Activity Patterns In Response Research Articles

Spinal and sensory neuromodulation of spinal neuronal networks in humans

The present experiments were designed to gain additionally insight into how the spinal networks process direct spinal stimulation and peripheral sensory inputs to control posture and locomotor movements. We have developed a plantar pressure stimulation system that can deliver naturalistic postural and gait-related patterns of pressure to the soles of the feet to simulate standing and walking, thereby activating and/or modulating the automated spinal circuitry responsible for standing and locomotion. In the present study we compare the patterns of activation among selected motor pools and the kinematic consequences of these activation patterns in response to patterned heel-to-toe mechanical stimulation of the soles of the feet, and/or transcutaneous electrical spinal stimulation, for postural and locomotion regulation. The studies were performed in healthy individuals (n = 12) as well as in subjects (n = 2) with motor complete spinal cord injury. We found that plantar pressure stimulation and/or spinal stimulation can effectively facilitate locomotor output in the subjects placed with their legs in gravity neutral position. We have shown synergistic effects of combining sensory and spinal cord stimulation, suggesting that the two networks are different, but complementary. Also we provide evidence that plantar stimulation could serve as a novel neuro-rehabilitation tool alone or as part of a multi-modal approach to restoring motor function after complete paralysis due to SCI.

S182 Introduction to neuroplasticity and its application in neurorehabilitation

Neuroplasticity is defined as the property of the brain to adapt to environmental pressures, experiences, and challenges including brain damage. It is a lifelong capacity of the brain to change and rewire itself in response to the stimulation of learning and experience. Based upon this input, several conclusions were recently appearing on the surface. First, there appears to be tremendous latent plasticity even in the adult brain. Second, the brain should be thought of, not as a hierarchy of organized autonomous modules, each of which delivers its output to the next level, but as a set of complex interacting networks that are in a state of dynamic equilibrium with the brain’s environment. Both principles can be potentially exploited in a clinical context to facilitate recovery of function. Promoting neuroplasticity in an enriched environment will eventually result in dendritic branching, synapses, glial processes, brain weight, and cortical thickness. Currently, it is believed that activity drives reorganization of cerebral networks, which is paralleled by functional improvements in cases of acquired brain injuries that are usually in need of intense rehabilitation programs. Numeral studies have demonstrated reorganization of brain activity pattern in response to intense training of motor and cognitive tasks and imagination of movements. For instance, promising results were shown using feedback techniques, like mirror visual feedback (MVF) improving chronic regional pain syndrome and hemiparesis following stroke. Evidence based therapeutic interventions using neuroplasticity as its base include aerobic exercise, bilateral arm training, constraint induced movement therapy,body weight supported treadmill training, mirror therapy, action observation, motor imagery/mental practice, functional electrical stimulation and music therapy.Promising therapies that may enhance training-induced cognitive and motor learning, such as brain stimulation and neuropharmacological interventions, were also identified, along with arousing questions involving more updated ways to use neuroplasticity in improving quality of life in cases of human disability.

Platelet Toll-like receptor (TLR) expression and TLR-mediated platelet activation in acute myocardial infarction

Both platelets and Toll-like receptors (TLRs) contribute to acute myocardial infarction (AMI). Platelet activation can occur post-AMI and despite treatment with anti-platelet therapy. TLRs may represent an alternative platelet activation pathway, although the role of platelet-TLRs in AMI is poorly characterized. The aim of this study was to examine platelet-TLR expression and TLR-mediated platelet activation in healthy and AMI subjects. Here, we report that platelets from AMI patients exhibit upregulation of some, but not other, TLRs. When examined by western blotting, platelet-TLR1 and TLR4 were significantly upregulated in AMI subjects compared to healthy subjects (both p<0.05). Platelet-TLR2 was slightly, but non-significantly, upregulated in AMI patients and platelet-TLR6 expression did not change across cohorts. Platelets from both healthy and AMI subjects exhibited distinct activation patterns in response to various TLR agonists (0.1–100μg/mL), as determined by flow cytometry. Healthy and AMI platelets became dose-dependently and directly activated in response to Pam3CSK4, a TLR2/1 agonist, but were directly potently activated only in response to the highest dose (100μg) of lipopolysaccharide (LPS), a TLR4 agonist. Platelet activation in response to both of these agonists was similar across cohorts, despite treatment with anti-platelet therapy in the AMI cohort. At all doses used in this study, platelets were unable to become directly activated by FSL-1, a TLR2/6 agonist. We conclude that the platelet-TLR2/1 activation pathway is functional post-AMI and despite treatment with anti-platelet therapy. The platelet-TLR4 pathway appears to be less likely, and the platelet-TLR2/6 pathways unlikely, to contribute to post-AMI platelet activation.

