Littérature scientifique sur le sujet « Sistema somatosensor »

A manutenção de uma determinada orientação corporal é obtida a partir do complexo relacionamento entre informação sensorial e atividade muscular. Desta forma, o objetivo deste estudo foi revisar o papel das informações visuais, somatossensoriais, vestibulares e auditivas para manutenção e controle postural. Método. foi realizada uma busca nas bases de dados CAPES e PubMed, nos últimos 24 anos, com as seguintes palavras-chave: postural control, sensory information, vestibular system, visual system, somatosensory system, auditory system e haptic system. Resultados. foram analisadas a influência de cada sistema sensorial, bem como sua integração para a manutenção e controle postural. Conclusão. a literatura apontou que existe uma redundância nas informações fornecidas pelos canais sensoriais. Assim, o sistema nervoso central escolhe a fonte principal para controlar a postura.

<p>Desde hace algunos años el grupo de investigación de Neurofisiología Comportamental de la Universidad Nacional de Colombia ha venido evaluando los cambios que ocurren en el sistema nervioso central luego de la lesión de un nervio periférico. Específicamente trabajamos con el modelo de lesión del nervio facial en roedores para evaluar las modificaciones funcionales y estructurales que ocurren en la corteza sensoriomotora primaria luego de la lesión. Al lesionarse el nervio facial, el cerebro entra en un programa de reorganización que incluye cambios electrofisiológicos en las neuronas de la corteza motora que comandan los movimientos faciales (M1). En este sentido, las células de la corteza motora cerebral se vuelven más excitables y modifican su respuesta ante estímulos sensoriales. La reorganización tras la lesión también incluye cambios morfológicos en M1: las células piramidales de la corteza motora retraen su árbol dendrítico y disminuye la densidad de sus espinas dendríticas. En asociación con estos cambios, las células de M1 disminuyen transitoriamente su inmunorreactividad para NeuN (marcador específico de núcleos neuronales) y aumentan la expresión de GAP43 (proteína de crecimiento axonal). Esto indica, posiblemente, un cambio metabólico celular en asociación con la búsqueda de nuevas dianas sinápticas. Finalmente, hallamos que la glía circundante en M1 (tanto astrocitos como microglía) se activa de manera muy temprana luego de lesiones del nervio facial. Esto podría indicar que el remodelamiento estructural y funcional hallado en las neuronas corticales es el resultado de la interacción entre la activación de la glía circundante y las células piramidales de M1 (aunque se necesitan muchos experimentos adicionales que así lo demuestren).</p><p> </p><p>Abstract</p><p>Our research group (Neurofisiología Comportamental, Universidad Nacional de Colombia) has evaluated changes in the central nervous system induced by peripheral nerve injuries. We have characterized facial nerve lesion-induced structural and functional changes in primary motor cortex pyramidal neurons (M1) in rodents. Following the lesion, M1 neurons modified their spontaneous basal firing frequency: they become more excitable. Moreover, we found changes in evoked-activity with somatosensory stimulation after facial nerve lesion. Morphologically, it was found that facial nerve lesion induced long-lasting changes in the dendritic morphology of M1 pyramidal neurons. Dendritic branching of the pyramidal cells underwent overall shrinkage and dendrites suffered transient spine pruning. Additionally, we evaluated the reorganization processes in the central nervous system by using both neuronal and glial markers. Decreased NeuN (neuronal nuclei antigen) immunoreactivity and increased GAP-43 (growth-associated protein 43) immunoreactivity were found M1 after facial nerve lesion. In addition, we also observed astrogliosis and microglial activation sourrounding M1 early after facial nerve injury. Taken together these findings suggest that facial nerve lesions induce widespread reorganization in M1 including neuronal shrinkage, axon sprouting as well as astrocytic and microglia activation. These results suggest that facial nerve injuries elicit active remodeling due to pyramidal neuron and glia interaction (although additional experiments that demonstrate it are needed)</p>

