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

Temporal determinants of language acquisition and bilingualism

Modern methods of investigation in conscious subjects have shown that in normal brain, language is catered for by several essential areas localised in the frontal and temperoparietal cortex and by widely dispersed neurones that serve subsidiary, specialised linguistic functions. These sensory specific, phonological, articulatory and semantic ‘modules’ are activated in parallel. A relatively limited amount of language heard during the sensitive period, when one or other cerebral hemisphere usually becomes dominant for language, is all that is required for any normal child to develop fluency. The specific details of the code, or ‘set’, developed are dependent on the language of the child's environment; they are culturally acquired, but the propensity for language is inborn. During this sensitive period, two languages may be as easily accommodated as one. In stark contrast to the acquisition of natural bilingualism, after about the age of 10 years, any new language is acquired with difficulty for it must be translated into the individual's established language or languages. If a nation is to become bilingual, full advantage of the evanescent sensitive period must be taken by regularly exposing the pre-school child, rather than the older child undergoing formal education, to two languages.

A quantitative dendritic analysis of Wernicke's area in humans. II. Gender, hemispheric, and environmental factors

This quantitative Golgi study extends our investigation of relationships between cortical dendrite systems in humans and higher cognitive functions. Here we examine the relationship between the basilar dendrites of supragranular pyramidal cells in Wernicke's area and selected intrinsic (i.e., gender and hemisphere) and extrinsic (i.e., education and personal history) variables. Tissue was obtained from 20 neurologically normal right-handers: 10 males (Mage = 52.2) and 10 females (Mage = 47.8). Several independent variables were investigated: GENDER (male, female), HEMISPHERE (left, right), and EDUCATION (less than high school, high school, and university). These were evaluated according to Total Dendritic Length, Mean Dendritic Length, and Dendritic Segment Count. A distinction was made between proximal (1st, 2nd, and 3rd order) and ontogenetically later developing distal (4th order and above) branches. There was significant interindividual variation in dendritic measurements, which roughly reflected individuals' personal backgrounds. Females exhibited slightly greater dendritic values and variability than males across the age range examined. On the whole, the left hemisphere maintained a slight advantage over the right hemisphere for all dendritic measures when all subjects were pooled, but these differences were not in a consistent direction across individuals. Education had a consistent and substantial effect such that dendritic measures increased as educational levels increased. Dendritic differences between independent variable levels were most clearly illustrated in the total dendritic length of 3rd and 4th order branches. Distal dendritic branches appeared to exhibit greater epigenetic flexibility than proximal dendrites. The present findings concur with environmental enrichment research results in animals and suggest that dendritic systems in humans function as a sensitive indicator of an individual's (a)vocational activities.

Cortical resections for intractable epilepsy of extratemporal origin: experience with seventeen cases over eleven years

Seventeen patients underwent surgery between 1981 and 1990 for intractable partial epilepsy arising outside the temporal lobe. Twelve had frontal seizure onset, two parietal, two occipital and one diffusely in the hemisphere. Localization was achieved using extraoperative electrocorticography (ECoG) in five cases and intraoperative ECoG was employed in 12. Fifteen patients underwent cortical resections, but two did not subsequently have a resection. Both of these had porencephalic cysts. Of the 15 who had resections six (40%) were seizure free after a mean of 7.3 years. One (7%) was almost seizure free, six (40%) had worthwhile improvement. Pathological examination revealed oligodendroglioma in three, recurrent meningioma in one, vascular malformations in two, glial hamartoma in one and gliosis in six. One case with gliosis initially was shown to have an underlying malignant astrocytoma 2 years later. All these patients had CT abnormalities prior to surgery. Two patients (13%) had no worthwhile improvement. Pathology in these two was ischaemic neurons and arachnoid thickening. Both had normal CT findings preoperatively. One patient had an increased hemiparesis postoperatively. There were three cases of postoperative infection. It is concluded that extratemporal resection can achieve good results for seizure control and intraoperative ECoG is an effective technique for localizing the epileptogenic area. The presence of a structural lesion carries a particularly favourable prognosis for seizure outcome and surgery should, therefore, be strongly considered in patients with intractable partial epilepsy who have evidence of underlying structural pathology.

