(a) An impairment of an organ or body function that cannot be assigned a numerical impairment percentage using the AMA's Guides will not be included in the employee's impairment rating.

(b) A mental impairment that does not originate from a documented physical dysfunction of the nervous system, and cannot be assigned a numerical percentage using the AMA's Guides, will not be included in the impairment rating for the employee. Mental impairments that are due to documented physical dysfunctions of the nervous system can be assigned numerical percentages using the AMA's Guides and will be included in the rating.