Biological brain

Realizes: general intelligence / perception, memory, reasoning, motor control

The human brain contains ~86 billion neurons connected by ~10¹⁵ synapses. Each neuron integrates thousands of synaptic inputs and fires a spike when its membrane potential crosses threshold — a leaky integrate-and-fire operation. Computation is massively parallel, spike-coded, and energy-efficient at ~20 W total. Synaptic weights are plastic: Hebbian learning and spike-timing-dependent plasticity (STDP) modify connection strengths in response to activity, implementing online learning with no separate training phase. The brain solves tasks — scene understanding, language, planning — that remain beyond engineered systems at equivalent energy budgets. Unlike every other entry, the substrate is also the substrate of the observer. Speed: ~100 Hz spike rate per neuron; millisecond reaction times; years of learning. Capacity: ~86 billion neurons; ~10¹⁵ synapses; ~20 W; general-purpose cognition.

Examples

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Human brain

~86 billion neurons, ~10¹⁵ synapses, 20W power consumption. Demonstrates general intelligence including language, reasoning, planning, and complex motor control through spike-based computation with synaptic plasticity

INTEGRATE-AND-FIRE WEIGHTED-SUM THRESHOLD MEMORY NONLINEAR-TRANSFORM seconds large pJ

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Mouse brain

~75 million neurons in a 0.4g brain consuming ~0.1W. Demonstrates spatial navigation, learning, memory formation, and sensorimotor integration. Used extensively in neuroscience research for understanding neural computation mechanisms

INTEGRATE-AND-FIRE WEIGHTED-SUM THRESHOLD MEMORY seconds medium pJ

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Crow brain (corvid intelligence)

~1.5 billion neurons in corvid brain demonstrating remarkable problem-solving, tool use, and social cognition. Despite lacking mammalian neocortex, achieves complex behaviors through dense pallial connectivity in a compact 15g brain

INTEGRATE-AND-FIRE WEIGHTED-SUM THRESHOLD MEMORY SEARCH seconds medium pJ