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What is oscillating? The electromagnetic field caused by (1) certain types of nerve cells(neurons) that can generate rhythmic firing/spiking on their own without any input or by (2) dynamically assembled groups of connected neurons that individually spike irregularly in response to input, but collectively generate an oscillating field due to synchronization mechanisms driven largely by their connectivity.[ 20 , 25 , 30, 37,38 , 40]Oscillations have been observed at different frequency ranges and have been given different names such as delta (1-4Hz), theta (4-8 Hz), alpha (8-12Hz), beta (12-30Hz), gamma (>30 Hz) etc. Figures 1 and 2 [30]Understanding these oscillatory patterns particularly by correlating with animal behavior, including humans, is serving as a valuable tool to reverse engineer mechanisms of brain function.[30]Several basic questions regarding oscillations remain unanswered requiring further study such as the details of their role, the neuronal mechanisms of their sources, how to interpret them, how to standardize measuring them etc.[44,46]What brain functions do these oscillations correlate with?Neurons fire in the backdrop of neighboring neurons, some of which may also be firing while the others listening, and they influence each other with excitatory and inhibitory connections. Figures 3,4 and 5. [20 , 25 ,30]The firing activity of neurons can be measured at different population scales - (1) individual neuron spiking, (2) activity of tens of thousands of neurons, (3) several millions and (4) the consolidated activity of multiple brain areas. The measurements can range from electric voltage recordings done inside neurons or outside in the space between them, to noninvasive measurement of the magnetic field registered outside the head. [ 26, 43]By measuring individual neuron firing spikes along with the background voltage oscillations in healthy/impaired humans and animals, oscillatory patterns with characteristic properties of frequency, modulation/coupling type etc. (Figure 6, 7 and 8) are beginning to emerge that correlate with different information/memory related activities such asCommunication across anatomically different regions of the brain.[7]Transient encoding, maintenance, and manipulation of memory (volatile/working memory, processing) [ 27, 35 ,42]Consolidating memory into long term storage (persistent memory) [41]Recall/Retrieval of memory from long term storage [41]What is an example of oscillations correlating with real life experience?Even though oscillations are present in all states of the brain, the example below highlights individual aspects where oscillations with different characteristics correlate with cognition,behavior, and memory.[14,7,8]Imagine the first time perception of a Ferrari sports car. The information about its color (red), the stimulus category (car) and its motion (moving fast) is processed in anatomically different regions in the brain, but simultaneously perceived together.These representations need to be linked by some mechanism to ensure that the brain assigns them to the same object. This binding function is made possible by communication across these different regions through coherent wave patterns.If this experience seemed so fantastic(novel experience), then we may also remember other details such as where we saw it (location) and even the minute detail of the aroma of a cheeseburger (smell) from a nearby restaurant as the Ferrari zips by.We may then immediately recall the experience internally (processing,working memory) reliving the experience or talk about it others.If the experience was so novel, the experience may be played in “fast forward” mode while we are asleep and consolidated into long term memory. Our recalling the experience to others over the course of next few days aids this consolidation and strengthening of this long term memory even further.A few months/years later, we may still recall that experience with all the minute detail including the aroma of cheeseburgers wafting in the air as the Ferrari zipped by.Of course, if one had little to no interest in cars, the memory would be transiently held, if at all it is, only to fade away soon or during the course of the day.Oscillations with characteristic properties of frequency, modulation and coupling type(multiple frequencies coupled in phase, amplitude etc.) correlate with each of the key aspects of this example – communication, processing,volatile memory, consolidation into persistent memory, and retrieval.What do we know so far about the role of oscillations?The firing of a neuron is driven by its input except for those special neurons that have intrinsic mechanisms to generate firing on their own.