Efeito combinado do exercício físico e da degradação da matriz extracelular na plasticidade do córtex cerebral após isquemia

O acidente vascular cerebral (AVC) é a maior causa de mortes e incapacidades neurológicas no Brasil, e mais de 80% deles são decorrentes de evento isquêmico. Os sobreviventes de AVC apresentam uma variedade de déficits motores, cognitivos e sensoriais, que prejudicam suas atividades de vida diária, limitando assim sua independência. Portanto, torna-se cada vez mais necessário elaborar estratégias terapêuticas que promovam a recuperação funcional de pacientes acometidos por AVC. Após isquemia do tecido nervoso, ocorre no meio extracelular a super expressão de moléculas inibitórias a regeneração neuronal e à plasticidade sináptica, como os proteoglicanos de sulfato de condroitina (PGSCs), o principal componente das redes perineuronais (RPNs). A remoção destas moléculas com a ação da enzima condroitinase ABC (ChABC) tem sido usada como estratégia para induzir a plasticidade neuronal. Outro fator que tem sido utilizado para estimular a neuroplasticidade é o exercício físico específico para o membro afetado após AVC. O exercício físico está relacionado à liberação de neurotrofinas, importantes para a regeneração do sistema nervoso. Portanto, a remoção dos PGSCs junto com o exercício físico pode potencializar a indução da plasticidade cerebral e recuperação funcional após lesão isquêmica experimental na área sensório-motora de ratos. Para testar nossa hipótese, utilizamos n=16 ratos (Ratus norvergicus) da linhagem Wistar, divididos nos seguintes grupos experimentais (todos com sobrevida de 21 dias após AVC isquêmico): Grupo Controle ou BSA (Isquemia experimental, implante de Elvax saturado com BSA); Grupo Exercício (Isquemia experimental, implante de Elvax saturado com BSA + exercício físico específico); Grupo ChABC (Isquemia experimental, implante de Elvax saturado com ChABC); e Grupo ChABC + Exercício (Isquemia experimental, implante de Elvax saturado com ChABC + exercício físico específico). A lesão isquêmica foi induzida através de microinjeções do vasoconstritor Endotelina-1 (ET-1) no córtex sensório-motor, na representação da pata anterior. Logo em seguida foi implantado uma microfatia de polímero de Etileno vinil acetato saturado com ChABC (grupos ChABC e ChABC + Exercício) ou BSA (grupos Controle e Exercício). Foram avaliadas a área de lesão e a degradação dos PGSCs, além da recuperação funcional da pata afetada através do teste da exploração vertical e do teste da escada horizontal. Avaliamos a área de lesão (mm²) com auxílio do programa ImageJ (NIH, USA), delimitando a área com palor celular e também marcada com azul de colanil que estava presente na solução de injeção do peptídeo vasoconstritor ET-1 e verificamos que não houve diferença significativa no tamanho da área de lesão entre os grupos Controle (0,48±0,12), Exercício (0,46±0,05), ChABC (0,50±0,18) e ChABC + Exercício (0,55±0,05) (ANOVA, pós-teste de Tukey, ***p<0,001; **<0,01; *p<0,5). Animais que foram submetidos à remoção enzimática dos PGSCs apresentaram imunomarcação para o anticorpo anti-condroitin-4-sulfato (C4S) na área de lesão ao final da sobrevida, não havendo evidencias de degradação de PGSCs nos grupos Controle e Exercício. Verificamos ainda no teste do cilindro que a indução da lesão isquêmica não provocou perda funcional ampla, não alterando o comportamento exploratório, nem a frequência de uso da pata anterior afetada dos animais após a lesão (grupo Controle: pré-lesão ou baseline (0,33±0,10), 3 (0,29±0,17), 7 (0,30±0,10), 14 (0,29±0,16) e 21 (0,27±0,13) dias após a lesão; grupo Exercício: pré-lesão ou baseline (0,30±0,12), 3 (0,32±0,24), 7 (0,19±0,37), 14 (0,31±0,10) e 21 (0,32±0,09) dias após a lesão; grupo ChABC: pré-lesão ou baseline (0,34±0,07), 3 (0,20±0,11), 7 (0,23±0,07), 14 (0,33±0,14) e 21 (0,39±0,16) dias após a lesão; grupo ChABC + Exercício: pré-lesão ou baseline (0,34±0,04), 3 (0,20±0,09), 7 (0,26±0,04), 14 (0,18±0,08) e 21 (0,27±0,04) dias após a lesão) (ANOVA, pós-teste de Tukey, ***p<0,001; **<0,01; *p<0,5). O grupo que teve apenas a remoção dos PGSCs apresentou um melhor desempenho motor no teste da escada horizontal, mantendo sua frequência de acertos quando comparado aos demais grupos, sendo que ao final da sobrevida de 21 dias, os grupos Controle e ChABC + Exercício alcançaram uma recuperação espontânea (equivalente ao teste pré-lesão), se aproximando do grupo ChABC. Apenas o grupo tratado somente com Exercício não alcançou a recuperação espontânea, apresentando um desempenho motor significativamente inferior aos demais grupos em todos os momentos de reavaliação (grupo Controle: pré-lesão ou baseline (7,70±0,54), 3 (5,30±0,71), 7 (5,4±1,14), 14 (5,20±0,37) e 21 (6,70±0,48) dias após a lesão; grupo Exercício: pré-lesão ou baseline (8,40±0,28), 3 (4,30±0,48), 7 (4,75±0,50), 14 (5,35±0,41) e 21 (5,05±0,67) dias após a lesão; grupo ChABC: pré-lesão ou baseline (7,65±0,97), 3 (6,90±0,65), 7 (7,80±0,37), 14 (7,15±0,87) e 21 (7,45±0,32) dias após a lesão; e grupo ChABC + Exercício: pré-lesão ou baseline (8,10±0,22), 3 (3,65±1,48), 7 (4,95±1,06), 14 (7,35±0,37) e 21 (6,70±0,48) dias após a lesão (ANOVA, pós-teste de Tukey, ***p<0,001; **<0,01; *p<0,5). Portanto, a remoção dos PGSCs, o exercício físico forçado precoce e sua associação não influenciaram no tamanho da área de lesão após isquemia focal no córtex sensório-motor. Porém, apenas a remoção dos PGSCs das redes perineuronais melhorou precocemente o desempenho motor do membro afetado após isquemia focal no córtex sensório-motor. Enquanto que a remoção dos PGSCs associada ao exercício físico melhorou o desempenho motor do membro afetado após a lesão, porém essa melhora foi tardia. E o exercício físico aplicado precocemente após isquemia focal no córtex sensório-motor prejudicou o desempenho motor do membro afetado.

