Cortical language localization in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients. 1989.

The localization of cortical sites essential for language was assessed by stimulation mapping in the left, dominant hemispheres of 117 patients. Sites were related to language when stimulation at a current below the threshold for afterdischarge evoked repeated statistically significant errors in object naming. The language center was highly localized in many patients to form several mosaics of 1 to 2 sq cm, usually one in the frontal and one or more in the temporoparietal lobe. The area of individual mosaics, and the total area related to language was usually much smaller than the traditional Broca-Wernicke areas. There was substantial individual variability in the exact location of language function, some of which correlated with the patient's sex and verbal intelligence. These features were present for patients as young as 4 years and as old as 80 years, and for those with lesions acquired in early life or adulthood. These findings indicate a need for revision of the classical model of language localization. The combination of discrete localization in individual patients but substantial individual variability between patients also has major clinical implications for cortical resections of the dominant hemisphere, for it means that language cannot be reliably localized on anatomic criteria alone. A maximal resection with minimal risk of postoperative aphasia requires individual localization of language with a technique like stimulation mapping.

Changes in power and coherence of brain activity in human sensorimotor cortex during performance of visuomotor tasks.

Electrocorticograms (ECoG) were recorded using subdural grid electrodes in forearm sensorimotor cortex of six human subjects. The subjects performed three visuomotor tasks, tracking a moving visual target with a joystick-controlled cursor; threading pieces of tubing; and pinching the fingers sequentially against the thumb. Control conditions were resting and active wrist extension. ECoGs were recorded at 14 sites in hand- and arm-sensorimotor area, functionally identified with electrical stimulation. For each behavior we computed spectral power of ECoG in each site and coherence in all pair-wise sites. In three out of six subjects, gamma-oscillations were observed when the subjects started the tasks. All subjects showed widespread power decrease in the range of 11-20 Hz and power increase in the 31-60 Hz ranges during performance of the visuomotor tasks. The changes in gamma-range power were more vigorous during the tracking and threading tasks compared with the wrist extension. Coherence analysis also showed similar task-related changes in coherence estimates. In contrast to the power changes, coherence estimates increased not only in gamma-range but also at lower frequencies during the manipulative visuomotor tasks. Paired sites with significant increases in coherence estimates were located within and between sensory and motor areas. These results support the hypothesis that coherent cortical activity may play a role in sensorimotor integration or attention.

Asymmetry of neuronal activity during extracellular microelectrode recording from left and right human temporal lobe neocortex during rhyming and line-matching.

Recordings of neuronal activity in humans have identified few correlates of the known hemispheric asymmetries of functional lateralization. Here, we examine single-unit activity recorded from both hemispheres during two delayed match-to-sample tasks that show strong hemispheric lateralization based on lesion effects; a line-matching (LM) task related to the right hemisphere, and a rhyming (RHY) task related to the left. Nineteen neuronal populations were recorded with extracellular microelectrodes from the left temporal neocortex of 11 awake patients, and 18 from the right in 9 patients during anterior temporal lobectomy for complex partial seizures under local anesthesia. All subjects were left hemisphere dominant for language. Twelve (32%) populations exhibited statistically significant changes in activity at p <.05. Although changes in firing frequency were recorded from both hemispheres during both tasks, the RHY task elicited changes in activity several hundred milliseconds earlier on the left side than on the right. The LM task, on the other hand, induced changes earlier on the right side than on the left. Both hemispheres contained units active during verbal responses regardless of which behavior elicited the response. Our results indicate that cerebral dominance is reflected in earlier neuronal activity in the anterior temporal lobe during tasks lateralized to that hemisphere.

Increased gamma-range activity in human sensorimotor cortex during performance of visuomotor tasks.

