From State-to-Trait Meditation: Reconfiguration of Central Executive and Default Mode Networks.

While brain default mode network (DMN) activation in human subjects has been associated with mind wandering, meditation practice has been found to suppress it and to increase psychological well-being. In addition to DMN activity reduction, experienced meditators (EMs) during meditation practice show an increased connectivity between the DMN and the central executive network (CEN). However, the gradual change between DMN and CEN configuration from pre-meditation, during meditation, and post-meditation is unknown. Here, we investigated the change in DMN and CEN configuration by means of brain activity and functional connectivity (FC) analyses in EMs across three back-to-back functional magnetic resonance imaging (fMRI) scans: pre-meditation baseline (trait), meditation (state), and post-meditation (state-to-trait). Pre-meditation baseline group comparison was also performed between EMs and healthy controls (HCs). Meditation trait was characterized by a significant reduction in activity and FC within DMN and increased anticorrelations between DMN and CEN. Conversely, meditation state and meditation state-to-trait periods showed increased activity and FC within the DMN and between DMN and CEN. However, the latter anticorrelations were only present in EMs with limited practice. The interactions between networks during these states by means of positive diametric activity (PDA) of the fractional amplitude of low-frequency fluctuations (fALFFs) defined as [Formula: see text] revealed no trait differences but significant increases during meditation state that persisted in meditation state-to-trait. The gradual reconfiguration in DMN and CEN suggest a neural mechanism by which the CEN negatively regulates the DMN and is probably responsible for the long-term trait changes seen in meditators and reported psychological well-being.

Child overweight and obesity are associated with reduced executive cognitive performance and brain alterations: a magnetic resonance imaging study in Mexican children.

BACKGROUND: Overweight and obesity in childhood is associated with negative physical and psychological effects. It has been proposed that obesity increase the risk for developing cognitive deficits, dementia and Alzheimer's disease and that it may be associated with marked differences in specific brain structure volumes. OBJECTIVE: The purpose of this study was a neurobiopsychological approach to examine the association between overweight and obesity, brain structure and a paediatric neuropsychological assessment in Mexican children between 6 and 8 years of age. METHODS: We investigated the relation between the body mass index (BMI), brain volumetric segmentation of subcortical gray and white matter regions obtained with magnetic resonance imaging and the Neuropsychological Assessment of Children standardized for Latin America. Thirty-three healthy Mexican children between 6 and 8 years of age, divided into normal weight (18 children) and overweight/obese (15 children) groups. RESULTS: Overweight/obese children showed reduced executive cognitive performance on neuropsychological evaluations (i.e. verbal fluidity, P = 0.03) and presented differences in brain structures related to learning and memory (reduced left hippocampal volumes, P = 0.04) and executive functions (larger white matter volumes in the left cerebellum, P = 0.04 and mid-posterior corpus callosum, P = 0.03). Additionally, we found a positive correlation between BMI and left globulus pallidus (P = 0.012, ρ = 0.43) volume and a negative correlation between BMI and neuropsychological evaluation scores (P = 0.033, ρ = -0.37). CONCLUSIONS: The findings contribute to the idea that there is a relationship between BMI, executive cognitive performance and brain structure that may underlie the causal chain that leads to obesity in adulthood.

Maduración dentaria en jovenes venezolanos estimada mediante el método de demirjian y colaboradores / Dental maturation in venezuelan young estimated though demirjian et al method

El objetivo de este trabajo fue estudiar la maduración dentaria en jóvenes venezolanos estimada mediante el método de Demirjian y cols. Se analizaron 284 radiografías panorámicas de pacientes de ambos sexos con edades cronológicas entre 8- 20 años. Se estudio la maduración dentaria de los 7 dientes inferiores izquierdos de acuerdo a los estadios del método de Demirjian y cols. y se calculó la edad dentaria. Se obtuvieron la media y la desviación estándar de la edad cronológica (EC) y la ED, la media de la EC a la cual se observaron los diferentes estadios de maduración y diferencias de medias entre la EC y la ED calculada. Al comparar las medias de las edades cronológicas en las que se observaron los estadios de maduración dentaria, las hembras tuvieron un desarrollo más avanzado que los varones. Se evidencio que el 100% de madurez dentaria, comienza a alcanzase alrededor de lo 13-14 años en la muestra estudiada. Contrastando la media de la EC con la ED, pudo verificarse que en ambos sexos, existe una consistente subestimación de la edad a partir de los 16 años, por ello en una submuestra de los grupos 8-16 se obtuvieron las diferencias de media entre la EC y ED, y se encontró una sobrestimación de la edad, estadísticamente significativa (-0,66 ±1,14 varones; -0,40± 1,38 hembras). Los datos del presente trabajo podrían ser utilizados como referencia de la maduración dentaria de los individuos de la muestra...

