Effectome · Lobeworks/17

An effectome is a causal map of a nervous system that gives, for each pair of neurons, how much and in which direction activating the first changes the activity of the second; it is estimated by perturbing neurons and recording the response, never read from anatomy alone.

Effectome. An effectome is a causal map of a nervous system that gives, for each pair of neurons, how much and in which direction activating the first changes the activity of the second; it is estimated by perturbing neurons and recording the response, never read from anatomy alone.

A connectome says which cells touch and through how many synapses; a projectome, coarser still, says which regions send fibres to which. Both are structure. The effectome is function: two cells joined by fifty synapses may barely affect each other if the receptor is weak or an inhibitory side path cancels them, and two cells with no contact may be strongly coupled through others. In the fly it is being estimated by switching neurons on with light (optogenetics) while recording the rest, and fitting a linear dynamical model that uses the connectome as its starting guess.

It is the datasheet the wiring lacks. In software terms a connectome is the call graph, every function with the functions it calls; the effectome is what a profiler with causal tracing would report, how much each call changes the result.

The first estimate in the fly found many small circuits. The dynamics came mostly from small groups of neurons acting largely independently of one another.

It depends on state. Under neuromodulation, hunger or sleep the same wiring can have different effects, so an effectome is measured in some condition and holds for that condition.

Questions: How is an effectome different from a connectome? A connectome is structure: which neurons touch and through how many synapses. An effectome is function: how much activating one neuron changes another, and with what sign. They can disagree, because a strong anatomical link can have a weak effect and two neurons with no contact can influence each other through intermediaries. In software terms the connectome is the call graph and the effectome is what a causal profiler would report. How is an effectome measured? By perturbing neurons and recording what follows. In the fly, neurons are switched on with light through optogenetics while the activity of others is recorded, and a linear dynamical model is fitted to the responses, with the connectome as its starting guess for which effects are possible. The first estimate found that the fly brain's dynamics come mostly from many small circuits acting largely independently.