OBJECTIVE: We documented changes in spectral power of human electrocorticograms (ECoG) during performance of sensorimotor tasks. METHODS: In 6 human subjects, ECoGs were recorded simultaneously from 14 subdural cortical sites in forearm sensorimotor cortex. The subjects performed 3 visuomotor tasks: tracking a moving visual target with a joystick-controlled cursor, threading pieces of tubing, and pinching the fingers sequentially against the thumb. Control conditions consisted of passive resting and active extension of the wrist. For each site the spectral power of the ECoG during these behaviors was computed for 5 10 Hz ranges between 10 and 60 Hz. RESULTS: All subjects showed power decreases in the range of 11-20 Hz and power increases in the 31-60 Hz range during performance of the visuomotor tasks, at sites in forearm sensorimotor cortex and adjacent areas. Simple wrist movements often produced little change in power. Three subjects showed episodes of explicit gamma oscillations during the visuomotor tasks. Different sites showed increases in gamma-range power for different tasks, indicating that the spatial distribution of the gamma activity is specific to the tasks. Cross-spectra showed that gamma activity could become synchronized between separate sites during particular tasks. CONCLUSIONS: Synchronized gamma-range activity in human sensorimotor cortex increases with performance of manipulative visuomotor tasks, supporting the hypothesis that coherent gamma oscillations may play a role in sensorimotor integration or attention.

Cerebral lateralization of neuronal activity during naming, reading and line-matching.

Changes in human right or left temporal cortical neuronal activity during language and visuospatial tasks were investigated during craniotomy under local anesthesia for medically intractable epilepsy in patients known to be left dominant for language based on preoperative intracarotid amobarbital perfusion testing. Extracellular recordings were obtained from 57 neuronal populations (26 from the left hemisphere) in the superior and middle temporal gyri of 34 patients. Frequency of activity was compared during over and silent object naming, word reading and line-matching. Although all recordings were from the cortex not essential for language, statistically significant changes in activity during these tasks were identified in 49% of the populations. Most populations showed significant changes to only one of the tasks, indicating discrete neural networks for reading and naming. Nearby neuronal populations recorded by the same microelectrode usually had different behavioral correlates. There were no significant differences in the proportion of neurons changing activity with language or spatial measures between right (non-dominant) or left (dominant) temporal lobes. Left superior and middle temporal gyrus populations, however, demonstrated significant early reductions in activity during overt or silent naming, while right middle temporal gyrus recordings showed significant early increased activity only during overt naming. Although reading measures elicited more activity from the non-dominant temporal lobe, early reductions in activity were recorded exclusively from the dominant side. Visuospatial tasks evoked changes in neuronal frequency predominantly in the middle temporal gyrus, and during one of these tasks, significant later increases in activity were present bilaterally. Our results indicate that the functional lateralization of cognitive behaviors may depend less on the anatomic location of the associated neuronal activity than on the neurophysiologic characteristics of that activity.

Functional cortex and subcortical white matter located within gliomas.

Some neurosurgeons state that intra-axial tumors may be resected with a low risk of neurological deficit if the tumor removal stays within the confines of the grossly abnormal tissue. This is thought to be so even when the lesion is presumably located in a functional area, providing that the adjacent normal-appearing cortex and subcortical white matter are not disturbed. This retrospective analysis presents evidence that this view is not always correct, because functioning motor, sensory, or language tissue can be located within a grossly obvious tumor or the surrounding infiltrated brain. Intraoperative stimulation mapping techniques identified 28 patients, ranging in age between 22 and 73 years, who showed evidence of functional tissue within the boundaries of infiltrative gliomas, as identified by correlation with computed tomography and magnetic resonance imaging scans, intraoperative ultrasound, gross visualization, and histological confirmation. Direct stimulation mapping of cortical and subcortical portions of the tumor during resections identified motor, sensory, naming, reading, or speech arrest function. Nineteen patients had new or worsened neurological deficits immediately after the operation, but after 3 months, only 6 continued to show new deficits whereas 18 showed no deficits and 2 improved. These results demonstrate that regardless of the degree of tumor infiltration, swelling, apparent necrosis, and gross distortion by the mass, functional cortex and subcortical white matter may be located within the tumor or the adjacent infiltrated brain. Therefore, to safely maximize glioma resection in these functional areas, intraoperative stimulation mapping may be used to identify functional cortical or subcortical tissue within, as well as adjacent to, the tumor, thus avoiding permanent injury.

Neuronal activity in human right lateral temporal cortex related to visuospatial memory and perception.

