Functional brain mapping can be categorized into non-invasive and invasive modalities. Each technique varies in spatial and temporal resolution, risk profile, and clinical utility.
| Modality | Principle | Use Case | Resolution |
|---|---|---|---|
| fMRI (functional MRI) | Measures BOLD signal during cognitive or motor tasks | Language, motor mapping pre-surgery | High spatial, low temporal |
| MEG (Magnetoencephalography) | Detects magnetic fields from neuronal activity | Epilepsy focus, motor/language mapping | High temporal, moderate spatial |
| TMS (Transcranial Magnetic Stimulation) | Magnetic pulses induce neuronal activity; responses are mapped | Motor and speech localization, outpatient mapping | Moderate spatial, moderate temporal |
| PET (Positron Emission Tomography) | Measures regional metabolism via radiotracer uptake | Tumor metabolism, epilepsy foci | Low spatial, poor temporal |
| Modality | Principle | Use Case | Resolution |
|---|---|---|---|
| ECoG (Electrocorticography) | Records electrical activity directly from cortex | Real-time seizure detection, functional mapping | Very high temporal and spatial |
| CSM (Cortical Stimulation Mapping) | Electrical stimulation of cortex during awake surgery | Functional validation of eloquent cortex (speech, motor) | Gold standard for eloquence |
| SEEG (Stereo-electroencephalography) | Intracerebral depth electrodes monitor deep cortical and subcortical areas | Refractory epilepsy, functional connectivity | High depth resolution |
The choice of modality depends on:
For example:
Tags: `functional_mapping` `modalities` `noninvasive` `invasive` `epilepsy_surgery` `fMRI` `CSM` `ECoG` `MEG` `TMS`
Intraoperative stimulation mapping.
see Functional Mapping.
see Process Mapping.
Functional brain mapping refers to the identification and localization of specific brain areas responsible for motor, sensory, language, memory, and higher cognitive functions. It is a cornerstone in modern neurosurgery, particularly in the treatment of lesions near or within eloquent cortex.
Functional mapping is essential for:
| Method | Invasiveness | Resolution | Use Case |
|---|---|---|---|
| fMRI | Non-invasive | High spatial, low temporal | Pre-op planning |
| MEG | Non-invasive | High temporal | Epilepsy, language |
| ECoG | Invasive | Very high | Real-time mapping |
| CSM | Invasive | Functional confirmation | Awake surgery |
| TMS | Non-invasive | Good spatial | Language/motor screening |
Tags: `functional_mapping` `brain_mapping` `fMRI` `ECoG` `CSM` `MEG` `TMS` `epilepsy` `glioma` `dbs` `language` `motor` `awake_surgery`
Functional brain mapping (FBM) is an integral part of contemporary neurosurgery. It is crucial for safe and optimal resection of brain lesions like gliomas. The eloquent regions of the like motor cortex, somatosensory, Wernicke's area, and Broca's area are usually mapped, either preoperatively or intraoperatively. Since its birth in the nineteenth century, FBM has witnessed immense modernization, radical refinements, and the introduction of novel techniques, most of which are non-invasive. Direct electrical stimulation of the cortex, despite its high invasiveness, remains the technique of choice. Non-invasive techniques like fMRI and magnetoencephalography allow us the convenience of multiple mappings with minimal discomfort to the patients. They are quick, easy to do, and allow thorough study. Different modalities are now being combined to yield better delineations like fMRI and diffusion tensor imaging.
Sagar et al., reviews the physical principles, applications, merits, shortcomings, and latest developments of nine FBM techniques. Other than neurosurgical operations, these techniques have also been applied to studies of stroke, Alzheimer's, and cognition. There are strong indications that the future of brain mapping shall see the non-invasive techniques playing a more dominant role as they become more sensitive and accurate due to advances in physics, refined algorithms, and subsequent validation against invasive techniques 1).
Intraoperative stimulation mapping.
The vast majority of centers use electrophysiological mapping techniques to finalize target selection during the implantation of deep brain stimulation (DBS) leads for the treatment of Parkinson's disease and tremor. This review discusses the techniques used for physiological mapping and addresses the questions of how various mapping strategies modify target selection and outcome following subthalamic nucleus (STN), globus pallidus internus (GPi), and ventralis intermedius (Vim) deep brain stimulation. Mapping strategies vary greatly across centers, but can be broadly categorized into those that use microelectrode or semimicroelectrode techniques to optimize position prior to implantation and macrostimulation through a macroelectrode or the DBS lead, and those that rely solely on macrostimulation and its threshold for clinical effects (benefits and side effects). Microelectrode criteria for implantation into the STN or GPi include length of the nucleus recorded, presence of movement-responsive neurons, and/or distance from the borders with adjacent structures. However, the threshold for the production of clinical benefits relative to side effects is, in most centers, the final, and sometimes only, determinant of DBS electrode position. Macrostimulation techniques for mapping, the utility of microelectrode mapping is reflected in its modification of electrode position in 17% to 87% of patients undergoing STN DBS, with average target adjustments of 1 to 4 mm. Nevertheless, with the absence of class I data, and in consideration of the large number of variables that impact clinical outcome, it is not possible to conclude that one technique is superior to the other in so far as motor Unified Parkinson's Disease Rating Scale outcome is concerned. Moreover, mapping technique is only one out of many variables that determine the outcome. The increase in surgical risk of intracranial hemorrhage correlated to the number of microelectrode trajectories must be considered against the risk of suboptimal benefits related to omission of this technique 2).