Indian Journal of Radiology Indian Journal of Radiology  

   Login   | Users online: 1959

Home Bookmark this page Print this page Email this page Small font sizeDefault font size Increase font size     


NEURORADIOLOGY Table of Contents   
Year : 2008  |  Volume : 18  |  Issue : 3  |  Page : 210-217
Clinical applications of functional MRI in epilepsy

Department of Imaging Sciences and Interventional Radiology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum - 695 011, India

Click here for correspondence address and email


The role of functional MRI (fMRI) in the presurgical evaluation of patients with intractable epilepsy is being increasingly recognized. Real-time fMRI is an easily performable diagnostic technique in the clinical setting. It has become a noninvasive alternative to intraoperative cortical stimulation and the Wada test for eloquent cortex mapping and language lateralization, respectively. Its role in predicting postsurgical memory outcome and in localizing the ictal activity is being recognized. This review article describes the biophysical basis of blood-oxygen-level-dependent (BOLD) fMRI and the methodology adopted, including the design, paradigms, the fMRI setup, and data analysis. Illustrative cases have been discussed, wherein the fMRI results influenced the seizure team's decisions with regard to diagnosis and therapy. Finally, the special issues involved in fMRI of epilepsy patients and the various challenges of clinical fMRI are detailed.

Keywords: Epilepsy; functional MRI

How to cite this article:
Kesavadas C, Thomas B. Clinical applications of functional MRI in epilepsy. Indian J Radiol Imaging 2008;18:210-7

How to cite this URL:
Kesavadas C, Thomas B. Clinical applications of functional MRI in epilepsy. Indian J Radiol Imaging [serial online] 2008 [cited 2020 Aug 12];18:210-7. Available from:
Functional MRI is a technique that maps the physiological or metabolic consequences of altered electrical activity in the brain. In contrast to positron emission tomography (PET), a similar brain mapping technique and one that has been used for many years to study brain function, fMRI is not based on ionizing radiation and thus can be repeated as often as is necessary in patients or normal volunteers. Electroencephalography (EEG) and magnetoencephalography (MEG) map the electrical activity in the brain. Although EEG and MEG have high temporal resolution (10-100 milliseconds), they suffer from poor spatial resolution (one to several centimeters). The blood-oxygen-level-dependent (BOLD) fMRI technique has a spatial resolution of a few millimeters and a temporal resolution of a few seconds. [1]

   Biophysical Basis of BOLD fMRI Top

Neuronal stimulation leads to a local increase in energy and oxygen consumption in functional areas. The subsequent local hemodynamic changes transmitted via neurovascular coupling are measured by fMRI. The close coupling between regional changes in brain metabolism and regional cerebral blood flow (CBF), called 'activation flow coupling' (AFC), was originally described by Roy and Sherrington in 1890. [2] The BOLD technique depends on the difference in the magnetic properties between oxygenated (oxy-Hb) and deoxygenated (deoxy-Hb) hemoglobin. The ferrous iron on the heme moiety of deoxy-Hb was shown to be paramagnetic by Thulborn and colleagues in 1982. [3] Paramagnetic deoxy-Hb produces local field inhomogeneities in the measurable range of MRI, resulting in signal decrease in susceptibility-weighted MRI-sequences (T2*), whereas diamagnetic oxy-Hb does not interfere with the external magnetic field. Ogawa and coworkers working on a rat model at 7 Tesla showed that the oxygenation of blood has a measurable effect on the MRI signal. [4] Kwong et al , in 1992, demonstrated that brain activation in human subjects produced a local signal increase that could be used for functional brain imaging. [5] In the same year, several others reported similar findings. [6],[7],[8]

When the neurons are stimulated there is an increase in local oxygen consumption that results in an initial decrease of oxy-Hb and an increase in deoxy-Hb in the functional area. To provide the active neurons with oxygenated blood, perfusion in capillaries and draining veins is enhanced within several seconds. As a result of this process, the initial decrease of local oxy-Hb is equalized and then overcompensated. [9] The deoxy-Hb is progressively washed out. This causes a reduction of local field inhomogeneity and an increase of the BOLD signal in T2*W MRI images [10] [Figure 1]. Although the 'initial dip' corresponds to the neuronal activity both temporally and spatially, this is more difficult to measure in clinical settings. [11] Electrophysiologically, it is the local field potential that changes with an increase in the BOLD signal and not the neuronal firing rate. [12]

   Design of fMRI Experiments and Data ­Acquisition Top

The most common imaging sequence used in fMRI studies is echoplanar imaging (EPI). [13] This is a very fast MRI imaging sequence, which can collect whole brain data within a few seconds. However, the spatial resolution is significantly lower than in anatomic MRI images. Also EPI images are sensitive to field inhomogeneities, leading to geometric distortion of the images in certain brain regions. In a typical fMRI experiment, a large set of images is acquired very quickly, while the patient or subject performs a task that shifts brain activity between two or more well-defined states (boxcar design) [Figure 2].

