Biomedical subjects

Tomás Ortiz

Publications and source records attributed to Tomás Ortiz.

At least 19 recordsLinked to original sources

PubMed2006

MEG spectral profile in Alzheimer's disease and mild cognitive impairment.

OBJECTIVE: In this study, we applied a novel procedure to calculate the mean frequency from the Magnetoencephalography (MEG) signals of 22 patients with Alzheimer's Disease (AD), 22 patients with mild cognitive impairment (MCI), and 21 healthy controls. A significant mean frequency decrease was expected in pathological groups. MCI subjects are expected to show intermediate mean frequency values between AD patients and controls. METHODS: MEG signal was obtained from a whole-head 148 channels magnetometer in a resting condition. We estimated the power spectral density from the MEG signal by means of the Fourier transform of the autocorrelation function. Then, we computed the mean frequency for each subject. RESULTS: Mean frequency was higher in controls (12.46 +/- 2.00 Hz, mean +/- SD) than in MCI subjects (10.82 +/- 2.21 Hz) with significant differences (P < 0.05). Moreover, mean frequency values in MCI subjects were higher than in AD patients (9.06 +/- 2.48 Hz, P < 0.05). We also detected a decrease of 0.17 Hz per year in mean frequency from normal subjects' MEG (P < 0.05) CONCLUSIONS: Results demonstrated that the approach adopted for the calculation of a mean frequency score seems to be adequate and sensitive to detect differences between normal aging, cognitive deterioration and AD. In addition, data may contribute to the theoretical discussion on the nature of mild cognitive impairment and its similitudes with Alzheimer's disease. SIGNIFICANCE: This paper may be considered a first step to obtain a reliable measure which summarizes spectral information, and might be of a potential clinical interest.

Age Factors↗

PubMed2006

Magnetoencephalographic parietal delta dipole density in mild cognitive impairment: preliminary results of a method to estimate the risk of developing Alzheimer disease.

BACKGROUND: Subjects with mild cognitive impairment (MCI) are at a higher risk of experiencing Alzheimer disease (AD). Magnetoencephalographic temporoparietal dipole densities of low-frequency activity are good predictors of individuals' cognitive status, and might be a useful tool to investigate the conversion from MCI to AD. OBJECTIVE: To investigate the role of low-frequency dipole densities as predictors of the risk of developing AD. DESIGN: Whole-head magnetoencephalographic recordings were obtained from 19 probable AD patients, 17 MCI patients, and 17 healthy control subjects. The generators of focal magnetic slow waves were located using a single moving dipole model. RESULTS: Left parietal delta dipole density permitted a reliable classification of AD and MCI patients. The MCI patients were divided into 2 groups based on the median left parietal delta dipole density, and were followed up for 2 years. The estimated relative risk of conversion to AD was increased by 350% in those MCI patients with high left parietal delta dipole density scores. CONCLUSIONS: Results confirmed the important role of parietal delta dipole density in the evaluation of AD and MCI. A magnetoencephalographic-based assessment of AD and MCI patients might be considered a useful clinical test in the near future.

Aged↗

PubMed2005

Brain dynamics of Arabic reading: a magnetoencephalographic study.

Arabic writing differs greatly from western scripts. To evaluate the influence of written Arabic on the pattern of language-related brain activation, a group of native Arab speakers and a control group of native Spanish speakers were scanned with magnetoencephalography during a reading task. In both groups, brain activity was strongly left lateralized during the time window between 200 and 500 ms after stimulus onset. During late latencies (beyond 500 ms), however, the right and the left hemispheres reached a similar activation level in the Arabic but not in the Spanish group. This suggests a time-dependent role of both hemispheres during Arabic language reading.

Adult↗

PubMed2005

Shifting-related brain magnetic activity in attention-deficit/hyperactivity disorder.

