Papel de las ráfagas de potenciales de acción en la detección de estímulos visuales en primates : regulación por la vía córtico-talámica

[Resumen] Actualmente, el Núcleo Geniculado Lateral (NGL) es considerado un elemento clave en el procesamiento de la visión. Dada la inmensa cantidad de información que fluye a través de la vía, es preciso seleccionar aquella más relevante previamente a su llegada a la corteza, dónde será procesada en detalle. Mediante la respuesta en ráfagas de bajo umbral, el NGL es capaz de detectar estímulos novedosos en el campo visual y enviar información sobre ellos a la corteza, la cual modula la actividad talámica a través de las aferencias córtico-talámicas (bucle tálamo-córtico-talámico). Mediante la resolución de dos tareas visuales, se demostró que las ráfagas se generan inmediatamente después de la aparición del estímulo visual, y que su respuesta varía en función del mismo: ante estímulos novedosos, el número de ráfagas es superior, y sus características intrínsecas diferentes (mayor duración y número de espigas). La aplicación de Estimulación magnética transcraneal (EMT) sobre la corteza visual primaria, mostró una modulación de las aferencias córticofugales sobre el NGL, disminuyendo la actividad talámica. Por tanto, el tálamo participa activamente en la transmisión y análisis inicial de la información visual, aunque existe un control cortical sobre la actividad del NGL a través de la vía córtico-talámica.[Resumo] Actualmente, o Núcleo Geniculado Lateral (NGL) é considerado un elemento clave no procesamento da visión. Dada a inmensa cantidade de información que flúe a través desta vía, é preciso seleccionar aquela máis relevante previamente á súa chegada á codia, onde será procesada en detalle. Mediante a resposta en trens de potenciais de baixo limiar, o NGL é capaz de detectar estímulos novidosos no campo visual e enviar información sobre eles á corteza, a cal modula a actividade talámica a través das aferencias córtico-talámicas (bucle tálamo-córtico-talámico). Mediante a resolución de dúas tarefas visuais, demostrouse que os trens de potenciais de baixo limiar se xeran inmediatamente despois da aparición do estímulo visual, e que a súa resposta varía en función deste: ante estímulos novidosos, o número de potenciais é superior, e as súas características intrínsecas diferentes (maior duración e número de espigas). A aplicación de Estimulación magnética transcraneal (EMT) sobre a corteza visual primaria, mostrou unha modulación das aferencias córticofugais sobre o NGL, disminuíndo a actividade talámica. Polo tanto, o tálamo participa activamente na trasmisión e análise inicial da información visual, aínda que existe un control da codia sobre a actividade do NGL a través da vía córtico-talámica.[Abstract] Currently, the lateral geniculate nucleus (LGN) is considered a key element in the vision processing. Given the vast amount of information that flows through this path, it is necessary to select the most relevant one prior to their arrival to the cortex, where they will be processed in detail. By replying in bursts of low threshold, the NGL is able to detect novel stimuli in the visual field and send information about them to the cortex, which modulates thalamic activity via corticothalamic feedback (thalamo-cortical-thalamic circuit). The resolution of two visual tasks, showed that the bursts are generated immediately after the onset of the visual stimulus, and that their response varies with the same: to novel stimuli, the number of bursts is higher, and their intrinsic characteristics are different (longer duration and number of spikes). The application of transcranial magnetic stimulation (TMS) over the primary visual cortex, showed a modulation of cortical afferents on NGL, decreasing thalamic activity. Therefore, the thalamus is actively involved in the transmission and initial analysis of visual information, although a cortical control of the activity of NGL by corticothalamic feedback exist

Bursting thalamic responses in awake monkey contribute to visual detection and are modulated by corticofugal feedback

[Abstract] The lateral geniculate nucleus is the gateway for visual information en route to the visual cortex. Neural activity is characterized by the existence of two firing modes: burst and tonic. Originally associated with sleep, bursts have now been postulated to be a part of the normal visual response, structured to increase the probability of cortical activation, able to act as a “wake-up” call to the cortex. We investigated a potential role for burst in the detection of novel stimuli by recording neuronal activity in the lateral geniculate nucleus (LGN) of behaving monkeys during a visual detection task. Our results show that bursts are often the neuron’s first response, and are more numerous in the response to attended target stimuli than to unattended distractor stimuli. Bursts are indicators of the task novelty, as repetition decreased bursting. Because the primary visual cortex is the major modulatory input to the LGN, we compared the results obtained in control conditions with those observed when cortical activity was reduced by TMS. This cortical deactivation reduced visual response related bursting by 90%. These results highlight a novel role for the thalamus, able to code higher order image attributes as important as novelty early in the thalamo-cortical conversation

Can pathway-specific LFPs be obtained in cytoarchitectonically complex structures?

[Abstract] Deciphering how the brain encodes the continuous flow of information contained in natural stimuli requires understanding the spontaneous activity of functional assemblies in multiple neuronal populations. A promising integrative approach that combines multisite recordings of local field potentials (LFP) with an independent component analysis (ICA) enables continuous readouts of population specific activities of functionally different neuron groups to be obtained. We previously used this technique successfully in the hippocampus, a single-layer neuronal structure. Here we provide numerical evidence that the cytoarchitectonic complexity of other brain structures does not compromise the value of the ICA-separated LFP components, given that spatial sampling of LFP is representative. The spatial distribution of an LFP component may be quite complex due to folded and multilayered structure of the neuronal aggregate. Nevertheless, the time course of each LFP component is still a reliable postsynaptic convolution of spikes fired by a homogeneous afferent population. This claim is supported by preliminary experimental data obtained in the lateral geniculate nucleus of the awake monkey.Ministerio de Ciencia e Innovación; BFU2010-19192Ministerio de Ciencia e Innovación; BFU2009-08169Ministerio de Ciencia e Innovación; FIS2010-2005

