Marta Parazzini

Transcranial Direct Current Stimulation: Estimation of the Electric Field and of the Current Density in an Anatomical Human Head Model

This paper investigates the spatial distribution of the electric field and of the current density in the brain tissues induced by transcranial direct current stimulation of the primary motor cortex. A numerical method was applied on a realistic human head model to calculate these field distributions in different brain structures, such as the cortex, the white matter, the cerebellum, the hippocampus, the medulla oblongata, the pons, the midbrain, and the thalamus. The influence of varying the anode area, the cathode area, and the injected current was also investigated. An electrode area as the one typically used in clinical practice (i.e., both electrodes equal to 35 cm2) resulted into complex and diffuse amplitude distributions over all the examined brain structures, with the region of maximum induced field being below or close to the anode. Variations in either the anode or cathode area corresponded to changes in the field amplitude distribution in all the brain tissues, with the former variation producing more diffuse effects. Variations in the injected current resulted, as could be expected, in linearly correlated changes in the field amplitudes.

Modelling the electric field and the current density generated by cerebellar transcranial DC stimulation in humans

OBJECTIVE Transcranial Direct Current Stimulation (tDCS) over the cerebellum (or cerebellar tDCS) modulates working memory, changes cerebello-brain interaction, and affects locomotion in humans. Also, the use of tDCS has been proposed for the treatment of disorders characterized by cerebellar dysfunction. Nonetheless, the electric field (E) and current density (J) spatial distributions generated by cerebellar tDCS are unknown. This work aimed to estimate E and J distributions during cerebellar tDCS. METHODS Computational electromagnetics techniques were applied in three human realistic models of different ages and gender. RESULTS The stronger E and J occurred mainly in the cerebellar cortex, with some spread (up to 4%) toward the occipital cortex. Also, changes by ±1cm in the position of the active electrode resulted in a small effect (up to 4%) in the E and J spatial distribution in the cerebellum. Finally, the E and J spreads to the brainstem and the heart were negligible, thus further supporting the safety of this technique. CONCLUSIONS Despite inter-individual differences, our modeling study confirms that the cerebellum is the structure mainly involved by cerebellar tDCS. SIGNIFICANCE Modeling approach reveals that during cerebellar tDCS the current spread to other structures outside the cerebellum is unlike to produce functional effects.

Transcranial cerebellar direct current stimulation and transcutaneous spinal cord direct current stimulation as innovative tools for neuroscientists

Two neuromodulatory techniques based on applying direct current (DC) non‐invasively through the skin, transcranial cerebellar direct current stimulation (tDCS) and transcutaneous spinal DCS, can induce prolonged functional changes consistent with a direct influence on the human cerebellum and spinal cord. In this article we review the major experimental works on cerebellar tDCS and on spinal tDCS, and their preliminary clinical applications. Cerebellar tDCS modulates cerebellar motor cortical inhibition, gait adaptation, motor behaviour, and cognition (learning, language, memory, attention). Spinal tDCS influences the ascending and descending spinal pathways, and spinal reflex excitability. In the anaesthetised mouse, DC stimulation applied under the skin along the entire spinal cord may affect GABAergic and glutamatergic systems. Preliminary clinical studies in patients with cerebellar disorders, and in animals and patients with spinal cord injuries, have reported beneficial effects. Overall the available data show that cerebellar tDCS and spinal tDCS are two novel approaches for inducing prolonged functional changes and neuroplasticity in the human cerebellum and spinal cord, and both are new tools for experimental and clinical neuroscientists.

Influence on the mechanisms of generation of distortion product otoacoustic emissions of mobile phone exposure

Mobile phones have become very commonly used throughout the world within a short period of time. Although there is no clear evidence to show harmful physiological effects of electromagnetic fields (EMF) at the levels used by mobile phones, there is widespread public concern that there may be potential for harm. Because mobile phones are usually held close to the ear, it is appropriate to study effects on hearing. In this study, the outer hair cell function of 15 subjects was assessed by DPOAE recording before and after a controlled EMF exposure. To increase the sensitivity of DPOAE recording to identify even small changes in hearing function, an inverse fast Fourier transform (IFFT) analysis and time-domain windowing was applied to separate the two generation mechanisms of DPOAE, the so-called place-fixed and wave-fixed mechanisms, in order to verify if EMF can affects the two DPOAE emission mechanisms. Statistical analysis of the data showed that 10 min of EMF exposure at the maximum power (2 W at 900 MHz or 1 W at 1800 MHz) does not induce any changes in either DPOAE generation mechanism.

