Complex sentence: Mental disorder, learning disability and mental retardation are not usually classed as primarily neurological, but the distinction can be a matter of debate either in regard to specific facts about the cause or nature of a condition, or the general understanding of brain and mind.
Split into simpler sentences: Mental disorder, learning disability and mental retardation are not usually classed as primarily neurological. However the distinction can be a matter of some debate, either in regard to specific facts about the cause of a condition or in regard to the general understanding of brain and mind.