The signal time course in each voxel of the slices and the time course of different tasks are correlated. This can identify voxels in brain that show statistically significant changes associated with the brain function under consideration. [1] Later these statistical maps (Z scores) are superimposed on a high-resolution anatomic image by using a coregistration technique for proper identification of the precise anatomic location of the origin of the signal. Although this appears complicated, most of this can now be done online using the real-time fMRI packages available in newer MRI machines.

Most of the clinical fMRI experiments use a boxcar or block design. It is the simplest and the most time-efficient approach for comparing brain response in different states. In this design, for relatively long periods (e.g., 30 s), a discrete cognitive or motor state is maintained (in the simplest form, two states: rest vs activity) and is alternated during scanning. Since this is not a physiological design (i.e., it is an artificial state), some tasks may not be suitable for this design. [1]

An alternative approach, which is more physiological, is an 'event'-related paradigm [Figure 3], in which discrete stimuli are repeated at variable times while scanning is in progress. However, this design needs longer acquisition times and is statistically more difficult to analyze and, hence, is used less often in clinical practice.

   fMRI Setup Top

fMRI applications in research laboratories can have permanent test setups. Here the results need not be immediately available. In contrast, fMRI in clinical / hospital settings, needs custom-tailored hardware, software, imaging protocols, and data evaluation techniques. A real-time fMRI processing tool is useful so that the results are available immediately. In a clinical setting we have to examine patients with existing deficits, and subjects may include uncooperative or sedated patients and children. At our institute we have set up a patient-friendly audiovisual projection system with a response box and synchronization device (synchronizes the visual/auditory stimulation with the MRI pulse). [Figure 4] illustrates the setup that we use for clinical studies.

   fMRI Paradigms Top

By using optimized and standardized protocols, fMRI examinations can be integrated into routine MRI imaging without major problems. To investigate motor function, self-triggered movements are most commonly used. Motor cortex mapping is done using paradigms that include tongue movements as well as finger and toe movements, contralateral to the side of the lesion, to localize the motor homunculus in relation to the lesion. Bilateral finger movement can help in comparing the ipsilateral motor cortex with that on the opposite side. To keep the likelihood of motion artifacts to a minimum, [14],[15] the following movement tasks are chosen: repetitive tongue movements, with closed mouth; opposition of fingers to thumb, with free choice of sequence; and repetitive flexion and extension of all five toes, without moving the ankle. Alternatively, in cases of mild paresis of the upper extremity, fist clenching/ releasing can be tested. The somatosensory functional areas can be studied by nonstandardized tactile stimuli (e.g., manual stroking of the hand by the examiner). [16]

Language functions are examined using various paradigms involving auditory or visual stimulation. A task commonly and easily performed in patients for the purpose of lateralization is the "verb generation task" (also called "verbal fluency task"). This task shows relatively consistent activation of the anterior language areas. Another task, the "semantic decision-making task", demonstrates more widely distributed networks, including the anterior and posterior language areas. [17] The "visual stimulation task" is performed by showing checkerboards during the active period and a blank screen during the rest period.

   Data Analysis Top

Each fMRI experiment generates a huge amount of data, which needs to be analyzed rigorously in order to obtain the best results. As mentioned earlier, for simple analysis, real-time fMRI processing will help. Our earlier studies have shown that real-time fMRI analysis by vendor-provided fMRI processing tool can give clinically useful information comparable to the time-tested postprocessing tools [18] [Figure 5]. Presently, we perform most of our fMRI studies using real-time fMRI processing. The fMRI results are then coregistered on 3D-FLAIR images. We have found coregistering on 3D-FLAIR more useful than on T1W 3D spoiled gradient images (3D FLASH/3D SPGR). [18]

For event-related paradigms and more complex boxcar paradigms involving more than two states, extensive computation may be required using any of the free or commercial softwares, such as statistical parametric mapping (SPM) ( ), FSL ( ) or Brain Voyager ( ).The basic idea of analysis of functional imaging data is to identify voxels that show signal changes that vary with the changes in the given cognitive or motor state of interest, across the time course of the experiment. This is quite a challenging problem as the fMRI signal changes are very small (of the order of 0.5-5%), leading to a high probability of false negative results. The chance of false positive activation is also very high. Different types of analysis like 'fixed effects,' 'random effects,' or 'mixed effects' can be undertaken. [1]