Electric field and current density distribution in an anatomical head model during transcranial direct current stimulation for tinnitus treatment

Tinnitus is considered an auditory phantom percept. Recently, transcranial direct current stimulation (tDCS) has been proposed as a new approach for tinnitus treatment including, as potential targets of interest, either the temporal and temporoparietal cortex or prefrontal areas. This study investigates and compares the spatial distribution of the magnitude of the electric field and the current density in the brain tissues during tDCS of different brain targets. A numerical method was applied on a realistic human head model to calculate these field distributions in different brain structures, such as the cortex, white matter, cerebellum, hippocampus, medulla oblongata, pons, midbrain, thalamus, and hypothalamus. Moreover, the same distributions were evaluated along the auditory pathways. Results of this study show that tDCS of the left temporoparietal cortex resulted in a widespread diffuse distribution of the magnitude of the electric fields (and also of the current density) on an area of the cortex larger than the target brain region. On the contrary, tDCS of the dorsolateral prefrontal cortex resulted in a stimulation mainly concentrated on the target itself. Differences in the magnitude distribution were also found on the structures along the auditory pathways. A sensitivity analysis was also performed, varying the electrode position and the human head models. Accurate estimation of the field distribution during tDCS in different regions of the head could be valuable to better determine and predict efficacy of tDCS for tinnitus suppression.

Cochlear maturation and otoacoustic emissions in preterm infants: a time-frequency approach.

Click-evoked otoacoustic emissions (CEOAEs) from preterm infants were analyzed to characterize developmental changes of cochlear active mechanisms. Due to their strong time-varying properties, CEOAEs were studied with a time-frequency approach--the wavelet transform (WT). By means of the WT, CEOAEs were decomposed into 12 frequency bands, spanning the 0.25-6.25 kHz range. For each band, the root-mean-square (RMS) level and latency were studied as functions of both frequency and age. Because CEOAEs were averaged using the non-linear mode of acquisition, the developmental changes in observed in this study are related to the non-linear component (which is actually the most predominant component of the active cochlear response) of CEOAEs, the linear one being mostly canceled out by non-linear averaging. In our study, there was evidence that properties of CEOAE non-linear components are related to the post-conception age (PCA) in that the levels and latency of CEOAE frequency components changed until the age of about 38 weeks post-conception, whereas after 38 weeks, CEOAE features were very similar to those of term newborns. In particular, the CEOAE levels increased and latency decreased with age. The observed changes in CEOAE properties seem to reveal a development of cochlear active mechanisms, although contributions from outer and middle ear development cannot be excluded. Also, in agreement with previous physiological and behavioral findings, our results revealed that the development of CEOAE properties was not the same for all the frequencies, being greater for frequencies 4 kHz, and resembled the development of the cochlear partition, which proceeds from base to apex.

Open ear hearing aids in tinnitus therapy: An efficacy comparison with sound generators

Abstract Objective: This study aimed to compare the effectiveness of tinnitus retraining therapy (TRT) with sound generators or with open ear hearing aids in the rehabilitation of tinnitus for a group of subjects who, according to Jastreboff categories, can be treated with both approaches to sound therapy (borderline of Category 1 and 2). Design: This study was a prospective data collection with a parallel-group design which entailed that each subject was randomly assigned to one of the two treatments group: half of the subjects were fitted binaurally with sound generators, and the other half with open ear hearing aids. Both groups received the same educational counselling sessions. Study sample: Ninety-one subjects passed the screening criteria and were enrolled into the study. Structured interviews, with a variety of measures evaluated through the use of visual-analog scales and the tinnitus handicap inventory self-administered questionnaire, were performed before the therapy and at 3, 6, and 12 months during the therapy. Results: Data showed a highly significant improvement in both tinnitus treatments starting from the first three months and up to one year of therapy, with a progressive and statistically significant decrease in the disability every three months. Conclusions: TRT was equally effective with sound generator or open ear hearing aids: they gave basically identical, statistically indistinguishable results. Sumario Objetivo: El objetivo de este estudio es comparar la efectividad de la terapia de re-entrenamiento del acúfeno (TRT), con generadores del sonido o con auxiliares auditivos con molde abierto en la rehabilitación del acúfeno, para un grupo de sujetos que, de acuerdo con las categorías de Jastreboff, pueden ser tratados con ambos enfoques hacia la terapia del sonido (límite entre la categoría 1 y la 2). Diseño: Este estudio fue una colección prospectiva de datos con un diseño de grupos paralelos en el que cada sujeto fue asignado al azar en uno de los dos grupos de tratamiento: la mitad de los sujetos fueron adaptados binauralmente con generadores de sonido y la otra mitad con auxiliares auditivos con molde abierto. Ambos grupos recibieron las mismas sesiones de asesoría. Muestra: 91 sujetos aprobaron el tamiz de criterios y fueron incluidos en el estudio. Se realizó una entrevista estructurada con una variedad de mediciones evaluadas en la Escala Visual Análoga y el Inventario del Impedimento por el Acúfeno, un cuestionario auto-administrado, antes de la terapia y a los 3, 6 y 12 meses durante la terapia. Resultados: Los datos mostraron una mejoría altamente significativa en ambos tratamientos desde los primeros tres meses y hasta el primer año de terapia con una significancia estadística progresiva y un descenso trimestral significativo en la discapacidad. Conclusiones: La TRT fue igualmente efectiva con generadores de sonido que con auxiliares auditivos de molde abierto: básicamente dieron resultados idénticos, estadísticamente indistinguibles.