Neuronal activity was recorded extracellularly from 22 neurons in the right lateral temporal cortex of 12 patients undergoing awake craniotomy for surgical treatment of epilepsy during tests of visuospatial function. These included: measures of short-term visuospatial memory; face, complex figure and line matching; labeling of facial emotional expressions; and a language task, object naming. Six neurons demonstrated significant changes during one or more of the three 1.3-s epochs following test presentation. All 6 of these neurons demonstrated inhibition during short-term visuospatial memory entry, or retrieval, or both. Four of the neurons also showed significant changes during one or more matching tasks; 8 of 10 of these changes were excitatory. One neuron also demonstrated excitation with labeling of facial emotional expression and another with naming. These data demonstrate in human right lateral temporal cortex a pattern of inhibition of neuronal activity during short-term visuospatial memory that contrasts with excitation during other functions, particularly figure matching.

Cortical localization of temporal lobe language sites in patients with gliomas.

In a series of 40 patients undergoing an awake craniotomy for the removal of a glioma of the dominant hemisphere temporal lobe, cortical stimulation mapping was used to localize essential language sites. These sites were localized to distinct temporal lobe sectors and compared with 83 patients without tumors who had undergone language mapping for the treatment of intractable epilepsy. In patients with and without temporal lobe gliomas, the superior temporal gyrus contained significantly more language sites than the middle temporal gyrus. Both patient populations also had language sites anterior to the central sulcus in the superior temporal gyrus (12-16%). The patients without tumors had significantly more language sites in the superior temporal gyrus, compared with the superior temporal gyrus of patients with temporal lobe tumors. Multiple variables were studied for their effect on preoperative and postoperative language deficits and included age, sex, number of language sites, histology, size of the tumor, and the distance of tumor resection margins from the nearest language site. The distance of the resection margin from the nearest language site was the most important variable in determining the improvement in preoperative language deficits, the duration of postoperative language deficits, and whether the postoperative language deficits were permanent. If the distance of the resection margin from the nearest language site was > 1 cm, significantly fewer permanent language deficits occurred. Cortical stimulation mapping for the identification of essential language sites in patients with gliomas of the dominant hemisphere temporal lobe will maximize the extent of tumor resection and minimize permanent language deficits.

Neuronal activity in human lateral temporal cortex during serial retrieval from short-term memory.

Neuronal activity was recorded extracellularly from 20 populations in the lateral cortex of the left anterior temporal lobe of 11 patients undergoing awake craniotomy for epilepsy, during an input-distraction-retrieval measure of recent verbal memory that also included two later successive retrievals of the same information after additional distracting tasks. Changes in activity were determined for each 1 sec epoch in three major comparisons: (1) the same visual cues used for naming an input to recent memory, naming without a memory component, and a spatial matching task; (2) memory input (MI), distraction (S), and initial cued retrieval (R1) from memory, where object naming was the input to memory and naming of other objects the distractors; (3) initial retrieval (R1) and the two subsequent serial retrievals of the same information (R2, R3). Control comparisons were also made with serial naming and viewing of blank slides, and repeated naming of the same objects. In comparison 1, 13 of the 20 populations showed consistently increased activity during memory input ("memory units"); two others showed changes during language measures. In comparison 2, a significant proportion of all 20 populations, and the 13 memory units considered alone showed increased activity in initial epochs of MI and R1, confirming earlier findings of increased lateral temporal neuronal activity at memory entry and initial retrieval. In comparison 3, a significant proportion of the memory units showed increased activity in early epochs of R1 and decreased activity in late epochs of R3. This decrease in populations with increased activity at R1 was also evident when R1 was compared to R2 or R2 to R3.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparing the extent of hippocampal removal to the outcome in terms of seizure control.

The relationship between the outcome of temporal lobectomy for epilepsy and the size of the hippocampectomy tailored to intraoperative electrocorticographic findings was evaluated in 52 patients, with at least 1 year of follow-up. In 22 patients, < 2.0 cm of hippocampus was removed. Postoperatively, 16 (72.7%) were class I (seizure-free), 3 (13.6%) were class II (rare seizures) and 3 (13.6%) were class IV (no worthwhile improvement). In 30 patients, > or = 2.0 cm of hippocampus was removed, and the results were as follows: 21 (70%) were class I, 4 (13.3%) were class II, 1 (3.3%) was class III (worthwhile improvement) and 4 (13.3%) were class IV. Statistically significant differences were not present.