Temporal Processing in the Visual Cortex of the Awake and Anesthetized Rat

The activity pattern and temporal dynamics within and between neuron ensembles are essential features of information processing and believed to be profoundly affected by anesthesia. Much of our general understanding of sensory information processing, including computational models aimed at mathematically simulating sensory information processing, rely on parameters derived from recordings conducted on animals under anesthesia. Due to the high variety of neuronal subtypes in the brain, population-based estimates of the impact of anesthesia may conceal unit- or ensemble-specific effects of the transition between states. Using chronically implanted tetrodes into primary visual cortex (V1) of rats, we conducted extracellular recordings of single units and followed the same cell ensembles in the awake and anesthetized states. We found that the transition from wakefulness to anesthesia involves unpredictable changes in temporal response characteristics. The latency of single-unit responses to visual stimulation was delayed in anesthesia, with large individual variations between units. Pair-wise correlations between units increased under anesthesia, indicating more synchronized activity. Further, the units within an ensemble show reproducible temporal activity patterns in response to visual stimuli that is changed between states, suggesting state-dependent sequences of activity. The current dataset, with recordings from the same neural ensembles across states, is well suited for validating and testing computational network models. This can lead to testable predictions, bring a deeper understanding of the experimental findings and improve models of neural information processing. Here, we exemplify such a workflow using a Brunel network model.

Neuronal substrates underlying stress resilience and susceptibility in rats.

BackgroundStress and stressful life events have repeatedly been shown as causally related to depression. The Chronic Mild Stress rat model is a valid model of stress-induced depression. Like humans, rats display great heterogeneity in their response to stress and adversity. Hence some individuals are stress-sensitive and prone to develop depression-like behaviour in response to modest stressors, while others are stress-resilient and remain essentially symptom free.ObjectivesCompared to the large body of research, which describes stress-induced maladaptive neurobiological changes, relatively little attention has been devoted to understand resiliency to stress. The aim of the present study was to identify changes in neuronal activity, associated with stress-resilient and stress-susceptible chronic mild stress endophenotypes, by examining c-Fos expression in 13 different brain areas. Changes in c-Fos expression have been reported as associated to stressful conditions.MethodsStress-induced modulation of neuronal activation patterns in response to the chronic mild stress paradigm was mapped using the immediate early gene expression c-Fos as a marker. Quantification of the c-Fos-like immunoreactivity responses was done by semi-automated profile counting procedures and design-based stereology.ResultsExposure to chronic mild stress significantly altered c-Fos expression in a total of 6 out of 13 investigated areas. Chronic mild stress was found to suppress the c-Fos response within the magnocellular ventral lateral geniculate nucleus of both stress subgroups. In the the lateral and ventral orbital cortices of stress-resilient rats, the c-Fos like immunoreactivity response was also repressed by stress exposure. On the contrary the c-Fos response within the amygdala, medial habenula, and infralimbic cortex was increased selectively for the stress-susceptible rats.ConclusionsThe study was initiated to characterize neuronal substrates associated with stress-coping mechanisms. Six areas, all of which represents limbic structures, were found to be sensitive to stress exposure. The effects within these areas associate to the hedonic status of the rats. Hence, these areas might be associated to stress-coping mechanisms underlying the chronic mild stress induced segregation into stress-susceptible and stress-resilient endophenotypes.

Comparative functional neuroanatomy between implicit and explicit memory tasks under negative emotional condition in schizophrenia

PurposeTo evaluate the brain activation patterns in response to negative emotion during implicit and explicit memory in patients with schizophrenia. Material and methodsFourteen patients with schizophrenia and 14 healthy controls were included in this study. The 3.0T fMRI was obtained while the subjects performed the implicit and explicit retrievals with unpleasant words. ResultsThe different predominant brain activation areas were observed during the implicit retrieval and explicit with unpleasant words. ConclusionThe differential neural mechanisms between implicit and explicit memory tasks associated with negative emotional processing in schizophrenia.

