## **Core Concept**
Obsession is a characteristic feature of **Obsessive-Compulsive Disorder (OCD)**, which is a type of anxiety disorder. OCD is primarily associated with the **brain's serotonin system** and its related neural circuits. The disorder involves recurrent, intrusive thoughts (obsessions) and repetitive behaviors (compulsions) that an individual feels compelled to perform.

## **Why the Correct Answer is Right**
The correct answer, , relates to OCD being a disorder of **thought or cognition**. In OCD, individuals experience persistent and unwanted thoughts, images, or urges (obsessions) that trigger anxiety and are typically followed by compulsions—repetitive behaviors or mental acts aimed at reducing anxiety. This cycle of obsession and compulsion significantly interferes with daily functioning. The underlying pathophysiology involves abnormalities in brain regions such as the **orbitofrontal cortex, anterior cingulate cortex**, and **basal ganglia**, which are connected to the serotonin and dopamine systems.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while emotions are indeed involved in OCD (as the disorder is classified under anxiety disorders), saying it's merely a disorder of emotion is too simplistic and doesn't capture the cognitive and behavioral aspects.
- **Option B:** This option is incorrect because OCD is not primarily classified as a disorder of motivation. Motivation can be affected indirectly due to the distressing nature of symptoms, but it's not the core issue.
- **Option D:** This option is incorrect because OCD is not primarily a disorder of memory. While memory can be affected in the sense that individuals might recall their obsessions and compulsions, the core symptoms revolve around intrusive thoughts and compulsive actions, not memory dysfunction.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that OCD is often treated with **Selective Serotonin Reuptake Inhibitors (SSRIs)**, which are a type of antidepressant. This treatment approach underscores the disorder's link to the serotonin system. Additionally, cognitive-behavioral therapy (CBT), particularly a type known as **Exposure and Response Prevention (ERP)**, is highly effective for OCD.

## **Correct Answer: C.**