“Wikipedia Proposal:Cortical Stimulation Mapping” Presented by: Heather Funk, Melissa Chavez, and Daniel Farrell

Introduction

The students of Joe Burdo’s BI481 Introduction to Neuroscience class have been given the task of editing underdeveloped or incomplete neuroscience articles. This project is related to the initiative founded by the Society for Neuroscience meant to improve information about neuroscience on Wikipedia. More about this project for BI 481 can be found here: user:NeuroJoe/BI481 Fall 2012 The Wikipedia article we will be renovating is Cortical stimulation mapping. This is a physically invasive procedure that aims to localize the function of specific brain regions through direct electrical stimulation of the cerebral cortex. It is often one of the tools neuroscientists use to study the relationship of cortical structure to systemic function. Although one of the earliest methods of analyzing the brain, cortical stimulation mapping is still useful for a number of clinical and therapeutic applications. Included are the topics we plan to expand upon. We have written a short introduction to each that explains how the section is relevant to the article as well as provides insight into the preliminary research we have done. The topic headings and sources of this article as listed below are subject to change as we further our research throughout the semester.

Topics

The topics that we have chosen to focus on for this article we have chosen not only for their prevalence in current neuroscience research involving cortical stimulation mapping but also because, together, they adequately explain its overall principles so that the reader might better understand the article’s subject. These topics include: history, procedure, somatotopy, clinical applications, and a comparison with other techniques.

History

The history of cortical stimulation mapping dates back to the late 19th century. The neurologists Sir David Ferrier and Sir Victor Horsley were some of the first to utilize this technique. Ferrier and Horsley employed CSM to further grasp the structure and function of the pre and post Rolandic areas, also known as the pre and post central gyri. Prior to the development of more advanced methods, in 1888 C.B. Nancrede utilized a battery operated bipolar probe in order to map the motor cortex. In 1937, Penfield and Boldrey were able to show that stimulating the precentral gyrus elicited a response contralaterally; a significant finding given that it correlated to the anatomy based on which part of the brain was stimulated. In the early 1900s Charles Sherrington began to use monopolar stimulation in order to elicit a motor response. This technique allowed Sherrington to determine that the precentral gyrus (pre-Rolandic area) is a motor cortex and the postcentral gyrus (post-Rolandic area) is a sensory cortex. These findings, which were repeated by Harvey Cushing, show that the Rolandic fissure is the point of separation between the motor and sensory cortices.

Procedure

Cortical Stimulation Mapping is an invasive procedure that has to be completed a craniotomy. Once the dura mater is peeled back, a subdural electrode is placed on the brain in order to measure the brain responses. The strip can be adjusted to elicit a response from a different area. CSM can be completed using anesthetized patients or awake patients.

Somatotopy

Cortical stimulation mapping is used for somatotopy to determine the areas of the cerebral cortex that connect through nerve fibers with different body parts. Cortical stimulation identifies which regions of the brain are vital for certain functions, thereby allowing a ‘map’ to be made which can be used to decide if brain areas are safe to remove. Cortical stimulation mapping led to the development of a homunculus for the motor and sensory cortices. A homunculus is a diagram of the brain showing its connections to different areas of the body. An example is the cortical homunculus of the primary motor cortex and the somatosensory cortex, which are separated by the central sulcus.

Motor Mapping

Functional testing of movement during cortical stimulation includes looking for active movement and inhibition of movement. Areas of the cortex that inhibit movement upon stimulation have been found in some cases to be supplemental and not vital to motor function. These areas have been removed without compromising a patient’s ability to move post-operation.

Language Mapping

During stimulation various language tasks are used to check brain function such as reading sentences, auditory comprehension, and spontaneous speech.

Clinical Applications

Epilepsy

CSM is routinely utilized for epileptic patients in order to pin point the focal point of the seizures. Once the focal point of the seizures is determined, this information, along with information provided by CSM, can aid the neurosurgeons with know what portions of the brain could potentially be resected without any negative post-operative neurological deficits.

