The caudate nucleus is part of the basal ganglia, located deep in the center of the brain. The caudate nucleus controls the filtering of thoughts. Sensory information is sorted here. Normally, unnecessary information is disregarded. In people with OCD, the caudate nucleus isn’t as effective at filtering, so they become overwhelmed with intrusive thoughts and urges. The caudate nucleus of a person with OCD is like a doorman who does a poor job keeping out the undesirables. The above paragraph is an excerpt from: The OCD Workbook:Your guide to breaking free from obsessive compulsive disorder

Does it say anything about the amygdala? This part is responsible for the processing of emotions including fear

https://www.amazon.com/dp/1572249218/ref=cm_sw_r_cp_tai_ADtwEb6RSAC22 The orbital cortex is in the front part of the brain, above the eyes. This is where thoughts and emotions combine. The orbital cortex tells us when something is wrong and when we should avoid something. It’s like an early warning system in the brain, and it seems to work overtime in people with OCD. When the caudate nucleus lets unnecessary thoughts and impulses through, this makes the orbital cortex’s job much more difficult. The cingulate gyrus, located in the center of the brain, helps shift attention from one thought or behavior to another. When it’s overactive, we get stuck in certain behaviors, thoughts, or ideas. The cingulate gyrus is also the part of the brain that signals danger, and as such, it’s the part that says something horrible will happen if you don’t carry out your compulsions.

Brain Lock does a good job of describing this process too. It’s really helpful to me to know physically what’s going on in my brain.

Yes here’s explanation from Brain Lock:Brain Lock, Twentieth Anniversary Edition: Free Yourself from Obsessive-Compulsive Behavior https://www.amazon.com/dp/006256143X/ref=cm_sw_r_cp_tai_cOvwEbTWRJNM8 • STRIATUM: The stratum is composed of two parts, the putamen and the caudate nucleus, which sit next to one another in the core of the brain, deep in the center. The putamen is the automatic transmission for that part of the brain that regulates motor or physical movement, and the caudate nucleus is the automatic transmission and filtering station for the front part of the brain that controls thought. • ORBITAL CORTEX: The orbital cortex is the underside of the front of the brain, the “hot spot” in OCD. The brain’s “error-detection circuit,” it is located directly over the eye sockets. Here, thought and emotion combine. The orbital cortex can inform you that something is right or wrong, whether it is something to approach or avoid. • CORTEX: The cortex is the outer surface of the brain. The frontal cortex is where the most advanced thinking and planning take place. • BASAL GANGLIA: The basal ganglia is essentially the same as the striatum; the terms are almost interchangeable. The caudate nucleus, which enables us to shift gears from one behavior to another, is part of the basal ganglia. • CINGULATE GYRUS: The cingulate gyrus is at the center of the brain, the deepest part of the cortex. It’s wired into your gut and heart-control centers and is responsible for giving you the feeling that something terrible is going to happen if you don’t act on your compulsions to wash, check, whatever. • THALAMUS: The thalamus is the central relay station for processing the body’s sensory information.