Which of the following is a symptom of a major depressive episode?

Diminished interest or pleasure in activities, also known as anhedonia, is a hallmark symptom of a major depressive episode. This symptom reflects a significant change in the individual's ability to experience joy or satisfaction in activities that were previously enjoyable or meaningful to them.

In major depressive episodes, individuals often report a profound lack of interest in hobbies, social interactions, and other daily activities, which can contribute to feelings of hopelessness and sadness. This symptom is critical in diagnosing major depressive disorder, as it typically constitutes one of the key diagnostic criteria according to established guidelines, such as those found in the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).

Other options, such as hallucinations and manic behavior, are not characteristic of major depressive episodes; hallucinations are more commonly associated with psychotic disorders, while manic behavior indicates a mood that is distinctly elevated, indicative of bipolar disorder rather than unipolar depression. Impulse control issues, while they can occur in various mental health disorders, do not specifically align with the core symptoms of major depressive episodes.

Thus, diminished interest or pleasure in activities is the most relevant symptom associated with a major depressive episode, making it the correct choice.