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Cortical control of striatal activity
No full textEl estriado es un núcleo clave dentro del bucle que comprende a la corteza cerebral, a los ganglios de la base y al tálamo. Recibe una masiva inervación, proveniente de casi todas las regiones corticales y del tálamo, que exhibe una delicada organización topográfica. El fruto del procesamiento intra-estriatal es luego transferido al resto de las estructuras que comprenden los ganglios de la base. El potencial de membrana de las neuronas estriatales de proyección (NEMs) registradas in vivo alterna entre dos estados subumbrales preferidos, un estado DOWN (eDOWN) muy polarizado y un estado UP (eUP) cercano al umbral de disparo de potenciales de acción. Dado que las NEMs sólo disparan potenciales de acción cuando alcanzan los eUP, estos eventos son vistos como una ventana de oportunidad para la transferencia de información a través del estriado. La transición al eUP de las NEMs depende de la entrada cortical, y además la oscilación periódica entre estados está dirigida por una actividad lenta sincronizada entre poblaciones de neuronas corticales, típica del sueño lento y de la anestesia, como lo delata la alta correlación entre el potencial de membrana de las NEMs y el electrocorticograma (ECoG). En el presente trabajo se pretende investigar con profundidad el control que la actividad cortical ejerce sobre el potencial de membrana de las NEMs. En primer lugar, se estudió de qué manera impactan en el potencial de membrana de las NEMs las propiedades dinámicas de la actividad de los circuitos corticales, como ser las transiciones entre estados sincronizados y desincronizados, repentinas perturbaciones de la fase de oscilación o epidosios de actividad sincrónica a frecuencias altas. Finalmente se analizó en qué medida la fina organización anatómica del sistema córtico-estriatal se expresa en las modulaciones del potencial de membrana de las NEMs. De manera general, los resultados de este trabajo establecen un estricto control cortical sobre las modulaciones de baja frecuencia del potencial de membrana de las NEMs. Más precisamente, los eUP están precisamente alineados en los dominios temporal y espacial con la actividad de ensambles de neuronas corticales. De esta manera, los eUP pueden considerarse representaciones subumbrales de la activación de ensambles de neuronas corticales. Entonces, el disparo de un potencial de acción por una NEM reflejaría un proceso de extracción de información relevante embebida en la señal general originada en ese ensamble cortical.The striatum is a key structure of the cortico-basal ganglia-thalamic loop. It receives massive inputs coming form almost the whole cerebral cortex and thalamus, and sends information back to the cortex via other basal ganglia nuclei and thalamus. The membrane potential of striatal projection neurons (MSNs) alternates between two preferred values, a polarized DOWN state and a depolarized UP state during which MSNs remain close to action potential threshold. Because MSNs can only fire action potentials during UP states, the UP state has been perceived as an enabling event that allows the translation of incoming information into action potential firing. It has long been known that transitions to the UP state are induced by cortical input. More recently, it has been reported that the rhythmic nature of MSNs alternation between UP and DOWN states is driven by oscillatory activity in cortical ensembles, as is evident in the high degree of correlation between striatal membrane potential fluctuations and slow wave activity recorded in the electrocorticogram. In the present work we report the fine control exerted by cortical activity on the membrane potential of MSNs. First, we characterized the impact of dynamically changing patterns of cortical activity, like transitions between synchronized and desynchronized activity states, perturbations of the phase of ongoing cortical oscillations and episodes of high frequency cortical oscillatory synchronization, on the MSN membrane potential. Second, we studied how the spatial organization of corticostriatal connections is represented in the subthreshold behavior of MSNs located in different striatal territories. The results of our work demonstrate that cortical activity exerts a strict control of the low frequency modulations of the MSN membrane potential. More specifically, the MSN UP states are precisely aligned in the time and space domains to episodes of persistent activity in cortical ensembles. This way, MSN UP states can be considered subthreshold representations of an active state in a cortical ensemble. Therefore, action potential firing by a MSN may reflect the extraction of relevant information embedded within a more general signal arising from this cortical ensemble.Fil: Kasanetz, Fernando. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina
Increased burst coding in deep layers of the ventral anterior cingulate cortex during neuropathic pain
