Modern psychiatric neurosurgery is not aimed at a fixed point on a map. It is aimed at a specific pathway in each patient's own brain, identified from their own imaging.
OCD, depression, and related conditions are increasingly understood as disorders of circuits: the cortico-striato-thalamo-cortical loops that connect the prefrontal cortex, the striatum, and the thalamus. Within these loops, the emotion-related (limbic) pathways appear to carry the most disabling symptoms. The goal of surgery is to act on that part of the network, while leaving the rest intact.
Much of this circuit passes through a compact band of white matter called the anterior limb of the internal capsule. Crucially, it is not uniform. Its ventral part carries the limbic (emotion) pathway, from the ventromedial prefrontal cortex toward the thalamus and brainstem reward centers. Its dorsal part carries the associative pathway, from the dorsolateral prefrontal cortex, which matters for thinking and planning.
Interrupting the ventral limbic pathway while preserving the dorsal associative pathway is associated with better outcomes and fewer side effects. The challenge is that the exact position of these pathways varies from person to person, so a single fixed coordinate is not enough.
Diffusion MRI lets us reconstruct these white-matter pathways in each individual, a technique called tractography. Using both deterministic and probabilistic methods, the limbic and associative pathways are mapped in the patient's own anatomy. Treatment, whether a laser lesion or a stimulating electrode, is then aimed at the limbic pathway most tied to symptoms, and shaped to spare the associative pathway next to it.
Published work points the same way: greater disconnection of the orbitofrontal and limbic pathways predicts a stronger response, while sparing the associative pathway limits unwanted cognitive effects. Tailoring the lesion or stimulation to each patient's pathways, rather than to a fixed target, is the principle behind this approach, and it is an active area of research, including work at the Neuronium Neuroscience Institute on connectivity-guided targeting.