Grid cell co-activity patterns remain stable across different behavioral states and experiences

Grid cells in the medial entorhinal cortex have been well studied while animals are exploring their environment; however, what they do when an animal is not navigating is less clear. Other cell types in the entorhinal-hippocampal network appear to have memory-related activity when an animal is inactive, so what grid cells do during quiescence is an important question. If grid cells show activity similar to place cells during rest and sleep, then it would imply that grid cells play an active role in memory functions rather than simply providing current sensory information to the hippocampus. Models have been proposed that make testable predictions about grid cell activity when spatial input is absent. The continuous attractor network model of grid cell pattern formation posits that grid cell patterning is a result of network connections between grid cells. As a result of this connectivity, these models hypothesize that grid cell co-activity patterns should be the same during sleep as during active navigation. In my first study, I investigated how spike time correlations between grid cell pairs during sleep compared to spike time correlations between the same grid cell pairs during waking activity. I found that the same correlation patterns were present regardless of whether spatial information was available to grid cells (i.e., during active navigation) or whether sensory input was absent (i.e., during sleep). These results support the continuous attractor network model hypothesis. In my second study, I examined whether novel experience changed grid cell co-activity patterns during active waking behaviors, rest, and sleep. I found that spike time correlations between grid cell pairs remained stable across behavioral states regardless of experience. In my last study, I looked at organized sequences of firing in grid cell ensembles to examine whether small changes in correlations led to detectable changes in more complex ensemble representations of experience. I found that grid cell ensemble activity did not appear to be influenced by different behaviors or novel experience. Taken together, these results suggest that grid cells are part of a low-dimensional, continuous attractor network and that grid cell activity patterns during sleep reflect connections in the grid cell network rather than representing specific experiences.Neuroscienc

Outflow boundary conditions for low-Mach buoyant computational fluid dynamics

General issues with outflow boundary conditions are discussed, as are the issues specific to flow with buoyancy such as unphysical build-up of fluid at the outflow boundary. Different solutions to these problems are detailed. The sponge-layer approach is used to model the outflow boundary in buoyant jets. The successes and shortcomings of the sponge-layer approach are made clear through comparisons with long domain simulations

Wine tasting: a neurophysiological measure of taste and olfaction interaction in the experience

In the last years have been provided evidences of sensory–sensory connectivity and influences of one modality over primary sensory cortex of another, a phenomena called crossmodality. Typically, for the wine tasting, sommeliers in addition to the use of the gustation, by the introduction of the wine into the mouth, employ the stimulation of the olfactory system both through a direct olfactory stimulation (by the nose) and a retro-nasal pathway (inhaling air while swirling the wine around in the mouth). Aim of the present study was to investigate the reaction to the wine gustation with and without the direct olfactory contribution, through an electroencephalographic index of approach or withdrawal (AW) motivation, and an autonomic index (Emotional Index – EI), deriving from the matching of heart rate and galvanic skin response activity and considered an indicator of emotional involvement. Results showed a statistically significant increase of the EI values in correspondence of wine tasting with the olfactory component (p<0.01) in comparison to the tasting without the direct olfactory contribution, and a trend of greater approach attitude was reported for the same condition. Data suggest an interaction of the two sensory modalities influencing the emotional and the cognitive aspects of wine tasting experience in a non-expert sampl

CXCL16/CXCR6 axis drives microglia/macrophages phenotype in physiological conditions and plays a crucial role in glioma

Microglia are patrolling cells that sense changes in the brain microenvironment and respond acquiring distinct phenotypes that can be either beneficial or detrimental for brain homeostasis. Anti-inflammatory microglia release soluble factors that might promote brain repair; however, in glioma, anti-inflammatory microglia dampen immune response and promote a brain microenvironment that foster tumor growth and invasion. The chemokine CXCL16 is expressed in the brain, where it is neuroprotective against brain ischemia, and it has been found to be over-expressed in glioblastoma (GBM). Considering that CXCL16 specific receptor CXCR6 is diffusely expressed in the brain including in microglia cells, we wanted to investigate the role of CXCL16 in the modulation of microglia cell activity and phenotype, and in the progression of glioma. Here we report that CXCL16 drives microglia polarization toward an anti-inflammatory phenotype, also restraining microglia polarization toward an inflammatory phenotype upon LPS and IFN? stimulation. In the context of glioma, we demonstrate that CXCL16 released by tumor cells is determinant in promoting glioma associated microglia/macrophages (GAMs) modulation toward an anti-inflammatory/pro-tumor phenotype, and that cxcr6ko mice, orthotopically implanted into the brain with GL261 glioma cells,survive longer compared to wild-type mice. We also describe that CXCL16/CXCR6 signaling acts directly on mouse glioma cells, as well as human primary GBM cells, promoting tumor cell growth, migration and invasion. All together these data suggest that CXCL16 signaling could represent a good target to modulate microglia phenotype in order to restrain inflammation or to limit glioma progression

The chemokine CXCL16 modulates neurotransmitter release in hippocampal CA1 area.

Chemokines have several physio-pathological roles in the brain. Among them, the modulation of synaptic contacts and neurotransmission recently emerged as crucial activities during brain development, in adulthood, upon neuroinflammation and neurodegenerative diseases. CXCL16 is a chemokine normally expressed in the brain, where it exerts neuroprotective activity against glutamate-induced damages through cross communication with astrocytes and the involvement of the adenosine receptor type 3 (A3R) and the chemokine CCL2. Here we demonstrated for the first time that CXCL16 exerts a modulatory activity on inhibitory and excitatory synaptic transmission in CA1 area. We found that CXCL16 increases the frequency of the miniature inhibitory synaptic currents (mIPSCs) and the paired-pulse ratio (PPR) of evoked IPSCs(eIPSCs), suggesting a presynaptic modulation of the probability of GABA release. In addition, CXCL16 increases the frequency of the miniature excitatory synaptic currents (mEPSCs) and reduces the PPR of evoked excitatory transmission, indicating that the chemokine also modulates and enhances the release of glutamate. These effects were not present in the A3RKO mice and in WT slices treated with minocycline, confirming the involvement of A3 receptors and introducing microglial cells as key mediators of the modulatory activity of CXCL16 on neurons