The surgery for epilepsy with speech arrest

The problems confronting patients with epilepsy, their families, and the surgeons wishing to help such patients, are discussed. It is important for physicians in other specialties to realize that epilepsy surgery is not nowadays complex, difficult, painful or uncertain; furthermore such operations are based on finding and removing focal lesions rather than "epileptogenic cortex" and the result in terms of integration of the patient into society is much improved if such intervention is performed while the patient is young, with time to gain academic and social skills after the operation. The selection of patients suitable for operation is discussed as well as methods of determining which hemisphere is dominant for speech and whether or not the focal lesion involves language centres. The majority of patients with drug resistant epilepsy suitable for operation have abnormalities in one temporal lobe. The pathological lesion is described and the advantages and disadvantages of various operations for temporal lobe epilepsy discussed. Extra-temporal cortical resection in the dominant hemisphere is also considered, particularly with reference to the preservation of language function. It is important that neurosurgeons realise that MRI and CT scanning have transformed epilepsy surgery from being a rather nebulous, time consuming art, to being for the majority of patients, a clear cut, straight forward procedure firmly based on "Oslerian" pathological principles. Far too few patients are being offered an operation (which renders 60-70% seizure free); neurosurgeons should respond to this challenge.

The effects of electrostimulation and of resective and stereotactic surgery on language and speech

A fairly comprehensive survey is offered of the effects which cortical and sub-cortical electrical stimulation have on language and speech. A survey is also given of the verbal consequences of resections or coagulations which generally follow electrical stimulation.

Temporal lobectomy for intractable epilepsy: experience with 58 cases over 21 years

Sixty patients with intractable complex partial seizures underwent surgery between 1969 and 1990, and 58 of these underwent a temporal resection. Of 39 patients who had chronic subdural electrocorticography (ECoG) 37 subsequently underwent an anterior temporal lobectomy (ATL) and two had the electrodes removed without resection. Two patients had bilateral depth electrodes placed and then had an ATL. Fourteen patients with evidence of temporal structural lesions had temporal resections with intraoperative ECoG and five had resection without ECoG. Mean length of follow-up for all patients was 6 years. Fifty-five per cent of cases were seizure-free postoperatively, 7% almost seizure-free, 21% had worthwhile improvement and 17% no improvement. The outcome for patients with structural lesions was particularly good. Nine patients complained of mild memory impairment postoperatively and one had a severe amnestic problem. One patient with an unsuspected tumour developed a hemiparesis and dysphasia. One other patient had persistent dysphasia. No mortality was attributable to the surgery. It is concluded that ATL is an excellent operation for the treatment of intractable epilepsy arising from the temporal lobe and chronic subdural ECoG is a safe and reliable method for localizing the seizure origin.

A quantitative dendritic analysis of Wernicke's area in humans. I. Lifespan changes

Age-related increases and decreases have been described in cortical dendritic neuropil. Here, we examine age-related changes in the basilar dendrites of supragranular pyramidal cells in human superior temporal gyrus (i.e., Wernicke's area) of left and right hemispheres. Tissue was obtained from 20 neurologically normal right-handers from 18-79 years: 10 males (Mage = 52.2 years; SDage = 17.4) and 10 females (Mage = 47.8; SDage = 20.5). In tissue prepared by a modified rapid Golgi technique, ten pyramidal cells were sampled from each hemisphere and evaluated according to the following parameters: total dendritic length, mean dendritic length, and dendritic segment count. Despite considerable interindividual variation, the data exhibited significant dendritic degeneration with aging. There was an age-related decrease in total dendritic length (r[20] = -0.44; P < 0.05) and especially in mean dendritic length (r[20] = -0.69; P < 0.001) with increasing age. Age-mean dendritic length correlations were negative for all segment orders and revealed a progressive decrease in segment length in more distal branches. The number of dendritic segments remained relatively stable across the age span sampled. The data also indicated that interhemispheric dendritic asymmetries decreased with age. Individuals under 50 years of age had significantly greater total dendritic length values in the left hemisphere. Interhemispheric dendritic differences were not significant in individuals over 50.

Resection of dominant opercular gliosis in refractory partial epilepsy. Report of two cases

Frontal opercular gliosis in the dominant hemisphere caused medically refractory partial epilepsy in two patients. Both patients were aphasic during their seizures, but otherwise had normal speech. Magnetic resonance images showed well-demarcated lesions resembling tumors in each patient; on heavily T2-weighted images, the lesions were hyperintense compared with normal brain. Cortical mapping with subdural grids localized speech to the area of the lesions; therefore, the resections were performed under local anesthesia and speech was tested throughout the procedure. Postoperatively, both patients were seizure-free and had no new neurological deficits. Well-demarcated lesions, even in the dominant operculum, can be safely removed in patients with medically refractory partial epilepsy.