Morphological and functional study of cerebral aging in rat

Aging is a physiological process characterized by a progressive decline of the “cellular homeostatic reserve”, refereed as the capability to respond suitably to exogenous and endogenous stressful stimuli. Due to their high energetic requests and post-mitotic nature, neurons are peculiarly susceptible to this phenomenon. However, the aged brain maintains a certain level of adaptive capacities and if properly stimulated may warrant a considerable functional recovery. Aim of the present research was to verify the plastic potentialities of the aging brain of rats subjected to two kind of exogenous stimuli: A) the replacement of the standard diet with a ketogenic regimen (the change forces the brain to use ketone bodies (KB) in alternative to glucose to satisfy the energetic needs) and B) a behavioural task able to induce the formation of inhibitory avoidance memory. A) Fifteen male Wistar rats of 19 months of age were divided into three groups (average body weight pair-matched), and fed for 8 weeks with different dietary regimens: i) diet containing 10% medium chain triglycerides (MCT); ii) diet containing 20% MCT; iii) standard commercial chow. Five young (5 months of age) and five old (26-27 months of age) animals fed with the standard diet were used as further controls. The following morphological parameters reflecting synaptic plasticity were evaluated in the stratum moleculare of the hippocampal CA1 region (SM CA1), in the outer molecular layer of the hippocampal dentate gyrus (OML DG), and in the granule cell layer of the cerebellar cortex (GCL-CCx): average area (S), numeric density (Nvs), and surface density (Sv) of synapses, and average volume (V), numeric density (Nvm), and volume density (Vv) of synaptic mitochondria. Moreover, succinic dehydrogenase (SDH) activity was cytochemically determined in Purkinje cells (PC) and V, Nvm, Vv, and cytochemical precipitate area/mitochondrial area (R) of SDH-positive mitochondria were evaluated. In SM CA1, MCT-KDs induced the early appearance of the morphological patterns typical of old animals: higher S and V, and lower Nvs and Nvm. On the contrary, in OML DG, Sv and Vv of MCT-KDs-fed rats were higher (as a result of higher Nvs and Nvm) vs. controls; these modifications are known to improve synaptic function and metabolic supply. The opposite effects of MCT-KDs might reflect the different susceptibility of these brain regions to the aging processes: OML DG is less vulnerable than SM CA1, and the reactivation of ketone bodies uptake and catabolism might occur more efficiently in this region, allowing the exploitation of their peculiar metabolic properties. In GCL-CCx, the results described a new scenario in comparison to that found in the hippocampal formation: 10%MCT-KD induced the early appearance of senescent patterns (decreased Nvs and Nvm; increased V), whereas 20%MCT-KD caused no changes. Since GCL-CCx is more vulnerable to age than DG, and less than CA1, these data further support the hypothesis that MCT-KDs effects in the aging brain critically depend on neuronal vulnerability to age, besides MCT percentage. Regarding PC, it was decided to evaluate only the metabolic effect of the dietetic regimen (20%MCT-KD) characterized by less side effects. KD counteracted age-related decrease in numeric density of SDH-positive mitochondria, and enhanced their energetic efficiency (R was significantly higher in MCT-KD-fed rats vs. all the controls). Since it is well known that Purkinje and dentate gyrus cells are less vulnerable to aging than CA1 neurons, these results corroborate our previous hypothesis. In conclusion, the A) experimental line provides the first evidence that morphological and functional parameters reflecting synaptic plasticity and mitochondrial metabolic competence may be modulated by MCT-KDs in the pre-senescent central nervous system, and that the effects may be heterogeneous in different brain regions. MCT-KDs seem to supply high energy metabolic intermediates and to be beneficial (“anti-aging”) for those neurons that maintain the capability to exploit them. This implies risks but also promising potentialities for the therapeutic use of these diets during aging B) Morphological parameters of synapses and synaptic mitochondria in SM CA1 were investigated in old (26-27 month-old) female Wistar rats following a single trial inhibitory avoidance task. In this memory protocol animals learn to avoid a dark compartment in which they received a mild, inescapable foot-shock. Rats were tested 3 and 6 or 9 hours after the training, divided into good and bad responders according to their performance (retention times above or below 100 s, respectively) and immediately sacrificed. Nvs, S, Sv, Nvm, V, and Vv were evaluated. In the good responder group, the numeric density of synapses and mitochondria was significantly higher and the average mitochondrial volume was significantly smaller 9 hours vs. 6 hours after the training. No significant differences were observed among bad responders. Thus, better performances in passive avoidance memory task are correlated with more efficient plastic remodeling of synaptic contacts and mitochondria in hippocampal CA1. These findings indicate that maintenance of synaptic plastic reactivity during aging is a critical requirement for preserving long-term memory consolidation.