The greatest problem during any fMRI experiment is subject motion. The BOLD signal is extremely sensitive to motion, which can spoil the whole experiment. Motion can be gross head movement or even the minimal brain motion associated with cardiac or respiratory cycles. Most of the analysis software includes some realignment and coregistration programs to minimize motion effects. Another step is performed using spatial smoothing and temporal filtering, to reduce the noise in the data. The images can then be normalized to a common brain space [e.g., Montreal Neurological Institute (MNI) template]. This step is utilized mostly in research studies and is not needed for individual patients in the clinical setting. Various statistical tests can then be applied on a voxel-by-voxel basis to test the significance of a particular voxel with an increased signal associated with a certain brain state. The commonly used method is 't' statistics. The 't' statistical maps are then superimposed on high-resolution anatomical images to obtain a clinically useful fMRI output.

   Clinical Applications in Patients with ­Epilepsy Top

fMRI has been used to study patients with a broad range of neurological disorders and across a wide spectrum of disease severity. The results have provided insights into the mechanism of disease as well as into normal brain function. The majority of the studies published have been performed in research settings. The clinical role of fMRI is being increasingly recognized. One of the earliest and best-validated clinical applications of fMRI was, and remains, presurgical assessment of brain function in patients with brain tumors and epilepsies. There is a substantial body of evidence that shows that fMRI is a good technique for localizing different body representations in the primary motor and somatosensory cortex, as well as for localizing and lateralizing language function prior to surgery. This diagnostic information permits function-preserving and safe treatment. We illustrate the clinical applications through patients whom we have investigated at our hospital during the last three years.

   Mapping the Eloquent Cortex Top

Mapping eloquent areas can be done using invasive methods such as intraoperative cortical stimulation in awake patients, implantation of a subdural grid, or intraoperative recording of sensory-evoked potentials. [19],[20] fMRI can obtain these data preoperatively and noninvasively. Together with its high sensitivity for visualizing brain lesions, fMRI can define the relation between the margin of a lesion and any adjacent functionally significant brain tissue. fMRI has the potential to predict possible deficits in motor and sensory perceptual functions or in language that would arise from intrinsic lesion expansion or from therapeutic interventions such as surgery. This helps in decision making during patient management. The relative risk of intervention vs nonintervention can be discussed and explained to the patient and the relatives. Further, a decision on the treatment option to be adopted can be made after considering the cost of treatment and the benefits that can be expected from the treatment.

Earlier studies aimed at comparing intraoperative corticography (ECoG) with fMRI revealed good spatial correlation between the two methods. [21],[22],[23] A few studies have also tried to assess the chances of postoperative deficits when a lesion was placed in, or was close to, the eloquent cortex. [24] Lee et al , evaluated the ways in which fMRI studies have influenced patient management. In patients with medically refractory epilepsy, fMRI results helped to assess the feasibility of resection in 70%, to plan the surgical procedure in 43%, and to select patients for invasive mapping in 52%. [25]

In our series of patients, fMRI results matched those from intraoperative cortical stimulation, for lesions in, or close to the eloquent cortex. They also matched Wada test results for language hemispheric dominance. [18] Eloquent cortex mapping was performed in epilepsy patients with tumor, gliosis, or malformation of cortical development in, or close to the eloquent cortex. Our neurosurgeons have found fMRI for eloquent cortex mapping most useful in patients with gliosis, in whom the distortion in anatomy makes prediction of the eloquent cortex extremely difficult. Usually gliotic lesions pull the functionally active areas towards them. Space-occupying lesions such as tumors of the brain primarily displace the functional cortex. For this reason, resection within the boundaries of a lesion should not directly damage the eloquent cortex and result in a significant deficit. In contrast, functional reorganization may or may not happen within the dysplastic cortex in malformations of cortical development. Our study using fMRI on cortical malformations showed that functional reorganization is unpredictable in these lesions. [26] The dysplastic cortex can retain useful brain function. The following three cases illustrate the usefulness of fMRI in selecting patients for surgery, tailoring surgical resection, and in predicting the postsurgical outcome [Figure 6],[Figure 7],[Figure 8].