Topography of the uncinate fascicle and adjacent temporal fiber tracts

Neurosurgical procedures in the anterior temporal lobe are common, in which different postoperative neuropsychological deficits may occur. For the refinement of the surgical approach 10 human hemispheres were dissected using the method of dissection by Klinger, to gain more data about the fiber tracts in the anterior temporal lobe, respectively the temporal stem. The uncinate fascicle has a form like a curved dumb-bell with a thin (about 2 mm thick), fan-like arrangement of fibers in the frontal and temporal lobe. The solid portion runs in the extreme and external capsule through the limen insulae. The topography of adjacent important fiber tracts (inferior occipito-frontal fascicle, Meyer's loop, anterior commissure, inferior thalamic bundle) could be displayed. According to the results possible neuropsychological deficits and surgical considerations are discussed.

Safe surgery of lesions near the motor cortex using intra-operative mapping techniques: a report on 50 patients

In 50 patients lesions located in or adjacent to the motor strip were microsurgically removed with the help of intra-operative electrophysiological mapping of the sensorimotor cortex. Mapping consisted of cortical stimulation and/or recording of somatosensory evoked potentials. Depending on the patient's pre-operative neurological status, surprisingly good results could be achieved: The surgery resulted in increased permanent sensorimotor deficit in only 4% of cases and in improved neurological status in 30% of cases. It is concluded that surgical removal of centrally located lesions using a microsurgical technique and intra-operative mapping of the motor cortex is safe and permits extensive or radical resection of lesions, even those in the motor cortex itself.

Topographic mapping of somatosensory evoked potentials helps identify motor cortex more quickly in the operating room

Median nerve somatosensory evoked potentials were recorded from exposed cerebral cortex during craniotomies. This technique is valuable when knowledge of the motor cortex location can influence surgical decisions about resection limits or biopsy sites. Two different recording techniques were compared: strips of electrodes and arrays of electrodes. The arrays recorded electrical potentials suitable for topographic mapping. We found that motor cortex could be identified more quickly when using the topographic mapping of SEPs from arrays. We conclude that topographic mapping of SEP from sensorimotor regions during craniotomies works well in general and can be done more quickly than the traditional electrode strip technique.

Cortical mapping and local anaesthetic resection as an aid to surgery of low and intermediate grade gliomas

We report four cases of the use of peroperative cortical mapping during craniotomy under local anaesthesia to define the relationship between the glioma and speech and somatosensory cortex. This enabled a radical subtotal (two cases) or an apparent total (two cases) excision of the tumour close to the somatosensory and speech cortex with no permanent neurological deficit. Use of this technique allows radical excision of intrinsic low and intermediate grade gliomas that would otherwise be considered unexcisable and may lead to an improved survival.

Functional anatomy of language processing: neuroimaging and the problem of individual variability

This paper discusses the long-standing concepts of a participation of frontal opercular and inferior parietal cortex in high-order language processing with respect to contradictory inferences from recent positron emission tomographic (PET) activation studies (cf. Petersen et al. [49]). The main thrust of the present argument is that the technique of intersubject PET image averaging may be inappropriate due to intersubject variability. Evidence is presented which suggests that intersubject variability is at least two-fold: (i) Intraoperative stimulation has demonstrated diversity in location of language functions in the left frontal and temporoparietal association cortex; (ii) Morphometrical imaging studies have demonstrated diversity of brain shape and gyral pattern which is difficult to correct by anatomical standardization of individual brains. Both factors add noise in spatially standardized PET images and may render circumscribed high-order language foci undetectable. It is argued that PET studies of higher cognitive functions including language must focus on individual anatomo-functional organization using techniques such as intrasubject averaging.

Combined endovascular embolization and surgery in the management of cerebral arteriovenous malformations: experience with 101 cases

The authors describe their experience with 101 cerebral arteriovenous malformations (AVM's) treated by endovascular embolization followed by surgical removal. Fifty-three patients presented with intracranial hemorrhage and 35 had seizures. Based on the classification of Spetzler and Martin, two AVM's were Grade I, 13 were Grade II, 26 were Grade III, 43 were Grade IV, and 17 were Grade V. Fifty-six AVM's were in the right hemisphere, 28 were in the left hemisphere, 12 were in the corpus callosum, and five involved the cerebellum. In 50 cases, presurgical obliteration of 50% to 75% of the AVM nidus was achieved by embolization, and in 31 cases this percentage increased to between 75% and 90%. In 97 (96%) patients, complete surgical removal of the AVM was obtained. Morbidity resulting from preoperative endovascular embolization was classified as mild in 3.9% of the cases, moderate in 6.9%, and severe in 1.98%. The death rate related to embolization was 0.9%. The immediate postsurgical morbidity was classified as mild in 5.9% of the cases, moderate in 10.8%, and severe in 5.9%. The overall long-term morbidity was mild in 5.9% of the cases, moderate in 6.9%, and severe in 1.98%. Two patients (1.98%) died due to intractable intraoperative hemorrhage and two (1.98%) as a result of postsurgical pulmonary complications.

