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Eduardo M Castillo

Publications and source records attributed to Eduardo M Castillo.

At least 19 recordsLinked to original sources
PubMed2006

A comparison of functional MRI and magnetoencephalography for receptive language mapping.

We compared functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) for the mapping of receptive language function. Participants performed the same language task in the two different imaging environments. MEG activation profiles showed prominent bilateral activity in superior temporal gyrus and left-lateralized activity in middle temporal gyrus. fMRI activation profiles revealed bilateral activity in prefrontal, superior temporal, middle temporal, and visual areas. Laterality quotients derived from the two modalities showed poor agreement between the two methods for commonly active regions of interest. Locations of peak activity also varied considerably within participants between the two methods.

Adult↗
PubMed2006

Magnetoencephalographic studies of language reorganization after cerebral insult.

We review our experience with the application of magnetoencephalography (MEG) to the study of reorganization of the mechanisms supporting auditory language comprehension. In 3 studies, patient populations with cerebral insult of differing etiology, including epilepsy, surgical resection, and stroke, performed a running recognition task for spoken words while MEG data were collected using a whole-head magnetometer. Increased activation in the right hemisphere after left temporal lobectomy was associated with greater relative activation in that hemisphere preoperatively. Patients with chronic seizure disorder secondary to mesial temporal sclerosis exhibited a tendency toward an interhemispheric shift of language function, and those with epilepsy secondary to neoplasm showed a tendency toward an intrahemispheric shift. Patients with aphasia secondary to unilateral left-hemisphere stroke exhibited a more bilateral and diffuse overall profile of activation within the left hemisphere than control subjects of similar age. Taken together, results provide evidence that reorganization of cortex subserving auditory comprehension can occur well into the fifth and sixth decades and that the nature of the plastic response is dependent on variables such as premorbid language laterality, etiology, and, in specific groups, age at insult.

Brain Diseases↗
PubMed2006

Time-locked brain activity associated with emotion: a pilot MEG study.

OBJECTIVE: To examine the time course of brain activation in response to emotionally evocative pictures. METHODS AND PROCEDURES: Regions of the brain involved in the processing of affective stimuli in response to picture sets rated unpleasant, pleasant and affectively neutral, as well as the order of activation of each region, were investigated using magnetoencephalography in 10 normal adult volunteers. RESULTS: Spatiotemporal maps were found consisting of two basic components. The first involving activation in the occipital and basal aspects of the temporal cortex- lasted, on average, 270 ms post-stimulus. The second component involving activation in the mesial temporal lobes (MTL) extended from 270 to 850 ms post-stimulus. After (serial) activating the mesial temporal lobe structures or simultaneous (parallel) to it, activation is also observed in the frontal structures. CONCLUSIONS: The temporal organization in the brain of an emotional stimulus requires the serial and alternating engagement of frontal and posterior cortices. It is suggested that lesions to the brain may disrupt this temporal course, altering the emotional response commonly observed in patients with brain injury.

Adult↗
PubMed2005

Cortical representation of dermatomes: MEG-derived maps after tactile stimulation.

Mechanical stimulation of skin receptors is known to evoke cortical responses arising from the somatosensory cortex. Here we present a magnetoencephalographic (MEG) study where dermatomal somatosensory-evoked fields (DSSEFs) were recorded after mechanical stimulation of sacral (S1), lumbar (L3), thoracic (Th7), and cervical (C4) dermatomes in three healthy volunteers. All MEG measurements were repeated in order to test the replicability of the results. DSSEFs were successfully measured and modeled in all three participants. The topography and temporal dynamics of cortical responses derived after stimulation of each dermatome are described. We found that cortical-evoked responses can be reliably recorded using MEG after mechanical stimulation of dermatomes when a sufficiently large skin region within the dermatome is stimulated. Primary sensory cortex response (SI) to each of the four dermatomes was replicable and showed stability over time. The MEG-derived individual maps of activation confirm the somatotopic representation of dermatomes in primary sensory cortex and the utility of MEG recordings in disentangling the interactions between primary and secondary sensory cortex during somatic perception.

Adult↗
PubMed2005

Reproducibility of measures of neurophysiological activity in Wernicke's area: a magnetic source imaging study.