   Lateralization of Language Functions Top

Intracarotid amobarbital testing (Wada testing) has been the gold standard for identifying lateralization of language and memory functions preoperatively, but it is invasive and therefore carries a small, but definite risk of complications. fMRI offers a promising noninvasive alternative approach. [27] While there is good agreement between the Wada and fMRI results, fMRI is more sensitive to involvement of the nondominant hemisphere. Binder et al , [28] reported a cross-validation study comparing language dominance determined by both fMRI and the Wada test in 22 patients. The majority of studies opine that semantic decision tasks should be used rather than verbal fluency tasks because the latter may lack the ability to activate the posterior language areas.

We have noted that visual presentation of the language paradigm gives much better and consistent results as compared to auditory presentation. Secondly, in a multilingual country like India, auditory language tasks may have to be modified according to the primary language of the patient. This can be solved to some extent by showing the nouns as pictures in the verb generation task. In our fMRI language studies we perform both the semantic decision task and the verbal fluency task by visual presentation. The former is done using a discrimination task of word pairs - related/unrelated, judging the meaning of sentences, and identifying grammatically accepted language. These tasks are preferably done in the primary language of the patient. The following two cases illustrate the usefulness of fMRI in language lateralization [Figure 9] and [Figure 10].

   Memory Top

Performing fMRI to map memory is more challenging than mapping language. fMRI has been found to be useful in predicting postoperative memory deficits. Memory processing involves encoding and retrieval of face, patterns, words, sceneries, etc. Paradigms for each of these tasks show activation in different areas. It is also difficult to separate brain activity related to memory from that related to other cognitive processes. [29] Detre et al , were the first to demonstrate that fMRI could be used to detect clinically relevant asymmetries in memory activation in patients with temporal lobe epilepsy. [30] In a study by Golby et al , fMRI was used to study the lateralization of memory encoding processes (patterns, faces, scenes, and words) within the mesial temporal lobe in patients with temporal lobe epilepsy. [31] Rabin et al , used a complex visual scene-encoding task that causes symmetrical mesial-temporal-lobe activation in controls, to determine a relationship between mesial temporal lobe activation asymmetry ratios and postsurgical memory outcome. [32] It was shown that increased activation ipsilateral to the seizure focus is associated with greater memory decline. A more recent study has shown similar results. [33] We have developed simple memory encoding paradigms that can be used in Indian patients with epilepsy. We have tested these in controls and have found the results to be consistent.

   Localizing Spontaneous Ictal Activity Top

Using a newer technique that allows concurrent EEG and fMRI, it is possible to localize the regional metabolic changes accompanying ictal activity. [34],[35] These techniques capitalize on the temporal resolution of EEG and spatial resolution of fMRI. The approach of concurrent EEG and fMRI recording tends to be more efficient and accurate as compared to the spike-triggered approach. These techniques may be of particular value in presurgical evaluation of neocortical epilepsy, where paroxysmal activity on EEG may remain poorly localized. In addition, these techniques may provide new insights into the anatomical and pathophysiological correlates of unifocal and multifocal spike discharges.

The MRI scanner is a hostile environment for EEG recordings. MR-compatible EEG recording equipment must ensure patient safety, sufficient quality of the EEG signals, and avoid compromising MRI image quality. Technical issues related to EEG-correlated fMRI have been addressed in detail in several previous articles [36] EEG-correlated fMRI has been shown to be a practicable method in epilepsy patients with frequent interictal epileptiform discharges on scalp EEG. [37],[38] A recently published study has evaluated the clinical usefulness of this technique in presurgical localization of the epileptogenic focus. [39]

