Indiana Code Title 34. Civil Law and Procedure § 34-45-2-3

Sec. 3. (a) This section applies in all suits by or against any person adjudged to be a mentally incompetent person or against the mentally incompetent person's guardian:

(b) Except as provided in subsection (c), neither party to the transaction is a competent witness to any matter that occurred before the appointment of the incompetent person's guardian.

(c) If the party to the transaction who is under guardianship is adjudged by the court to be competent to testify, the other party to the suit shall not be excluded.

(d) This section does not apply to a contract made or transaction had before February 27, 1903.

(e) Either party to a suit under this section has the right to call and examine an adverse party as a witness. The court may require a party to a suit or other person to testify. An abuse of discretion under this subsection is reviewable on appeal.