**Question:** Bilateral ablation of which of the following structures results in the inability to form long-term memories?

**Core Concept:** Long-term memories are formed through a complex process involving the hippocampus, amygdala, and the cortex. These structures are part of the limbic system, which is responsible for emotional processing and learning.

**Why the Correct Answer is Right:** The hippocampus (A) plays a critical role in the formation of new memories, particularly those involving spatial learning and navigation. Ablation of the hippocampus would disrupt this process, leading to memory impairment.

**Why Each Wrong Option is Incorrect:**
A. The amygdala (B) is important for emotional memory processing, but it is not as directly involved in the formation of long-term memories as the hippocampus.
B. The prefrontal cortex (C) is involved in higher cognitive functions, but it is not responsible for memory formation.
D. The corpus callosum (D) is responsible for communication between the two hemispheres of the brain, but it is not directly related to memory formation.

**Clinical Pearl:** The amygdala (B) is often associated with the "emotional tagging" of memories, meaning that emotional experiences tend to be more strongly encoded and thus more likely to become long-term memories.

**Correct Answer:** . B. amygdala