When scientists say an octopus has nine brains, they mean it — though perhaps not in the way you might imagine. The central brain in an octopus's head is just one piece of a highly distributed neural architecture that makes this animal unlike anything else on Earth.
What Are the 9 Brains of an Octopus?
An octopus has:
- One central brain — a donut-shaped structure wrapped around the esophagus, located in the octopus's head (mantle)
- Eight brachial ganglia — dense clusters of nerve cells located in each of the eight arms, functioning as semi-autonomous mini-brains
Neurons in a typical octopus — similar in number to a dog's brain, and far more than any other invertebrate.
The remarkable thing is not just the number of brains, but where the neurons are: approximately two-thirds of all octopus neurons are located in the arms, not in the central brain. Each arm contains around 40–50 million neurons — enough to process sensory information, make decisions, and control movement entirely on its own.
What Can an Octopus Arm Do Without the Brain?
Quite a lot, actually. Scientists have demonstrated that severed octopus arms continue to respond to stimuli for up to an hour after being detached. They will attempt to pass food toward where the octopus's mouth would be — even without a brain or body attached. This shows that the arm's local ganglia can process sensory signals and coordinate complex motor responses independently.
In experiments at the Hebrew University of Jerusalem, researchers showed that octopus arms produce two types of movement: exploratory movements (which the central brain initiates and can override) and reflexive local movements (controlled entirely by the arm's own ganglia, without central brain involvement).
How Does the Central Brain Communicate With the Arms?
The central brain sends high-level commands — "reach toward that crab" or "pull back" — rather than detailed motor instructions. The arms then figure out the specifics themselves. This is called a distributed nervous system, and it has several advantages:
- Speed: Arms can react to touch or taste without waiting for the central brain to process the signal and send back instructions — saving critical milliseconds when catching prey or escaping predators.
- Parallel processing: All eight arms can independently explore, taste, and manipulate objects simultaneously, rather than the brain having to coordinate each arm one at a time.
- Efficiency: The central brain doesn't get overwhelmed with low-level sensory data from millions of suckers — the arms filter and process locally, only sending important signals upward.
| Structure | Neuron Count (approx.) | Function |
|---|---|---|
| Central brain (lobes) | ~170 million | Decision making, learning, coordination |
| Each arm (brachial ganglia) | ~40–50 million | Local sensing, movement, reflexes |
| Optic lobes (eyes) | ~120 million total | Vision processing |
| Total | ~500 million | — |
Does This Make Octopuses Intelligent?
Yes — and profoundly so for an invertebrate. Octopuses can solve multi-step puzzles, use tools (they've been documented carrying coconut shells as portable shelters), recognize individual human faces, navigate mazes, and display what appears to be play behavior. They have both short-term and long-term memory.
Perhaps most intriguingly, octopuses have been observed appearing to dream — their skin rapidly changing color and pattern during sleep, suggesting active neural processing of experiences from the day. This is extremely unusual behavior for an invertebrate.
Why Do Octopuses Need So Much Brain Power?
The short answer is: camouflage, hunting, and problem-solving in complex environments. An octopus's ability to change skin color, texture, and pattern in real time requires enormous neural processing. Simultaneously managing eight semi-independent arms, each with hundreds of suckers that can taste and feel independently, requires a distributed system. And surviving without a protective shell in an ocean full of predators requires rapid learning and creative problem-solving.
Frequently Asked Questions
Is an octopus smarter than a dog?
Difficult to compare — intelligence manifests differently across species. Octopuses match or exceed dogs in some cognitive tests (maze navigation, object permanence), while dogs outperform octopuses in social intelligence. They have similar neuron counts but very different brain architectures.
Can octopuses learn from each other?
Octopuses are solitary animals and do not naturally observe or learn from other octopuses in the wild. However, laboratory experiments have shown they can learn by watching another octopus perform a task — a surprisingly advanced form of social learning for an animal that lives alone.