   Challenges for Presurgical fMRI Top

  1. Patients with epilepsy on long-term antiepileptic medication and those who have frequent seizures can have low intelligence quotients (IQ). These patients may not co-operate for difficult tasks such as the language and memory tasks. They may, however, be able to perform simpler motor tasks. Before fMRI is performed, each of our epilepsy patients undergoes a neuropsychology test for assessing the IQ. [18]
  2. The effects of medication on the BOLD signal response have not been systematically studied as yet. In a study by Jokeit et al , [40] the extent of fMRI activation of the mesial temporal lobes induced by a task based on the retrieval of individual visuospatial knowledge was correlated with the serum carbamazepine level in 21 patients with refractory temporal lobe epilepsy. The study showed that the carbamazepine level can significantly influence the amount of fMRI activation.
  3. Ictal and interictal epileptic activity in a patient with epilepsy can influence the lateralization of mesiotemporal memory functions and language functions. [41],[42] The next three challenges mentioned are some of the general challenges for clinical fMRI. [43]
  4. Head motion: Signal intensity changes observed in fMRI images are small. These may be contaminated by gross head motion. Additional minor contamination results from physiologic brain motion (pulsation of the brain, overlying vessels, and cerebrospinal fluid). Head movement during the acquisition phase can be restricted by fixation of the head with straps. However we have found that patients find this uncomfortable. Postprocessing techniques in the offline tools, like realignment and coregistration can help in correcting for head movement. Stimulation paradigms that induce less patient head motion are preferred. Finally, patient cooperation is an essential element both in task compliance and in restricting head motion. If we are planning to do a routine MRI brain study along with fMRI, it is better to do the fMRI study first when patient cooperation is better. In patients in whom we have performed fMRI immediately after the routine brain study we have seen the head movement to be more. Secondly, adequate training before imaging could increase the familiarity with the imaging process. We have found training to be extremely useful in pediatric fMRI and we have been able to do fMRI studies for language lateralization in children as young as 5-6 years of age [Figure 10].
  5. There is a concern that fMRI examinations at a field strength of 1.5 Tesla images predominantly large, draining veins. Gao et al , have shown that fMRI images weighted toward the microcirculation may be obtained at 1.5T, if the pulse sequence is designed for minimizing inflow effects and maximizing BOLD contribution. [44] Maximizing the fMRI signal toward the site of neuronal activity can also be achieved by optimizing the mode of stimulation as shown by the study of Le Rumeur et al . [45]
  6. Does the absence of a BOLD signal in a cortical area indicate with certainty a lack of electrical neuronal activity in that area? Different pathologic conditions could weaken the hemodynamic response that is the source of the fMRI signal. Examples of this include peritumoral vasogenic edema producing mechanical vascular compression and drugs administered to the patient causing change in the hemodynamic autoregulation.

   Conclusions Top

Mapping sensorimotor, visual, language, and memory function using fMRI can identify the eloquent cortex and predict postoperative deficits of specific functions during the presurgical workup of patients with epilepsy. In selected patients with frequent interictal epileptiform discharges, EEG-correlated fMRI has the potential to identify the cortical areas involved in generating the discharges. Better and better techniques are slowly evolving to solve challenges in clinical fMRI. With the availability of higher Tesla magnets, faster sequences, and better paradigms and postprocessing tools, the clinical application of this technique in patients with epilepsy is going to increase in the years to come.

   Acknowledgements Top

The authors thank Mrs. Annamma George (speech therapist), Ms. Haritha, Mr. Sujesh, Dr. Niranjan (biomedical engineers) and the MR technologists for helping us perform the fMRI studies. The authors thank Mr. Vikas and Mr. Liji for the illustrations.