Resection of intrinsic tumors from nondominant face motor cortex using stimulation mapping: report of two cases

We report two right-handed patients who underwent resection of intrinsic glial tumors from the nondominant hemisphere, face motor cortex. Both patients underwent preoperative assessment with computed tomography and magnetic resonance imaging localizing the tumor in the inferior region of the Rolandic cortex. With the patients under general anesthesia and without muscular paralysis, the tumor volume was determined by intraoperative ultrasound and resective surgery accomplished with the aid of cortical and subcortical stimulation mapping techniques. Radical resection of the tumor from the face motor cortex was achieved in both patients. A transient contralateral facial weakness and apraxia were noted in each patient, and this resolved within 6 to 8 weeks following surgery. Removal of intrinsic tumors involving the nondominant face motor cortex may be safely achieved using brain mapping techniques to localize inferior Rolandic cortex and avoid resection of the hand motor cortex and descending subcortical motor pathways. Permanent disability will be prevented due to the bilateral representation of face motor function at the neocortical level. However, due to language localization in cortical zones contiguous with the dominant hemisphere, face motor cortex, we do not recommend resection of this region.

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.

Language function following anterior temporal lobectomy

The authors report the results of a prospective investigation that evaluated postoperative changes in language function after dominant (29 cases) or nondominant (35 cases) anterior temporal lobectomy for treatment of complex partial seizures. These patients received conservative resection of lateral temporal cortex but aggressive resection of medial temporal cortex. None of the patients underwent functional mapping of cortical language ability. All patients were assessed with a standardized aphasia battery (Multilingual Aphasia Examination) before and 6 months after surgery. Postoperatively, the dominant anterior temporal lobectomy group did not show any significant losses in language function compared to patients who underwent nondominant anterior temporal lobectomy. In addition, the dominant temporal lobectomy group showed significant postoperative improvement in complex receptive language comprehension compared to the nondominant group. These results suggest that patients with complex partial seizures of medial temporal lobe onset can undergo a conservative resection of lateral temporal cortex without language mapping. Such surgery carries little risk to language function and provides an excellent postoperative surgical outcome.

Material specific learning during electrical stimulation of the human hippocampus

Material specific learning was assessed during unilateral electrical stimulation of the hippocampus through intracerebrally implanted electrodes in 30 patients with unilateral temporal lobe epilepsy (TLE). Verbal learning significantly decreased in patients with right TLE after stimulation of the left, but not the right, hippocampus. No verbal learning impairment was observed in left TLE patients following stimulation of either hippocampus. Visuospatial memory performance significantly decreased following stimulation of the right hippocampus regardless of the side of seizure onset. Results suggest that the contralateral "nonepileptic" hippocampus does not assume the material specific mnestic functions of the dysfunctional hippocampus associated with longstanding epilepsy.

Correlation of motor cortex brain mapping data with magnetic resonance imaging

Brain maps derived intraoperatively from patients undergoing tumor resection were correlated retrospectively with magnetic resonance (MR) images with respect to the precise localization of the motor cortex in an attempt to identify useful preoperative MR imaging landmarks that correspond to functional brain regions. Superior axial T2-weighted MR images consistently localized the central sulcus, whereas parasagittal and farlateral sagittal images readily identified the rolandic (sensorimotor) cortex, as a functional unit, based on the cingulate-marginal sulcus and insula, respectively. It is therefore concluded that multiplanar MR images may serve as a useful preoperative planning aid prior to removing intrinsic brain tumors within or adjacent to the motor cortex.

Cortical mapping and resection under local anaesthetic as an aid to surgery of low and intermediate grade gliomas

We report four cases of the use of per-operative cortical mapping during craniotomy under local anaesthesia to define the relationship between the glioma and speech and somatosensory cortex. This enabled a radical subtotal (two cases) or an apparent total (two cases) excision of the tumour close to somatosensory and speech cortex with no permanent neurological deficit. Use of this technique allows radical excision of intrinsic low and intermediate grade gliomas that would otherwise be considered unexcisable and may lead to an improved survival.