Local interactions between steady-state visually evoked potentials at nearby flickering frequencies

Steady-state visually evoked potentials (SSVEP) are widely used to index top-down cognitive processing in human electroencephalogram (EEG) studies. Typically, two stimuli flickering at different temporal frequencies (TFs) are presented, each producing a distinct response in the EEG at its flicker frequency. However, how SSVEP responses in EEG are modulated in the presence of a competing flickering stimulus just due to sensory interactions is not well understood. We have previously shown in local field potentials (LFP) recorded from awake monkeys that when two overlapping full screen gratings are counter-phased at different TFs, there is an asymmetric SSVEP response suppression, with greater suppression from lower TFs, which further depends on the relative orientations of the gratings (stronger suppression and asymmetry for parallel compared to orthogonal gratings). Here, we first confirmed these effects in both male and female human EEG recordings. Then, we mapped the response suppression of one stimulus (target) by a competing stimulus (mask) over a much wider range than the previous study. Surprisingly, we found that the suppression was not stronger at low frequencies in general, but systematically varied depending on the target TF, indicating local interactions between the two competing stimuli. These results were confirmed in both human EEG and monkey LFP and electrocorticogram (ECoG) data. Our results show that sensory interactions between multiple SSVEPs are more complex than shown previously and are influenced by both local and global factors, underscoring the need to cautiously interpret the results of studies involving SSVEP paradigms.

Contribution of linear and nonlinear mechanisms to predictive motion estimation

Successful behavior relies on the ability to use information obtained from past experience to predict what is likely to occur in the future. A salient example of predictive encoding comes from the vertebrate retina, where neural circuits encode information that can be used to estimate the trajectory of a moving object. Predictive computations should be a general property of sensory systems, but the features needed to identify these computations across neural systems are not well understood. Here, we identify several properties of predictive computations in the primate retina that likely generalize across sensory systems. These features include calculating the derivative of incoming signals, sparse signal integration, and delayed response suppression. These findings provide a deeper understanding of how the brain carries out predictive computations and identify features that can be used to recognize these computations throughout the brain.

5-HT1A Receptors Alter Temporal Responses to Broadband Vocalizations in the Mouse Inferior Colliculus Through Response Suppression

Neuromodulatory systems may provide information on social context to auditory brain regions, but relatively few studies have assessed the effects of neuromodulation on auditory responses to acoustic social signals. To address this issue, we measured the influence of the serotonergic system on the responses of neurons in a mouse auditory midbrain nucleus, the inferior colliculus (IC), to vocal signals. Broadband vocalizations (BBVs) are human-audible signals produced by mice in distress as well as by female mice in opposite-sex interactions. The production of BBVs is context-dependent in that they are produced both at early stages of interactions as females physically reject males and at later stages as males mount females. Serotonin in the IC of males corresponds to these events, and is elevated more in males that experience less female rejection. We measured the responses of single IC neurons to five recorded examples of BBVs in anesthetized mice. We then locally activated the 5-HT1A receptor through iontophoretic application of 8-OH-DPAT. IC neurons showed little selectivity for different BBVs, but spike trains were characterized by local regions of high spike probability, which we called “response features.” Response features varied across neurons and also across calls for individual neurons, ranging from 1 to 7 response features for responses of single neurons to single calls. 8-OH-DPAT suppressed spikes and also reduced the numbers of response features. The weakest response features were the most likely to disappear, suggestive of an “iceberg”-like effect in which activation of the 5-HT1A receptor suppressed weakly suprathreshold response features below the spiking threshold. Because serotonin in the IC is more likely to be elevated for mounting-associated BBVs than for rejection-associated BBVs, these effects of the 5-HT1A receptor could contribute to the differential auditory processing of BBVs in different behavioral subcontexts.