Dissociation of cortical and single unit activity in spoken and signed languages.

Based on stroke and other lesion data, the cortical organization of sign language has been shown to be in the verbal language-dominant hemisphere. However, finer detail of the cortical organization of sign language is not readily available. Intraoperative cortical mapping of spoken and American Sign Language (ASL) was performed in a hearing patient proficient in ASL undergoing an awake operation for intractable epilepsy. We found the dissociation of essential cortical language sites for spoken and signed languages, the relationship of these sites to the interpretation of ASL, and the importance of the anterior temporal lobe in the language-dominant hemisphere for proper ASL handshapes. Single unit recordings in the anterior temporal lobe, at a site later identified to be important in handshape formation, showed sustained activity during naming with superimposed increases in activity during overt speech.

Use of propofol (Diprivan) for awake craniotomies: technical note.

We describe the use of propofol (Diprivan) to provide patient comfort during the initial stages of awake craniotomies.

Neuronal activity related to faces and matching in human right nondominant temporal cortex.

Neuronal activity was recorded from 13 sites in right nondominant superior and middle temporal gyrus during matching of faces (FM), matching of complex figures (CM), labelling of facial emotional expression (FE) and object naming (N) in 11 patients undergoing craniotomy under local anaesthesia. These extracellular recordings were divided into 21 neuronal populations of one to a few cells, using amplitude window discriminators. Sixty-two percent of those populations showed statistically significant changes in activity during FM; 52% during FE; 38% during N and 38% during CM. Fifty-one percent of changes were in the first 1.3 s of each task and 33% in the next 1.3 s, when overt speech responses to the tasks occurred. Significant changes lasting throughout the 4 s allotted to each task were not seen. Functional correlates of some populations were derived from patterns of changes during FM and other tasks: four populations were related to 'matching', in that significant changes occurred with FM and CM. One of these populations, and six other populations were related to face perception, with significant change with FM and FE, confirming the presence in man of neuronal activity related to faces, as previously described from primate cortex. Six populations increased activity with overt speech; four of these showed greater increases when overt speech was in response to a visuospatial task compared with the lexical task.

Postoperative deficits and functional recovery following removal of tumors involving the dominant hemisphere supplementary motor area.

The supplementary motor area (SMA) is a region located within each cerebral hemisphere at the posterior mesial border of the frontal lobe adjacent to the falx. The functional significance of this area has been somewhat unclear, and information regarding its influence on motor output has largely been based on evoked responses to direct stimulation in primates and humans. In this series of patients with primary and metastatic tumors involving the dominant hemisphere SMA, a distinct pattern of postoperative deficits and recovery has emerged which emphasizes the role of this critical area in the initiation of motor activity, including speech. Based upon this analysis, ablation of this region after first identifying the primary motor cortex may be accomplished without risk of permanent loss of motor activity or speech function, despite the initial severe deficits.

Seizures of fronto-orbital origin: a proven case.

Distinguishing characteristics of seizures of frontal origin have not been clearly delineated. We describe a case of seizures of proven fronto-orbital origin to provide further definition of characteristics of seizures arising in that lobe. A 36-year-old man had medically intractable seizures since age 8 years. Clinically the seizures were stereotyped, with cessation of activity followed by turning of head and body to the right and then by struggling, kicking, and vocalizations indicating fear. Total seizure duration was approximately 30 s, with an apparent abrupt return of consciousness. The interictal scalp EEGs were similar to those of primary generalized epilepsy, with bisynchronous though asymmetric epileptiform activity anteriorly. Ictal scalp recordings were not localizing. Recordings from bilateral frontal and temporal subdural electrodes showed an electrical focus in the right fronto-orbital region which was confirmed by electrocorticography (ECoG) at the time of craniotomy. The right fronto-orbital cortex was resected and on pathologic examination showed gliotic tissue and intracytoplasmic neuronal inclusions of periodic acid-Schiff (PAS)-positive granules consistent with lipofuscinosis. The patient has remained seizure-free for 6 years after operation.