Long-term potentiation and neural network activity in the neonatal rat cerebral cortex in vivo

Long-term potentiation in the neonatal rat rnbarrel cortex in vivo rnLong-term potentiation (LTP) is important for the activity-dependent formation of early cortical circuits. In the neonatal rodent barrel cortex LTP has been so far only studied in vitro. I combined voltage-sensitive dye imaging with extracellular multi-electrode recordings to study whisker stimulation-induced LTP for both the slope of field potential and the number of multi-unit activity in the whisker-to-barrel cortex pathway of the neonatal rat barrel cortex in vivo. Single whisker stimulation at 2 Hz for 10 min induced an age-dependent expression of LTP in postnatal day (P) 0 to P14 rats with the strongest expression of LTP at P3-P5. The magnitude of LTP was largest in the stimulated barrel-related column, smaller in the surrounding septal region and no LTP could be observed in the neighboring barrel. Current source density analyses revealed an LTP-associated increase of synaptic current sinks in layer IV / lower layer II/III at P3-P5 and in the cortical plate / upper layer V at P0-P1. This study demonstrates for the first time an age-dependent and spatially confined LTP in the barrel cortex of the newborn rat in vivo. These activity-dependent modifications during the critical period may play an important role in the development and refinement of the topographic map in the barrel cortex. (An et al., 2012)rnEarly motor activity triggered by gamma and spindle bursts in neonatal rat motor cortexrnSelf-generated neuronal activity generated in subcortical regions drives early spontaneous motor activity, which is a hallmark of the developing sensorimotor system. However, the neuronal activity patterns and functions of neonatal primary motor cortex (M1) in the early movements are still unknown. I combined voltage-sensitive dye imaging with simultaneous extracellular multi-electrode recordings in the neonatal rat S1 and M1 in vivo. At P3-P5, gamma and spindle bursts observed in M1 could trigger early paw movements. Furthermore, the paw movements could be also elicited by the focal electrical stimulation of M1 at layer V. Local inactivation of M1 could significantly attenuate paw movements, suggesting that the neonatal M1 operates in motor mode. In contrast, the neonatal M1 can also operate in sensory mode. Early spontaneous movements and sensory stimulations of paw trigger gamma and spindle bursts in M1. Blockade of peripheral sensory input from the paw completely abolished sensory evoked gamma and spindle bursts. Moreover, both sensory evoked and spontaneously occurring gamma and spindle bursts mediated interactions between S1 and M1. Accordingly, local inactivation of the S1 profoundly reduced paw stimulation-induced and spontaneously occurring gamma and spindle bursts in M1, indicating that S1 plays a critical role in generation of the activity patterns in M1. This study proposes that both self-generated and sensory evoked gamma and spindle bursts in M1 may contribute to the refinement and maturation of corticospinal and sensorimotor networks required for sensorimotor coordination.rn

