Julian experiences persistent, distressing thoughts that his hands are covered in invisible toxins. To relieve this intense anxiety, he feels compelled to wash his hands exactly seven times in a specific sequence. His psychiatrist suggests that Julian's symptoms might be due to an imbalance in chemical messengers in his brain and hyperactive communication between specific neural regions.

Discuss the biological approach to explaining obsessive-compulsive disorder (OCD). Refer to Julian's case in your answer.