Luisa Lopez

A neuromagnetic study of movement-related somatosensory gating in the human brain

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under three different experimental conditions: (1) electrical stimulation of the right index finger (task S); (2) voluntary movement of the same finger (M); (3) M+S condition, consisting of voluntary movements of the right index finger triggering the electrical stimulus at the very beginning of the electromyogram. The three conditions were administered in random order every 5–8 s. In addition, the task somatosensory evoked fields (task SEFs) gathered during condition (1) were compared with control SEFs recorded at the beginning of the experiment during rest. In all subjects the overlay of somatosensory stimulation on movement provoked a decrement in brain responsiveness (gating) as determined by the amplitude of gated SEFs. The latter was found as the difference between the neuromagnetic fields during M+S condition (overlaying of movement and sensory stimulation) minus neuromagnetic fields under M condition (M only). The gating effect was found to begin approximately 30 ms after movement onset, and to last for the whole period of the ongoing movement. The theoretical locus of gating was estimated by dipole localisation of the difference between task SEFs and gated SEFS using a moving dipole model. The site of the “early” gating effect (<40 ms) was found to be more anteriorly located than the “later” (>40 ms) gating effect. The task SEFs were found to be larger (significant after 30 ms) than the control SEFs elicited under the basal condition. The results are discussed with respect to timing, mechanism (centrifugal and centripetal), locus and selectivity of gating. In addition, the results are discussed with regard to clinical application (measuring attentional deficits in patients with impairments of higher mental functions and measuring gating deficits in patients with disturbed sensorimotor integration).

Scalp-recorded oscillatory potentials evoked by transient pattern-reversal visual stimulation in man

Replicable oscillatory potentials, time-locked to pattern stimuli (9.0 degrees central; counterphase reversal at 2.13 Hz) were dissociated from conventional, broad-band VEPs recorded in healthy volunteers at occipital scalp locations by high-pass digital filtering at 17.0-20.0 Hz. Nine consecutive wavelets were identified with a 56.4 +/- 8.4 msec mean latency of the first replicable wavelet and mean peak-to-peak amplitude varying between 0.9 and 2.0 muV. The first 2 wavelets had significantly shorter latencies than wave N70 of unfiltered VEP, whereas the last 2 wavelets had longer latencies than N145. Latency and amplitude values varied as a function of contrast and spatial frequency of the stimulus, with shorter latencies and larger amplitudes at 60-90% contrast level and tuning of amplitude at 5.0 c/deg. All wavelets were correlated with wave P100 of unfiltered VEP, while a correlation with N70 of VEP was observed only for those wavelets with latencies in the range of wave P100. Two patients with documented brain lesions involving the visual system are described as examples of oscillatory responses occurring irrespective of filter bandpass and instead of the expected conventional VEP when the generation of these is interfered with by brain pathology. A substantial cortical contribution to the origin of the oscillatory response is conceivable. It is suggested that the oscillatory response to pattern-reversal stimulation reflects events in the visual system that are parallel to, and partly independent of, the conventional VEP, with potential application in research or for clinical purposes.

The development of postural strategies in children: a factorial design study.

BackgroundThe present study investigates balance control mechanisms, their variations with the absence of visual input, and their development in children from 7 to 11 years old, in order to provide insights on the development of balance control in the pediatric population.MethodsPosturographic data were recorded during 60 s trials administered on a sample population of 148 primary school children while stepping and then quietly standing on a force plate in two different vision conditions: eyes closed and eyes open. The extraction of posturographic parameters on the quiet standing phase of the experiment was preceded by the implementation of an algorithm to identify the settling time after stepping on the force plate. The effect of different conditions on posturographic parameters was tested with a two-way ANOVA (Age × Vision), and the corresponding eyes-closed/eyes-open (Romberg) Ratios underwent a one-way ANOVA.ResultsSeveral posturographic measures were found to be sensitive to testing condition (eyes closed vs. eyes open) and some of them to age and anthropometric parameters. The latter relationship did not explain all the data variability with age. An evident modification of postural strategy was observed between 7 and 11 years old children.ConclusionSimple measures extracted from posturographic signals resulted sensitive to vision and age: data acquired from force plate made it possible to confirm the hypothesis of the development of postural strategies in children as a more mature selection and re-weighting of proprioceptive inputs to postural control in absence of visual input.