Human neural stem cells enhance structural plasticity and axonal transport in the ischaemic brain

Stem cell transplantation promises new hope for the treatment of stroke although significant questions remain about how the grafted cells elicit their effects. One hypothesis is that transplanted stem cells enhance endogenous repair mechanisms activated after cerebral ischaemia. Recognizing that bilateral reorganization of surviving circuits is associated with recovery after stroke, we investigated the ability of transplanted human neural progenitor cells to enhance this structural plasticity. Our results show the first evidence that human neural progenitor cell treatment can significantly increase dendritic plasticity in both the ipsi- and contralesional cortex and this coincides with stem cell-induced functional recovery. Moreover, stem cell-grafted rats demonstrated increased corticocortical, corticostriatal, corticothalamic and corticospinal axonal rewiring from the contralesional side; with the transcallosal and corticospinal axonal sprouting correlating with functional recovery. Furthermore, we demonstrate that axonal transport, which is critical for both proper axonal function and axonal sprouting, is inhibited by stroke and that this is rescued by the stem cell treatment, thus identifying another novel potential mechanism of action of transplanted cells. Finally, we established in vitro co-culture assays in which these stem cells mimicked the effects observed in vivo. Through immunodepletion studies, we identified vascular endothelial growth factor, thrombospondins 1 and 2, and slit as mediators partially responsible for stem cell-induced effects on dendritic sprouting, axonal plasticity and axonal transport in vitro. Thus, we postulate that human neural progenitor cells aid recovery after stroke through secretion of factors that enhance brain repair and plasticity.

Theta burst TMS increases cerebral blood flow in the primary motor cortex during motor performance as assessed by arterial spin labeling (ASL)

Theta burst stimulation (TBS) is a novel variant of repetitive transcranial magnetic stimulation (rTMS), which induces changes in neuronal excitability persisting up to 1h. When elicited in the primary motor cortex, such physiological modulations might also have an impact on motor behavior. In the present study, we applied TBS in combination with pseudo continuous arterial spin labeling (pCASL) in order to address the question of whether TBS effects are measurable by means of changes in physiological parameters such as cerebral blood flow (CBF) and if TBS-induced plasticity can modify motor behavior. Twelve right-handed healthy subjects were stimulated using an inhibitory TBS protocol at subthreshold stimulation intensity targeted over the right motor cortex. The control condition consisted of within-subject Sham treatment in a crossover design. PCASL was performed before (pre TBS/pre Sham) and immediately after treatment (post TBS/post Sham). During the pCASL runs, the subjects performed a sequential fingertapping task with the left hand at individual maximum speed. There was a significant increase of CBF in the primary motor cortex after TBS, but not after Sham. It is assumed that inhibitory TBS induced a "local virtual lesion" which leads to the mobilization of more neuronal resources. There was no TBS-specific modulation in motor behavior, which might indicate that acute changes in brain plasticity caused by TBS are immediately compensated. This compensatory reaction seems to be observable at the metabolic, but not at the behavioral level.

Vascular endothelial growth factor induces contralesional corticobulbar plasticity and functional neurological recovery in the ischemic brain

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor, which also has neuroprotective activity. In view of these dual actions on vessels and neurons, we were interested whether VEGF promotes long distance axonal plasticity in the ischemic brain. Herein, we show that VEGF promotes neurological stroke recovery in mice when delivered in a delayed way starting 3 days after middle cerebral artery occlusion. Using anterograde tract-tracing experiments that we combined with histochemical and molecular biological studies, we demonstrate that although VEGF promoted angiogenesis predominantly in the ischemic hemisphere, pronounced axonal sprouting was induced by VEGF in the contralesional, but not the ipsilesional corticobulbar system. Corticobulbar plasticity was accompanied by the deactivation of the matrix metalloproteinase MMP9 in the lesioned hemisphere and the transient downregulation of the axonal growth inhibitors NG2 proteoglycan and brevican and the guidance molecules ephrin B1/2 in the contralesional hemisphere. The regulation of matrix proteinases, growth inhibitors, and guidance molecules offers insights how brain plasticity is controlled in the ischemic brain.

Brain fiber tract plasticity in experimental spinal cord injury: diffusion tensor imaging.