Activity patterns in response to symptoms in patients being treated for chronic fatigue syndrome: An experience sampling methodology study.

Objective: Cognitive–behavioral models of chronic fatigue syndrome (CFS) propose that patients respond to symptoms with 2 predominant activity patterns—activity limitation and all-or-nothing behaviors—both of which may contribute to illness persistence. The current study investigated whether activity patterns occurred at the same time as, or followed on from, patient symptom experience and affect. Method: Twenty-three adults with CFS were recruited from U.K. CFS services. Experience sampling methodology (ESM) was used to assess fluctuations in patient symptom experience, affect, and activity management patterns over 10 assessments per day for a total of 6 days. Assessments were conducted within patients’ daily life and were delivered through an app on touchscreen Android mobile phones. Multilevel model analyses were conducted to examine the role of self-reported patient fatigue, pain, and affect as predictors of change in activity patterns at the same and subsequent assessment. Results: Current experience of fatigue-related symptoms and pain predicted higher patient activity limitation at the current and subsequent assessments whereas subjective wellness predicted higher all-or-nothing behavior at both times. Current pain predicted less all-or-nothing behavior at the subsequent assessment. In contrast to hypotheses, current positive affect was predictive of current activity limitation whereas current negative affect was predictive of current all-or-nothing behavior. Both activity patterns varied at the momentary level. Conclusions: Patient symptom experiences appear to be driving patient activity management patterns in line with the cognitive–behavioral model of CFS. ESM offers a useful method for examining multiple interacting variables within the context of patients’ daily life.

Neuroanatomical assessment of the impact of negative emotion on explicit memory in patients with obsessive-compulsive disorder.

The aim of this study was to identify the brain activation patterns associated with emotionally neutral or unpleasant words during explicit memory tasks in patients with obsessive-compulsive disorder (OCD) using a functional MRI. Sixteen patients with OCD (mean age=31.4±10.1 years) and 16 healthy controls (mean age=32.6±5.8 years) who had no history of neurological or psychiatric illness underwent functional MRI examinations on a 3-T Siemens MR Scanner. The stimulation paradigm consisted of five times rest-condition, two times encoding of two-syllable words, and two times explicit retrieval of the previously learned words. Six different words were presented for 3 s each in the encoding and retrieval tasks. In the retrieval task, the same words as those used at the encoding task were presented randomly. Brain activation maps were quantified and analyzed using SPM8 and MRIcron software. During the explicit retrieval tasks with emotionally neutral words, the predominant activation areas observed in patients with OCD included the angular gyrus and the supramarginal gyrus, whereas healthy controls showed significantly higher activity in the postcentral gyrus (P<0.005). During the explicit retrieval tasks with unpleasant words, patients with OCD showed significantly higher activity, compared with healthy controls, in the cerebellum, posterior cingulate gyrus, middle occipital gyrus, middle temporal gyrus, and inferior frontal gyrus (P<0.005); however, no predominant activation areas in healthy controls over patients with OCD were observed. This study showed differential brain activation patterns in response to emotionally neutral and unpleasant words in patients with OCD. This finding will be useful in assessing the neural mechanisms associated with emotional effect on the impairment of memory retrieval in OCD.

Working memory load influences perceptual ambiguity by competing for fronto-parietal attentional resources

A visual stimulus is defined as ambiguous when observers perceive it as having at least two distinct and spontaneously alternating interpretations. Neuroimaging studies suggest an involvement of a right fronto-parietal network regulating the balance between stable percepts and the triggering of alternative interpretations. As spontaneous perceptual reversals may occur even in the absence of attention to these stimuli, we investigated neural activity patterns in response to perceptual changes of ambiguous Necker cube under different amounts of working memory load using a dual-task design. We hypothesized that the same regions that process working memory load are involved in perceptual switching and confirmed the prediction that perceptual reversals led to fMRI responses that linearly depended on load. Accordingly, posterior Superior Parietal Lobule, anterior Prefrontal and Dorsolateral Prefrontal cortices exhibited differential BOLD signal changes in response to perceptual reversals under working memory load. Our results also suggest that the posterior Superior Parietal Lobule may be directly involved in the emergence of perceptual reversals, given that it specifically reflects both perceptual versus real changes and load levels. The anterior Prefrontal and Dorsolateral Prefrontal cortices, showing a significant interaction between reversal levels and load, might subserve a modulatory role in such reversals, in a mirror symmetric way: in the former activation is suppressed by the highest loads, and in the latter deactivation is reduced by highest loads, suggesting a more direct role of the aPFC in reversal generation.