Naloxone prevents cell-mediated immune alterations in adult mice following repeated mild stress in the neonatal period

Mild stress plus mild pain (solvent injection) applied daily to neonatal mice induces hormonal, behavioural and metabolic changes perduring in the adult life. We investigated whether daily mild stress to neonatal mice induces also long‐term defined changes of immune response, and whether immune changes are prevented through repeated administration of the opioid antagonist naloxone. Mild stress plus solvent injection administered from birth to the 21st postnatal day causes not only behavioural and metabolic changes, but also long‐term (up to 110 days of life) splenocytes modifications, consisting in: increased release of the Th‐1 type cytokines interleukin‐2 (IL‐2) (from an average of 346 to 788 pg ml−1), interferon‐γ (from 1770 to 3942) and tumour necrosis factor‐α (from 760 to 1241); decreased release of the Th‐2 type cytokines IL‐4 (from 49.1 to 28.4) and IL‐10 (from 1508 to 877). Moreover, enhanced natural killer‐cell activity; enhanced proliferative splenocytes properties in resting conditions and following phytohemoagglutinin and concanavalin‐A stimulation are observed. Immunological, behavioural and metabolic changes are prevented by the opioid antagonist (−)naloxone (1 mg kg−1 per day s.c., administered instead of solvent) but not by the biologically inactive enantiomorph (+)naloxone. In conclusion, endogenous opioid systems sensitive to naloxone are involved in long‐lasting enhancement of the Th‐1 type cytokines and cell‐mediated immunological response caused by repeated mild stress administered postnatally.

Synchronized ∼15.0–35.0 Hz oscillatory response to spatially modulated visual patterns in man

When suitably stimulated, neurons in the striate visual cortex of cats fire in bursts at 20-60 Hz and the membrane potential oscillates rhythmically in the same frequency range and in phase. These oscillations reflect intrinsic properties of mammalian neurons, occur in coherent spatial patterns that depend on the segregation and stimulus selectivity of stimulated cells, and mediate in long-range synchronization across columns and over large cortical areas of cells responding to the same stimulus property/properties. The pool of activated neurons may be adequate in size to drive cellular oscillations into local fields and mass responses. Accordingly, stimulus-dependent oscillatory activity in the same frequency range was described in man after contrast stimulation. Our results describe oscillatory potentials at approximately 15.0-35.0 Hz that in man are (partly) independent from, and anticipate the occurrence of, the conventional low-frequency visual response evoked by transient, foveal stimulation with spatially-modulated patterns.

Magnetically recorded oscillatory responses to luminance stimulation in man

Fast-frequency (ca. 100-110 Hz) oscillatory potentials superimposed on waves N2 and P2 of conventional broad-band VEP were magnetically recorded in man from occipital locations in response to monocular transient flash stimulation with full-field flashes (3.5 cd.s.m-2 intensity) and in spots (1, 1.5, or 2.0 cm in diameter). These oscillations proved replicable between- and within-subject and were phase-locked to retinal oscillatory potentials, with maximum correlation at approximately 35 ms and mean delay (as measured between the first measurable peaks) of 27.4 +/- 1.6 ms. When stimuli were in spots at increasing eccentricity (5, 15, or 25 degrees) from foveal fixation, broad-band VEP were recorded regardless of diameter and eccentricity of spot, whereas oscillatory responses were not detectable at eccentricity of, or greater than, 15 degrees. This observation suggests that broad-band VEP and the oscillatory response are generated by (partly) distinct neuronal populations and/or functional arrangements and that there is some functional connection between cortical oscillatory responses and stimulus-related events triggered in central retina.

A chronic implant to record electroretinogram, visual evoked potentials and oscillatory potentials in awake, freely moving rats for pharmacological studies.