Diffusion tensor imaging (DTI) and immunohistochemistry were performed in spinal cord injured rats to understand the basis for activation of multiple regions in the brain observed in functional magnetic resonance imaging (fMRI) studies. The measured fractional anisotropy (FA), a scalar measure of diffusion anisotropy, along the region encompassing corticospinal tracts (CST) indicates significant differences between control and injured groups in the 3 to 4 mm area posterior to bregma that correspond to internal capsule and cerebral peduncle. Additionally, DTI-based tractography in injured animals showed increased number of fibers that extend towards the cortex terminating in the regions that were activated in fMRI. Both the internal capsule and cerebral peduncle demonstrated an increase in GFAP-immunoreactivity compared to control animals. GAP-43 expression also indicates plasticity in the internal capsule. These studies suggest that the previously observed multiple regions of activation in spinal cord injury are, at least in part, due to the formation of new fibers.

Learning reward timing in cortex through reward dependent expression of synaptic plasticity.

The ability to represent time is an essential component of cognition but its neural basis is unknown. Although extensively studied both behaviorally and electrophysiologically, a general theoretical framework describing the elementary neural mechanisms used by the brain to learn temporal representations is lacking. It is commonly believed that the underlying cellular mechanisms reside in high order cortical regions but recent studies show sustained neural activity in primary sensory cortices that can represent the timing of expected reward. Here, we show that local cortical networks can learn temporal representations through a simple framework predicated on reward dependent expression of synaptic plasticity. We assert that temporal representations are stored in the lateral synaptic connections between neurons and demonstrate that reward-modulated plasticity is sufficient to learn these representations. We implement our model numerically to explain reward-time learning in the primary visual cortex (V1), demonstrate experimental support, and suggest additional experimentally verifiable predictions.

Cortical reorganisation of cerebral networks after childhood stroke: impact on outcome.

BACKGROUND Recovery after arterial ischaemic stroke is known to largely depend on the plastic properties of the brain. The present study examines changes in the network topography of the developing brain after stroke. Effects of brain damage are best assessed by examining entire networks rather than single sites of structural lesions. Relating these changes to post-stroke neuropsychological variables and motor abilities will improve understanding of functional plasticity after stroke. Inclusion of healthy controls will provide additional insight into children's normal brain development. Resting state functional magnetic resonance imaging is a valid approach to topographically investigate the reorganisation of functional networks after a brain lesion. Transcranial magnetic stimulation provides complementary output information. This study will investigate functional reorganisation after paediatric arterial ischaemic stroke by means of resting state functional magnetic resonance imaging and transcranial magnetic stimulation in a cross-sectional plus longitudinal study design. The general aim of this study is to better understand neuroplasticity of the developing brain after stroke in order to develop more efficacious therapy and to improve the post-stroke functional outcome. METHODS The cross-sectional part of the study will investigate the functional cerebral networks of 35 children with chronic arterial ischaemic stroke (time of the lesion >2 years). In the longitudinal part, 15 children with acute arterial ischaemic stroke (shortly after the acute phase of the stroke) will be included and investigations will be performed 3 times within the subsequent 9 months. We will also recruit 50 healthy controls, matched for age and sex. The neuroimaging and neurophysiological data will be correlated with neuropsychological and neurological variables. DISCUSSION This study is the first to combine resting state functional magnetic resonance imaging and transcranial magnetic stimulation in a paediatric population diagnosed with arterial ischaemic stroke. Thus, this study has the potential to uniquely contribute to the understanding of neuronal plasticity in the brains of healthy children and those with acute or chronic brain injury. It is expected that the results will lead to the development of optimal interventions after arterial ischaemic stroke.

Random positions of dendritic spines in human cerebral cortex

Dendritic spines establish most excitatory synapses in the brain and are located in Purkinje cell’s dendrites along helical paths, perhaps maximizing the probability to contact different axons. To test whether spine helixes also occur in neocortex, we reconstructed >500 dendritic segments from adult human cortex obtained from autopsies. With Fourier analysis and spatial statistics, we analyzed spine position along apical and basal dendrites of layer 3 pyramidal neurons from frontal, temporal, and cingulate cortex. Although we occasionally detected helical positioning, for the great majority of dendrites we could not reject the null hypothesis of spatial randomness in spine locations, either in apical or basal dendrites, in neurons of different cortical areas or among spines of different volumes and lengths. We conclude that in adult human neocortex spine positions are mostly random. We discuss the relevance of these results for spine formation and plasticity and their functional impact for cortical circuits.