The aim of the present investigation was to study the dentaria maturation of Venezuelan young estimated though Demirjian´s et al. method. Two hundred and eighty four dentaria panoramic radiographs from patients of both sexes, with chronological ages between 8-20 years, were analyzed. Dentaria maturation of the 7 left lower teeth was calculated, according to the stages proposed by Demirjian et al. and dentaria age was calculated (DA) following the method of the author. Mean values and standard deviation of the chronological age (CA) and DA, by age group, mean of the CA to which different stages of maturation were observed and mean differences between the CA and the DA, were calculated. When comparing the mean chronological ages witch the dentaria maturation stages were observed; females had more advanced development than males. It was noticed that 100% of dentaria maturity, was reached out around 13-14 years in the studied sample. Contrasting mean CA with DA, it could be confirmed that in both sexes, there is a consistent underestimation of age from 16 years, so in a subsample of 8-16 groups mean differences between the EC and ED were obtained, and found an statistically significant overestimation of age (males -0.66 ± 1.14, females -0.40 ± 1.38). The data presented here could be used as a reference for dentaria maturation of the individuals in the sample...

Event-Related Functional Magnetic Resonance Images during the Perception of Phantom Limb. A Brushing Task.

The phantom limb phenomenon has been used in amputee patients as a paradigm to study plasticity, mainly of the sensorimotor cortex. Nevertheless, most functional studies have been done in upper limb amputee patients using magnetoencephalography and functional magnetic resonance image imaging (fMRI). In addition, the actual experience of phantom limb sensation has not been widely used to study the neural mechanism of the human brain as a conscious knowledge of the phantom limb perception like the integration of the body image in amputee patients. fMRI studies of patients with lower limb amputation have recently been published, but none of these used an event-related design to try to observe only the stimulus application, correlating images with the subject's indication of phantom perception and discarding images with no phantom perception. In this work, we used the event-related fMRI design in two right-handed patients with identical right, transfemoral amputations, performing the same sensitive stimulation in a 3.0 T MR scanner. For comparison, we applied the same paradigm to six control subjects to compare the resulting functional maps. We found areas with statistical significance in the sensorimotor cortex contralateral to the site of stimulation, in the parietal lobe in Brodmann areas 3 in both cases (Patients and Control Subjects), but we also found activation in the Brodmann areas 6, 40, and 5 with stimulation of the stump. We observed a specific activation of the frontoparietal circuit during phantom limb perception in both amputee patients.

Abnormal functioning of the thalamocortical system underlies the conscious awareness of the phantom limb phenomenon.

Phantom limb (PL), a phenomenon experienced by most patients after amputation, has mostly served as a paradigm to study experiences that appear to be associated with neural plasticity within the CNS. However, the subjective nature of PL experiences has had no definitive means of reliable assessment other than using patients' direct reports, nor was there a way to study the neural mechanisms involved in the conscious awareness of this mental phenomenon. Here we obtained patients' indirect responses to PL experiences for an objective evaluation using functional magnetic resonance imaging (fMRI). Six control subjects and six lower limb (LL) amputees participated in a motor imagery task for both the intact and the particular phantom toes. While all subjects shared neural processing of distinctive regional cerebral activations during motor imagery of the intact toes (prefrontal (PF), supplementary motor area (SMA), primary motor cortex (M1), superior temporal gyrus (STG)), it was only during motor imagery of the amputated toes in amputees that we observed an increased blood oxygen level-dependent (BOLD) signal in the contralateral basal ganglia at the medial globus pallidus (MGP), substantia nigra (SN), and thalamus. This increased BOLD signal in the basal ganglia-thalamus-cortex pathway during imaginary movement of the phantom toes may reflect an abnormal open loop functioning of the thalamocortical system underlying the conscious awareness of the phantom phenomenon. We suggest that the reduction in afferent information contributes to and coalesces with the higher-level reorganization resulting in the subjective conscious awareness of the phantom limb.