Electroretinogram (ERG), widely used to study the pharmacological effects of drugs in animal models (e.g., diabetic retinopathy), is usually recorded in anesthetized rats. We report here a novel simple method to obtain chronic implantation of electrodes for simultaneous recording at the retinal and cortical levels in freely moving, unanesthetized animals. We recorded cortical (VEPs) and retinal (ERGs) responses evoked by light (flash) stimuli in awake rats and compared the results in the same rats anesthetized with urethane (0.6 mg/kg) before and after the monocular administration of scopolamine methyl bromide (1‰solution). We also compared the retinal responses with those derived from a classic acute corneal electrode. Anesthesia induced consistent changes of several VEP and ERG parameters like an increase of both latency and amplitude. In particular, the analysis of the variation of latency, amplitude, and spectral content of rapid oscillatory potentials could be important for a functional evaluation of the visual system in unanesthetized versus anesthetized animals.

Modulation of flash stimulation intensity and frequency: effects on visual evoked potentials and oscillatory potentials recorded in awake, freely moving mice.

Visual evoked potentials (VEP) responses to flash stimulation at nine intensities, from 0.611 to 945.6 cd/m(2)*s, and two frequencies (0.2 and 1 Hz) were recorded and oscillatory potentials (OPs) extracted after digital 50-Hz high pass filtering in unanaesthetized unrestrained mice. Both VEP and OPs morphology were replicable for all conditions and were similar to values reported in the literature. In particular OPs spectral analysis showed that the main frequency component remained stable at 66-77 Hz, for both stimulation frequencies, although it displayed an increase in amplitude, as a function of stimulus intensity. OPs amplitude at 1 Hz versus 0.2 Hz stimulus frequency was higher after taking into account the different noise contributions in the two conditions. Root mean square values calculated at selected time windows, revealed that, at 1 Hz, the main contribution to OPs occurs at the onset of the response (14-27 ms) while, at 0.2 Hz, the higher RMS was recorded later (42-56 ms). This difference accounts for the longer duration of the oscillatory event in the 0.2-Hz condition and suggests that oscillatory activity, modulated and carried along the visual pathway, is recorded at the cortical electrode after further elaboration at the cortical/subcortical level, depending on stimulus properties.

Evaluation of a Motion-Based Platform for Practicing Phonological Awareness of Preschool Children.

The aim of this study is to introduce a new platform, called En Plein, for the kinesthetic practice of phonological skills by preschool children and to examine its feasibility in combination with more traditional teaching methods. The rationale is that the manipulation of structural phonological units is important to train the necessary prerequisites for writing and reading and to help the identification of early learning disability precursors. The system includes a large number of phonological activities for children and allows interaction with a playful virtual environment via a cartoon-avatar controlled by a gesture-based natural user interface. En Plein relies on the Microsoft Kinect™ motion sensor. In the pilot study, the system has been placed in a classroom of an Italian kindergarten for 5 weeks of training. A test for assessing the phonological skills in Italian language for kindergarten (Valutazione delle Competenze Metafonologiche [CMF]) has been administered before and after training. Children who worked with the platform showed improvements in their phonological awareness (mean increase of CMF scores of 9%), while their peers who received only the traditional education had a mean increase of CMF scores of 1%. Results from this preliminary study show that children who used the system were more confident in manipulating structural phonological units, increased their awareness of words sound structures and generalized these skills by applying them to different tasks. The performance of En Plein is particularly encouraging for future large-scale applications in kindergartens and possible tests with children at risk of developing specific learning disabilities.

Effects of intravenous L-acetylcarnitine on retinal oscillatory potentials

L-acetylcarnitine is a compound with cholinergic properties and putative action on the visual system and the glucose metabolism. Ten healthy, emmertropic volunteers (age range: 21 to 28 years) were studied. Each subject was administered 5, 10, and 30 mg/kg acute intravenous doses of L-acetylcarnitine and matching placebo. Retinal oscillatory potentials to full-field flash stimulation were recorded before and 30, 60, and 120 min after administration. A systematic reduction of the implicit time of the P2 and N2 oscillatory potential components was observed after administration of the 10 and 30 mg/kg doses: significant changes were not evident at the 5 mg dose or after placebo. The latency reduction was significantly correlated with the postdrug increment of the L-acetylcarnitine plasma concentration. No other systematic modification in latency of amplitude was observed.