[30,37,38 ]Certain physical,electrical and chemical properties of a neuron dictate the time length of the sampling window of its input from other neurons, to be in the range of 10-30 msecs. A neuron will fire based on the input it samples in this time window. If an input spike to a neuron comes slightly later than this 10-30 msec time window, it will be sampled in the next time window - so it will be part of the next "event" as far as this neuron is concerned. Figure 2 [30, 34 ,45]Memory of events is encoded in the connection strengths between neurons. The altering of connection strengths between a pair of neurons also requires the participating neuron pair to be in certain activity states within a time window of 10-30 msecs.[30, 35 ,39]The 10-30 msec time constraint for the input sampling window and the same time constraint for the encoding of memory mandates a synchronization mechanism to make neurons fire in this short time window to constitute an event and to potentially store it, despite the individual irregular spiking behavior. [ 27, 32]For example, while information can be encoded quite sparsely in a small set of connected neurons for an aspect of sensory stimulus (e.g. the concept of a celebrity like Jennifer Aniston evoked by a photograph of her), it still requires sufficient number of neurons in this sparse set to fire synchronously to both constitute that information and subsequently recall that information. [ 17 , 18 , 21 , 35 , 41]This synchronous firing is made possible largely by the inhibitory actions of intermediate neurons that connect this sparse set, generating a local oscillating field. These inhibitory neurons help collectively time the spiking of these neurons to millisecond precision within certain phases of the oscillation field. Inhibitory neurons appear to also play a key role in containing the size of oscillating sparse group of neurons. This containment avoids an explosive growth in the group size of spiking neurons due to connectivity with other neurons Figure 11.[50, 20 ,40]The field oscillations that emerge from the synchronizing action of inhibitory neurons on the collective firing of the excitatory neurons satisfy the 10-30 msec constraint and hence have a frequency greater than 30 Hz ( 1000/30 = 33). Each oscillation conceptually frames spikes into time window slots with slot widths determined by the frequency. The spiking group of neurons that fire within a time slot may vary with each slot creating a temporal sequence of events [ 19] Figure 14The power in these high frequency oscillations ( > 30 Hz) is not much, given only a sparse set of neurons are typically involved. So these oscillations, on their own cannot transmit information across different anatomical regions of the brain, other than rare instances where direct wiring between distant regions have enabled synchronous oscillations across those regions Figure 13.[ 2 ,6 ,8]There are slower frequency oscillations involving larger number of neurons and hence with more power in their oscillations. The lower power high frequency oscillations that encapsulate information spikes "ride on" these higher power lower frequency oscillations by different modulation schemes. The longer time windows of these low frequency oscillations serve to nest and temporally serialize the higher frequency oscillations that encapsulate episodic events Figures 13 and 14.[11, 12 , 13 , 14 , 15 , 16 , 19 , 22 , 23 , 24 , 28 , 29 ,36 , 42,8]This appears to be the general mechanism behind communication of information between different parts of the brain. The saving of Ferrari sports car into persistent memory appears to be facilitated by similar coupling between higher and slower frequency oscillations. [ 43, 47, 48, 49 ,50]Humans and other mammals have a working memory store that is anatomically distinct from a long term memory store. While sleeping, a high frequency oscillating wave form ( ~ 200 Hz) has been observed in the working memory region that appears to perform a fast replay of memories encoded during the day and this replay is coordinated by a slower oscillation to consolidate some of those memories into the long term memory store. Figures 9,10 and 15. [31, 33 , 52 , 53]In the Ferrari car example, the simultaneous perception of different aspects of the car stored in different anatomical regions appear to be made possible by phase synchronized oscillations across these regions- communication through coherence. Figure 7 (image Ba) and Figure 12 [7, 13]FiguresFigure 1. Oscillatory classes in the cortex. State of the art Buzsaki Lab [Open]Figure 2. a, Location of the recording electrodes. b, c, Raster plots of 25 pyramidal cells that were active during a 1-s period of spatial exploration out of 68 simultaneously recorded neurons. b, Neurons are arranged in order of physical position in the CA1 pyramidal layer (colour-code refers to locations in a). Vertical lines indicate troughs of theta waves (bottom trace). Location-specific synchrony is not apparent in the population activity. c, The same spike rasters shown in b, reordered by stochastic search over all possible orderings to highlight synchrony between anatomically distributed populations. 