OBJECTIVE: The purpose of this study was to evaluate the reproducibility of estimates of neurophysiological activity obtained with Magnetic Source Imaging. METHODS: Split-half data sets were obtained from 14 healthy volunteers during performance of a continuous recognition task for spoken words. The concurrent validity of spatiotemporal activation maps obtained with this task has been previously verified through comparisons with the Wada test and electrocortical stimulation mapping. Consecutive late activity sources (> 200 ms after stimulus onset) were modeled independently as equivalent current dipoles (ECDs) and used to identify the location of language-specific cortex in the left hemisphere (Wernicke's area). RESULTS: Linear displacement of the geometric center of the cluster of ECDs in this region ranged between 2 and 8 mm across subjects. Intraparticipant variability (range) in the onset latency of activity was +/-50 ms, while the range of change in global field power for the entire set of ECDs in Wernicke's area was less than 17% in all cases. CONCLUSIONS: The results indicate that despite its many conceptual limitations the ECD model can provide reliable estimates of regional cortical activity associated with the engagement of linguistic processes. SIGNIFICANCE: The results highlight the need for reproducibility studies when research questions pose particular requirements for precision of estimates of regional neurophysiological activity.

Adult↗
PubMed2005

Early development of neurophysiological processes involved in normal reading and reading disability: a magnetic source imaging study.

This longitudinal study examined the development of the brain mechanism involved in phonological decoding in beginning readers using magnetic source imaging. Kindergarten students were assigned to 2 groups: those who showed mastery of skills that are important predictors of proficient reading (low-risk group) and those who initially did not show mastery but later benefited from systematic reading instruction and developed average-range reading skills at the end of Grade 1 (high-risk responders). Spatiotemporal profiles of brain activity were obtained during performance of letter-sound and pseudoword naming tasks before and after Grade 1 instruction. With few exceptions, low-risk children showed early development of brain activation profiles that are typical of older skilled readers. Provided that temporoparietal and visual association areas were recruited into the brain mechanism that supported reading, the majority of high-risk responder children benefited from systematic reading instruction and developed adequate reading abilities.

Analysis of Variance↗
PubMed2005

Toward the substitution of invasive electroencephalography in epilepsy surgery.

The authors compared the localization accuracy of interictal magnetoencephalography (MEG) with ictal and interictal invasive video electroencephalography (VEEG) in identifying the epileptogenic zone in epilepsy surgery candidates. Forty-one patients, 29 with temporal lobe epilepsy (TLE) and 12 with extratemporal lobe epilepsy (ETLE), participated. Only patients with interictal changes during the MEG recordings were included. A comparison of the accuracy of invasive VEEG and MEG seizure zone identification was based on the degree of overlap between the location of the actual surgical resection and the zone identified by each method, and the success of surgery in reducing seizure activity. No statistical differences were observed between the accuracy of invasive VEEG and MEG in determining the location of the seizure zone across TLE and ETLE cases. Invasive VEEG and MEG localization judgments were correct in 54% and 56% of the cases, respectively. Separate group analyses suggested that MEG may be less beneficial relative to invasive VEEG in ETLE than TLE cases. MEG is of statistically equivalent accuracy to invasive VEEG, despite the fact that its use has not reached optimal conditions. The authors predict the replacement of the more invasive procedure with MEG in the near future for TLE cases, subsequent to the optimization of the conditions under which preoperative MEG is performed.

Adolescent↗
PubMed2004

Integrating sensory and motor mapping in a comprehensive MEG protocol: clinical validity and replicability.

Considerable evidence supports the idea of magnetoencephalography (MEG) being a valuable noninvasive tool for presurgical mapping of sensory and motor functions. In this study, we test the validity and replicability of a new experimental paradigm for simultaneous sensory and motor mapping using MEG recordings. This comprehensive sensorimotor protocol (CSSMP), where external mechanic stimulation serves as a cue for voluntary movements, allows the recording of sensory and motor cortical responses during a single activation task. The stability and replicability of MEG-derived recordings during this paradigm were tested in a group of eight neurologically normal volunteers and six patients with perirolandic lesions. We found that a common sensorimotor cortical network, engaging sensory (S1, S2) and motor (M1) areas, was reliably activated in all subjects and patients and that the results remained exceptionally stable over time. Additionally, the clinical validity of the MEG-derived maps of activation was tested through intraoperative electrocortical stimulation mapping in the group of patients. The MEG-derived anatomical maps for specific sensory (S1) and motor (M1) responses were verified, by direct cortical mapping, and confirmed with the patient's surgical outcome. The results of this validation study show that the so-called CSSMP is a reliable and reproducible method for assessing simultaneously sensory and motor areas. This method minimizes methodological problems and improves our knowledge of the spatiotemporal organization of the sensorimotor cortical network and helps to optimize the surgical management of patients with perirolandic lesions.

