Kwabena Boahen 2006

human brain at rest dissipates about 20 watts
10^12 neurons x 10^3 synapes x 10 spikes/s = 10^16 events/s = 10^-15 J/op
Blue Gene: 10^15 ops/s @ 10^6 watts = 10^-9 J/op
must make up six orders of magnitude!
Carver Mead: "Analog VLSI" -- use transistors as analog devices
1pA per ion channel means avg. neuron has 100 channels open at a time
terrible noise levels (1/sqrt(n) = 10%), compare to 60dB S/N ~ 1M:1
Neurogrid: 1M neurons with 6B connections @ < 1 watt total by 2008

Dharmendra Modha 2007

human brain: about 10^15 synapses
assume 1 Hz. average firing to get 2 * 10^15 synaptic events per second
if each event represents 350 OPS, then the humans compute at 350 PFLOPS
mice at 45TFLOPS -- within reach of Blue Gene
mouse neurons via Braitenberg & Schuz 1998:
	16M neurons, 80% of which are excitatory
	8K synapses/neuron
	axonal delays of 1-20ms
	0.09 local probability of connection
uses 4-parameter spiking neuron model by Izhikevich 2004
uses STDP synapse model by Song, Miller, Abbott 2000
cat visual cortex connectivity via Binzeggar, Douglas, Martin 2004:
	77% excitatory -> excitatory
	11% inhibitory -> excitatory
	10% excitatory -> inhibitory
	 2% inhibitory -> inhibitory
macaque white matter connectivity via (meta-analysis)
currently performance is non-realtime: 1 sec of model in 10 real seconds

Henry Markram 2006

1M cortical colums in human brain, 100K neurons per column
about 20 anatomical types of cortical neuron (9 inhibitory 10 excitatory)
each anatomical type can produce different electrical behaviors
electrical behavior depends on mixture of ion channels expressed by cell
several million ion channels can be expressed per neuron
overall column "recipe" is remarkably similar from column to column
any neuron can connect to any other by just growing a synapse
each neuron connects to approximately 10% of other neurons in the column
connection morphology is characteristic of pre-post neuron types
first simulation is one column with 10K neurons
uses Blue Gene, one processor per neuron
speculation: not enough information in spikes to explain qualia
1 petaflop general-purpose computer about enough for mouse brain

Almut Schuz 2007

human cortex: ~ 10^10 neurons, ~ 10^8 input neurons
most of the cortex connects to itself
85% of the neurons are pyramidal, connecting both locally and distantly
probability of connection falls off with distance
connection probability per distance curve looks the same in all layers
a pair of cells prefers to share no more than one synapse
about 90% of cortical synapses are excitatory
results suggest Hebbian cell assemblies
connectivity in other brain areas isn't as supportive of cell assemblies

Ed Callaway 2007

cortical circuits display "fine-scale and cell-type specificity"
~ 12 types of inhibitory cells in cortex, accounting for 20% of all cells
inhibitory types fall into two groups: fast-spiking and non-fast-spiking
method: record from brain slices bathed in caged glutamate
UV activates glutamate -- more accurate than electrical stimulation
about 24 neurons respond to each stimulus
results: neurons connect preferentially based on cell type
only 1 in 5 neighboring pairs of neurons are directly connected
relatively independent subnetworks exist within cortical columns
on the horizon: molecular and genetic methods in vivo
allatostatin & GFP transgenic mice -- turn specific cell types on and off
modified rabies -- light up all neurons one hop upstream of target cell