'Cell assembly' organization is now visible, with repeatedly synchronous firing of some subpopulations (circled). Organization of cell assemblies in the hippocampus, Nature 2003Figure 3. Pacemaker neuron network that drives breathing. The top left figure shows a collection of pacemaker neurons in brainstem that drive breathing under normal conditions. The red and the blue circles are excitatory pacemaker neurons - the grey circles are the inhibitory non-pacemaker neurons.These red and blue pacemaker neurons generate spikes without any input. The figure to its right shows a red pacemaker neuron functioning alone under low oxygen conditions (hypoxia) generating the gasping response - the other pacemakers ( white circles labeled E) and inhibitory neurons (white circles labeled I) have gone silent. Pacemaker neurons and neuronal network: an integrative view, Current Opinion in Neurobiology, 2004Figure 4. Central pattern generators. (a) Early work suggested two hypotheses for the generation of rhythmic and alternating movements. In the reflex chain model (left) sensory neurons innervating a muscle fire and excite interneurons that activate motor neurons to the antagonist muscle. Right, in a central pattern generator (CPG) model a central circuit generates rhythmic patterns of activity in the motor neurons to antagonist muscles. (b) Fictive motor patterns resemble those recorded in vivo. Top left, picture of a lobster with electromyographic recording (EMG) wires implanted to measure stomach motor patterns in the behaving animal. Top right, EMG recordings showing that triphasic motor pattern generated by the LP, PY, and PD neurons. Modified from [34]. Bottom left, in vitro preparation, showing the dissected stomatogastric nervous system in a saline-filled dish with extracellular recording electrodes on the motor nerves and intracellular recordings from the somata of the stomatogastric ganglion motor neurons. Bottom right, unpublished recordings by V. Thirumalai made in vitro from the stomatogastric ganglion of the lobster, Homarus americanus. The top three traces are simultaneous intracellular recordings from the somata of the LP, PY, and PD neurons, and the bottom trace is an extracellular recording from the motor nerve that carries the axons of these neurons. Note the similarity of the in vivo recordings and the fictive motor patterns produced in vitro in the absence of sensory inputs. STG, stomatogastric ganglion; OG, esophageal ganglion; CoG, commissural ganglion; lvn, lateral ventricular nerve. Central pattern generators and the control of rhythmic movements, Cell 2001Figure 5. Cellular mechanisms underlying pattern generation. (a) Neurons have different intrinsic properties. Some neurons fire bursts of action potentials endogenously (panel 1). In some neurons depolarizing current pulses trigger plateau potentials that outlast the duration of the depolarization but that can be terminated by hyperpolarizing current pulses (panel 2). Some neurons respond to inhibition with rebound firing (panel 3), and others show spike frequency adaptation (panel 4). (b)Rhythms can be generated by endogenous bursters, or can be an emergent property of synaptic coupling between non-bursting neurons. In pacemaker driven networks a pacemaker neuron or neuron (red) can synaptically drive an antagonist (green) to fire in alternation. The simplest example of a network oscillator is one formed between two neurons that fire non-rhythmically in isolation, but fire in alternating bursts as a consequence of reciprocal inhibition.Central pattern generators and the control of rhythmic movements, Cell 2001Figure 6. Oscillatory coupling mechanisms. (a) Schematic view of the human brain showing hot spots of transient gamma oscillations (i–iv) andtheta oscillation in the hippocampus (HI); entorhinal cortex (EC). Oscillators of the same and different kind (e.g., theta, gamma) caninfluence each other in the same and different structures, thereby modulating the phase, amplitude, or both. (b) Phase-phase coupling ofgamma oscillations between two areas. Synthetic data used for illustration purposes. Coherence spectrum (or other, more specific,phase-specific measures) between the two signals can determine the strength of phase coupling. (c) Cross-frequency phase-amplitudecoupling. Although phase coupling between gamma waves is absent, the envelope of gamma waves at the two cortical sites is modulatedby the common theta rhythm. This can be revealed by the power-power correlation (comodugram; right). (d) Gamma