[Methylphenidate and short-term memory in young females with attention deficit hyperactivity disorder. A study using functional magnetic resonance imaging]. / Metilfenidato y memoria a corto plazo en mujeres jovenes con trastorno por deficit de atencion/hiperactividad. Estudio de resonancia magnetica funcional.

INTRODUCTION: Attention deficit/hyperactivity disorder (ADHD) is a common behavioral disorder found mainly in males, thus current knowledge on its clinical expression in female adults is extremely limited. AIM. To evaluate the behavioral and neural substrates associated with the performance of a short-term memory task in female ADHD adults, with and without methylphenidate exposure, with respect to a control group. SUBJECTS AND METHODS: Two groups of eight young right-handed, female, university students with ADHD and healthy controls matched by age, gender, handedness and academic level, voluntarily participated. All subjects performed twice an easy auditory short-term memory task (ADHD group without, and 90 minutes post-intake of methylphenidate 0.4 mg/kg in a counterbalanced order). The BOLD-fMRI response was used as a measure of neural activity during task performance. RESULTS: ADHD subjects showed a tendency to improve their performances under medication, showing an increased widespread functional activation, especially relevant over left frontal and cerebellar areas, in comparison with control subjects. CONCLUSIONS: Methylphenidate slightly improves short-term memory task performance in adult female ADHD subjects by modifying underlying neural functioning patterns.

Metilfenidato y memoria a corto plazo en mujeres jóvenes con trastorno por déficit de atención/hiperactividad. Estudio de resonancia magnética funcional / Methylphenidate and short-term memory in young females with attention deficit hyperactivity disorder. A study using functional magnetic resonance imaging

Introducción. El trastorno por déficit de atención/hiperactividad (TDAH) afecta predominantemente al sexo masculino, por lo que el conocimiento acerca de su expresión clínica y los efectos del tratamiento en el sexo femenino es muy limitado. Objetivo. Evaluar la respuesta funcional asociada a la ejecución de una tarea sencilla de memoria a corto plazo en mujeres con TDAH sin y bajo la exposición a metilfenidato respecto a un grupo control sano. Sujetos y métodos. Ocho mujeres universitarias, diestras, con diagnóstico de TDAH subtipo inatento y un grupo de controles sanos ejecutaron una tarea auditiva de memoria a corto plazo en dos ocasiones (sin y con ingestión de una dosis terapéutica de metilfenidato en el grupo con TDAH) mientras se registraba la respuesta funcional cerebral con la técnica BOLD de resonancia magnética funcional. Resultados. El grupo con TDAH mostró una tendencia a mejorar la ejecución basal de la tarea con la administración del medicamento. El grupo con TDAH medicado incrementó su actividad funcional en lóbulos frontales, temporal bilateral, parietal derecho y cerebelo izquierdo respecto a los niveles obtenidos durante la ejecución sin metilfenidato. En contraste, los controles sanos mostraron menor activación en el lóbulo frontal bilateral y parietal derecho durante la segunda ejecución de la tarea. Conclusión. El metilfenidato genera una activación funcional más amplia en mujeres adultas con TDAH que coincide con una tendencia a la mejoría en la ejecución conductual de una tarea sencilla de memoria a corto plazo (AU)