Random positioning of dendritic spines in the human cerebral cortex

Dendritic spines establish most excitatory synapses in the brain and are located in Purkinje cell?s dendrites along helical paths, perhaps maximizing the probability to contact different axons. To test whether spine helixes also occur in neocortex, we reconstructed ?500 dendritic segments from adult human cortex obtained from autopsies. With Fourier analysis and spatial statistics, we analyzed spine position along apical and basal dendrites of layer 3 pyramidal neurons from frontal, temporal, and cingulate cortex. Although we occasionally detected helical positioning, for the great majority of dendrites we could not reject the null hypothesis of spatial randomness in spine locations, either in apical or basal dendrites, in neurons of different cortical areas or among spines of different volumes and lengths. We conclude that in adult human neocortex spine positions are mostly random. We discuss the relevance of these results for spine formation and plasticity and their functional impact for cortical circuits.

Modelado y Evaluación de Entornos Virtuales Interactivos para Rehabilitación Cognitiva en Daño Cerebral

El Daño Cerebral (DC) se refiere a cualquier lesión producida en el cerebro y que afecta a su funcionalidad. Se ha convertido en una de las principales causas de discapacidad neurológica de las sociedades desarrolladas. Hasta la más sencilla de las actividades y acciones que realizamos en nuestro día a día involucran a los procesos cognitivos. Por ello, la alteración de las funciones cognitivas como consecuencia del DC, limita no sólo la calidad de vida del paciente sino también la de las persona de su entorno. La rehabilitación cognitiva trata de aumentar la autonomía y calidad de vida del paciente minimizando o compensando los desórdenes funciones causados por el episodio de DC. La plasticidad cerebral es una propiedad intrínseca al sistema nervioso humano por la que en función a la experiencia se crean nuevos patrones de conectividad. El propósito de la neurorrehabilitación es precisamente modular esta propiedad intrínseca a partir de ejercicios específicos, los cuales podrían derivar en la recuperación parcial o total de las funciones afectadas. La incorporación de la tecnología a las terapias de rehabilitación ha permitido desarrollar nuevas metodologías de trabajo. Esto ha ayudado a hacer frente a las dificultades de la rehabilitación que los procesos tradicionales no logran abarcar. A pesar del gran avance realizado en los Ãoltimos años, todavía existen debilidades en el proceso de rehabilitación; por ejemplo, la trasferencia a la vida real de las habilidades logradas durante la terapia de rehabilitación, así como su generalización a otras actividades cotidianas. Los entornos virtuales pueden reproducir situaciones cotidianas. Permiten simular, de forma controlada, los requisitos conductuales que encontramos en la vida real. En un contexto terapéutico, puede ser utilizado por el neuropsicólogo para corregir en el paciente comportamientos patológicos no deseados, realizar intervenciones terapéuticas sobre Actividades de Vida Diaria que estimulen conductas adaptativas. A pesar de que las tecnologías actuales tienen potencial suficiente para aportar nuevos beneficios al proceso de rehabilitación, existe cierta reticencia a su incorporación a la clínica diaria. A día de hoy, no se ha podido demostrar que su uso aporte una mejorar significativa con respecto a otro tipo de intervención; en otras palabras, no existe evidencia científica de la eficacia del uso de entornos virtuales interactivos en rehabilitación. En este contexto, la presente Tesis Doctoral trata de abordar los aspectos que mantienen a los entornos virtuales interactivos al margen de la rutina clínica diaria. Se estudian las diferentes etapas del proceso de rehabilitación cognitiva relacionado con la integración y uso de estos entornos: diseño de las actividades, su implementación en el entorno virtual, y finalmente la ejecución por el paciente y análisis de los respectivos datos. Por tanto, los bloques en los que queda dividido el trabajo de investigación expuesto en esta memoria son: 1. Diseño de las AVD. La definición y configuración de los elementos que componen la AVD permite al terapeuta diseñar estrategias de intervención terapéutica para actuar sobre el comportamiento del paciente durante la ejecución de la actividad. En esta parte de la tesis se pretende formalizar el diseño de las AVD de tal forma que el terapeuta pueda explotar el potencial tecnológico de los entornos virtuales interactivos abstrayéndose de la complejidad implícita a la tecnología. Para hacer viable este planteamiento se propone una metodología que permita modelar la definición de las AVD, representar el conocimiento implícito en ellas, y asistir al neuropsicólogo durante el proceso de diseño de la intervención clínica. 2. Entorno virtual interactivo. El gran avance tecnológico producido durante los Ãoltimos años permite reproducir AVD interactivas en un contexto de uso clínico. El objetivo perseguido en esta parte de la Tesis es el de extraer las características potenciales de esta solución tecnológica y aplicarla a las necesidades y requisitos de la rehabilitación cognitiva. Se propone el uso de la tecnología de Vídeo Interactivo para el desarrollo de estos entornos virtuales. Para la evaluación de la misma se realiza un estudio experimental dividido en dos fases con la participación de sujetos sanos y pacientes, donde se valora su idoneidad para ser utilizado en terapias de rehabilitación cognitiva. 