Brain Activity in Response to Trauma-specific, Negative, and Neutral Stimuli. A fMRI Study of Recent Road Traffic Accident Survivors.

Most studies of neuro-functional patterns in trauma-exposed individuals have been conducted considerable time after the traumatic event. Hence little is known about neuro-functional processing shortly after trauma-exposure. We investigated brain activity patterns in response to trauma reminders as well as neutral and negative stimuli in individuals who had recently (within 3 weeks) been involved in a road traffic accident (RTA). Twenty-three RTA survivors and 17 non-trauma-exposed healthy controls (HCs) underwent functional MRI while viewing Trauma-specific, Negative, and Neutral pictures. Data were analyzed from four a priori regions of interest, including bilateral amygdala, subcallosal cortex, and medial prefrontal cortex. In addition, we performed a whole brain analysis and functional connectivity analysis during stimulus presentation. For both groups, Negative stimuli elicited more activity in the amygdala bilaterally than did Neutral and Trauma-specific stimuli. The whole brain analysis revealed higher activation in sensory processing related areas (bilateral occipital and temporal cortices and thalamus) as well as frontal and superior parietal areas, for the RTA group compared to HC, for Trauma-specific stimuli contrasted with Neutral stimuli. We also observed higher functional connectivity for Trauma-specific stimuli, between bilateral amygdala and somatosensory areas, for the RTA group compared to controls, when contrasted with Neutral stimuli. We argue that these results might indicate an attentional sensory processing bias toward Trauma-specific stimuli for trauma exposed individuals, a result in line with findings from the post-traumatic stress disorder literature.

Molecular and behavioral profiling of Dbx1-derived neurons in the arcuate, lateral and ventromedial hypothalamic nuclei.

BackgroundNeurons in the hypothalamus function to regulate the state of the animal during both learned and innate behaviors, and alterations in hypothalamic development may contribute to pathological conditions such as anxiety, depression or obesity. Despite many studies of hypothalamic development and function, the link between embryonic development and innate behaviors remains unexplored. Here, focusing on the embryonically expressed homeodomain-containing gene Developing Brain Homeobox 1 (Dbx1), we explored the relationship between embryonic lineage, post-natal neuronal identity and lineage-specific responses to innate cues. We found that Dbx1 is widely expressed across multiple developing hypothalamic subdomains. Using standard and inducible fate-mapping to trace the Dbx1-derived neurons, we identified their contribution to specific neuronal subtypes across hypothalamic nuclei and further mapped their activation patterns in response to a series of well-defined innate behaviors.ResultsDbx1-derived neurons occupy multiple postnatal hypothalamic nuclei including the lateral hypothalamus (LH), arcuate nucleus (Arc) and the ventral medial hypothalamus (VMH). Within these nuclei, Dbx1+ progenitors generate a large proportion of the Pmch-, Nesfatin-, Cart-, Hcrt-, Agrp- and ERα-expressing neuronal populations, and to a lesser extent the Pomc-, TH- and Aromatase-expressing populations. Inducible fate-mapping reveals distinct temporal windows for development of the Dbx1-derived LH and Arc populations, with Agrp+ and Cart+ populations in the Arc arising early (E7.5-E9.5), while Pmch+ and Hcrt+ populations in the LH derived from progenitors expressing Dbx1 later (E9.5-E11.5). Moreover, as revealed by c-Fos labeling, Dbx1-derived cells in male and female LH, Arc and VMH are responsive during mating and aggression. In contrast, Dbx1-lineage cells in the Arc and LH have a broader behavioral tuning, which includes responding to fasting and predator odor cues.ConclusionWe define a novel fate map of the hypothalamus with respect to Dbx1 expression in hypothalamic progenitor zones. We demonstrate that in a temporally regulated manner, Dbx1-derived neurons contribute to molecularly distinct neuronal populations in the LH, Arc and VMH that have been implicated in a variety of hypothalamic-driven behaviors. Consistent with this, Dbx1-derived neurons in the LH, Arc and VMH are activated during stress and other innate behavioral responses, implicating their involvement in these diverse behaviors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13064-016-0067-9) contains supplementary material, which is available to authorized users.