Introduction. Attention deficit/hyperactivity disorder (ADHD) is a common behavioral disorder found mainly in males, thus current knowledge on its clinical expression in female adults is extremely limited. Aim. To evaluate the behavioral and neural substrates associated with the performance of a short-term memory task in female ADHD adults, with and without methylphenidate exposure, with respect to a control group. Subjects and methods. Two groups of eight young right-handed, female, university students with ADHD and healthy controls matched by age, gender, handedness and academic level, voluntarily participated. All subjects performed twice an easy auditory short-term memory task (ADHD group without, and 90 minutes post-intake of methylphenidate 0.4 mg/kg in a counterbalanced order). The BOLD-fMRI response was used as a measure of neural activity during task performance. Results. ADHD subjects showed a tendency to improve their performances under medication, showing an increased widespread functional activation, especially relevant over left frontal and cerebellar areas, in comparison with control subjects. Conclusions. Methylphenidate slightly improves short-term memory task performance in adult female ADHD subjects by modifying underlying neural functioning patterns (AU)

Comparison of different statistical analyses in visual stimulus fMRI.

The present study evaluated four different clinically relevant statistical approaches with respect to a response to a visual stimulus paradigm. Healthy volunteers were subjected to a visual stimulus consisting of a checkerboard black-and-white box car pattern with on-off blocks of 10s. Simultaneously, sensitivity encoding (SENSE) dynamic MR imaging was acquired using a 1.5 T MR system. Statistical analyses were conducted with z-cluster analysis, Student's t-test, Spearman's correlation, and time-series normalized cross-correlation. A figure-of-merit for neural activity was measured from calculated maps using pixel counting. The results demonstrated that the index of activity estimated from the number of "activated" pixels did not differ markedly among the four different statistical methods, except when comparing the cross-correlation statistics with z-clustering in the whole brain, implying that all methods lead to similar statistical information when using fMRI to map the activity of the visual cortex in response to a visual stimulus.

Year 2000 status of MRI in Mexico.

The development of clinical magnetic resonance imaging in Mexico has followed a different course from that in the U.S. and Europe. The first clinical unit was installed in Mexico in the late 1980s at the very beginning of clinical applications worldwide. Since then, installations have proceeded at a sedate pace that now brings the installed total to 66 imagers. The largest fraction of these units (28, or 42%) is in Mexico City, with a broad distribution across the remaining 23 Mexican states. There is a noticeable increase of the number of units (20, or 30%) in the states bordering the U.S., while the states bordering nations to the south have no units. More than half the units (38, or 58%) are 0.5 T units, while a further 35% are 1.0 T or higher. Slower addition of units in Mexico relative to the U.S. is attributed to the higher fraction of public-funded hospitals and the inherent conservatism of such institutions when considering new technologies. Present public planning for health care development suggests that the coming decade will see more rapid installation of units to meet growing demand in Mexico for the latest medical technology. Experience over the past two decades indicates the need for more systematic training of technical and clinical personnel to implement these additions. The National University (Universidad Nacional Autónoma de México (UNAM) and the Metropolitan University (Universidad Autónoma Metropolitana (UAM) are collaborating with diverse clinical facilities to create such a program. J. Magn. Reson. Imaging 2001;13:813-817.

Brain somatic representation of phantom and intact limb: a fMRI study case report.

Reports on phantom limb patients concerning neuronal reorganization using non-invasive methods have focused mainly on the cortical regions and suggest the presence of pain as the cause of this reorganization. The phantom limb, however, includes other somatic and motor sensations other than pain. Here we describe the results of non-painful stimulation in cortical and subcortical lateralization and reorganization and also examine the involvement of subcortical structures in phantom limb telescoping perception. We describe an enlarged contralateral cortical representation of the stump, a cortical and thalamic bilateral representation of the remaining leg, and a neuronal correlate of a telescoping perception of the phantom limb. The missing leg produces an enlarged cortical representation due to abnormal information and the remaining leg has a bilateral SII representation, which could be related to new, compensatory functions. The telescoping perception of a phantom limb by the stimulation of misallocation points was correlated with lenticular nuclei, thalamic and cingulate gyrus activation. We therefore propose that the reorganization concept of a phantom limb, applied mainly to the cortex, must extend to the thalamic and the somatosensory and motor systems (pathways and relay nuclei).

Inhibition of rat corneal angiogenesis by 16-kDa prolactin and by endogenous prolactin-like molecules.

