Wednesday, July 04, 2007

Swarm intelligence

The National Geographic has a fascinating article on swarm intelligence or the ability of colonies/herds of animals/ robots to exhibit greater intelligence and decision making abilities as a whole as compared to the relatively dumb intelligence exhibited at the individual level. While the article lists various ways in which the swarms solve problems, the one explanation that caught my eye was how ant colonies decide how many ants to send on a foraging trip the next day. To me an individual ant in a colony seemed like a neuron, which aggregates inputs from other neurons (the equivalent here is comes in contact with other ants- the early patrollers) and if the neuron gets a threshold amount of spikes in a close duration of time, then it fires (the equivalent here being if an ant comes in contact with many early forager ants , which are 'fired' or have the scent associated with foraging, then it decides to go out for foraging) . Read on for yourself and see if the analogy makes any sense.

Ants communicate by touch and smell. When one ant bumps into another, it sniffs with its antennae to find out if the other belongs to the same nest and where it has been working. (Ants that work outside the nest smell different from those that stay inside.) Before they leave the nest each day, foragers normally wait for early morning patrollers to return. As patrollers enter the nest, they touch antennae briefly with foragers.

"When a forager has contact with a patroller, it's a stimulus for the forager to go out," Gordon says. "But the forager needs several contacts no more than ten seconds apart before it will go out."

To see how this works, Gordon and her collaborator Michael Greene of the University of Colorado at Denver captured patroller ants as they left a nest one morning. After waiting half an hour, they simulated the ants' return by dropping glass beads into the nest entrance at regular intervals—some coated with patroller scent, some with maintenance worker scent, some with no scent. Only the beads coated with patroller scent stimulated foragers to leave the nest. Their conclusion: Foragers use the rate of their encounters with patrollers to tell if it's safe to go out. (If you bump into patrollers at the right rate, it's time to go foraging. If not, better wait. It might be too windy, or there might be a hungry lizard waiting out there.) Once the ants start foraging and bringing back food, other ants join the effort, depending on the rate at which they encounter returning foragers.

The idea of ants making a yes or no decision of going out on foraging, based on the inputs they receive from other ants (the contact with others who have returned from foraging) and also based on the rate of that contact, seems very much akin to how a neuron behaves. No wonder the colonies are able to solve complex problems. Now that we know that they use scents to identify different types of ants, maybe we can also look up any data that may suggest that the ants smell differently in different locations of the nest/colony. If that is so, then we can also have ants specialized to perform some special function based on where in space (relative to the colony), they are. This may be akin to different regions of the brain having different localized functions.

Hat Tip: Mind Hacks

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