BACKGROUND: Current theories suggest a role for frontal-striatal circuits in the pathogenesis of attention-deficit/hyperactivity disorder (ADHD). METHODS: We used magnetoencephalography (MEG) to measure event-related brain activity during a simplified version of the Wisconsin Card Sorting Test in children with DSM-IV combined type ADHD (ADHD-C) or predominantly inattentive type ADHD (ADHD-PI) and in age- and intelligence-matched control children. RESULTS: In control children, set-shifting cues evoked a higher degree of activation in the medial temporal lobe (MTL) between 200 and 300 msec than non-shifting cues, with MTL activation predicting later activity in left anterior cingulate cortex (ACC) (at 400-500 msec). This MTL-ACC response pattern was diminished in children with ADHD. By contrast, children with ADHD showed early activity in regions barely activated in control children, such as left inferior parietal lobe and posterior superior temporal gyrus. CONCLUSIONS: These preliminary data support theories of frontal dysfunction in ADHD but also suggest that deficits in higher-level functions might be secondary to disruptions in earlier limbic processes.

Adolescent↗

PubMed2005

Proton magnetic resonance spectroscopy and magnetoencephalographic estimation of delta dipole density: a combination of techniques that may contribute to the diagnosis of Alzheimer's disease.

Whole-head magnetoencephalographic recordings were obtained from 10 patients with Alzheimer's disease (AD) and 10 healthy controls in a resting position. Spectroscopic examinations were performed by means of a 1.5-tesla whole-body scanner in the temporoparietal regions of both hemispheres. The relationship between (1)H-MRS-based and magnetoencephalography (MEG)-based measures and their conjoined capability to improve the diagnosis of AD were investigated in this study. Logistic regression analyses were performed. Three separated logistic models were calculated for (1)H-MRS-based metabolites, low-frequency magnetic activity, and the combination of both measures. A combined myoinositol/N-acetyl aspartate (mI/NAA)-delta dipole density (DD) model predicted the diagnosis with 90% sensitivity and 100% specificity. Additionally, the combination of temporoparietal mI/NAA and delta DD values explained the variability of individuals' cognitive status. The results support the notion that a multidisciplinary approach may improve the understanding and diagnosis of AD.

Acetylglucosamine↗

PubMed2005

Is medial temporal lobe activation specific for encoding long-term memories?

Several neuroimaging studies have consistently demonstrated the critical involvement of prefrontal cortices and medial temporal lobes during long-term encoding. While the contribution of prefrontal lobes to working memory is well established, the role of the MTL structures remains controversial. To address this issue, we registered the neuromagnetic brain patterns of eight adult volunteers while they performed two working memory tasks (verbal and spatial) using magnetoencephalography (MEG). MEG recordings can provide real-time measures of brain activity, thus allowing detailed tracking of the time-course of brain activation during the encoding phase. We detected sustained and material-specific activity on the MTLs during the encoding phase of a working memory task, based on verbal and spatial information. Two peaks of activation were noted in the left MTL during word encoding in two non-consecutive time periods (500-600 ms and 700-800 ms after stimulus onset). Right MTL laterality was found for encoding locations when we collapsed activity sources in a wider time period (400-800 ms). In addition, we provided the spatiotemporal profiles of what seems to be two different brain circuits specific for each type of material. Finally, following an emerging conceptualization of working memory, we hypothesized that encoding processes mediated by the MTL to long-term memory would also apply to working memory.

Adult↗

PubMed2005

Prefrontal brain magnetic activity: effects of memory task demands.

Changes in spatiotemporal profiles of brain magnetic activity were investigated in healthy volunteers as a function of varying demands for phonological storage of spoken pseudowords. Greater activity for the phonological memory task was restricted to the dorsolateral prefrontal cortex (DLPFC) in the left hemisphere. During performance of the memory task, activity was initially found in the left superior temporal gyrus (between 100 and 200 ms), followed by activity in the ventrolateral prefrontal, motor, and premotor cortices (between 200 and 300 ms). Activity in DLPFCs was first observed consistently across participants later, between 300 and 400 ms. The data are consistent with the purported role of posterior temporal cortices in phonological analysis and in the online storage of phonological information, the contribution of ventrolateral and motor processing areas in establishment and short-term maintenance of articulatory representations through rehearsal, and the role of DLPFCs in the executive control of the maintenance operation.

Acoustic Stimulation↗

PubMed2005

Activity in human medial temporal lobe associated with encoding process in spatial working memory revealed by magnetoencephalography.