Cross-modal symbolic processing can elicit either an N2 or a protracted N2/N400 response.

A cross-modal symbolic paradigm was used to elicit EEG activity related to semantic incongruence. Twenty-five undergraduate students viewed pairings of visual lexical cues (e.g., DOG) with congruent (50% of trials) or incongruent (50%) auditory nonlexical stimuli (animal vocalizations; e.g., sound of a dog woofing or a cat meowing). In one condition, many different pairs of congruent/incongruent stimuli were shown, whereas in a second condition only two pairs of stimuli were repeatedly shown. A typical N400-like pattern of incongruence-related activity (including activity in the N2 time window) was evident in the condition using many stimuli, whereas the incongruence-related activity in the two-stimuli condition was confined to differential N2-like activity. A supplementary analysis excluded stimulus characteristics as the source of this differential activity between conditions. We found that a single individual performing a fixed task can demonstrate either a protracted N400-like pattern of activity or a more temporally focused N2-like pattern of activity in response to the same stimulus, which suggests that the N2 may be a precursor to the protracted N400 response.

The polygenic risk for bipolar disorder influences brain regional function relating to visual and default state processing of emotional information.

Genome-wise association studies have identified a number of common single-nucleotide polymorphisms (SNPs), each of small effect, associated with risk to bipolar disorder (BD). Several risk-conferring SNPs have been individually shown to influence regional brain activation thus linking genetic risk for BD to altered brain function. The current study examined whether the polygenic risk score method, which models the cumulative load of all known risk-conferring SNPs, may be useful in the identification of brain regions whose function may be related to the polygenic architecture of BD. We calculated the individual polygenic risk score for BD (PGR-BD) in forty-one patients with the disorder, twenty-five unaffected first-degree relatives and forty-six unrelated healthy controls using the most recent Psychiatric Genomics Consortium data. Functional magnetic resonance imaging was used to define task-related brain activation patterns in response to facial affect and working memory processing. We found significant effects of the PGR-BD score on task-related activation irrespective of diagnostic group. There was a negative association between the PGR-BD score and activation in the visual association cortex during facial affect processing. In contrast, the PGR-BD score was associated with failure to deactivate the ventromedial prefrontal region of the default mode network during working memory processing. These results are consistent with the threshold-liability model of BD, and demonstrate the usefulness of the PGR-BD score in identifying brain functional alternations associated with vulnerability to BD. Additionally, our findings suggest that the polygenic architecture of BD is not regionally confined but impacts on the task-dependent recruitment of multiple brain regions.

Gender differences in justice evaluations: Evidence from fMRI.

Justice research examining gender differences has yielded contrasting findings. This study enlists advanced techniques in cognitive neuroscience (fMRI) to examine gender differences in brain activation patterns in response to procedural and distributive justice manipulations. We integrate social role, information processing, justice, and neuroscience literature to posit and test for gender differences in 2 neural subsystems known to be involved in the appraisal of self-relevant events. Results indicate that the relationship between justice information processing and neural activity in areas representing these subsystems is significantly influenced by gender, with greater activation for females than males during consideration of both procedural and distributive justice information. In addition, we find evidence that gender and distributive injustice interact to influence bargaining behavior, with females rejecting ultimatum game offers more frequently than males. Results also demonstrate activation in the ventromedial prefrontal cortex (vmPFC) and ventral striatum brain regions during procedural justice evaluation is associated with offer rejection in females, but not in males. Managerial implications based on the study's support for gender differences in justice perceptions are discussed.

MSG-Evoked c-Fos Activity in the Nucleus of the Solitary Tract Is Dependent upon Fluid Delivery and Stimulation Parameters.

