The concept of "multiple personalities" is often associated with a condition called Dissociative Identity Disorder (DID). In DID, a person experiences the presence of two or more distinct personality states or identities, also known as "alters." These identities may have their own unique behaviors, memories, and characteristics.
People with DID can indeed interact with their alters. The interactions can vary in nature, ranging from passive influence (where one alter observes or is aware of what another alter is doing) to co-consciousness (where two or more alters are aware of each other and may communicate internally) to more direct switches between alters, where one alter becomes dominant over the others and takes control of the person's behavior.
These interactions can be complex and differ from person to person. For some individuals with DID, the interactions between alters might be cooperative and supportive, while in others, there could be conflicts and struggles. Additionally, some individuals with DID might have more amnesic barriers between alters, making communication and awareness of each other more limited.
It's important to recognize that DID is a complex and often misunderstood disorder. Individuals with DID have experienced severe trauma in their lives, and the disorder is considered a coping mechanism to deal with overwhelming and often life-threatening experiences. Treatment for DID typically involves therapy, which aims to foster communication and cooperation among the different alters to work towards integration and healing.