Effects of mobile phone exposure on time frequency fine structure of transiently evoked otoacoustic emissions

Mobile phones have become very commonly used worldwide within a short period of time. To date there is only limited knowledge about interaction between electromagnetic fields (EMFs) emitted by mobile phones and the auditory function. Moreover, there is widespread concern that there may be potential for harm. The aim of this study was to assess potential subtle changes in cochlear function by measuring the temporal and spectral fine structure of transiently evoked otoacoustic emissions (TEOAE) in normal hearing subjects after exposure to EMFs emitted by Global System for Mobile Communication (GSM) mobile phones. TEOAEs were recorded in 27 healthy young adults before and after 10 min of real or sham exposure in a double-blind design. TEOAE data were analyzed both globally (broadband analysis) and using the Wavelet Transform (analysis of the time-frequency fine structure). The broadband analysis revealed no significant effect on TEOAEs related to exposure, confirming results of previous studies; in addition, no significant change was detected in the analysis of the elementary wavelet components, suggesting that the temporal and spectral fine structure of TEOAEs is not affected by 10 min exposure to low-intensity EMFs emitted by GSM mobile phones.

Electromagnetic Fields from Mobile Phones do not Affect the Inner Auditory System of Sprague-Dawley Rats

Abstract Galloni, P., Parazzini, M., Piscitelli, M., Pinto, R., Lovisolo, G. A., Tognola, G., Marino, C. and Ravazzani, P. Electromagnetic Fields from Mobile Phones do not Affect the Inner Auditory System of Sprague-Dawley Rats. Radiat. Res. 164, 798–804 (2005). The auditory system is the first biological structure facing the electromagnetic fields emitted by mobile phones. The aim of this study was to evaluate the cochlear functionality of Sprague-Dawley rats exposed to electromagnetic fields at the typical frequencies of GSM mobile phones (900 and 1800 MHz) by distortion product otoacoustic emissions, which are a well-known indicator of the status of the cochleas outer hair cells. A population of 48 rats was divided into exposed and sham-exposed groups. Three sets of four loop antennas, one for sham-exposed animals and two for exposed animals, were used for the local exposures. Rats were exposed 2 h/day, 5 days/week for 4 weeks at a local SAR of 2 W/kg in the ear. Distortion product otoacoustic emissions tests were carried out before, during and after the exposure. The analysis of the data shows no statistically significant differences between the audiological signals recorded for the different groups.

3-D acquisition and quantitative measurements of anatomical parts by optical scanning and image reconstruction from unorganized range data

A simple method for direct acquisition of a cloud of points from an object surface is presented together with a novel surface reconstruction algorithm used to obtain an explicit three-dimensional (3-D) model for the measured object. This technique is aimed at relatively accurate but simple and reliable 3-D reconstruction of anatomical parts for biomedical applications. A prototype 3-D scanning system is presented: the physical acquisition system and the image reconstruction algorithm are described. Measurements on objects of well-known geometrical features and dimensions are performed in order to assess accuracy and repeatability levels of this 3-D acquisition system. Robustness to noise of the proposed reconstruction algorithm is determined by simulation with synthetic test surfaces. Finally, the first measurements (acquisition + reconstruction) of closed surfaces from human organs are reported.