Nella presente tesi di dottorato, ho esplorato se fenomeni di apprendimento Hebbiano possano governare il funzionamento dei sistemi cross-modali e sensorimotori del cervello umano. A tal fine, durante il mio dottorato, ho sviluppato e testato due nuovi protocolli Paired Associative Stimulation (PAS), una classe di tecniche di stimolazione cerebrale non invasiva in cui una stimolazione sensoriale periferica viene ripetutamente accoppiata con un impulso di stimolazione magnetica transcranica (TMS) su un’area bersaglio al fine di indurre plasticità associativa Hebbiana. I due protocolli PAS presentati nella mia tesi mirano a due sistemi cerebrali sensoriali-motori con funzionamento a specchio (tactile mirror system e action observation network), sfruttando rispettivamente una via cross-corticale visuo-tattile (cross-modal PAS) e una visuo-motoria (mirror PAS). Nel primo capitolo del presente lavoro, dopo una breve introduzione al concetto di plasticità associativa Hebbiana, fornirò una revisione esaustiva dei protocolli PAS che mirano ai sistemi sensorimotori, proponendo una classificazione in tre macro-categorie (within-system, cross-systems e cortico-cortical), a seconda delle caratteristiche delle stimolazioni accoppiate. Nel secondo capitolo descriverò le principali proprietà del sistema dei neuroni specchio (MNS) considerando anche le sue proprietà cross-modali visuo-tattili ed i meccanismi di plasticità neuronale che sono stati ipotizzati alla base dello sviluppo dei neuroni specchio. Nel terzo capitolo, introdurrò il cross-modal PAS (cm-PAS), un nuovo cross-systems PAS sviluppato per sfruttare le proprietà visuo-tattili della corteccia somatosensoriale primaria, al fine di indurre plasticità associativa Hebbiana in tale regione sensoriale. In una serie di tre esperimenti, ho testo la dipendenza temporale (Esperimento 1), la specificità corticale (Esperimento 2) e visiva (Esperimento 3) del protocollo, misurando possibili cambiamenti nell'acuità tattile dei partecipanti. Nell'esperimento 3, ho valutato anche possibili cambiamenti neurofisiologici all'interno di S1, registrando i potenziali evocati somatosensoriali. Infine, in un quarto esperimento, la dipendenza temporale del cm-PAS è stata ulteriormente studiata, testando l'ipotesi che meccanismi anticipatori di tipo predittivo possano svolgere un ruolo centrale nell'efficacia del protocollo. Nel quarto capitolo introdurrò un secondo cross-systems PAS: il mirror PAS (m-PAS) che sfrutta le proprietà ‘mirror’ visuo-motorie del cervello umano. A differenza del cm-PAS, questo secondo protocollo sfrutta la natura associativa dell'integrazione visuo-motoria all'interno del MNS, mirando a indurre un nuovo, atipico, fenomeno di risonanza motoria attraverso apprendimento Hebbiano. In tre esperimenti ho testato la dipendenza temporale (Esperimento 1), la specificità visiva (Esperimento 2) e corticale (Esperimento 3) del protocollo registrando i potenziali evocati motori durante la visione di semplici movimenti (i.e., risonanza motoria). Inoltre, nel terzo esperimento, ho esplorato anche possibili effetti comportamentali dell’m-PAS, utilizzando un compito di compatibilità imitativa che sfrutta il fenomeno dell'imitazione automatica. Infine, nel capitolo conclusivo, discuterò i risultati teorici, metodologici e clinici e le prospettive future che derivano da questi due protocolli.