phase-phasecoupling between two cortical sites, whose powers are modulated by the common theta rhythm. Both gamma coherence and gammapower-power coupling are high. (e) Cross-frequency phase-phase coupling. Phases of theta and gamma oscillations are correlated, asshown by the phase-phase plot of the two frequencies. (f) Hippocampal theta oscillation can modulate gamma power by its duty cycleat multiple neocortical areas so that the results of the local computations are returned to the hippocampus during the accrual(‘‘readiness’’) phase of the slow oscillation. Mechanisms of gamma oscillations, Annual review Neurosciance 2012 [Open]Figure 7.Putative functions of phase synchronization. A | Neural oscillations may show phase synchronization (left; stable phase relationships) or may show no phase synchronization (right; variable phase relationships). Methods for the quantification of phase synchronization have been described extensively elsewhere116, 142. B | Potential roles of phase synchronization in neural processing. Blue curves represent oscillations of neural assemblies in two brain regions, arrows denote interregional information transfer. Ba | Phase synchronization of neural assemblies coordinates the timing of synaptic inputs to a common target region. Coincident activity (indicated by the box surrounding two coinciding spikes) thus reliably induces action potentials. Bb | Phase synchronization between multiple brain regions allows for efficient information transfer (indicated by the arrows) during excitable periods (the box indicates the first such period). Bc | Precise timing of action potentials resulting from phase synchronization between two regions can induce spike timing-dependent plasticity of the synaptic connections (depicted on the right) between these regions. Consequently, communication is facilitated further (indicated by thicker arrows). Bd | The putative function of theta phase synchronization between two regions. The propensity of action potentials that are propagated from region 2 to region 1 (indicated by the arrows) to induce synaptic plasticity in region 1 depends on the theta phase in region 1 during which the action potentials arrive. Therefore, phase synchronization in the theta range may serve to recruit memory-related regions (for example, the hippocampus) during periods of high susceptibility to synaptic potentiation (solid arrows). LTD, long-term depression; LTP, long-term potentiation. The role of phase synchronization in memory processes, Nature reviews 2011Figure 8. Phase amplitude Cross Frequency Coupling (CFC) occurs between distinct brain rhythms, but varies as a function of cortical area and task demands... The functional role of cross-frequency coupling, Cell, 2010 [Open]Figure 9. Reactivation of spike sequences. This figure shows a schematic illustration of how CA1 pyramidal cells tend to fire in the same order during sleep as during a prior track running session [37,38]. Upper panel: firing probability of six hippocampal pyramidal cells A–F as a function of the location of the rat as it traverses the linear track.Bottom panels: spike times of the same cells during sleep before and after the track running. Note that in the first sleep (the sleep before track running), cells fire in an order that is unrelated to ensemble firing patterns during subsequent track running. However, in sleep after exploration, the order of cell firing during an SWR reflects the order in which the cells fired during track running.Play it again:reactivation of waking experience and memory, Cell 2010 [Open]Figure 10. Proposed roles of the prefrontal cortex (PFC) in the formation and recall of remote memories. Initially, memories are encoded in hippocampal–neocortical networks (A, thick lines). At this early time point, the hippocampus is crucial for integrating information from distributed cortical modules, each representing individual components of a memory. However, over time direct projections from the hippocampus are thought to transfer a high-order representation of the memory to the PFC (B), which then uses this information to facilitate the transfer of information from the hippocampus to the neocortex, via the entorhinal and perirhinal cortices. As initially proposed for the hippocampus, the PFC may also use this version of the memory to strengthen the connections between the distributed cortical modules involved in the memory (thick lines), and to integrate the memory within related preexisting memories. Later, the PFC may also use this memory to identify and recall context-relevant information from remote memory stores. Finally, during recall of remote memories, the PFC appears to inhibit hippocampal activity (blue line), thereby preventing the encoding of redundant information. Nature Reviews Neuroscience, Frankland & Bontempi, 2005. Hippocampal