PURPOSE: The cornea is an avascular organ, where induction of new blood vessels involves the turn-on of proangiogenic factors and/or the turn-off of antiangiogenic regulators. Prolactin (PRL) fragments of 14 kDa and 16 kDa bind to endothelial cell receptors and inhibit angiogenesis. This study was designed to determine whether antiangiogenic PRL-like molecules are involved in cornea avascularity. METHODS: Sixteen-kDa PRL and basic fibroblast growth factor (bFGF) or anti-PRL antibodies were placed into rat cornea micropockets and neovascularization evaluated by the optical density associated with capillaries stained by the peroxidase reaction and by the number of vessels growing into the implants. Prolactin receptors in corneal epithelium were investigated by immunocytochemistry. RESULTS: bFGF induced a dose-dependent stimulation of corneal neovascularization. This effect was inhibited by coadministration of 16-kDa PRL, as indicated by a 65% reduction in vessel density and a 50% decrement in the incidence of angiogenic responses. Corneal angiogenic reactions of different intensities were induced by implantation of polyclonal and monoclonal anti-PRL antibodies. Corneal epithelial cells were labeled by several anti-PRL receptor monoclonal antibodies. CONCLUSIONS: These findings show that exogenous 16-kDa PRL inhibits bFGF-induced corneal neovascularization and suggest that PRL-like molecules with antiangiogenic actions function in the cornea. PRL receptors in the corneal epithelium may imply that PRL in the cornea derives from lacrimal PRL internalized through an intracellular pathway. These observations are consistent with the notion that members of the PRL family are potential regulators of corneal angiogenesis.

Acetylcholinesterase-positive innervation is present at undifferentiated stages of the sea turtle Lepidochelis olivacea embryo gonads: implications for temperature-dependent sex determination.

In embryos of different reptile species, incubation temperature triggers a cascade of endocrine events that lead to gonad sex differentiation. The cellular and molecular mechanisms by which temperature sets in motion this process are still controversial. Here, we begin evaluating the possible participation of the nervous system in temperature-dependent sex determination by showing the existence and origin of acetylcholinesterase (AchE)-positive nerve fibers in undifferentiated gonads of the Lepidochelys olivacea (L. olivacea) sea turtle putative male and female embryos, along the thermosensitive period for sex determination (TPSD; stages 20-27). AChE-positive nerve bundles and fibers were readily visualized until developmental stage 24 and thereafter. DiI injections and confocal imaging showed that some of these gonadal nerves arise from the lower thoracic and upper lumbar spinal cord levels, and might thus be sensory in nature. Because the vertebrate spinal cord is capable of integrating by itself thermoregulatory responses with no intervention of uppermost levels of the central nervous system, we also evaluated spinal cord maturation during the TPSD. The maturation of the spinal cord was more advanced in putative female than in male embryos, when sex determination is taking place for each sex; this process starts and ends earlier in male than in female embryos. Together these observations open the possibility that the spinal cord and the innervation derived from it could play a direct role in driving or modulating the process of temperature-dependent gonad sex determination and/or differentiation, particularly in female L. olivacea embryos.

Comparable activity levels in developmentally deprived and non-deprived layer IV cortical columns of the adult rat primary somatosensory cortex.

It has been suggested that evoked neural activity levels promote the selective construction of the primary somatosensory cortex (S1) neuropil. Sensory deprivation after S1 formation has, however, no effects on its postnatal growth. This indicates that S1 neuropil elaboration is independent from the ongoing levels of evoked cortical activity, and/or that sensory deprivation does not reduce overall levels of S1 evoked activity. We thus indirectly evaluated chronic and acute levels of neural activity in the developmentally, sensory deprived adult S1. Relative succinic dehydrogenase activity and 3H2-deoxyglucose uptake were comparable in control and deprived barrels. Our observations support the idea that normal levels of evoked neural activity prevent atrophic changes in the developmentally deprived adult S1. They can not rule out, however, that early selective S1 neuropil construction occurs independent from evoked neural activity levels.

Increased neural activity in transgenic mice with brain IGF-I overexpression: a [3H]2DG study.