In the present doctoral thesis, I have explored whether Hebbian learning may rule the functioning of cross-modal and sensory-motor networks of the human brain. To this aim, during my doctorate, I have developed and tested two novel Paired Associative Stimulation (PAS) protocols, a class of non-invasive brain stimulation techniques in which a peripheral, sensory, stimulation is repeatedly paired with a Transcranial Magnetic Stimulation (TMS) pulse to induce Hebbian associative plasticity. The two PAS protocols presented in my thesis target sensory-motor networks with mirror functioning, exploiting a visuo-tactile (cross-modal PAS), and a visuo-motor pathway (mirror PAS), respectively. In the first chapter of the present work, after a brief introduction to the concept of Hebbian associative plasticity, I will provide an exhaustive review of PAS protocols targeting sensory-motor systems, proposing a classification in three macro-categories: within-system, cross-systems, and cortico-cortical protocols, according to the characteristics of the paired stimulations. In the second chapter, I will describe the principal properties of the Mirror Neuron System (MNS) also considering its cross-modal (i.e., visuo-tactile) characteristics and the plastic mechanisms that are been hypothesize at the ground of the development of mirror neurons’ matching properties. In the third chapter, I will introduce the cross-modal PAS (cm-PAS), a novel cross-systems PAS developed to exploit the visuo-tactile mirroring properties of the primary somatosensory cortex (S1) to induce Hebbian associative plasticity in such primary sensory region. In a series of three experiments, timing dependency (Experiment 1), cortical (Experiment 2), and visual specificity (Experiment 3) of the protocol have been tested, by measuring changes in participants’ tactile acuity. In Experiment 3, also possible neurophysiological changes within S1 has been assessed, recording somatosensory-evoked potentials (SEP). Then, in a fourth experiment, cm-PAS timing dependency has been further investigated, testing the hypothesis that anticipatory, predictive-like, mechanisms within S1 may play a central role in the effectiveness of the protocol. In the fourth chapter, a second cross-systems PAS will be introduced: the mirror PAS (m-PAS) which exploits visuo-motor mirroring properties of the human brain. Differently from the cm-PAS, this second protocol targets visuo-motor integration within the MNS and aims at induce a novel, atypical, motor resonance phenomena (assessed recording motor-evoked potentials – MEPs) following Hebbian learning. In three experiments, timing dependency (Experiment 1), visual (Experiment 2), and cortical specificity (Experiment 3) of the protocol have been tested. Furthermore, in the third experiment, the behavioral effects of the m-PAS are explored, using an imitative compatibility task exploiting automatic imitation phenomenon. Finally, in the conclusive chapter, I will discuss theoretical, methodological, and clinical outcomes and future perspectives that arise from these two protocols and the related results.

The generation of cognitive maps is influenced by different senses such as vision, audition or smell. However, the tactile information system -a highly developed system in the rat- and its influence on spatial processing, has hardly been studied. The availability of precise tactile information in the hippocampus (Pereira et al., 2007) is highly suggestive of a possible influence of tactile information on spatial processing. In this study we aimed to test if somatosensory information contributes to the cognitive map creation and spatial representation. The deprivation of the tactile sense without the possibility of using other senses (total darkness, homogeneous odour and uniform white noise), should then affect the coding of spatial information and could be detected as an alteration in place cell properties such as firing rate, location and/or extension of the firing fields. These types of changes would demonstrate that somatosensory inputs are involved in the cognitive map creation. To carry out this study we developed three kinds of experiments. First, we developed a paradigm (Gener et al., 2009) to temporarily deprive the tactile input using locally applied local anaesthesia (lidocaine). In a second part, we demonstrate that this deprivation was effective in the awake animal, altering the behaviour during tactile discrimination protocols and reducing successful trials from 88% to chance (48%). Finally, we applied the deprivation technique to characterise the cognitive map creation. With that purpose, we first demonstrated that place cells recorded in a controlled environment were sensitive to tactile cues, such that the rotation of the cues induce the rotation of the firing fields. Next, when tactile information was deprived, the place cells’ fields showed changes in their compactness and size. The results of this study suggest that somatosensory input information transduced by the whiskers contributes to the cognitive map creation. Those findings respond to some of the questions about hippocampus integration’s of sensory information.

