In order to understand how we get rid of established habits/behavior: Can myelinated connections be dissolved or are new connections created that bypass those connections?
Myelin is a greatly extended and modified plasma membrane wrapped around the nerve axon in a spiral fashion (Morell & Quarles, 1999). It typically forms on long axons to increase conduction speed and efficiency.
Learning predominantly takes place in cortical areas and it is believed that it mainly depends on synaptic changes, such as long-term potentiation (LTP) of synapses. Forgetting things is believed to be mediated through long-term depression (LTD).
Both LTP and LTD are synaptic processes and do not involve myelin, as that substance is found around axons. Although there is a lot more to learning than I can cover here, I dare say it doesn't involve myelination, and forgetting things doesn't involve demyelination, or vice versa.
Demyelination typically results in disease. The most common one being multiple sclerosis, characterized by blurred or double vision, thinking problems, lack of coordination, loss of balance, numbness, tingling and weakness in an arm or leg.
- Morell & Quarles. The Myelin Sheath. In: Siegel GJ et al., (eds). Basic Neurochemistry. 6th ed. Philadelphia: Lippincott-Raven (1999)
- Purves et al., (eds). Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001