The marker of neuronal activation, c-Fos, can be used to visualize spatial patterns of neural activity in response to taste stimulation. Because animals will not voluntarily consume aversive tastes, these stimuli are infused directly into the oral cavity via intraoral cannulae, whereas appetitive stimuli are given in drinking bottles. Differences in these 2 methods make comparison of taste-evoked brain activity between results that utilize these methods problematic. Surprisingly, the intraoral cannulae experimental conditions that produce a similar pattern of c-Fos activity in response to taste stimulation remain unexplored. Stimulation pattern (e.g., constant/intermittent) and hydration state (e.g., water-restricted/hydrated) are the 2 primary differences between delivering tastes via bottles versus intraoral cannulae. Thus, we quantified monosodium glutamate (MSG)-evoked brain activity, as measured by c-Fos, in the nucleus of the solitary tract (nTS; primary taste nucleus) across several conditions. The number and pattern of c-Fos neurons in the nTS of animals that were water-restricted and received a constant infusion of MSG via intraoral cannula most closely mimicked animals that consumed MSG from a bottle. Therefore, in order to compare c-Fos activity between cannulae-stimulated and bottle-stimulated animals, cannulated animals should be water restricted prior to stimulation, and receive taste stimuli at a constant flow.

Recurrent networks expect

How the brain anticipates future events is one of the most intriguing questions in neural information processing. The brain does not simply respond to the external world but in predictably structured environments like natural language, birdsong and somatosensory flow in fluids predicts it [1]. Reactions are improved by predictive encoding of what sensory stimuli may occur as well as when they may occur. Quantitative studies of implicit timing in streaming perceptual discrimination tasks show that performance is enhanced if stimuli occur at expected times according to an established rhythm. The neural basis for implicit timing is not fully understood but oscillatory entrainment mechanisms have been suggested [2]. Recent studies confirm that low-frequency brain oscillations do become phase entrained in such tasks. Phase entrainment increases with the temporal regularity of the sensory stream and correlates with enhanced discrimination performance [3]. It is not limited to sensory cortices; larger scale cortical networks, as well as subcortical networks like the basal ganglia [4], may also be coherently modulated by the predictability of stimuli streams. The presence of large scale oscillatory entrainment suggests that network mediated neuronal ensemble dynamics may be involved. Recurrent neural networks generate complex but reproducible temporally extended dynamical activity patterns in response to input stimuli [5,6]. Such transient activity patterns have been suggested to provide a natural substrate for working memory and a representation of elapsed time. Here we add to the understanding of how random recurrent neural networks support neural information processing by demonstrating that temporal expectation also naturally emerges from their dynamics. We show that the weakly chaotic oscillations generated by recurrent networks can be phase synchronized [7] by temporally regular stimulus sequences. We show network responses are maximally discriminative when stimuli fall at their preferred phase in phase entrained networks (Figure ​(Figure1).1). Discriminability increases continuously with both temporal regularity and stimulus type predictability which also interact. Our results do not depend on specific network characteristics, are resilient to the presence of network noise and random distractor stimuli and are consistent with multiple streaming perceptual discrimination studies. Figure 1 Excess correct classification probability of on-time target stimuli compared to mistimed target stimuli (100 ms early, black ; 100 ms late, red) in a temporally regular streaming task with inter-trial-interval 800 ms. Results are plotted versus the Lyapunov ...

Cerebral Hemodynamic Responses During Dynamic Posturography: Analysis with a Multichannel Near-Infrared Spectroscopy System.

To investigate cortical roles in standing balance, cortical hemodynamic activity was recorded from the right hemisphere using near-infrared spectroscopy (NIRS) while subjects underwent the sensory organization test (SOT) protocol that systematically disrupts sensory integration processes (i.e., somatosensory or visual inputs or both). Eleven healthy men underwent the SOT during NIRS recording. Group statistical analyses were performed based on changes in oxygenated hemoglobin concentration in 10 different cortical regions of interest and on a general linear analysis with NIRS statistical parametric mapping. The statistical analyses indicated significant activation in the right frontal operculum (f-Op), right parietal operculum (p-Op), and right superior temporal gyrus (STG), right posterior parietal cortex (PPC), right dorsal and ventral premotor cortex (PMC), and the supplementary motor area (SMA) under various conditions. The activation patterns in response to specific combinations of SOT conditions suggested that (1) f-Op, p-Op, and STG are essential for sensory integration when standing balance is perturbed; (2) the SMA is involved in the execution of volitional action and establishment of new motor programs to maintain postural balance; and (3) the PPC and PMC are involved in the updating and computation of spatial reference frames during instances of sensory conflict between vestibular and visual information.

