Long-term memory prepares neural activity for perception

Past experience provides a rich source of predictive information about the world that could be used to guide and optimize ongoing perception. However, the neural mechanisms that integrate information coded in long-term memory (LTM) with ongoing perceptual processing remain unknown. Here, we explore how the contents of LTM optimize perception by modulating anticipatory brain states. By using a paradigm that integrates LTM and attentional orienting, we first demonstrate that the contents of LTM sharpen perceptual sensitivity for targets presented at memory-predicted spatial locations. Next, we examine oscillations in EEG to show that memory-guided attention is associated with spatially specific desynchronization of alpha-band activity over visual cortex. Additionally, we use functional MRI to confirm that target-predictive spatial information stored in LTM triggers spatiotopic modulation of preparatory activity in extrastriate visual cortex. Finally, functional MRI results also implicate an integrated cortical network, including the hippocampus and a dorsal frontoparietal circuit, as a likely candidate for organizing preparatory states in visual cortex according to the contents of LTM.     

Disassociation between preprandial gut peptide release and food-anticipatory activity

Animals learn to anticipate a meal as evidenced by increases in premeal activity. This learned response appears to be independent of the nutrient status of an animal because food-anticipatory activity (FAA) can be seen after entrainment by a highly palatable food when rats remain ad libitum on chow. Mealtime feeding not only induces an increase in activity but also appears to entrain the secretion of various peptides prior to a meal including insulin, ghrelin, and glucagon-like peptide-1 (GLP-1). It is not clear whether these meal-anticipatory changes in peptides are causally associated with FAA. To assess whether FAA and preprandial peptide changes co-occur with meal entrainment using different diets, rats were conditioned to receive a 6-h chow meal, 6-h high-fat meal, or 2 h access of chocolate while ad libitum on chow in the middle of the light cycle. FAA was measured for 4 h prior to mealtime. Rats were then killed at 90, 60, and 30 min prior to mealtime and plasma was collected. Although the chocolate-entrained rats showed comparable FAA with the nonchocolate-entrained animals, they did not show anticipatory increases in the ghrelin or GLP-1. All entrainment conditions induced a decrease in insulin and an increase in glucose prior to mealtime. These data suggest that separate mechanisms may underlie the preprandial increases in ghrelin and GLP-1 and changes in FAA, insulin, and glucose.     

Relationship between psychological state and level of activity of extrinsic gut innervation in patients with a functional gut disorder

BACKGROUND: Anxiety and depression are known to be associated with alterations in central autonomic activity, and this may manifest as a functional gut disturbance. However, the final expression of motility disturbance is non-specific and non-quantifiable. This study examines the relationship between psychological state and psychosocial functioning with a new direct measure of the level of activity of extrinsic autonomic gut innervation, rectal mucosal Doppler blood flow. MATERIALS AND METHODS: Thirty four female patients (mean age 36 years, range 19--45) with constipation for greater than five years and 19 healthy women (mean age 38 years, range 21--60) were studied. They completed the general health questionnaire-28 point scale (GHQ-28; psychosocial functioning) and the Bem sex role inventory (BSRI; an index of women's psychological feelings about their own femininity). On the same day they underwent measurement of rectal mucosal Doppler blood flow, a new validated measure of the activity of gut extrinsic nerve innervation. Measurements were made during the follicular phase and in the fasted state. RESULTS: Women with constipation scored higher on the total GHQ-28 score and the somatisation (p=0.05) and anxiety (p=0.05) subscales of the GHQ-28. There was a negative correlation between mucosal blood flow and GHQ somatisation subscale (r=-0.45, p<0.005), anxiety (r=-0.38, p<0.05), and depression (r=-0.40, p<0.01) scores in women with constipation. Although constipated women scored no higher than controls on the BSRI, there was a significant negative correlation between blood flow and BSRI score (r=-0.49, p<0.005) for constipated women. CONCLUSIONS: General psychosocial function, somatisation, anxiety, depression, and feelings about female role are impaired in women with constipation and associated with altered rectal mucosal blood flow, a measure of extrinsic gut innervation. These findings suggest that psychological factors are likely to influence gut function via autonomic efferent neural pathways.     