Slow-wave activity in the S1HL cortex is contributed by different layer-specific field potential sources during development

Spontaneous correlated activity in cortical columns is criticalfor postnatal circuit refinement.We used spatial discriminationtechniques to explore the late maturation of synaptic pathways through the laminar distribution of the field potential (FP) generators underlying spontaneous and evoked activities ofthe S1HL cortex in juvenile (P14 –P16) and adult anesthetized rats. Juveniles exhibit an intermittent FP pattern resembling Up/Down states in adults, but with much reduced power and different laminar distribution. Whereas FPs in active periods are dominated by a layer VI generator in juveniles, in adults a developing multipart generatortakes over, displaying current sinks in middle layers (III–V). The blockade of excitatory transmission in upper and middle layers of adults recovered the juvenile-like FP profiles. In additiontothe layer VI generator, a gamma-specific generator in supragranular layers wasthe same in both age groups.While searching for dynamical coupling among generators in juveniles we found significant cross-correlation in one-half of the tested pairs, whereas excessive coherence hindered their efficient separation in adults. Also, potentials evoked by tactile and electrical stimuli showed different short-latency dipoles between the two age groups, and the juveniles lacked the characteristic long latency UP state currents in middle layers. In addition, the mean firing rate of neurons was lower in juveniles. Thus, cortical FPs originate from different intracolumnar segments as they become active postnatally. We suggest that although some cortical segments are active early postnatally, a functional sensory-motor control relies on a delayed maturation and network integration of synaptic connections in middle layers

Can pathway-specific LFPs be obtained in cytoarchitectonically complex structures?

Deciphering how the brain encodes the continuous flow of information contained in natural stimuli requires understanding the spontaneous activity of functional assemblies in multiple neuronal populations. A promising integrative approach that combines multisite recordings of local field potentials (LFP) with an independent component analysis (ICA) enables continuous readouts of population specific activities of functionally different neuron groups to be obtained. We previously used this technique successfully in the hippocampus, a single-layer neuronal structure. Here we provide numerical evidence that the cytoarchitectonic complexity of other brain structures does not compromise the value of the ICA-separated LFP components, given that spatial sampling of LFP is representative. The spatial distribution of an LFP component may be quite complex due to folded and multilayered structure of the neuronal aggregate. Nevertheless, the time course of each LFP component is still a reliable postsynaptic convolution of spikes fired by a homogeneous afferent population. This claim is supported by preliminary experimental data obtained in the lateral geniculate nucleus of the awake monkey.This work was supported by Grants BFU2010-19192, BFU2009-08169 and FIS2010-20054 from the former Spanish Ministry of Science and Innovation.Peer reviewedPeer Reviewe

Local and Volume-Conducted Contributions to Cortical Field Potentials

Brain field potentials (FPs) can reach far from their sources, making difficult to know which waves come from where. We show that modern algorithms efficiently segregate the local and remote contributions to cortical FPs by recovering the generator-specific spatial voltage profiles. We investigated experimentally and numerically the local and remote origin of FPs in different cortical areas in anesthetized rats. All cortices examined show significant state, layer, and region dependent contribution of remote activity, while the voltage profiles help identify their subcortical or remote cortical origin. Co-activation of different cortical modules can be discriminated by the distinctive spatial features of the corresponding profiles. All frequency bands contain remote activity, thus influencing the FP time course, in cases drastically. The reach of different FP patterns is boosted by spatial coherence and curved geometry of the sources. For instance, slow cortical oscillations reached the entire brain, while hippocampal theta reached only some portions of the cortex. In anterior cortices, most alpha oscillations have a remote origin, while in the visual cortex the remote theta and gamma even surpass the local contribution. The quantitative approach to local and distant FP contributions helps to refine functional connectivity among cortical regions, and their relation to behavior.We thank S. Hernández-Recio and V.J. López-Madrona for continuous discussion, and M. Sefton at BiomedRed for editorial support. The authors acknowledge the support of the Ministry of Economy and Competitiveness of Spain (Grants BFU2013-41533R and SAF2016-80100-R to O.H., FIS2017-82900-P to V.A.M., and BES-2014-071052 to D.T)

Further support of conspecificity of oak and mango powdery mildew and first report of erysiphe quercicola and erysiphe alphitoides on mango in mainland Europe

Mango leaves and inflorescences infected by powdery mildew in southern Spain were analyzed using multigene sequencing (ITS + 4 single-copy coding genes) to identify the causal agent. Erysiphe quercicola was detected in 97% out of 140 samples, collected in six different orchards in the Malaga region. Among these, a small proportion also yielded E. alphitoides (8% of all samples) and E. alphitoides was found alone in 3% of samples. A phylogenetic approach was completed by cross inoculations between oak and mango, which led to typical symptoms, supporting the conspecificity of oak and mango powdery mildews. To our knowledge, this is the first report of E. quercicola and E. alphitoides causing powdery mildew on mango trees in mainland Spain, and thus mainland Europe, based on unequivocal phylogenetic and biological evidence. Our study thus confirmed the broad host range of both E. quercicola and E. alphitoides. These results have practical implications in terms of the demonstrated ability for host range expansion in powdery mildews. They also open interesting prospects to the elucidation of molecular mechanisms underlying the ability to infect single versus multiple and unrelated host plants since these two closely related powdery mildew species belong to a small clade with both generalist and specialist powdery mildews