memory consolidation during sleep: a comparison of mammals and birds. biol Rev Camb Philos Soc. 2011[Open]Figure 11. Segregation of cell assemblies by inhibition. A. A ring of pyramidal neurons (1–6), mutually innervating an interneuron (i). The synaptic strength between the interneuron and pyramidal cell 4 is stronger than between other pairs. When pyramidal cell one receives an input (arrow), cells 1 to 3 are activiated while 4 to 6 remain silent (segregated).... Neural syntax: cell assemblies, synapsembles, and Readers[Open]Figure 12. Individual subdural recording sites from the patients studied by Watrous et al.1 (blue, prefrontal; green, parietal; orange, precuneus; yellow, parahippocampal).The red oscillation (1–4 Hz) represents coherence between brain regions during spatial memory. The orange oscillation (7–10 Hz) represents coherence between these regions during temporal memory. Multiplexed memories:a view from human cortex, Nature Neuroscience 2013[Open]Figure 13. Power spectrum of EEG from the right temporal lobe in a sleeping human subject. Subdural recording. Note the near-linear decrease of log power with increasing log frequency from .5 to 100 Hz. Neuronal oscillations in cortical networks, Science 2004[Open]Figure 14. Schematic of a neural code. The ovals at top represent states of the same network during two gamma cycles (active cells are black and constitute the ensemble that codes for a particular item). Different ensembles are active in different gamma cycles. The Theta-Gamma Neural Code, Neuron 2013Figure 15. Three phenomena that occur during sleep have been linked to memory enhancement—slow-wave oscillations in brain electrical activity, reactivation of recent experiences, and changes in synaptic connectivity but the strength of the evidence (indicated by arrow thickness) varies. As shown in red, Yang et al. link both reactivation and slow-wave sleep to changes in synaptic connectivity that enhance learning. Memories-getting wired during sleep, Science 6, June 2014ReferencesSome of the references below require subscription for viewing while others have open access. The ones that have open access are marked "[Open]".State of the art, Buzsaki lab [Open]Neuronal oscillations in cortical networks - Science, 2004 [Open]Organization of cell assemblies in hippocampus, Nature 2003Pacemaker neurons and neuronal network: an integrative view, Current Opinion in Neurobiology, 2004Central pattern generators and the control of rhythmic movements, Cell 2001 [Open]Mechanisms of gamma oscillations, Annual review Neuroscience 2012 [Open]The role of phase synchronization in memory processes, Nature reviews 2011The functional role of cross-frequency coupling, Cell, 2010 [Open]Play it again:reactivation of waking experience and memory, Cell 2010 [Open]Hippocampal memory consolidation during sleep: a comparison of mammals and birds. biol Rev Camb Philos Soc. 2011[Open]Membrane Resonance Enables Stable and Robust Gamma Oscillations,Cerebral cortex, 2012Multifaceted roles for low-frequency oscillations in bottom-up and top-down processing during navigation and memory, NeuroImage 2014Multiplexed memories: a view from human cortex, Nature Neuroscience 2013 [Open] This is a review of the paper cited below [14]. A hypothesis called the 'spectral fingerprint' proposes that frequency band-specific inter-regional coherence subserves many cognitive processes. This hypothesis does not state that information is being encoded in low frequency oscillations. Rather, the idea is that setting two or more regions in phase coherence facilitates information transfer in single-unit volleys by local adjustments in likelihood of spiking.Frequency-specific network connectivity increases underlie accurate spatiotemporal memory retrieval, Nature Neuroscience, 2013 [Open]Gamma Oscillatory Firing Reveals Distinct Populations of Pyramidal Cells in the CA1 Region of the Hippocampus, Journal of Neuroscience, 2008 [Open]Recognition memory and theta-gamma interactions in the hippocampus, Hippocampus 2013Modulation of theta phase sync during a recognition memory task, Cognitive neuroscience and neuropsychology, 2012[Open]Phase-dependent neuronal coding of objects in short-term memory, PNAS 2009 [Open]Segmentation of spatial experience by hippocampal theta sequences, Nature Neuroscience 2012 [Open] This paper suggests based on encoding of spatial paths in rats, a mechanism for cognitive chunking of experience. When a rat navigates its environment, ongoing experiences are compressed into theta sequences. The spatial paths represented by theta sequences extend ahead of the animal while accelerating and begin farther behind the animal during deceleration.Spontaneous synchronization in nature IEEE 1997 [ Open] Discusses the prevalence of mutual synchronization of oscillators in nature