Nitrous oxide: suppression of focal epileptiform activity during inhalation, and spreading of seizure activity following withdrawal.

Intraoperative brain surface electrocorticography (ECoG) is an integral part of the surgical excision of epileptogenic foci. If surgical excision is performed under general anesthesia, anesthetics should be selected that do not seriously interfere with the ECoG. We report a case where nitrous oxide appeared to suppress focal epileptiform activity at the time of intraoperative ECoG, and subsequent withdrawal of nitrous oxide produced generalized electrical seizure activity. We recommend that low concentrations of volatile anesthetics may be preferrable to nitrous oxide when ECoG is performed during epilepsy surgery in anesthetized patients.

Neurophysiological monitoring during astrocytoma surgery.

The technique of direct stimulation mapping of the cortex is used to identify regions of language representation in the dominant cerebral hemosphere and the Rolandic cortex in either hemisphere. The use of electrocorticography to remove epileptogenic zones in patients with difficult-to-control seizures is described. The article presents the authors' experience with brain mapping during glioma surgery to maximize the extent of tumor resection and minimize surgical morbidity.

Electrocorticographic (ECoG) correlates of language. I. Desynchronization in temporal language cortex during object naming.

The electrocorticogram (ECoG) was recorded during a language task, silent naming, from sites identified as essential for naming by electrical stimulation mapping and from surrounding cortex of left dominant temporal cortex at craniotomies under local anesthesia. The ECoG was analyzed quantitatively for a reduction in spectral density in 7-12 Hz frequencies indicating 'desynchronization.' These measurements were made on the averaged ECoG in 3 subjects and on individual ECoG segments in 4. Statistically significant increases in desynchronization were identified during silent naming at most sites essential for language, most often in the epoch from 700 to 1200 msec after presentation of the item to be named. During silent naming, there was a greater degree of desynchronization at those sites than in surrounding cortex. At several sites essential for language in several subjects, significantly less desynchronization was evident during a spatial task using physically identical stimuli. Thus, localized desynchronization in temporal cortex is an ECoG change with temporal, anatomic, and sometimes behavioral specificity to a language task. This finding provides insights into cortical physiologic mechanisms active during human language.

Brain mapping techniques to maximize resection, safety, and seizure control in children with brain tumors.

Intraoperative brain mapping techniques were used to localize language cortex, sensorimotor pathways, and seizure foci in children with supratentorial brain tumors. The methods of direct cortical and subcortical stimulation, in addition to electrocorticography, enabled us to maximize tumor resection, minimize morbidity, and eradicate epileptogenic zones which were always adjacent to, but not involving, the tumor nidus. Language localization was found to be quite variable in the children tested and anatomically unpredictable based on the preoperative neurological or radiological examination. Physiological mapping techniques, therefore, appear to be safe, reliable, and very useful for operations on tumors located within or adjacent to eloquent brain regions in the pediatric population.

Cortical language localization in left, dominant hemisphere. An electrical stimulation mapping investigation in 117 patients.

The localization of cortical sites essential for language was assessed by stimulation mapping in the left, dominant hemispheres of 117 patients. Sites were related to language when stimulation at a current below the threshold for afterdischarge evoked repeated statistically significant errors in object naming. The language center was highly localized in many patients to form several mosaics of 1 to 2 sq cm, usually one in the frontal and one or more in the temporoparietal lobe. The area of individual mosaics, and the total area related to language was usually much smaller than the traditional Broca-Wernicke areas. There was substantial individual variability in the exact location of language function, some of which correlated with the patient's sex and verbal intelligence. These features were present for patients as young as 4 years and as old as 80 years, and for those with lesions acquired in early life or adulthood. These findings indicate a need for revision of the classical model of language localization. The combination of discrete localization in individual patients but substantial individual variability between patients also has major clinical implications for cortical resections of the dominant hemisphere, for it means that language cannot be reliably localized on anatomic criteria alone. A maximal resection with minimal risk of postoperative aphasia requires individual localization of language with a technique like stimulation mapping.