  "You never forget how to ride a bike", -- but how is that possible? The brain
is able to learn complex skills, stop the practice for years, learn other
skills in between, and still retrieve the original knowledge when necessary.
The mechanisms of this capability, referred to as lifelong learning (or
continual learning, CL), are unknown. We suggest a bio-plausible
meta-plasticity rule building on classical work in CL which we summarize in two
principles: (i) neurons are context selective, and (ii) a local availability
variable partially freezes the plasticity if the neuron was relevant for
previous tasks. In a new neuro-centric formalization of these principles, we
suggest that neuron selectivity and neuron-wide consolidation is a simple and
viable meta-plasticity hypothesis to enable CL in the brain. In simulation,
this simple model balances forgetting and consolidation leading to better
transfer learning than contemporary CL algorithms on image recognition and
natural language processing CL benchmarks.