Emotion-Induced Topological Changes in Functional Brain Networks

In facial expression perception, a distributed network is activated according to stimulus context. We proposed that an interaction between brain activation and stimulus context in response to facial expressions could signify a pattern of interactivity across the whole brain network beyond the face processing network. Functional magnetic resonance imaging data were acquired for 19 young healthy subjects who were exposed to either emotionally neutral or negative facial expressions. We constructed group-wise functional brain networks for 12 face processing areas [bilateral inferior occipital gyri (IOG), fusiform gyri (FG), superior temporal sulci (STS), amygdalae (AMG), inferior frontal gyri (IFG), and orbitofrontal cortices (OFC)] and for 73 whole brain areas, based on partial correlation of mean activation across subjects. We compared the topological properties of the networks with respect to functional distance-based measures, global and local efficiency, between the two types of face stimulus. In both face processing and whole brain networks, global efficiency was lower and local efficiency was higher for negative faces relative to neutral faces, indicating that network topology differed according to stimulus context. Particularly in the face processing network, emotion-induced changes in network topology were attributable to interactions between core (bilateral IOG, FG, and STS) and extended (bilateral AMG, IFG, and OFC) systems. These results suggest that changes in brain activation patterns in response to emotional face stimuli could be revealed as changes in the topological properties of functional brain networks for the whole brain as well as for face processing areas.

Neurons in the barrel cortex turn into processing whisker and odor signals: a cellular mechanism for the storage and retrieval of associative signals

Associative learning and memory are essential to logical thinking and cognition. How the neurons are recruited as associative memory cells to encode multiple input signals for their associated storage and distinguishable retrieval remains unclear. We studied this issue in the barrel cortex by in vivo two-photon calcium imaging, electrophysiology, and neural tracing in our mouse model that the simultaneous whisker and olfaction stimulations led to odorant-induced whisker motion. After this cross-modal reflex arose, the barrel and piriform cortices connected. More than 40% of barrel cortical neurons became to encode odor signal alongside whisker signal. Some of these neurons expressed distinct activity patterns in response to acquired odor signal and innate whisker signal, and others encoded similar pattern in response to these signals. In the meantime, certain barrel cortical astrocytes encoded odorant and whisker signals. After associative learning, the neurons and astrocytes in the sensory cortices are able to store the newly learnt signal (cross-modal memory) besides the innate signal (native-modal memory). Such associative memory cells distinguish the differences of these signals by programming different codes and signify the historical associations of these signals by similar codes in information retrievals.

Beaver (Castor fiber) activity patterns in a predator-free landscape. What is keeping them in the dark?

Activity patterns play an important role in the fitness of animals. Energy conservation, physiological adaptations, prey availability, competition, and predation caused by predators and humans are all important parameters influencing when, and where, animals are active. Over time, however, a change in such external factors can lead to a shift in optimal activity patterns. In this paper, we use camera traps to study the daily activity patterns of Eurasian beavers (Castor fiber) reintroduced into an atypical, predator-free landscape. We explore if and how beavers have adjusted their activity patterns in the absence of predators, and whether this varies with day length and moonshine. Our results reveal that beavers in our study area have a mainly crepuscular and nocturnal activity pattern, similar to animals in more natural landscapes with predators. Changes in day length had only a limited effect on the duration of beavers’ activity, but, contrary to our expectations, beaver activity increased during bright moonlight. Activity patterns were also clearly bimodal during nights with bright moonlight, but unimodal during dark nights. The shape of their activity pattern did change throughout the year. These results suggest that beavers can alter their activity patterns in response to external cues, but that the current absence of predators has not resulted in a relaxation of their nocturnal activity patterns. We discuss our results in light of historical human persecution and suggest that beaver activity patterns continue to be influenced by ghosts of predators past.