Cushing, Penfield, and cortical stimulation

Deep Brain Stimulation of the Posterior Insula in Chronic Pain: A Theoretical Framework

INTRODUCTION

To date, clinical trials of deep brain stimulation (DBS) for refractory chronic pain have yielded unsatisfying results. Recent evidence suggests that the posterior insula may represent a promising DBS target for this indication.

METHODS

We present a narrative review highlighting the theoretical basis of posterior insula DBS in patients with chronic pain.

RESULTS

Neuroanatomical studies identified the posterior insula as an important cortical relay center for pain and interoception. Intracranial neuronal recordings showed that the earliest response to painful laser stimulation occurs in the posterior insula. The posterior insula is one of the only regions in the brain whose low-frequency electrical stimulation can elicit painful sensations. Most chronic pain syndromes, such as fibromyalgia, had abnormal functional connectivity of the posterior insula on functional imaging. Finally, preliminary results indicated that high-frequency electrical stimulation of the posterior insula can acutely increase pain thresholds.

CONCLUSION

In light of the converging evidence from neuroanatomical, brain lesion, neuroimaging, and intracranial recording and stimulation as well as non-invasive stimulation studies, it appears that the insula is a critical hub for central integration and processing of painful stimuli, whose high-frequency electrical stimulation has the potential to relieve patients from the sensory and affective burden of chronic pain.

Biological Mechanism of Specific Relationship between Gan (Liver) Meridian of Foot-Jueyin and Genitals

From the perspective view of Chinese medicine, the Gan (Liver) meridian of Foot-Jueyin starts from the great toe, running upward along the medial side of the thigh to the perineal area, where it curves around the external genitalia and goes up to the lower abdomen. In clinical practice, acupoints in the feet of the Gan meridian of Foot-Jueyin are used to treat the genitourinary and external genitalia diseases. Studies have shown that reproductive system diseases have specific pathological reactions in the places (radial side of tibia and foot) where Gan meridian of Foot-Jueyin passes by. Why does this happen? In this article, we begin by briefly reviewing the evidences linking foot and genitalia. We then explore the potential mechanism of the relationship between genitals and the Gan meridian of Foot-Jueyin. The brain cerebral cortex is characterized by cortical interactions. Numerous studies show that different cerebral cortex function areas (especially the adjacent areas) are overlapping and interact with each other. Finally, we presume that there is a specific connection between the feet and the genitals. Physiologically in the cortical homunculus, the genital area lies adjacent or overlapped to the foot areas, the two areas may interact with each other. The functional reorganization between different areas of the cerebral cortex under pathological conditions may be the underlying mechanism of the relationship between the feet and the genitals.

A Review of Passive Brain Mapping Techniques in Neurological Surgery

Brain mapping is a quintessential part of neurosurgical practice. Accordingly, much of our understanding of the brain's functional organization, and in particular the motor homunculus, is largely attributable to the clinical investigations of past neurosurgeons. Traditionally mapping was invasive and involved the application of electrical current to the exposed brain to observe focal disruption of function or to elicit overt actions. More recently, a wide variety of techniques have been developed that do not require electrical stimulation and often do not require any explicit participation by the subject. Collectively we refer to these as passive mapping modalities. Here we review the spectrum of passive mapping used by neurosurgeons for mapping and surgical planning that ranges from invasive intracranial recordings to noninvasive imaging as well as regimented task-based protocols to completely task-free paradigms that can be performed intraoperatively while under anesthesia.

A brief history of cortical functional localization and its relevance to neurosurgery

Modern cortical mapping is a cornerstone for safe supratentorial glioma resection in eloquent brain and allows maximal resection with improved functional outcomes. The unlocking of brain functionality through close observation and eventually via cortical stimulation has a fascinating history and was made possible by contributions from early physician-philosophers and neurosurgery’s founding fathers. Without an understanding of brain function and functional localization, none of today’s modern cortical mapping would be possible.