Similarities found in brain architecture of sea slugs and complex animals

A recent study published in the Journal of Neuroscience has found similarities between the brain architecture of sea slugs and that of more complex animals with segmented bodies, jointed skeletons, and appendages. The research suggests that animals with complex bodies and behaviors adapted a network of neurons, called the “A-cluster,” that already existed in simpler organisms, rather than developing an entirely new set of neural circuits.

The A-cluster, which is a small network of 23 neurons, controls locomotion and posture in sea slugs. The researchers videotaped sea slug movements and recorded responses to nerve stimulation and specific neurons in the sea slug brain to investigate whether the similarities between sea slugs and more complex creatures evolved independently or whether those with segmented body parts and appendages inherited their neural circuitry from a common ancestor.

The sea slug, Pleurobranchea californica, was observed using cilia on its foot to crawl and paddling through secreted mucus. For a postural turn towards or away from a stimulus, it simply shortened one side of its body and escaped from predators with a frantic, rocking swim, all driven by the A-cluster.

The study suggests that the circuits driving locomotion in animals with complex bodies and behaviors have close functional analogies in the simpler gastropod mollusks and may share a common inheritance. The reticular system in mammals translates specific instructions for action choices from higher brain regions for posture and locomotion and relies on serotonin-producing neurons to control body movements. The study found similar serotonin-producing neurons in the A-cluster of sea slugs driving behaviors like pursuit, avoidance, and escape.

Source: University of Illinois at Urbana-Champaign

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