3. Monitorización de las AVD. El uso de estos entornos virtuales interactivos expone al paciente ante una gran cantidad de estímulos e interacciones. Este hecho requiere de instrumentos de monitorización avanzado que aporten al terapeuta información objetiva sobre el comportamiento del paciente, lo que le podría permitir por ejemplo evaluar la eficacia del tratamiento. En este apartado se propone el uso de métricas basadas en la atención visual y la interacción con el entorno para conocer datos sobre el comportamiento del paciente durante la AVD. Se desarrolla un sistema de monitorización integrado con el entorno virtual que ofrece los instrumentos necesarios para la evaluación de estas métricas para su uso clínico. La metodología propuesta ha permitido diseñar una AVD basada en la definición de intervenciones terapéuticas. Posteriormente esta AVD has sido implementada mediante la tecnología de vídeo interactivo, creando así el prototipo de un entorno virtual para ser utilizado por pacientes con déficit cognitivo. Los resultados del estudio experimental mediante el cual ha sido evaluado demuestran la robustez y usabilidad del sistema, así como su capacidad para intervenir sobre el comportamiento del paciente. El sistema monitorización que ha sido integrado con el entorno virtual aporta datos objetivos sobre el comportamiento del paciente durante la ejecución de la actividad. Los resultados obtenidos permiten contrastar las hipótesis de investigación planteadas en la Tesis Doctoral, aportando soluciones que pueden ayudar a la integración de los entornos virtuales interactivos en la rutina clínica. Esto abre una nueva vía de investigación y desarrollo que podría suponer un gran progreso y mejora en los procesos de neurorrehabilitación cognitiva en daño cerebral. ABSTRACT Brain injury (BI) refers to medical conditions that occur in the brain, altering its function. It becomes one of the main neurological disabilities in the developed society. Cognitive processes determine individual performance in Activities of Daily Living (ADL), thus, the cognitive disorders after BI result in a loss of autonomy and independence, affecting the patient’s quality of life. Cognitive rehabilitation seeks to increase patients’ autonomy and quality of life minimizing or compensating functional disorders showed by BI patients. Brain plasticity is an intrinsic property of the human nervous system whereby its structure is changed depending on experience. Neurorehabilitation pursuits a precise modulation of this intrinsic property, based on specific exercises to induce functional changes, which could result in partial or total recovery of the affected functions. The new methodologies that can be approached by applying technologies to the rehabilitation process, permit to deal with the difficulties which are out of the scope of the traditional rehabilitation. Despite this huge breakthrough, there are still weaknesses in the rehabilitation process, such as the transferring to the real life those skills reached along the therapy, and its generalization to others daily activities. Virtual environments reproduce daily situations. Behavioural requirements which are similar to those we perceive in real life, are simulated in a controlled way. In these virtual environments the therapist is allowed to interact with patients without even being present, inhibiting unsuitable behaviour patterns, stimulating correct answers throughout the simulation and enhancing stimuli with supplementary information when necessary. Despite the benefits which could be brought to the cognitive rehabilitation by applying the potential of the current technologies, there are barriers for widespread use of interactive virtual environments in clinical routine. At present, the evidence that these technologies bring a significant improvement to the cognitive therapies is limited. In other words, there is no evidence about the efficacy of using virtual environments in rehabilitation. In this context, this work aims to address those issues which keep the virtual environments out of the clinical routine. The stages of the cognitive rehabilitation process, which are related with the use and integration of these environments, are analysed: activities design, its implementation in the virtual environment, and the patient’s performance and the data analysis. Hence, the thesis is comprised of the main chapters that are listed below: 1. ADL Design.Definition and configuration of the elements which comprise the ADL allow the therapist to design intervention strategies to influence over the patient behaviour along the activity performance. This chapter aims to formalise the AVD design in order to help neuropsychologists to make use of the interactive virtual environments’ potential but isolating them from the complexity of the technology. With this purpose a new methodology is proposed as an instrument to model the ADL definition, to manage its implied knowledge and to assist the clinician along the design process of the therapeutic intervention. 2. Interactive virtual environment. Continuous advancements make the technology feasible for re-creating rehabilitation therapies based on ADL. The goal of this stage is to analyse the main features of virtual environments in order to apply them according to the cognitive rehabilitation’s requirements. The interactive video is proposed as the technology to develop virtual environments. Experimental study is carried out to assess the suitability of the interactive video to be used by cognitive rehabilitation. 3. ADL monitoring system. This kind of virtual environments bring patients in front lots of stimuli and interactions. Thus, advanced monitoring instruments are needed to provide therapist with objective information about patient’s behaviour. This thesis chapter propose the use of metrics rely on visual patients’ visual attention and their interactions with the environment. A monitoring system has been developed and integrated with the interactive video-based virtual environment, providing neuropsychologist with the instruments to evaluate the clinical force of this metrics. Therapeutic interventions-based ADL has been designed by using the proposed methodology. Interactive video technology has been used to develop the ADL, resulting in a virtual environment prototype to be use by patients who suffer a cognitive deficits. An experimental study has been performed to evaluate the virtual environment, whose overcomes show the usability and solidity of the system, and also its capacity to have influence over patient’s behaviour. The monitoring system, which has been embedded in the virtual environment, provides objective information about patients’ behaviour along their activity performance. Research hypothesis of the Thesis are proven by the obtained results. They could help to incorporate the interactive virtual environments in the clinical routine. This may be a significant step forward to enhance the cognitive neurorehabilitation processes in brain injury.

