Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 1 Speed limits in mammalian brains: Speed limits in mammalian brains: scaling constraints from biophysics scaling constraints from biophysics Sam Wang Princeton University synapse.princeton.edu/~sam/kitp.ppt Optical physiology and Optical physiology and synaptic learning rules: synaptic learning rules: Shari Shari Gelber Gelber Daniel O’Connor Daniel O’Connor Ilker Ozden Ilker Ozden Dmitry Dmitry Sarkisov Sarkisov Shy Shy Shoham Shoham Megan Sullivan Megan Sullivan Gayle Wittenberg Gayle Wittenberg Brain scaling and Brain scaling and evolution: evolution: Mark Mark Burish Burish Damon Clark Damon Clark Kim Harrison Kim Harrison Hao Hao Yuan Kueh Yuan Kueh Jennifer Shultz Jennifer Shultz Matt Wagers Matt Wagers Krysta Wyatt Krysta Wyatt Laboratory of Sam Wang Laboratory of Sam Wang
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Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 1
Speed limits in mammalian brains: Speed limits in mammalian brains: scaling constraints from biophysicsscaling constraints from biophysics
Mark Mark BurishBurishDamon ClarkDamon ClarkKim HarrisonKim HarrisonHaoHao Yuan KuehYuan KuehJennifer ShultzJennifer ShultzMatt WagersMatt WagersKrysta WyattKrysta Wyatt
Laboratory of Sam WangLaboratory of Sam Wang
Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 2
H.J. Jerison
P.R. Hof
Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 3
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Ramon y Cajal
Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 4
Axons
Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 5
Functional advantages of axon size and type
Compactness (35-70% of axons)Per-spike energy cost (30-65%)Extreme speed (0-5%)
Explaining scaling trends with biophysical principlesExplaining scaling trends with biophysical principles
•• Are white matter axons under selection pressure for speed?Are white matter axons under selection pressure for speed?Synaptic delays and action potentials: 1 Synaptic delays and action potentials: 1 msecmsecSynaptic potentials: 10Synaptic potentials: 10--100 100 msecmsecCrossCross--brain conduction: brain conduction: 1010--200 200 msecmsec
•• Can Can ultrastructuralultrastructural trends account for gross scaling trends?trends account for gross scaling trends?Geometric “ accounting”Geometric “ accounting”
Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 6
The neocortex
gray matter• external rind
containing neuronal cell bodies and local connections
white matter• closely packed axons
making long-distance connections
Speed Limits in Mammalian Brains: Scaling Constraints from Biophysics
Dr. Sam Wang, Princeton (KITP Brain Program 9/02/04) 7