Animal studies have suggested that working memory may be affected after lesions in the medial temporal lobe, although this assumption has not been corroborated by neuropsychological studies in humans. However, very recently, several functional neuroimaging studies in humans have successfully observed activation of the medial temporal lobe during working memory tasks. The main aim of this study was to investigate the contribution of the medial temporal lobe to the encoding process in spatial working memory. To address this issue we registered the neuromagnetic brain patterns of eight adult volunteers while they performed a spatial working memory task and more perceptual task using identical stimuli. After a initial phase (between 200 and 400 ms) without differences in activation, the medial temporal lobe showed a sustained activity, more evident in the right hemisphere, lasting up to 800 ms during the encoding stage of the spatial working memory task, while the activation in the perceptual task terminated earlier (approximately 400 ms after stimulus onset). The finding of a continued activation of the medial temporal lobe strongly suggests the contribution of this brain region to encoding operations in working memory.

Adult↗

PubMed2005

Increased occipital delta dipole density in major depressive disorder determined by magnetoencephalography.

OBJECTIVE: To test the hypothesis that there is increased low-frequency activity located predominantly in the frontal lobe in patients with major depressive disorder using magnetoencephalography. METHODS: We carried out an unmatched or separate sampling case-control study of 31 medication-free patients who met the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), criteria for major depressive disorder and were outpatients of the Hospital Central de la Defensa, Madrid, and 22 healthy control subjects with no history of mental illness. A logistic regression analysis was employed to examine the predictive value of magnetoencephalography dipole density scores in the diagnosis of depression. We attempted to locate generators of focal magnetic slow waves by employing a single moving dipole model and by calculating dipole densities in prefrontal, frontal, parietal, temporal and occipital areas. The study lasted from February 2001 to January 2003. RESULTS: Only 2 dipole density scores, right occipital delta and left temporal delta, were significantly related to depression. According to the comparison of univariate and multivariate models and odds ratios, the right occipital delta dipole density is the factor with the greatest predictive power for depression, and the only one to show a significant correlation with severity of depression. CONCLUSIONS: We did not find any frontal lobe functional alteration. Our study provides, to the best of our knowledge, the first evidence of abnormal focal magnetic low-frequency activity in the occipital lobe of untreated patients with depression. Increased occipital lobe delta dipole density seems to be a reliable risk factor for depression, which correlates with disease severity according to the Hamilton Rating Scale for Depression.

Adult↗

PubMed2004

[Temporal lobe seizure recorded by magnetoencephalography: case report].

Ictal onset localization is a important factor in presurgical evaluation of epilepsy. This paper describes the localization of a seizure onset recorded by magnetoencephalography (MEG) from a 12-year-old male patient who suffered from complex partial drug-resistant seizures. MRI revealed a 20mm diameter lesion located in left hippocampus. Scalp EEG showed left temporal theta waves. Interictal MEG registrations detected isolated spike-wave activity posterior and inferior to the MRI lesion. Ictal MEG showed continuous spike-wave activity (2 Hz). Dipole localization sited seizure onset in the inferior left temporal gyrus, the same localization of the interictal MEG activity. This ictal activity spreads bilaterally to frontal areas. Intrasurgical electrocorticography recording confirmed interictal MEG results.

Child↗

PubMed2004

Time modulated prefrontal and parietal activity during the maintenance of integrated information as revealed by magnetoencephalography.

Using magnetoencephalography, we investigated the spatiotemporal patterns of brain magnetic activity responsible for maintaining verbal and spatial information in either an integrated or an unintegrated fashion. Considering time dimension, we noted a greater activation of a fronto-parietal network in early latencies during the maintenance of integrated information, and a different pattern during the maintenance of unintegrated material, showing a greater activation in a fronto-posterior network in late latencies. The greater activation found in certain areas which are traditionally reported as being engaged in spatial working memory (i.e. superior frontal gyri, dorsolateral prefrontal cortex, superior and inferior parietal lobes) when subjects maintained integrated information could be explained by a greater weight of the spatial dimension. It is as if words somehow acquired a spatial attribute, thus exerting a greater load in a neural network specialized in spatial working memory. Alternatively, and not mutually exclusive, we also propose that during the maintenance of integrated information the allocation of cognitive resources is less interfering than during the maintenance of unintegrated information, making it easier.

Adult↗

PubMed2004

Activation of the prefrontal cortex in the human visual aesthetic perception.

