ReviewAnatomy and physiology of the basal ganglia: Implications for DBS in psychiatry
Introduction
Contemporary movement disorder surgery on the brain has evolved from empiric observations on movement behavior after neurological lesions. So too has the development of psychiatric surgical procedures followed the observation of how lesions in the brain changed cognitive and affective behavior.
In the late 19th century, the first modern surgical procedure was attempted in Switzerland after Friedrich Goltz's canine experiments in which removal of the temporal lobes resulted in animals that were more tame and calmer than the unoperated ones (Goltz, 1881). In 1891, drawing from these animal studies, a Swiss psychiatrist named Gottlieb Burckhardt reported the results of a series of surgical procedures in which he drilled holes in the heads of six severely agitated psychiatric patients and extracted sections of their frontal lobes (Burckhardt, 1891). Although in Burckhardt's series of six patients, three were considered “successes”, and two “partial-successes”, pressure from his colleagues led him to abandon his efforts.
This tenuous translation of animal research into clinical practice continued in the 20th century as John Fulton's work on frontal lobe ablation in chimpanzees were seized upon by Egas Moniz and then Walter Freeman to become a surgical procedure that is perhaps more reviled and synonymous with bad medicine than any other medical practice in history—the frontal lobotomy. A frail physiological basis coupled with an uncontrolled and unexamined practice led to a virtual banning of surgery for psychiatric disorders by the 1970s.
The context of the recent resurgence of interest in developing a surgical approach to psychiatric disorders is both eerily similar and vastly different than the one that led to the era of lobotomy. Today, much like the early 20th century, there exists a cohort of psychiatric patients who are completely resistant to the conventional treatment measures of the day.
But what differs today is vast. There is an agreed-upon system for classifying psychiatric disorders, which, while itself evolving, is reliable and systematic. The therapeutic nihilism of the early to mid-20th century has been replaced by optimism and an array of generally effective treatments; the subset of patients most suitable for surgical intervention is therefore both smaller and better defined. The ethical norms and the regulatory context of today provide significant safeguards against misuse of psychiatric neurosurgery. Technical advances have enabled the surgery itself to be both precise and better tolerated. This is most exemplified by the recent introduction of neuromodulation technologies into neurosurgical practice such as deep brain stimulation (DBS). Just as DBS has revolutionized the practice of movement disorder surgery, its application to psychiatric illness has become the cutting edge of functional and restorative neurosurgery. Coupled with the development of DBS is a vastly superior knowledge of the anatomy and physiology of psychiatric symptomatology than what was understood in the days of Moniz and Freeman, and powerful tools to advance that understanding further.
Section snippets
Anatomical considerations
The essence of any neurosurgical procedure, even one that inherently seeks to alter physiology, is one of anatomy. DBS systems need to be deployed in anatomic regions that have efficient access to anatomic networks subserving psychiatric phenomenona. Even though anatomical models relevant to core dimensions of psychopathology continue to evolve, it is clear that anatomic relationships of the basal ganglia, the thalamus, and other cortical and subcortical structures are vital for gaining insight
Obsessive–compulsive disorder (OCD)
Recent functional imaging studies have consistently found evidence that corroborates the role of the above anatomic areas in OCD pathophsyiology. It is important to assess functional imaging data of psychiatric patients (which are presented as group, and not individual data), carefully, as activation phenomena seen in them overlap those in healthy individuals. Furthermore, it is often difficult to distinguish changes that are markers for symptom amelioration versus activity subserving “normal”
The DBS experience: current state-of-the-art
The previous section has described the basic neuroanatomical landscape in which DBS might be deployed in order to modulate neural circuits and thus bring about amelioration in psychiatric symptoms. DBS has inherent advantages over previous lesioning procedures. Unlike ablative procedures that are inherently irreversible, DBS offers a non-ablative approach that can be altered dynamically according to the benefits and side effects on the patient. This provides a higher degree of safety than the
Conclusion
Understanding the anatomy and physiology of psychiatric disease is an evolving process. Surgical intervention is, by definition, an anatomically based endeavor. The knowledge of the anatomy of the basal ganglia lead to the initial insights into the physiology of PD gained from lesions made during early movement disorder surgery. So too will such insights serve the efforts into applying DBS to address psychiatric illness. The discovery of the MPTP primate model and the subsequent quantum leap in
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