Neuro-Oncology

Cortical stimulation mapping may be used in neuro-oncology as a tool to identify the areas of a patient’s brain that are critical for functions such as the language and motor pathways. This sort of pre-surgical planning allows for the physician to avoid these crucial areas as much as possible during a tumor resection, minimizing potential loss of function. This procedure is considered standard for operations involving gliomas.

Vision

Mapping of the occipital cortex has possible use to develop a “prosthesis for the blind”. Electrical stimulation in the has been found to cause “visual illusions” called phosphenes such as light, colors, or shadows.

A Comparison with Other Techniques

Cortical Stimulation Mapping is considered the gold standard, as determined by the gold standard (test), for mapping functional regions of the brain to create a presurgical plan that maximizes the patient’s functional outcome. Its history of beneficial outcomes and the amount of information already established about the technique makes it advantageous in clinical and research applications. However, because it has the disadvantage of being an intraoperative technique, there is growing debate about its status as the gold standard. Instead, many new procedures that do not carry the same amount of surgical risk are being considered.

Transcranial Magnetic Stimulation

Transcranial Magnetic Stimulation has been gaining increasing interest as a possible non-invasive tool for studying the relationships between specific cortical areas and brain function. It is also being researched for its possibilities as a therapeutic method for treating depression as well as a means of in aiding in stroke recovery. Research on this method is ongoing as its mechanisms are understood on a basic level however much is still to be determined about its exact effect on the activation state of the brain. Guidelines by the FDA for its safe use are also still incomplete.

Links to other Wikipedia Articles

These pages are existing Wikipedia pages that are relevant to CSM:

Cortical Homunculus

Electrocorticography

Division of Workload

We have divided the workload among our group according to topic. Melissa Chavez is responsible for the Introduction, Neuro-Oncology, and comparing cortical stimulation mapping to Transcranial Magnetic Stimulation topics. Heather Funk is working on the History, Procedure, and Epilepsy categories. Daniel Farrell is doing research for the topics of Somatotopy, Clinical Applications in Vision, and comparing cortical stimulation mapping. We are also committing ourselves to a number of self-imposed deadlines in order to break up the work throughout the semester and ensure that our project is thorough and on time.

References

Adhikary SD, Thiruvenkatarajan V, Babu KS, Tharyan P. The effects of anaesthetic agents on cortical mapping during neurosurgical procedures involving eloquent areas of the brain. Cochrane Database of Systematic Reviews 2011, Issue 11 . Art . No .:CD006679 . DOI :10.1002/ 14651858.CD006679.pub2.
Berger MS OG. 1992. Intraoperative brain mapping techniques in neuro-oncology. Stereotactic and Functional Neurosurgery 48(1-4):153-61.
Duffau H. 2012. The challenge to remove diffuse low-grade gliomas while preserving brain functions. Acta Neurochirurgica 154(4):569-74.
Functional Mapping through Cortical Stimulation. NYU Langone Medical Center. Comprehensive Epilepsy Center.
Gates JR. 1995. Transcranial magnetic stimulation.. Neuroimaging Clinics of North America 5(4):711-20.
Kim PE. and Singh M. 2003. Functional magnetic resonance imaging for brain mapping in neurosurgery.. Neurosurgical Focus 15(1).
Mandonnet E, Winkler P, Duffau H. 2010. Direct electrical stimulation as an input gate into brain functional networks: Principles, advantages and limitation. Acta Neurochirurgica 152(2):185-93.
Ruohonen J and Karhu J. 2010. Navigated transcranial magnetic stimulation. Neurophysiologie Clinique-Clinical Neurophysiology 40(1):7-17.
Sanai N. BM. 2010. Intraoperative stimulation techniques for functional pathway preservation and glioma resection. Neurosurg Focus 28(2).
Silverstein, Justin. (2011). Mapping the Motor and Sensory Cortices: A Historical Look and a Current Case Study in Sensorimotor Localization and Direct Cortical Motor Stimulation. The Neurodiagnostic Journal. 52, 1. Proquest Central. Pg 54-68.