Full text linkNeuropathic pain induces changes in neuronal excitability and synaptic connectivity in deep layers of the anterior cingulate cortex (ACC) that play a central role in the sensory, emotional and affective consequences of the disease. However, how this impacts ACC in vivo activity is not completely understood. Using a mouse model, we found that neuropathic pain caused an increase in ACC in vivo activity, as measured by the indirect activity marker c-Fos and juxtacellular electrophysiological recordings. The enhanced firing rate of ACC neurons in lesioned animals was based on a change in the firing pattern towards bursting activity. Despite the proportion of ACC neurons recruited by noxious stimuli was unchanged during neuropathic pain, responses to noxious stimuli were characterized by increased bursting. Thus, this change in coding pattern may have important implications for the processing of nociceptive information in the ACC and could be of great interest to guide the search for new treatment strategies for chronic pain
Plasticity of Cortico-striatal Neurons of the Caudal Anterior Cingulate Cortex During Experimental Neuropathic Pain
No full textMaladaptive neuronal plasticity is a main mechanism for the development and maintenance of pathological pain. Affective, motivational and cognitive deficits that are comorbid with pain involve cellular and synaptic modifications in the anterior cingulate cortex (ACC), a major brain mediator of pain perception. Here we use a model of neuropathic pain (NP) in male mice and ex-vivo electrophysiology to investigate whether layer 5 caudal ACC (cACC) neurons projecting to the dorsomedial striatum (DMS), a critical region for motivational regulation of behavior, are involved in aberrant neuronal plasticity. We found that while the intrinsic excitability of cortico-striatal cACC neurons (cACC-CS) was preserved in NP animals, excitatory postsynaptic potentials (EPSP) induced after stimulation of distal inputs were enlarged. The highest synaptic responses were evident both after single stimuli and in each of the EPSP that compose responses to trains of stimuli, and were accompanied by increased synaptically-driven action potentials. EPSP temporal summation was intact in ACC-CS neurons from NP mice, suggesting that the plastic changes were not due to alterations in dendritic integration but rather through synaptic mechanisms. These results demonstrate for the first time that NP affects cACC neurons that project to the DMS and reinforce the notion that maladaptive plasticity of the cortico-striatal pathway may be a key factor in sustaining pathological pain.Fil: Trujillo, María Jesús. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Ilarraz, Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; ArgentinaFil: Kasanetz, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Fisiología y Biofísica Bernardo Houssay. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Fisiología y Biofísica Bernardo Houssay; Argentin
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Brain oscillations, medium spiny neurons, and dopamine
Full text link1. The striatum is part of a multisynaptic loop involved in translating higher order cognitive activity into action. The main striatal computational unit is the medium spiny neuron, which integrates inputs arriving from widely distributed cortical neurons and provides the sole striatal output. 2. The membrane potential of medium spiny neurons’ displays shifts between a very negative resting state (down state) and depolarizing plateaus (up states) which are driven by the excitatory cortical inputs. 3. Because striatal spiny neurons fire action potentials only during the up state, these plateau depolarizations are perceived as enabling events that allow information processing through cerebral cortex – basal ganglia circuits. In vivo intracellular recording techniques allow to investigate simultaneously the subthreshold behavior of the medium spiny neuron membrane potential (which is a “reading” of distributed patterns of cortical activity) and medium spiny neuron firing (which is an index of striatal output). 4. Recent studies combining intracellular recordings of striatal neurons with field potential recordings of the cerebral cortex illustrate how the analysis of the input–output transformations performed by medium spiny neurons may help to unveil some aspects of information processing in cerebral cortex – basal ganglia circuits, and to understand the origin of the clinical manifestations of Parkinson’s disease and other neurologic and neuropsychiatric disorders that result from alterations in dopamine-dependent information processing in the cerebral cortex – basal ganglia circuits.Fil: Murer, Mario Gustavo. Universidad de Buenos Aires. Facultad de Medicina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Tseng, Kuei Y.. Universidad de Buenos Aires. Facultad de Medicina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Kasanetz, Fernando. Universidad de Buenos Aires. Facultad de Medicina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Belluscio, Mariano Andres. Universidad de Buenos Aires. Facultad de Medicina; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay; ArgentinaFil: Riquelme, Luis Alberto. Universidad de Buenos Aires. Facultad de Medicina; Argentin
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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