competition
DESCRIPTION
Elements of robustness:. feedback. degeneracy. competition. modularity. Feedback. A classic example of feedback in neural circuits: error correction during smooth pursuit. feedback. retinal inputs. Feedback Controller. ~100 ms. Sensed Variable. Feedforward Controller. eye - PowerPoint PPT PresentationTRANSCRIPT
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competition
degeneracy
modularity
feedback
Elements of robustness:
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Feedback
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FeedbackController
~100 msretinalinputs
Goal FeedforwardController Eyeball+ eye
movementSensedVariable
feedback
A classic example of feedback in neural circuits: error correction during smooth pursuit
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Degeneracy
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A classic example of degeneracy in biology: the genetic code
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Swensen & Bean, J. Neurosci. 2005
cell 1 cell 2
Neuron-level degeneracy:robustness of bursting in cerebellar Purkinje cells
acutely dissociated Purkinje somata
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Swensen & Bean, J. Neurosci. 2005
cell 1
cell 2
cell 3
cell 4
cell 5
cell 6
Neuron-level degeneracy:robustness of bursting in cerebellar Purkinje cells
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Neuron-level degeneracy:robustness of bursting in cerebellar Purkinje cells
Swensen & Bean, J. Neurosci. 2005
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Neuron-level degeneracy:robustness of bursting in cerebellar Purkinje cells
Swensen & Bean, J. Neurosci. 2005
An acute decrease in Na+ conductance produces a compensatory increase in voltage-dependent and Ca2+–dependent K+ conductances.
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Neuron-level degeneracy:robustness of bursting in cerebellar Purkinje cells
Swensen & Bean, J. Neurosci. 2005
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Neuron-level degeneracy:robustness of bursting in cerebellar Purkinje cells
Swensen & Bean, J. Neurosci. 2005
A chronic decrease in Na+ conductance produces a compensatory increase in Ca2+ conductance.
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Degeneracy and feedback
input outputsystemvariables
set point
homeostat
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input outputsystemvariables
set point homeostat
Degeneracy and feedback
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Goldman, Golowasch, Marder, & Abbott, J. Neurosci. 2001
Mapping the state space of neuron-level degeneracy:robustness of bursting in stomatogastric ganglion neurons
model stomatogastric ganglion neuron
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Goldman, Golowasch, Marder, & Abbott, J. Neurosci. 2001
Mapping the state space of neuron-level degeneracy:robustness of bursting in stomatogastric ganglion neurons
model stomatogastric ganglion neuron
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Evolvability - the capacity to adapt by natural selection
Evolution - adaptation by natural selection
Degeneracy can increase evolvability by distributing system outcomes near phenotypic transition boundaries.
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Prinz et al. Nature 2004
Circuit-level degeneracy:robustness of patterns in the stomastogastric ganglion
data
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Prinz et al. Nature Neuroscience 2004
Circuit-level degeneracy:robustness of patterns in the stomastogastric ganglion
model
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Competition
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A classic example of competition in neural circuits: the developing neuromuscular junction
Luo & O’Leary, Ann. Rev. Neurosci. 2005
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Another classic example of competition in neural circuits: developing ocular dominance columns
Luo & O’Leary, Ann. Rev. Neurosci. 2005
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Competitive synaptic interactions: spike-timing dependent plasticity
Song & Abbott, Nat. Neurosci. 1999Abbott, Zoology 2003
pre leads post pre lags post
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presynaptic rate = 10 Hz presynaptic rate = 13 Hz
Competitive synaptic interactions: spike-timing dependent plasticity
Song & Abbott, Nat. Neurosci. 1999Abbott, Zoology 2003
Homeostatic control of total excitatory drive over a range of presynaptic firing rates.
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Modularity
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A classic example of modularity in biology:the domain structure of genes and proteins
“Exon shuffling” was recognized early in molecular biology as a potential mechanism to generate diverse novel proteins based on existing functional building-blocks.
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Bell, Han, & Sawtell, Annu. Rev. Neurosci. 2008Oertel & Young, Trends Neurosci. 2004Roberts & Portfors, Biol. Cybern. 2008
Modularity in neural circuitsa putative example: “cerebellar-like” circuits
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Bell, Han, & Sawtell, Annu. Rev. Neurosci. 2008Oertel & Young, Trends Neurosci. 2004Roberts & Portfors, Biol. Cybern. 2008
Modularity in neural circuits
mammalian cerebellum mammalian dorsal cochlear nucleusteleost cerebellum
teleost medial octavolateral nucleus mormyrid electrosensory lobe gymnotid electrosensory lobe
“cerebellar-like” circuits in vertebrates
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Bell, Han, & Sawtell, Annu. Rev. Neurosci. 2008Oertel & Young, Trends Neurosci. 2004Roberts & Portfors, Biol. Cybern. 2008
Modularity in neural circuits
common anatomical features of cerebellar-like circuits:• large principal cells (often GABAergic) having large spiny dendrites• principal cells receive excitatory input from a very large population of granule cells forming parallel axon bundles that target the spiny dendrites of principal cells• principal cells also receive excitatory ascending input from sensory regions targeting the perisomatic/proximal region of principal cells
common functional features of cerebellar-like circuits:• parallel fibers carry “higher-level” information (higher-level sensory signals, corollary discharges, proprioceptive info)• ascending inputs by contrast carry lower-level information (pertaining to the same sensory modality or sensorimotor task)• parallel fiber signals can in principle “predict” the lower-level signals• “prediction” is learned by pairing parallel fiber input with ascending sensory input• pairing produces a depression of parallel fiber inputs (anti-Hebbian plasticity)
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Modularity can permit an organism to process a new input without evolving an entirely novel circuit from scratch—in effect, building diverse objects using existing building-blocks.
What “modules” (if any) might be the circuit-level equivalent of protein domains at the molecular level?
Sharma, Angelucci, & Sur, Nature 2001von Melchner, Pallas, & Sur, Nature 2001
Modularity in neural circuitsre-routing experiments show that auditory cortex can process visual inputs
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• shorten summary (to ~400 words)
• add an assessment (probably >300 words)
• identify major problems, if any
• identify unusual strengths, if any
• for each major point, state the implications clearly
• for each major problem, indicate appropriate solutions