Adult↗
PubMed2004

Spatiotemporal patterns of language-specific brain activity in patients with chronic aphasia after stroke using magnetoencephalography.

Six participants with chronic aphasia secondary to first-ever ischemic stroke within the middle cerebral artery (MCA) distribution of the left hemisphere and six neurologically intact controls of similar age were given a running recognition memory task for words while the magnetic flux normal to the scalp surface was measured with a whole-head neuromagnetometer. This task had been previously shown to be valid for the localization and lateralization of brain activity specific to receptive language function. As expected, patients exhibited relatively decreased activation in areas known to be involved in receptive language function, including superior temporal gyrus (STG) in the left hemisphere, as well as increased activation of areas outside of the left STG that might potentially support language function. Decreased activation within left STG was associated with a reduction in receptive language in patients, as was increased activation outside of left STG. Results support hypotheses suggesting that peri-lesional areas outside premorbid language areas may assume receptive language function after aphasia secondary to stroke, but that better recovery occurs when putative premorbid language areas are able to normalize.

Aged↗
PubMed2004

Magnetocephalography: a noninvasive alternative to the Wada procedure.

OBJECT: In this study the authors evaluated the sensitivity and selectivity of a noninvasive language mapping procedure based on magnetoencephalography (MEG), for determining hemispheric dominance for language functions. METHODS: Magnetic activation profiles of the brain were obtained from 100 surgical candidates (age range 8-56 years) with medically intractable seizure disorder by using a whole-head MEG system within the context of a word recognition task. The degree of language-specific activity was indexed according to the number of consecutive sources (modeled as single, moving current dipoles) in perisylvian brain areas. Only activity sources that were observed with a high degree of spatial and temporal overlap in two split-half data sets were used to compute the MEG laterality index. Independently, all patients underwent Wada testing for the determination of hemispheric dominance for language. Independent clinical judgments based on MEG and Wada data showed a high degree of concordance (87%). Magnetoencephalography laterality judgments had an overall sensitivity of 98%, but a lower selectivity of 83%, which was due to the fact that MEG detected more activity in the nondominant hemisphere than was predicted based on the Wada test. A number of objective criteria were derived based on this large patient series to ensure data quality and bolster the clinical usefulness of MEG for language mapping. CONCLUSIONS: Although the availability of MEG is still limited across epilepsy surgery centers, this study method may be substituted for the Wada procedure in assessing hemispheric dominance for language in select cases.

Adolescent↗
PubMed2003

Abnormal activation of temporoparietal language areas during phonetic analysis in children with dyslexia.

Event-related magnetic fields were recorded using magnetoencephalography in children with (n=12) and without (n=11) dyslexia while they discriminated between pairs of syllables from a voice onset time series (/ga/-/ka/). Nonimpaired readers exhibited left-hemisphere predominance of activity after the resolution of the N1m, whereas children with dyslexia experienced a sharp peak of relative activation in right temporoparietal areas between 300 and 700 ms post-stimulus onset. Increased relative activation in right temporoparietal areas was correlated with reduced performance on phonological processing measures. Results are consistent with the notion that deficits in appreciating the sound structure of both written and spoken language are associated with abnormal neurophysiological activity in temporoparietal language areas in children with dyslexia.

Child↗
PubMed2003

Brain mechanisms for reading in children with and without dyslexia: a review of studies of normal development and plasticity.

In this article we review our experience with the application of magnetic source imaging (MSI), the newest of the functional imaging methods, to the study of brain mechanisms for reading among children who read normally and among those with dyslexia. After giving a general description of MSI, we present evidence for reliable and valid maps of the brain mechanism for aural language comprehension as well as for reading. Next, we present data from 39 normal readers, 40 children with dyslexia, and 30 younger children at risk for developing a reading disability. These data show different brain activation maps for individual children with dyslexia and children at risk for dyslexia than for those of normal readers. Such differences most likely reflect aberrant brain organization underlying phonological decoding, rather than variables such as degree of effort. Finally, we present preliminary data demonstrating that the aberrant activation profiles of children with dyslexia may return to normative patterns as a result of a successful reading intervention that enables children to improve phonological decoding skills.

