How close are we to mapping every connection in a mammalian brain?Can we draw a complete wiring diagram of a brain?
or, simply: Can we draw a complete wiring diagram of a brain?or, precisely: How close are we to mapping every connection in a mammalian brain?
A whole adult fly is mapped at synapse resolution and a mouse cortical fragment now contains more than half a billion detected synapses; the whole mouse remains an estimated three orders of magnitude larger.Researchers have mapped a whole fly brain and a tiny piece of mouse brain. The hard part is scaling that detail across an entire mammal without losing or inventing connections.
MICrONS maps a mammal millimeter - A roughly one-cubic-millimeter mouse visual-cortex volume contained more than 200,000 cells and about 524 million detected synapses, registered to activity from around 75,000 neurons. Next up - Mouse-EM center reaches scheduled award endpoint (expected Aug 2028).
State of playWhere brain connectomics stands right now
The current stage, the honest metric, and the single threshold that gates the next stage. Each threshold is a falsifiable claim with a named next test.How far up the ladder we've climbed, the honest verdict, and the one thing blocking the next step.
Researchers have mapped a whole fly brain and a tiny piece of mouse brain. The hard part is scaling that detail across an entire mammal without losing or inventing connections.A whole adult fly is mapped at synapse resolution and a mouse cortical fragment now contains more than half a billion detected synapses; the whole mouse remains an estimated three orders of magnitude larger.
Wire-map an entire mouse brainWhole mouse synaptic connectome Next test: Demonstrate an end-to-end acquisition and proofreading pipeline across a whole mouse region that preserves both local synapses and long-range axons.
The thresholds that gate the next stageWhat has to happen next
Each threshold is a falsifiable claim with a named next test; the gap chart shows how far today's metric sits from the goal.Each row is one thing that has to be proven — and how far today's number is from the target.
The record behind the verdict
Major events set large; context events set small but never hidden. Everything below the TODAY rule is a schedule, not a result.
Synapses enter the microscope
Synapses enter the microscope begins with synaptic cleft resolved by electron microscopy. The result established the next question for the field.
The first complete network
The first complete network begins with first complete animal wiring diagram. The result established the next question for the field.
Connectomes split by scale
Connectomes split by scale moved the field from the human connectome is defined to human connectome project announced. The results narrowed the next question without closing it.
Automation completes an insect brain
Automation completes an insect brain moved the field from adult fly hemibrain released to whole mouse cell atlas reaches 32 million cells. The results narrowed the next question without closing it.
The mammalian scaling test
The mammalian scaling test begins with microns maps a mammal millimeter. The result established the next question for the field.
Events outside the declared eras
Events outside the declared eras moved the field from human cortical millimeter reconstructed to mouse-em center reaches scheduled award endpoint. The results narrowed the next question without closing it.
Why the meters read the way they do
The learning curves and comparisons that justify each threshold's percentage. Every series is measured, with the source event linked in the timeline above.
Read the evidence more closely
Definitions, system boundaries and experimental caveats behind the headline record.
01A connectome is not one resolution
The Human Connectome Project used diffusion and functional MRI to infer macro-scale links among brain regions. Dense EM connectomics instead traces membranes and synapses in fixed tissue. Whole-brain coverage in one does not imply synaptic resolution in the other.
02The target denominator is uncertain
No authoritative experiment has counted every mouse-brain synapse. The visual therefore plots sourced reconstructed numerators and treats 500 billion only as an order-of-magnitude target, without converting it into a completion percentage. Region, age, preparation and the definition of a detected synapse all affect comparisons.
03Segmentation is not verification
Machine learning now supplies most initial segmentation and synapse detection, but false splits, false merges and missed synapses remain. FlyWire estimated 33 person-years of manual proofreading and still describes its resource as correctable rather than error-free.
If the remaining tests pass
Downstream capabilities, drawn dashed because they depend on results not yet in.
Where every number comes from
10 sources — every figure on this page traces to one.
- C. elegans nervous-system reconstruction referencencbi.nlm.nih.gov
- The human connectome: structural descriptionpubmed.ncbi.nlm.nih.gov
- Adult fly hemibrain reconstructionelifesciences.org
- Complete larval fly brain connectomepubmed.ncbi.nlm.nih.gov
- FlyWire whole adult brainnature.com
- One cubic millimeter of human cortexnature.com
- MICrONS functional connectomicspubmed.ncbi.nlm.nih.gov
- NIH BRAIN CONNECTS awardsbraininitiative.nih.gov
- NIH BRAIN 2.0 mouse-connectome assessmentnih.gov
- Mouse-brain volume and synapse-density scalingpmc.ncbi.nlm.nih.gov