   References Top

1.Matthews PM, Jezzard P. Functional magnetic resonance imaging. J Neurol Neurosurg Psychiatry 2004;75:6-12.  Back to cited text no. 1  [PUBMED]  [FULLTEXT]
2.Roy CS, Sherrington CS. On the regulation of the blood-supply of the brain. J Physiol 1890;11:85-158.  Back to cited text no. 2  [PUBMED]  [FULLTEXT]
3.Thulborn KR, Waterton JC, Mathews PM, Radha GK. Oxygenation dependence of the transverse relaxation time of water protons in whole blood at high field. Biochim Biophys Acta 1982;714:265-70.  Back to cited text no. 3    
4.Ogawa S, Lee TM, Nayak AS, Glynn P. Oxygeneration sensitive contrast in magnetic resonance image of sodent brain at high magnetic fields. Magn Reson Med 1990;14:68-78.  Back to cited text no. 4  [PUBMED]  
5.Kwong KK, Belliveau JW, Chesler DA, Goldberg IE, Weisskoff RM, Poncelet BP, et al . Dynamic magnetic resonance imaging of human brain activity during primary sensory stimulation. Proc Natl Acad Sci 1992;89:5675-9.  Back to cited text no. 5  [PUBMED]  [FULLTEXT]
6.Bandettini PA, Wong EC, Hinks RS, Tikofsky RS, Hyde JS. Time course EPI of human brain function during taskactivation. Magn Reson Med 1992;25:390-7.  Back to cited text no. 6  [PUBMED]  
7.Fration J, Bruhn H, Merboldt KD, Hanicke W, Math D. Dynamic MR imaging of human brain oxygenation during rest and photic stimulation. J Magn Reson Imaing 1992;2:501-5.  Back to cited text no. 7    
8.Ogawa S, Tank DW, Memon R, Ellermann JM, Kim SG, Merkle H, et al . Intrinsic signal charges accompanying sensory stimulation: Functional brain mapping with magnetic resonance imaging. Proc Natl Acad Sci 1992;89:5951-5.  Back to cited text no. 8    
9.Fox PT, Raichle ME. Focal physiological uncoupling of cerebral blood flow and oxidative metabolism during somatosensory stimulation in human subjects. Proc Natl Acad Sci 1986;83:1140-4.  Back to cited text no. 9  [PUBMED]  [FULLTEXT]
10.Turner R, Le Bihan D, Moonen CT, Despres D, Frank J. Echo-planar time course MRI of cat brain oxygenation changes. Magn Reson Med 1991;22:159-66.  Back to cited text no. 10  [PUBMED]  
11.Duong TQ, Kim DS, Ugurbil K, et al . Spatiotemporal dynamics of the BOLD fMRI signals: Toward mapping submillimeter cortical columns using the early negative response. Magn Reson Med 2000;44:231-42.  Back to cited text no. 11    
12.Logothetis NK, Pauls J, Augath M, et al . Neurophysiological investigation of the basis of the fMRI signal. Nature 2001;412:150-7.  Back to cited text no. 12  [PUBMED]  [FULLTEXT]
13.Mansfield P. Multi-planar image formation using NMR spin echoes. J Phys Chem 1977;10:L55-8.  Back to cited text no. 13    
14.Hoeller M, Krings T, Reinges MH, Hans FJ, Gilsbach JM, Thron A. Movement artefacts and MR BOLD signal increase during different paradigms for mapping the sensorimotor cortex. Acta Neurochir (Wien) 2002;144:279-84.  Back to cited text no. 14  [PUBMED]  [FULLTEXT]
15.Krings T, Reinges MH, Erberich S, Kemeny S, Rohde V, Spetzger U, et al. Functional MRI for presurgical planning: Problems, artefacts, and solution strategies. J Neurol Neurosurg Psychiatry 2001;70:749-60.  Back to cited text no. 15  [PUBMED]  [FULLTEXT]
16.Hammeke TA, Yetkin FZ, Mueller WM, Morris GL, Haughton VM, Rao SM, et al. Functional magnetic resonance imaging of somatosensory stimulation. Neurosurgery 1994;35:677-81.  Back to cited text no. 16  [PUBMED]  [FULLTEXT]
17.Binder JR, Frost JA, Hammeke TA, Cox RW, Rao SM, Prieto T. Human brain language areas identified by functional magnetic resonance imaging. J Neurosci 1997;17:353-62.  Back to cited text no. 17  [PUBMED]  [FULLTEXT]
18.Kesavadas C, Thomas B, Sujesh S, Ashalata R, Abraham M, Gupta AK, et al. Real-time functional MR imaging (fMRI) for presurgical evaluation of paediatric epilepsy. Pediatr Radiol 2007;37:964-74.  Back to cited text no. 18  [PUBMED]  [FULLTEXT]
19.Berger MS, Cohen WA, Ojemann GA. Correlation of motor cortex brain mapping data with magnetic resonance imaging. J Neurosurg 1990;72:383-7.  Back to cited text no. 19  [PUBMED]  
20.Gregorie EM, Goldring S. Localization of function in the ­excision of lesions from the sensorimotor region. J Neurosurg 1984;61:1047-54.  Back to cited text no. 20  [PUBMED]  
21.Jack CR Jr, Thompson RM, Butts RK, Sharbrough FW, Kelly PJ, Hanson DP, et al . Sensory motor cortex: Correlation of presurgical mapping with functional MR imaging and invasive cortical mapping. Radiology 1994;190:85-92.  Back to cited text no. 21  [PUBMED]  [FULLTEXT]
22.Lehericy S, Duffau H, Cornu P, Capelle L, Pidoux B, Carpentier A, et al . Correspondence between functional magnetic resonance imaging somatotopy and individual brain anatomy of the central region: Comparison with intraoperative stimulation in patients with brain tumors. J Neurosurg 2000;92:589-98.  Back to cited text no. 22    
23.Puce A, Constable RT, Luby ML, McCarthy G, Nobre AC, ­Spencer DD, et al . Functional magnetic resonance imaging of sensory and motor cortex: Comparison with electrophysiological localization. J Neurosurg 1995;83:262-70.  Back to cited text no. 23    
24.Yetkin FZ, Mueller WM, Morris GL, McAuliffe TL, Ulmer JL, Cox RW, et al . Functional MR activation correlated with intraoperative cortical mapping. AJNR Am J Neuroradiol 1997;18:1311-5.  Back to cited text no. 24  [PUBMED]  [FULLTEXT]
25.Lee CC, Ward HA, Sharbrough FW, Meyer FB, Marsh WR, Raffel C, et al . Assessment of functional MR imaging in neurosurgical planning. AJNR Am J Neuroradiol 1999;20:1511-9.  Back to cited text no. 25  [PUBMED]  [FULLTEXT]
26.Kesavadas C, Thomas B, Sujesh S, Gupta AK. Functional MR Imaging (fMRI) Study of cortical reorganisation in focal cortical dysplasia (FCD) Proceedings of Radiological Society of North America (RSNA) 2007.  Back to cited text no. 26    
27.Adcock JE, Wise RG, Oxbury JM, Oxbury SM, Matthews PM. Quantitative fMRI assessment of the differences in lateralization of language-related brain activation in patients with temporal lobe epilepsy. Neuroimage 2003;18:423-38.  Back to cited text no. 27  [PUBMED]  [FULLTEXT]
28.Binder JR, Swanson SJ, Hammeke TA, Morris GL, Mueller WM, Fischer M, et al . Haughton determination of language dominance using functional MRI: A comparison with the Wada test. Neurology 1996;46:978-84.  Back to cited text no. 28  [PUBMED]  
29.Jokeit H, Okujava M, Woermann FG. Memory fMRI lateralizes temporal lobe epilepsy. Neurology 2001;57:1786-93.  Back to cited text no. 29  [PUBMED]  [FULLTEXT]
30.Detre JA, Maccotta L, King D, Alsop DC, Glosser G, D'Esposito M, et al . Functional MRI lateralization of memory in temporal lobe epilepsy. Neurology 1998;50:926-32.  Back to cited text no. 30  [PUBMED]  
31.Golby AJ, Poldrack RA, Illes J, Chen D, Desmond JE, Gabrieli JD. Memory lateralization in medial temporal lobe epilepsy assessed by functional MRI. Epilepsia 2002;43:855-63.  Back to cited text no. 31  [PUBMED]  [FULLTEXT]
32.Rabin ML, Narayan VM, Kimberg DY, Casasanto DJ, Glosser G, Tracy JI, et al . Functional MRI predicts post-surgical memory following temporal lobectomy. Brain 2004;127:2286-98.  Back to cited text no. 32  [PUBMED]  [FULLTEXT]
33.Powell HW, Richardson MP, Symms MR, Boulby PA, Thompson PJ, Duncan JS, et al . Preoperative fMRI predicts memory decline following anterior temporal lobe resection. J Neurol Neurosurg Psychiatry 2007 Sep 26 [Epub ahead of print] PMID: 17898035.  Back to cited text no. 33    
34.Krakow K, Woermann FG, Symms MR, Allen PJ, Lemieux L, ­Barker GJ, et al . EEG-triggered functional MRI of interctal epileptiform activity in patients with partial seizures. Brain 1999;122:1679-88.  Back to cited text no. 34    
35.Lemieux L, Saleek-Haddadi A, Josephs O, Allen P, Toms N, Scott C, et al . Event-related fMRI with simultaneous and continuous EEG: Description of the method and intital case report. Neuroimage 2001;14:780-7.  Back to cited text no. 35    
36.Krakow K, Allen PJ, Symms MR, Lemieux L, Josephs O, Fish DR. EEG recording during fMRI experiments: Image quality. Hum Brain Mapp 2000;10:10-5.  Back to cited text no. 36  [PUBMED]  [FULLTEXT]
37.Aghakhani Y, Bagshaw AP, Benar CG, Hawco C, Andermann F, Dubeau F, et al . fMRI activation during spike and wave discharges in idiopathic generalized epilepsy. Brain 2004;127:1127-44.  Back to cited text no. 37    
38.Gotman J, Grova C, Bagshaw A, Kobayashi E, Aghakhani Y, Dubeau F. Generalized epileptic discharges show thalamocortical activation and suspension of the default state of the brain. Proc Natl Acad Sci USA 2005;102:15236-40.  Back to cited text no. 38  [PUBMED]  [FULLTEXT]
39.Zijlmans M, Huiskamp G, Hersevoort M, Seppenwoolde JH, van Huffelen AC, Leijten FS. EEG-fMRI in the preoperative work-up for epilepsy surgery. Brain 2007;130:2343-53.  Back to cited text no. 39  [PUBMED]  [FULLTEXT]
40.Jokeit H, Okujava M, Woermann FG. Carbamazepine reduces memory induced activation of mesial temporal lobe structures: A pharmacological fMRI-study. BMC Neurol 2001;1:6.  Back to cited text no. 40  [PUBMED]  [FULLTEXT]
41.Janszky J, Ollech I, Jokeit H, Kontopoulou K, Mertens M, Pohlmann-Eden B, et al . Epileptic activity influences the lateralization of mesiotemporal fMRI activity. Neurology 2004;63:1813-7.  Back to cited text no. 41  [PUBMED]  [FULLTEXT]
42.Jayakar P, Bernal B, Santiago Medina L, Altman N. False lateralization of language cortex on functional MRI after a cluster of focal seizures. Neurology 2002;58:490-2.  Back to cited text no. 42  [PUBMED]  [FULLTEXT]
43.Sunaert S, Yousry TA. Clinical applications of functional magnetic resonance imaging. Neuroimaging Clin N Am 2001;11:221-36.  Back to cited text no. 43  [PUBMED]  
44.Gao JH, Milller I, Lai S, Xiong J, Fox PT. Quantitative assessment of blood inflow effects in functional MRI signals. Magn Reson Med 1996;36:314-9.  Back to cited text no. 44    
45.Le Rumeur E, Allard M, Poiseau E, Jannin P. Role of the mode of sensory stimulation in presurgical brain mapping in which functional magnetic resonance imaging is used. J Neurosurg 2000;93:427-31.  Back to cited text no. 45  [PUBMED]  

Correspondence Address:
Chandrasekharan Kesavadas
Department of Imaging Sciences and Interventional Radiology, Sree Chitra Tirunal Institute for Medical Sciences and Technology, Trivandrum - 695 011
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-3026.41829

Rights and Permissions


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]

This article has been cited by
1 Can fMRI safely replace the Wada test for preoperative assessment of language lateralisation? A meta-analysis and systematic review
P. R. Bauer,J. B. Reitsma,B. M. Houweling,C. H. Ferrier,N. F. Ramsey
Journal of Neurology, Neurosurgery & Psychiatry. 2014; 85(5): 581
[Pubmed] | [DOI]
2 Clinical Applications of Functional MR Imaging
Artem S. Belyaev,Kyung K. Peck,Nicole M. Petrovich Brennan,Andrei I. Holodny
Magnetic Resonance Imaging Clinics of North America. 2013; 21(2): 269
[Pubmed] | [DOI]
3 Clinical Applications of Functional MR Imaging
Belyaev, A.S. and Peck, K.K. and Petrovich Brennan, N.M. and Holodny, A.I.
Magnetic Resonance Imaging Clinics of North America. 2013; 21(2): 269-278
4 Resting state functional magnetic resonance imaging: An emerging clinical tool
Kesavadas, C.
Neurology India. 2013; 61(2): 103-104
5 Preoperative functional MRI of motor and sensory cortices: how imaging can save vital functions
Christina Stathopoulos, Nicole Brennan, Kyung K Peck, Andrei I Holodny
Imaging in Medicine. 2012; 4(1): 77
[VIEW] | [DOI]
6 Motor and sensory mapping
Holodny, A.I., Shevzov-Zebrun, N., Brennan, N., Peck, K.K.
Neurosurgery Clinics of North America. 2011; 22(2): 207-218
7 Motor and Sensory Mapping
Andrei I. Holodny,Nina Shevzov-Zebrun,Nicole Brennan,Kyung K. Peck
Neurosurgery Clinics of North America. 2011; 22(2): 207
[Pubmed] | [DOI]
8 Language and memory lateralization and localization using different fMRI paradigms in Arabic speaking patients: Initial experience
Hossam Moussa Sakr
The Egyptian Journal of Radiology and Nuclear Medicine. 2011;
[VIEW] | [DOI]
9 Structural and functional neuroimaging in intractable epilepsy
Chinchure, S., Kesavadas, C., Thomas, B.
Neurology India. 2010; 58(3): 361-370
10 Neuroimaging techniques in epilepsy
Lai, V. and Mak, H.K.F. and Yung, A.W.Y. and Ho, W.Y. and Hung, K.N.
Hong Kong Medical Journal. 2010; 16(4): 292-298


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Email Alert *
    Add to My List *
* Registration required (free)  

    Biophysical Basi...
    Design of fMRI E...
    fMRI Setup
    fMRI Paradigms
    Data Analysis
    Clinical Applica...
    Mapping the Eloq...
    Lateralization o...
    Localizing Spont...
    Challenges for P...
    Article Figures

 Article Access Statistics
    PDF Downloaded1303    
    Comments [Add]    
    Cited by others 10    

Recommend this journal