Gastric myoelectrical activity and gut hormone secretion in myotonic dystrophy

BACKGROUND: Myotonic dystrophy (MD) is a systemic disease affecting striated, cardiac and smooth muscles, as well as nerve structures and endocrine glands. Patients with MD may suffer from slow gastric emptying. OBJECTIVE: To study electrogastrograms (EGG) and postprandial gut hormone profiles in MD in order to evaluate whether disturbances in these regulatory mechanisms could explain, or contribute to, the delayed gastric emptying. SUBJECTS: Ten patients with MD complaining of symptoms consistent with slow gastric emptying, and ten healthy matched controls. METHODS: After an overnight fast, the patients and the control subjects were examined with standard EGG using surface electrodes before and during intake of a standard meal. Blood tests were drawn at regular time intervals for hormone analyses. RESULTS: The EGG in MD showed a reduced amount of normal three cycles per minute activity compared with controls (P < 0.04). The dominant frequency in MD was less stable than in controls (P < 0.03), and the power of the signal showed less increase after a meal. The postprandial increase in plasma motilin (P < 0.05) and glucagon-like peptide-1 (GLP-1) (P < 0.001) was significantly less pronounced in MD compared with controls, whereas the plasma concentrations of cholecystokinin (CCK), neurotensin (NT), peptide YY (PYY) and somatostatin (SOM) did not differ significantly. CONCLUSION: Disturbed electrophysiological control of the stomach and impaired secretion of gastrointestinal peptide hormones could contribute to slow gastric emptying in MD. Combined impairment of gastric pacing and gastrointestinal hormone responses was found in patients with the most prominent retardation of gastric emptying.     

Baseline brain activity fluctuations predict somatosensory perception in humans

In perceptual experiments, within-individual fluctuations in perception are observed across multiple presentations of the same stimuli, a phenomenon that remains only partially understood. Here, by means of thulium-yttrium/aluminum-garnet laser and event-related functional MRI, we tested whether variability in perception of identical stimuli relates to differences in prestimulus, baseline brain activity. Results indicate a positive relationship between conscious perception of low-intensity somatosensory stimuli and immediately preceding levels of baseline activity in medial thalamus and the lateral frontoparietal network, respectively, which are thought to relate to vigilance and "external monitoring." Conversely, there was a negative correlation between subsequent reporting of conscious perception and baseline activity in a set of regions encompassing posterior cingulate/precuneus and temporoparietal cortices, possibly relating to introspection and self-oriented processes. At nociceptive levels of stimulation, pain-intensity ratings positively correlated with baseline fluctuations in anterior cingulate cortex in an area known to be involved in the affective dimension of pain. These results suggest that baseline brain-activity fluctuations may profoundly modify our conscious perception of the external world.     

Dysregulation of gut microbiome is linked to disease activity of rheumatic diseases

Clinical Rheumatology - Objective rheumatism refers to a large group of diseases with different etiology, mainly characterized by autoimmune disorder. Intestinal flora combines with the digestive...     

Conscious sedation for endoscopic procedures

Despite the fact that gastrointestinal endoscopy is a safe procedure, significant complications can occur. According to the literature most complications are related to sedation and compared with perioperative mortality under general anaesthesia, the mortality for this procedure appears high. Strict implementation of existing guidelines is warranted.     

Neuronal thresholds and choice-related activity of otolith afferent fibers during heading perception

