Inside a bee's brain

The parts and what they do

The mushroom bodies are the structure most of the cognition literature is about. They are proportionally large in social insects, and in honey bees they grow measurably as a worker moves from nursing to foraging — a structural change in an adult brain, driven by what the animal is doing.

What a million neurons buys

The comparison people reach for is a human brain at roughly eighty-six billion neurons, and it is not the useful one. The useful comparison is with the tasks: a forager holds route memories, flower identities, a time-compensated sun compass, a distance estimate, a scent memory and a social signal, and runs all of it inside a body weighing about a tenth of a gram.

Miniaturisation has costs, and they are visible. Spatial resolution in the compound eye is poor. The gustatory receptor repertoire is small. Individual neurons are noisy. What the brain does instead is specialise heavily and reuse aggressively, which is why the same mushroom-body circuitry supports olfactory, visual and relational learning.

Memory, in phases

• Short-term memory forms within seconds of a rewarded pairing and decays in minutes.
• Mid-term memory follows, lasting hours and not requiring new protein synthesis.
• Long-term memory requires protein synthesis and multiple learning trials, and can last most of a forager's remaining life.
• Consolidation into the long-term phase depends on sleep. Sleep-deprived bees consolidate navigational memory worse and dance less precisely the following day.

The phase structure is close enough to that in vertebrates that bees are used as a model for the molecular basis of memory formation generally, which is a large part of why the field is as well funded as it is.

A brain that changes with the job

A worker's brain is not fixed at emergence. As she moves from cleaning cells to nursing to guarding to foraging, the mushroom bodies grow: the dense neuropil regions expand and the branching of individual neurons increases. The change tracks experience rather than age, and a bee forced to forage early shows it early.

That matters for how the whole subject should be read. The colony does not contain twenty thousand identical processors running a shared program. It contains individuals whose brains have been shaped by what they have done, which is part of why consistent behavioural differences between individuals are as robust as they are.

The consciousness argument

A serious scholarly argument holds that the insect central complex performs an integrative function analogous to the vertebrate midbrain, and that this is the kind of structure subjective experience is associated with. It is a position with real proponents and real opponents, and it is a debate about how to interpret an anatomy rather than a finding about bees.