such as the synchronized flashing on an off by Southeast Asian fireflies. When they begin to congregate in the early hours of night, their flickerings are uncoordinated. But as the night goes on, they build up synchrony and eventually whole treefuls pulsate in silent concert. Steven Strogatz, the author of this paper also mentioned Winfree's work on the nonlinear dynamics of large systems of coupled oscillators. Coupled oscillators are one of models used to explain the the emergence of synchronized oscillations among neurons.Concept cells: the building blocks of declarative memory functions, Nature reviews 2012 [Open]The Theta-Gamma Neural Code, Neuron 2013. This paper proposes a “neural code” of information processing/memory storage in the brain of rats though it remains to be seen if this code or a variant of it is ubiquitous across speciesFast Global Oscillations in Networks of Integrate-and-Fire Neurons with Low Firing Rates, Neural computation 1999 [ Open]The theta/gamma discrete phase code occuring during the hippocampal phase precession may be a more general brain coding scheme, Hippocampus 2005Layer and frequency dependencies of phase response properties of pyramidal neurons in rat motor cortex, European Journal of Neuroscience 2007Local field potentials, BOLD and spiking activity - relationships and physiological mechanisms, Nature 2010Theta-alpha cross-frequency synchronization facilitates working memory control - a modeling study, SpringerPlus 2013Analytical Insights on Theta-Gamma Coupled Neural Oscillators, Journal of mathematicl Neuroscience, 2013The principle of coherence in multi-level brain information processing, Progress in Biophysics and molecular biology 2013Neurophysiological and computational principles of cortical rhythms in cognition, Physiol Rev 2010 [Open] This review paper discusses a framework that goes beyond the conventional theory of coupled oscillators to explain field oscillations and reconciles the apparent dichotomy between irregular single neuron activity and field potential oscillations.Why there are compliementary learning systems in the hippocampus and neocortex:Insights from the successes and failures of connectionist models of learning and memory,Pshcological review 1995 [Open]A Synaptically Controlled, Associative Signal for Hebbian Plasticity in Hippocampal Neurons, Science 1997Hippocampal-cortical interaction during periods of subcortical silence, Nature 2012Reliability of spike timing in neocortical neurons, Science 1995 [Open] This paper offers evidence for a possible role for spike timing in the processing of information. A constant stimulus to a neuron leads to spike trains which become imprecise over time, whereas stimuli with fluctuations resembling synaptic activity (constant input along with computer generated filtered Gaussian white noise) produces spike trains with timings reproducible to less than 1 millisecond. Even though this experiment has no physiological significance since it does not factor in actual delays present in real life scenario (such as synaptic transmission delays) it is consistent with theories of cortical information processing where spike timing is important.Oscillatory correlates of memory in non-human primates, NeuroImage 2014Theta oscillations orchestrate medial temporal lobe and neocortex in remembering autobiographical memories, NeuroImage 2014[ Open]Principles of rhythmic motor pattern generation Phys. Review 1996Central pattern generators for bipedal locomotion, J. Math. Biol 2006[Open]The spike timing dependence of plasticity, Neuron 2012[Open] This paper reviews the cellular mechanisms for spike time dependent plasticity. When neuron A spikes ~0 to 20 msecs before neuron B, which it connects to fires, long term potentiation (connection strengthening) occurs. If neuron B precedes the spiking of neuron A by ~0 to 20-100 msecs, long term depression (connection weakening) occurs.Phase locking control in the Circle Map, Nonlinear dynamics 2007 This paper discusses how phase-locking between two oscillators happens when the ratio of their frequencies become locked in a ratio of p/q of integer numbers over some finite domain of parameter values.Brain oscillations and memory, Current opinion in neurobiology 2010 [Open]Working memory and neural oscillations: alpha-gamma versus theta-gamma codes for distinct working memory information? Cell 2014[Open]Detection of n:m phase locking from noisy data: application to magnetoencephalography, Physical review letters, 1998 [Open]Assessment of cross-frequency coupling with confidence using generalized linear models, NeuroImage 2013 [Open]Role of experience and oscillations in transforming a rate code into a temporal code, Nature 2002[Open]A Method for Event-related Phase/Amplitude Coupling, NeuroImage 2013[Open] The first author of this paper, