Variability of intraoperative electrocortical stimulation mapping parameters across and within individuals.

OBJECT Electrocortical stimulation mapping is regarded as the gold standard of intraoperative mapping for predicting functional outcomes. Nevertheless, methodologies across institutions are inconsistent. Although many vary and maximize stimulation currents at each cortical site, some use a single current level to map the entire exposed cortex. The former comes at the cost of possibly inducing additional afterdischarge activity. The authors retrospectively reviewed their eperience with intraoperative electrocortical stimulation mapping to characterize variability of both mapping and afterdischarge thresholds. METHODS Seventeen patients satisfied the study inclusion criteria. Significant variability in mapping thresholds was identified within individuals and across the patient population. Moreover, a statistically significant difference in mapping thresholds was demonstrated between the frontal and parietal/temporal lobes (p = 0.007, one-way analysis of variance). The authors report a surprisingly high incidence of afterdischarge during mapping, wide variability in afterdischarge thresholds within individuals and across the study population, and mapping thresholds regularly exceeding afterdischarge thresholds in neighboring cortex. Differences in afterdischarge thresholds across lobes only approached significance (p = 0.086). CONCLUSIONS To maximize identification of eloquent cortices in some clinical situations, it may be advantageous to maximize currents at each cortical site regardless of adjacent afterdischarge threshold rather than to map the entire exposed cortex at a single current level. Moreover, the current findings highlight the need for electrocorticography during electrocortical stimulation mapping, both to identify when afterdischarges occur and to verify stimulation by recording stimu lation artifacts. The advantages and limitations of maximizing currents at each cortical site as well as mapping at a single current level are discussed.

[1]  Harry A. Whitaker,et al.  Language localization and variability , 1978, Brain and Language.

[2]  J. V. Van Buren,et al.  Mechanism and localization of speech in the parietotemporal cortex. , 1978, Neurosurgery.

[3]  G A Ojemann,et al.  Individual variability in cortical localization of language. , 1979, Journal of neurosurgery.

[4]  D. Le Bihan,et al.  Functional MRI during word generation, using conventional equipment , 1995, Neurology.

[5]  G. Ojemann.  Ojemann's data: Provocative but mysterious , 1983, Behavioral and Brain Sciences.

[6]  S. Bookheimer,et al.  Regional cerebral blood flow during object naming and word reading , 1995 .

[7]  Nader Pouratian,et al.  Spatial/temporal correlation of BOLD and optical intrinsic signals in humans , 2002, Magnetic resonance in medicine.

[8]  H. Lüders,et al.  Anatomic Distribution of Cortical Language Sites in the Basal Temporal Language Area in Patients with Left Temporal Lobe Epilepsy , 1994, Epilepsia.

[9]  W. Penfield,et al.  The Cerebral Cortex of Man: A Clinical Study of Localization of Function , 1968 .

[10]  I. Fried,et al.  The asleep-awake-asleep anesthetic technique for intraoperative language mapping. , 1998, Neurosurgery.

[11]  A W Toga,et al.  Optical imaging of bilingual cortical representations. Case report. , 2000, Journal of neurosurgery.

[12]  H. Jasper,et al.  Epilepsy and the functional anatomy of the human brain , 1985 .

[13]  Nader Pouratian,et al.  Category-specific naming deficit identified by intraoperative stimulation mapping and postoperative neuropsychological testing. Case report. , 2003, Journal of neurosurgery.

[14]  W PENFIELD,et al.  The supplementary motor area of the cerebral cortex; a clinical and experimental study. , 1951, A.M.A. archives of neurology and psychiatry.

[15]  H. Duffau,et al.  Intra-Operative Direct Electrical Stimulations of the Central Nervous System: The Salpêtrière Experience With 60 Patients , 1999, Acta Neurochirurgica.

[16]  R P Lesser,et al.  Cortical Afterdischarge and Functional Response Thresholds: Results of Extraoperative Testing , 1984, Epilepsia.

[17]  C. Woolsey,et al.  Localization in somatic sensory and motor areas of human cerebral cortex as determined by direct recording of evoked potentials and electrical stimulation. , 1979, Journal of neurosurgery.

[18]  G. Ojemann,et al.  Cortical language localization in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients. , 1989, Journal of neurosurgery.

[19]  R P Lesser,et al.  Electrical stimulation of Wernicke's area interferes with comprehension , 1986, Neurology.

[20]  S. Bookheimer,et al.  Form and Content Dissociating Syntax and Semantics in Sentence Comprehension , 1999, Neuron.

[21]  R P Lesser,et al.  Characterization of the basal temporal language area in patients with left temporal lobe epilepsy , 1990, Neurology.

[22]  W H Theodore,et al.  Regional cerebral blood flow during auditory responsive naming: evidence for cross‐modality neural activation , 1998, Neuroreport.

[23]  Nader Pouratian,et al.  Utility of preoperative functional magnetic resonance imaging for identifying language cortices in patients with vascular malformations. , 2002, Journal of neurosurgery.

[24]  G A Ojemann,et al.  Functional mapping of cortical language areas in adults. Intraoperative approaches. , 1993, Advances in neurology.

[25]  E. Kaplan,et al.  The Boston naming test , 2001 .

[26]  Mitchel S. Berger,et al.  Brain Mapping Techniques to Maximize Resection, Safety, and Seizure Control in Children with Brain Tumors , 1989 .

[27]  M M Haglund,et al.  Optical imaging of bipolar cortical stimulation. , 1993, Journal of neurosurgery.

[28]  R. Lesser,et al.  Electrical Stimulation and Language , 1994, Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society.