Final answer:
Lower brain volume associated with a dissociative disorder is commonly seen in the amygdala and hippocampus, areas critical for emotion and memory processing.
Step-by-step explanation:
If Abigail suffers from a dissociative disorder, she will likely show lower volume in the amygdala and hippocampus, which are brain regions associated with the processing of emotions and memory. Research has indicated that changes in the structure and function of these areas are commonly seen in individuals with mood and anxiety disorders. The amygdala is involved in learning fear and emotional processing, while the hippocampus is crucial for memory function and also plays a role in emotional processing. Therefore, the correct answer to which brain regions might show lower volume concerning a dissociative disorder is likely 'B. The amygdala and hippocampus.'