved in these akinetic
and hyperkinetic disorders have led to a complete reevaluation of
the current model of the functional organization of the basal
ganglia in both health and disease.
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- Who is cutting-edge, in cerebellar technology? Spinal cord
Olfactory bulb Tectum Cerebellum ++- Expansion recoding, Private
teachers Basal ganglia -(-)- Massive funnelling Tonic output firing
Hippocampus (+) n + DG input sparsifier CA1 feed-forward Neocortex
(+) n + Lamination, Arealization Computational paradigms 100s Myrs
old that we fail to understand