How activity of sensory neurons leads to perceptual decisions remains a challenge to understand. Correlations between choices and single neuron firing rates have been found early in vestibular processing, in the brainstem and cerebellum. To investigate the origins of choice-related activity, we have recorded from otolith afferent fibers while animals performed a fine heading discrimination task. We find that afferent fibers have similar discrimination thresholds as central cells, and the most sensitive fibers have thresholds that are only twofold or threefold greater than perceptual thresholds. Unlike brainstem and cerebellar nuclei neurons, spike counts from afferent fibers do not exhibit trial-by-trial correlations with perceptual decisions. This finding may reflect the fact that otolith afferent responses are poorly suited for driving heading perception because they fail to discriminate self-motion from changes in orientation relative to gravity. Alternatively, if choice probabilities reflect top-down inference signals, they are not relayed to the vestibular periphery.The neural basis of perception holds a long-standing fascination for neuroscientists. How do the properties of single neurons and populations of neurons relate to, and account for, sensory perception? In all sensory systems, information about the world is first translated into neural activity by peripheral receptor neurons, and then transformed by multiple stages of subcortical and cortical processing into a perceptual decision. How and where does perception emerge from multiple neural representations that appear to be at least partially redundant? These questions have been addressed often in sensory and multisensory cortex (e.g., in refs. 1–3 for vestibular perception), but much less is known about how the activity of sensory afferents relates to perceptual sensitivity and perceptual decisions.One way to assess a potential role of sensory neurons in a perceptual task is to compare neuronal and perceptual sensitivity, measured simultaneously in the same subject (4). Although this comparison has been done many times for cortical neurons (1, 5–7), little is known about how the sensitivity of peripheral afferents compares with behavior apart from microneurography studies of tactile afferents in humans (8, 9). To our knowledge, the present study provides the first direct comparison of afferent neuronal sensitivity and perceptual sensitivity, measured simultaneously in experimental animals. Results of such comparisons have important implications for understanding how population encoding and decoding may constrain and shape the information that guides behavior.Another way that neuroscientists have explored the functional links between sensory neurons and perception is by measuring the trial-by-trial correlations between neural activity and perceptual decisions, which are typically quantified as “choice probabilities” (CPs) (10). The “bottom-up” explanation of CPs is that trial-to-trial variability in the activity of sensory neurons drives variability in decisions; in contrast, the “top-down” explanation is that higher level signals related to decisions or featural attention are fed back to modulate the responses of sensory neurons (reviewed in ref. 11). To our knowledge, CPs have never been measured for primary afferents in any sensory system. Such measurements are potentially of interest because they may help clarify whether trial-to-trial response variability at the sensory periphery can be correlated with decisions, and whether top-down signals may propagate all of the way back to afferents.For some sensory systems and perceptual tasks, the relationships between afferent activity, behavioral sensitivity, and perceptual decisions cannot be examined because afferents do not exhibit the same forms of stimulus selectivity seen in the cortex (e.g., binocular disparity or direction tuning in primate visual neurons). In this regard, the vestibular system may provide an alternative model to probe the origin of CPs because similar basic forms of spatiotemporal directional selectivity are seen at many levels of processing, from afferents to cortex (12). Recently, we provided the first demonstration (13), to our knowledge, that subcortical neurons in the vestibular nuclei (VN) and cerebellar nuclei (CN) could exhibit robust CPs, and these effects were even larger than those effects measured in some cortical areas under identical stimulus conditions (e.g., ref. 1). Interestingly, we also found that the CPs of these subcortical neurons were correlated with the degree to which the neurons represented translation (heading) without being confounded by head orientation relative to gravity. This result suggested that CPs might emerge in the vestibular pathways after resolution of the tilt-translation ambiguity (14). If so, this logic predicts that otolith afferents, which encode the net gravitoinertial acceleration, and therefore confound tilt and translation (15), would not exhibit CPs.We simultaneously measured heading discrimination performance while recording from otolith afferents, the primary sensory neurons that carry linear acceleration information to the brain. We addressed the following questions. First, how does the heading sensitivity of otolith afferents compare with central vestibular neurons? Are central vestibular neurons more sensitive than afferents because they have greater average modulation amplitudes than afferents (16–23), or do changes in response variability counteract these differences in response gain? Second, do otolith afferents show choice-related activity, and how do CPs of afferents compare with CPs measured in central neurons and cortical areas?     