Visual aesthetic perception ("aesthetics") or the capacity to visually perceive a particular attribute added to other features of objects, such as form, color, and movement, was fixed during human evolutionary lineage as a trait not shared with any great ape. Although prefrontal brain expansion is mentioned as responsible for the appearance of such human trait, no current knowledge exists on the role of prefrontal areas in the aesthetic perception. The visual brain consists of "several parallel multistage processing systems, each specialized in a given task such as, color or motion" [Bartels, A. & Zeki, S. (1999) Proc. R. Soc. London Ser. B 265, 2327-2332]. Here we report the results of an experiment carried out with magnetoencephalography which shows that the prefrontal area is selectively activated in humans during the perception of objects qualified as "beautiful" by the participants. Therefore, aesthetics can be hypothetically considered as an attribute perceived by means of a particular brain processing system, in which the prefrontal cortex seems to play a key role.

Adult↗

PubMed2004

Task-specific sensory and motor preparatory activation revealed by contingent magnetic variation.

The present report studied the magnetic counterpart (CMV) of the auditory contingent negative variation (CNV). The ear where the target auditory stimulus would be presented was cued with a visual central arrow at a validity of 84%. The subject's behavioral response and the magnetoencephalographic (MEG) and electroencephalographic (EEG) signals were recorded. The central cue diminished reaction times (RTs) to the auditory target in the valid conditions with respect to the invalid conditions, indicating that the attentional manipulation was effective. The averaged magnetic field power during the preparatory period was significantly higher than baseline, suggesting the simultaneous presence of a magnetic counterpart of the electric CNV--the CMV. The field maps of the CMV grand averages showed two different and well-established periods: an early one with a magnetic field distribution that suggests a central source, and a late one with a field topography comparable to a low-intensity auditory-evoked field (M1). Single-dipole analysis of the preparatory phase in the subject's magnetic resonance images (MRI) demonstrated the presence of dipolar activity in the posterior cingulate (PCC) and posterior parietal cortices (PPC), superior temporal gyrus (STG) and motor cortices (MC). The lateralization of this activity depended on the orientation of the central cue. These results suggest that the action and perceptual-related areas needed to process the expected subsequent imperative task are recruited during the preparatory periods, influencing the behavioral RTs.

Acoustic Stimulation↗

PubMed2004

Time-modulated enhancing of the fronto-parietal circuits in the very-old elders.

Several studies have shown that memory circuits can be reorganised as a function of age. Brain magnetic activity evoked by a memory task was recorded in 19 healthy elderly subjects divided into two groups, a young-elder group (mean age of 62) and senior-elder group (mean age of 76). The young-elder group showed greater activity over the left medial temporal lobe in the late latency windows (between 400 and 800 ms) than the senior-elder group. The senior-elder group showed an initial increased activity (between 150 and 400 ms) over the complex of motor areas, followed by an increased activity in the left temporo-parietal cortex at the late latency window. These results revealed a reorganization of brain networks supporting memory in the eldest subjects. Furthermore, these circuits are reorganised in a time-dependent manner, meaning the rehearsal articulatory process active in the early time window followed by a phonological storage and recognition process in the late latency window.

Aged↗

PubMed2004

Limbic paroxysmal magnetoencephalographic activity in 12 obsessive-compulsive disorder patients: a new diagnostic finding.

BACKGROUND: We describe frontotemporal paroxysmal rhythmic activity recorded by magnetoencephalography (MEG) in patients with obsessive-compulsive disorder (OCD). METHOD: Twelve patients with OCD (per ICD-10 and DSM-IV criteria), aged 18 to 65 years, were assessed using MEG. Patients' classification according to the Yale Brown OCD Scale was as follows: severe = 8, moderate = 3, and mild = 1. MEG findings were compared with those of 12 age- and sex-matched healthy subjects (control group) with no previous history of psychiatric or neurologic disorders. All study participants underwent neurologic and basic medical examinations, including magnetic resonance imaging, electrocardiograms (EEGs), and electrooculograms. The study was conducted between January 2001 and January 2002. RESULTS: Two types of MEG activity were observed in patients with OCD: (1) frontotemporal paroxysmal rhythmic activity with low-amplitude spikes (< 1 picoTesla) in 92% (11/12) of patients and (2) intermittent isolated spikes and sharp waves in all patients (12/12). The OCD group had paroxysmal rhythmic MEG activity in the cingulate cortex (12/12), insula (10/12), hippocampus (9/12), temporal superior gyrus and angular and supramarginal gyri (9/12), precentral and post-central gyri (8/12), orbitofrontal cortex (5/12), and parietal lobes (5/12). MEG recordings were normal in the control group, and EEG findings were normal in both the OCD and control groups. CONCLUSIONS: Frontotemporal paroxysmal rhythmic activity with a preferential limbic distribution is a sensitive MEG finding in patients with OCD. Although the pathophysiology of this abnormality remains unknown, a corticostriatal network dysfunction was hypothesized.