Corticostriatal suppression of appetitive Pavlovian conditioned responding

ABSTRACTThe capacity to suppress learned responses is essential for animals to adapt in dynamic environments. Extinction is a process by which animals learn to suppress conditioned responding when an expected outcome is omitted. The infralimbic cortex (IL) to nucleus accumbens shell (NAcS) neural circuit is implicated in suppressing conditioned responding after extinction, especially in the context of operant cocaine-seeking behaviour. However, the role of the IL-to-NAcS neural circuit in the extinction of responding to appetitive Pavlovian cues is unknown and the psychological mechanisms involved in response suppression following extinction are unclear. We trained rats to associate a 10 s auditory conditioned stimulus (CS; 14 trials per session) with a sucrose unconditioned stimulus (US; 0.2 mL per CS) in a specific context and then, following extinction in a different context, precipitated a renewal of CS responding by presenting the CS alone in the original Pavlovian conditioning context. Unilateral, optogenetic stimulation of the IL-to-NAcS circuit selectively during CS trials suppressed renewal. In a separate experiment, IL-to-NAcS stimulation suppressed CS responding regardless of prior extinction and impaired extinction retrieval. Finally, IL-to-NAcS stimulation during the CS did not suppress the acquisition of Pavlovian conditioning but was required for the subsequent expression of CS responding. These results are consistent with multiple studies showing that the IL-to-NAcS neural circuit is involved in the suppression of operant cocaine-seeking, extending these findings to appetitive Pavlovian cues. The suppression of appetitive Pavlovian responding following IL-to-NAcS circuit stimulation does not, however, appear to require an extinction-dependent process.SIGNIFICANCE STATEMENTExtinction is a form of inhibitory learning through which animals learn to suppress conditioned responding in the face of non-reinforcement. We investigated the role of infralimbic (IL) cortex inputs to the nucleus accumbens shell (NAcS) in the extinction of responding to appetitive Pavlovian cues and the psychological mechanisms involved in response suppression following extinction. Using in vivo optogenetics, we found that stimulating the IL-to-NAcS neural circuit suppressed context-induced renewal of conditioned responding after extinction. In a separate experiment, stimulating the IL-to-NAcS circuit suppressed conditioned responding in an extinction-independent manner. These findings can be leveraged by future research aimed at understanding how corticostriatal circuits contribute to behavioural flexibility and mental disorders that involve the suppression of learned behaviours.

PERAN SISTEM IMUN TERHADAP TERJADINYA PNEUMONIA TERKAIT STROKE

THE ROLE OF IMMUNE SYSTEM ON THE OCCURRENCE OF STROKE- ASSOCIATED PNEUMONIAABSTRACTStroke associated pneumonia (SAP) is one of the medical complication which associated with high mortality rate. Several studies conclude two factors involve significantly in pathophysiology of SAP, one of which is immunodepression state. Immunodepression occurs by 3 main pathways, symphathetic system activation, parasymphathetic system activation, and HPA (hypothalamus-pituitary-adrenal) axis activation. Simultaneously, they induce proinflammatory response suppression and immune cells alternation, which lead to an infection like pneumonia. Therefore, establishing an effective immunomodulation therapy could be one of the main focus in comprehensive stroke management’s future studies.Keywords: Immunodepression, stroke-associated pneumoniaABSTRAKKomplikasi pneumonia terkait stroke menjadi salah satu faktor penyebab mortalitas tertinggi. Studi-studi menyimpulkan bahwa ada dua faktor yang berperan pada patofisiologi pneumonia, salah satunya adalah imunodepresi terkait stroke. Imunodepresi terjadi melalui 3 jaras, yaitu aktivitas simpatis, aktivitas parasimpatis, dan aksis hipotalamus- pituitari-adrenal. Secara simultan, ketiganya menekan respons proinflamasi dan mengubah sel-sel imun sehingga pneumonia dapat mudah terjadi. Pembuatan terapi imunomodulasi yang dapat mencegah infeksi namun tidak memperburuk kondisi iskemia dapat menjadi fokus studi penanganan stroke komprehensif di masa datang.Kata kunci: Imunodepresi, pneumonia terkait stroke