Conscious updating is a rhythmic process

As the visual world changes, its representation in our consciousness must be constantly updated. Given that the external changes are continuous, it appears plausible that conscious updating is continuous as well. Alternatively, this updating could be periodic, if, for example, its implementation at the neural level relies on oscillatory activity. The flash-lag illusion, where a briefly presented flash in the vicinity of a moving object is misperceived to lag behind the moving object, is a useful tool for studying the dynamics of conscious updating. Here, we show that the trial-by-trial variability in updating, measured by the flash-lag effect (FLE), is highly correlated with the phase of spontaneous EEG oscillations in occipital (5-10 Hz) and frontocentral (12-20 Hz) cortices just around the reference event (flash onset). Further, the periodicity in each region independently influences the updating process, suggesting a two-stage periodic mechanism. We conclude that conscious updating is not continuous; rather, it follows a rhythmic pattern.     

Conscious off-pump coronary artery bypass surgery

BACKGROUND: Cardiothoracic surgery has been previously performed successfully under thoracic epidural anesthesia alone. Between October 2001 and December 2003, we performed 123 conscious off-pump coronary artery bypass surgeries using epidural anesthesia as the sole anesthetic. This technique is an alternative to cardiothoracic surgery performed under general anesthesia. Certain modifications in the technique facilitate the process. METHODS AND RESULTS: There were 24 female patients and 99 male patients with mean age of 58.6 +/- 6.2 years; 12 patients underwent repeat coronary artery bypass surgery. All the patients underwent epidural catheterization on the evening before surgery. Out of the 123 patients scheduled for coronary artery bypass graft surgery, 120 underwent off-pump coronary artery bypass graft surgery successfully; 4 patients underwent off-pump surgery via left thoracotomy and the rest through mid sternotomy. These patients received 295 grafts in all (single graft in 26 patients, double in 42 patients, triple in 35 patients, and quadruple in 20 patients). Three patients required conversion to general anesthesia and one to cardiopulmonary bypass. There was no mortality in the group. CONCLUSIONS: Our experience suggests that by modifying the surgical techniques, we can accomplish conscious coronary artery bypass surgery.     

Altered gut microbial profile is associated with abnormal metabolism activity of Autism Spectrum Disorder

ABSTRACT

Autism Spectrum Disorder (ASD) is a severe neurodevelopmental disorder. To enhance the understanding of the gut microbiota structure in ASD children at different ages as well as the relationship between gut microbiota and fecal metabolites, we first used the 16S rRNA sequencing to evaluate the gut microbial population in a cohort of 143 children aged 2–13 years old. We found that the α-diversity of ASD group showed no significant change with age, while the TD group showed increased α-diversity with age, which indicates that the compositional development of the gut microbiota in ASD varies at different ages in ways that are not consistent with TD group. Recent studies have shown that chronic constipation is one of the most commonly obvious gastrointestinal (GI) symptoms along with ASD core symptoms. To further investigate the potential interaction effects between ASD and GI symptoms, the 30 C-ASD and their aged-matched TD were picked out to perform metagenomics analysis. We observed that C-ASD group displayed decreased diversity, depletion of species of Sutterella, Prevotella, and Bacteroides as well as dysregulation of associated metabolism activities, which may involve in the pathogenesis of C-ASD. Consistent with metagenomic analysis, liquid chromatography-mass spectrometry (LC/MS) revealed some of the differential metabolites between C-ASD and TD group were involved in the metabolic network of neurotransmitters including serotonin, dopamine, histidine, and GABA. Furthermore, we found these differences in metabolites were associated with altered abundance of specific bacteria. The study suggested possible future modalities for ASD intervention through targeting the specific bacteria associated with neurotransmitter metabolism.     

Covariation of activity in visual and prefrontal cortex associated with subjective visual perception

Visual areas of the occipitotemporal pathway are thought to be essential for the conscious perception of objects, but the contribution of other cortical regions and the neural mechanisms leading to the awareness of a visual stimulus remain unclear. By using functional MRI in humans exposed to bistable viewing conditions, subjective visual perception was related to covariation of activity in multiple extrastriate ventral, parietal, and prefrontal cortical areas. The coordination of activity among these regions was not linked to external sensory or motor events; rather, it reflected internal changes in perception and varied in strength with the frequency of perceptual events, suggesting that functional interactions between visual and prefrontal cortex may contribute to conscious vision. Because similar cortical systems have been implicated in short-term memory and motor planning, the results also imply that related neural processes may underlie visual awareness and the organization of voluntary behavior contingent on sensory cues.