Adolescent↗
PubMed2003

Multimodality neuroimaging evaluation improves the detection of subtle cortical dysplasia in seizure patients.

The purpose of this study is to investigate if multimodality neuroimaging evaluation increases the detection of subtle focal cortical dysplasia as part of an epilepsy surgery evaluation. Three patients with normal magnetic resonance imaging and histopathological findings of focal cortical dysplasia were reviewed. Their magnetoencephalography recordings were performed on whole-head magnetoencephalography system. Magnetic resonance images were re-evaluated with special inspection in limited regions guided by magnetoencephalography spike localization. Two patients had ictal and interictal single photon emission computed tomography study after administration of Tc99m ECD. In two patients we found tiny focal abnormalities including slightly increased cortical thickness and blurred gray-white matter junction at the locations of interictal events after re-evaluation of the MR images indicating focal cortical dysplasia. The third patient showed focal atrophic change. All patients are seizure free after surgery. Both ictal and interictal single photon emission computed tomography showed hyperperfusion in the dysplastic cortex regions. Multimodality neuroimaging study can improve the detection of focal cortical dysplasia. Normal magnetic resonance images should be re-evaluated for subtle signs of focal cortical dysplasia especially when magnetoencephalography recording demonstrate focal epileptic discharges.

Adolescent↗
PubMed2003

Neuroimaging features of epidermal nevus syndrome.

Epidermal nevus syndrome is a kind of neurocutaneous syndrome that is associated with epidermal nevus and a variety of congenital CNS disorders. Clinical presentations include seizures, paresis, mental retardation, and developmental delay. We report three cases with MR imaging and magnetoencephalography findings; one patient underwent ictal and interictal single photon emission CT. Both structural and functional imaging studies indicated that the frontal lobes had lesser involvement or were intact. One patient underwent hemispherectomy because of the medically intractable seizure. He remained seizure free with topiramate monotherapy.

Abnormalities, Multiple↗
PubMed2002

Contributions of magnetic source imaging to the understanding of dyslexia.

The problem in dyslexia is difficulty learning how the printed word maps onto spoken language. Magnetic Source Imaging protocols were used in three studies. The first study with dyslexic children showed greater activity in the right temporoparietal region. The second study showed the aberrant neural circuit was present in initial stages of reading acquisition. The third study demonstrated that the aberrant profile could be normalized following intensive instruction. These findings suggest that dyslexia represents a functional deficit in the neural circuit that mediates the conversion of print to sound, which is amenable to change given adequate instruction.

Adolescent↗
PubMed2002

Brain mechanisms for reading words and pseudowords: an integrated approach.

The present study tested two predictions of dual-process models of reading: (i) that the brain structures involved in sublexical phonological analysis and those involved in whole-word phonological access during reading are different; and (ii) that reading of meaningful items, by means of the addressed phonology process, is mediated by different brain structures than reading of meaningless letter strings. We obtained brain activation profiles using Magnetic Source Imaging and, in addition, pronunciation latencies during reading of: (i) exception words (primarily involving addressed phonology and having meaning), (ii) pseudohomophones (requiring assembled phonology and having meaning), and (iii) pseudowords (requiring assembled phonology but having no meaning). Reading of meaningful items entailed a high degree of activation of the left posterior middle temporal gyrus (MTGp) and mesial temporal lobe areas, whereas reading the meaningless pseudowords was associated with much reduced activation of these two regions. Reading of all three types of print resulted in activation of the posterior superior temporal gyrus (STGp), inferior parietal and basal temporal areas. In addition, pronunciation speed of exception words correlated significantly with the onset of activity in MTGp but not STGp, whereas the opposite was true for pseudohomophones and pseudowords. These findings are consistent with the existence of two different brain mechanisms that support phonological processing in word reading: one mechanism that subserves assembled phonology and depends on the posterior part of STGp, and a second mechanism that is responsible for pronouncing words with rare print-to-sound correspondences and does not necessarily involve this region but instead appears to depend on MTGp.

Adult↗