La La sensibilidad al dolor y el riesgo sufrir dolor crónico representan fenómenos complejos de naturaleza multidimensional, con una importante variabilidad interindividual. El objetivo de esta tesis doctoral se centró en explorar los factores genéticos y psicosociales implicados en la modulación del dolor y el riesgo a sufrir dolor crónico mediante seis estudios. Los dos primeros exploraron el efecto de factores genéticos y de la edad de inicio de la menopausia en la sensibilidad al dolor en pacientes con fibromialgia en comparación con voluntarias sanas. El primer estudio reveló un incremento de la frecuencia de alelos asociados a una reducida actividad de la enzima COMT en pacientes con síndrome de fibromialgia, junto con una elevada sensibilidad al dolor en estos grupos. El segundo estudio mostró que las pacientes con fibromialgia presentaron una edad de inicio de la menopausia más temprana que las controles. Asimismo, se encontró que las pacientes con menopausia temprana mostraban mayor sensibilidad al dolor que las pacientes con aparición tardía de la menopausia. Los dos siguientes examinaron el papel de factores genéticos en la actividad metabólica cerebral asociada al dolor, la respuesta de analgesia por placebo y en una tarea de funciones ejecutivas. El tercer estudio reveló que el alelo met66 del polimorfismo Val66Met en el gen BDNF se asociaba a un fenotipo de vulnerabilidad, resistencia a la analgesia por placebo, incrementos en la actividad dopaminérgica durante el procesamiento de dolor y reducciones durante la condición placebo. Asimismo, se observó que estos efectos eran dependientes del género del sujeto, con una mayor exacerbación en mujeres y con efectos nulos en hombres. El cuarto estudio mostró aumentos en la actividad del sistema opioide asociados a la respuesta de analgesia por placebo en portadores del alelo C del polimorfismo funcional C385A del gen FAAH. Por otro lado, no se encontraron diferencias significativas debidas a este polimorfismo en la respuesta al dolor en ausencia de placebo, ni en la activación del sistema dopaminérgico. Finalmente, los dos últimos estudios exploraron la modulación social analizando cambios en la actividad eléctrica cerebral como consecuencia de la observación de dolor y tacto en otros. El quinto estudio mostró diferencias en los potenciales evocados visuales en función de la percepción de expresiones faciales de dolor y enfado. El sexto estudio reveló que la observación de experiencias somatosensoriales dolorosas y no dolorosas en otras personas modulaba la amplitud de los potenciales somatosensoriales. Todos estos datos subrayan la naturaleza multidimensional de la respuesta al dolor y resaltan el papel de los factores genéticos y psicosociales en la persistencia del dolor a lo largo del tiempo.
Pain sensitivity and risk for chronic pain constitute complex multidimensional phenomena that vary significantly among individuals. The objective of the present Doctoral Thesis was focused on exploring genetic and psychosocial factors involved in the modulation of pain and chronic pain risk throughout six studies. The first two studies explored the effect of genetic factors and age-of-onset of menopause in pain sensitivity in fibromyalgia patients as compared to healthy volunteers. The first study showed an increased frequency of alleles associated with a reduced activity of COMT enzyme in patients with fibromyalgia syndrome, coupled with high sensitivity to pain in these groups. The second study showed that patients with fibromyalgia had an ageof- onset of menopause earlier than controls. We also found that patients with early menopause showed higher pain sensitivity than patients with late age-of-onset of menopause. The next two studies explored brain metabolic activity in response to pain and placebo analgesia and during an executive function task. The third study revealed that met66 allele of the Val66Met polymorphism in the BDNF gene was associated with a phenotype of vulnerability, strength, placebo analgesia, increases in dopaminergic activity during the processing of pain and reductions during the placebo condition. It was also noted that these effects were dependent on gender, being exacerbated in women as compared to men. The fourth study showed increases in placebo analgesia and in placebo-induced opioid activity in the C385 allele of the functional polymorphism C385A of the FAAH gene. Furthermore, there were no significant differences due to this polymorphism in the pain response in absence of placebo, or in dopaminergic system activation. Finally, the latter two studies explored the social modulation of brain electrical activity during observation of pain and somatosensory experiences in other´s. The fifth study showed differences in visual evoked potentials during the sight of pain and anger faces. The sixth study showed that observation of painful and non-painful experiences in others modulated the amplitude of somatosensory evoked potentials in the onlooker. These data underscore the multidimensional nature of pain response and highlight the role of genetic and psychosocial factors in the persistence of pain.