Adult↗

PubMed2003

Modulation of brain magnetic activity by different verbal learning strategies.

In this study we examined spatiotemporal profiles of brain activity in the context of tasks designed to engage different verbal learning strategies (serial order, phonological, and semantic). The profile of activation associated with the serial-order strategy, which resulted in poor recall performance, featured early activation of the inferior frontal, sensorimotor, and insular region in the left hemisphere, between 200 and 400 ms after stimulus onset. Subsequently, activation was more prominent in dorsolateral prefrontal cortices bilaterally. In contrast, activation profiles associated with the phonological strategy featured predominantly activation of the superior temporal gyrus in the left hemisphere between 500 and 600 ms. Predominant activation of the left middle temporal gyrus, between 500 and 700 ms, was the key feature of the activation profile observed when the semantic elaboration strategy was utilized. These results suggest that different brain circuits are engaged to support learning of new verbal information as a function of the level and type of initial processing applied to the stimuli.

Adult↗

PubMed2003

Magnetoencephalographic localization of peritumoral temporal epileptic focus previous surgical resection.

UNLABELLED: Magnetoencephalography (MEG) is suggested as a localizing technique of epileptogenic areas in drug-resistant seizure patients due to intracraneal lesions. A male 42-year-old patient who begins at 26 with partial complex drug-resistant seizures is put forward. MRI shows a 9 mm diameter lesion located in left superior temporal gyrus which seems compatible with cavernoma. Both conventional and sleep deprivation EEGs have proved normal. Sleep EEG shows sharp waves in left temporal region. MEG helps to localize interictal spike and spike-wave activity, as well as wide slow wave (2-7 Hz) activity areas. Craniotomy under analgesia and aware sedation conditions is carried out. Intrasurgery cortical electric stimulation assisted by neuronavigator causes a limited partial complex seizure which the patient recognizes to be exactly like his. Thus, MEG localization of the epileptogenic area is confirmed. Surgical resection of both the lesion and the epileptogenic area is carried out. The patient remains free from seizures 9 months after surgery. A control MEG study reveals no epileptogenic nor slow wave activity. CONCLUSION: in this particular case, MEG has proven to be a useful presurgical evaluation technique to localize epileptogenic activity, validated by intrasurgical cortical stimulation.

Adult↗

PubMed2003

Correlations of hippocampal atrophy and focal low-frequency magnetic activity in Alzheimer disease: volumetric MR imaging-magnetoencephalographic study.

BACKGROUND AND PURPOSE: Patients with Alzheimer disease (AD) have more low-frequency activity on conventional EEG and increased focal magnetoencephalographic (MEG) dipole density (DD) in delta and theta bands. This activity concurs with atrophy and reduced metabolic and perfusion rates, particularly in temporoparietal structures. The relationship between functional and structural measures and their conjoined capability to improve the diagnosis of AD were assessed in this study. METHODS: Whole-head MEG recordings were obtained in 15 patients in whom the diagnosis of AD had been made and in 16 healthy control subjects during a resting condition. MR imaging volumetric data were also obtained; these included global cerebral, temporal lobe, and hippocampal volumes. RESULTS: DD in the delta and theta bands was enhanced in the AD group compared with the healthy control subjects. Slow-wave activity differed significantly between the groups in the temporoparietal regions of both hemispheres. Left hippocampal volume was correlated with left temporal and parietal delta DD and left temporal theta DD. A combination of left hippocampal volume and left temporal theta DD enabled correct classification in 87.1% of the patients with AD or control subjects. CONCLUSION: Results support the predominant role of temporoparietal hypofunction as defined by DD and hippocampal structural deficits shown on MR images in patients with AD. A multidisciplinary perspective of different techniques may improve our understanding of the disease and our diagnostic abilities.

Aged↗