To evaluate whether insulin-like growth factor-I (IGF-I) modulates neural activity in vivo, relative levels of brain [3H]2-deoxyglucose (2DG) uptake were compared in adult behaving and anesthetized wild type (wt) mice, and transgenic (Tg) mice with either brain IGF-I overexpression or ectopic brain expression of IGF binding protein-1 (IGFBP-1). Overall, awake behaving IGF-I Tg mice showed significant increases in brain 2DG uptake compared with wt and IGFBP-1 Tg mice. These differences were eliminated after anesthesia. 2DG uptake was similar in awake behaving, and anesthetized wt and IGFBP-1 Tg mice. Our observations thus suggest that IGF-I increases neural activity levels in vivo, and that it is not involved in regulating glucose consumption in the adult brain.

Brain mapping with functional MR imaging: comparison of gradient-echo--based exogenous and endogenous contrast techniques.

PURPOSE: To compare directly the two most widely used methods of functional magnetic resonance (MR) imaging--dynamic contrast material-enhanced MR imaging and blood oxygenation level-dependent (BOLD) MR imaging. MATERIALS AND METHODS: Five healthy volunteers underwent dynamic contrast-enhanced and BOLD MR imaging with a conventional 1.5-T MR unit during visual stimulation and a dark control state. BOLD studies were performed with a gradient-echo sequence, and dynamic MR imaging was performed with an echo-shifted gradient-echo sequence after intravenous administration of a bolus of gadopentetate dimeglumine. RESULTS: A significantly greater percentage signal change was found with dynamic MR imaging than with the BOLD technique. The extent of area activated was also significantly greater. CONCLUSION: With standard clinical imagers and these gradient-echo-based techniques, greater percentage activation and area of activation can be achieved with dynamic MR imaging than with BOLD MR imaging.

3-dimensional functional imaging of human brain using echo-shifted FLASH MRI.

A 3-dimensional MRI method has been developed for functional mapping of the human brain, based on blood oxygenation level dependent (BOLD) contrast mechanisms. The method uses recently introduced principles of echo-shifted FLASH to acquire a single 3D data set in 20 s. The technique was tested on a conventional 1.5 Tesla clinical scanner with a standard head coil using visual stimulation with a 8 Hz flashing white light, or a varying checkerboard pattern. Areas of increased signal intensity were identified in the visual cortex, consistent with the known functional organization.

Functional brain MR imaging based on bolus tracking with a fast T2*-sensitized gradient-echo method.

Dynamic physiological scanning, based on temporary changes in local field homogeneity during the passage of a contrast agent bolus, has been performed hitherto with echo-planar imaging (EPI) or conventional gradient-recalled techniques (FLASH). Here, it is shown that the T2* sensitivity of conventional FLASH techniques can be improved drastically on a conventional whole body instrument by delaying the gradient-echo until the subsequent TR-period without increasing total imaging time. Examples are given for a full k-space matrix (128 x 256) obtained within 2 s with a TE of 25 ms, resulting in images free of artifacts. The method is applied to bolus tracking through the brain of healthy volunteers during visual stimulation and in the dark. An average increase of regional cerebral blood volume (rCBV) in the visual cortex of 10.9% (n = 9, p = .001) was found.

Measurement of brain activity with bolus administration of contrast agent and gradient-echo MR imaging.

This study was performed to measure changes in cerebral blood volume (CBV) associated with visual activation by use of bolus administration of contrast agent and conventional, clinically configured magnetic resonance (MR) hardware and software. Fast gradient-recalled acquisition in the steady state technique was used to study five healthy subjects during visual activation and a control dark state. MR images were obtained every 2.048 seconds for 2 minutes. A bolus of gadopentetate dimeglumine was injected during visual stimulation and darkness. Cine images produced from the series of rapid images clearly depicted arterial, capillary, and venous phases. Analysis of serial concentration maps derived from the rapid images revealed expected differences between the relative CBV of gray matter and that of white matter, as well as significantly increased relative CBV in calcarine cortex during visual activation versus the control state (mean increase, 15.24%; range, 6.41%-27.78%; P < .05). These results confirm those reported in echo-planar imaging studies and demonstrate that brain function can be assessed with the bolus method by means of MR imaging hardware and software with conventional clinical configurations.