Role of brain allopregnanolone in the plasticity of γ-aminobutyric acid type A receptor in rat brain during pregnancy and after delivery

The relation between changes in brain and plasma concentrations of neurosteroids and the function and structure of γ-aminobutyric acid type A (GABAA) receptors in the brain during pregnancy and after delivery was investigated in rats. In contrast with plasma, where all steroids increased in parallel, the kinetics of changes in the cerebrocortical concentrations of progesterone, allopregnanolone (AP), and allotetrahydrodeoxycorticosterone (THDOC) diverged during pregnancy. Progesterone was already maximally increased between days 10 and 15, whereas AP and allotetrahydrodeoxycorticosterone peaked around day 19. The stimulatory effect of muscimol on 36Cl− uptake by cerebrocortical membrane vesicles was decreased on days 15 and 19 of pregnancy and increased 2 days after delivery. Moreover, the expression in cerebral cortex and hippocampus of the mRNA encoding for γ2L GABAA receptor subunit decreased during pregnancy and had returned to control values 2 days after delivery. Also α1,α2, α3, α4, β1, β2, β3, and γ2S mRNAs were measured and failed to change during pregnancy. Subchronic administration of finasteride, a 5α-reductase inhibitor, to pregnant rats reduced the concentrations of AP more in brain than in plasma as well as prevented the decreases in both the stimulatory effect of muscimol on 36Cl− uptake and the decrease of γ2L mRNA observed during pregnancy. These results indicate that the plasticity of GABAA receptors during pregnancy and after delivery is functionally related to fluctuations in endogenous brain concentrations of AP whose rate of synthesis/metabolism appears to differ in the brain, compared with plasma, in pregnant rats.

A synaptic basis for memory storage in the cerebral cortex

A cardinal feature of neurons in the cerebral cortex is stimulus selectivity, and experience-dependent shifts in selectivity are a common correlate of memory formation. We have used a theoretical “learning rule,” devised to account for experience-dependent shifts in neuronal selectivity, to guide experiments on the elementary mechanisms of synaptic plasticity in hippocampus and neocortex. These experiments reveal that many synapses in hippocampus and neocortex are bidirectionally modifiable, that the modifications persist long enough to contribute to long-term memory storage, and that key variables governing the sign of synaptic plasticity are the amount of NMDA receptor activation and the recent history of cortical activity.

Rapidly induced auditory plasticity: The ventriloquism aftereffect

Cortical representational plasticity has been well documented after peripheral and central injuries or improvements in perceptual and motor abilities. This has led to inferences that the changes in cortical representations parallel and account for the improvement in performance during the period of skill acquisition. There have also been several examples of rapidly induced changes in cortical neuronal response properties, for example, by intracortical microstimulation or by classical conditioning paradigms. This report describes similar rapidly induced changes in a cortically mediated perception in human subjects, the ventriloquism aftereffect, which presumably reflects a corresponding change in the cortical representation of acoustic space. The ventriloquism aftereffect describes an enduring shift in the perception of the spatial location of acoustic stimuli after a period of exposure of spatially disparate and simultaneously presented acoustic and visual stimuli. Exposure of a mismatch of 8° for 20–30 min is sufficient to shift the perception of acoustic space by approximately the same amount across subjects and acoustic frequencies. Given that the cerebral cortex is necessary for the perception of acoustic space, it is likely that the ventriloquism aftereffect reflects a change in the cortical representation of acoustic space. Comparisons between the responses of single cortical neurons in the behaving macaque monkey and the stimulus parameters that give rise to the ventriloquism aftereffect suggest that the changes in the cortical representation of acoustic space may begin as early as the primary auditory cortex.