Which condition is associated with a lack of flat affect and good previous functioning?

The correct choice, Brief Psychotic Disorder, is characterized by the sudden onset of psychotic symptoms, such as hallucinations or delusions, that typically last less than a month. Individuals with this disorder often have a period of good functioning prior to the onset of symptoms, and it is common for them to retain emotional expressiveness, thus lacking the flat affect often seen in other psychotic disorders.

In contrast to Brief Psychotic Disorder, conditions like Schizophrenia are typically associated with negative symptoms, such as flat affect, and a more chronic course of dysfunction. Mood Disorders can vary greatly, but they often include significant mood disturbances that influence affect, and the overall previous functioning can be more variable. Delusional Disorder may not present with overtly psychotic symptoms like hallucinations and involves persistent delusions without marked flattening of affect, but previous functioning can also be more intact compared to broader psychotic disorders.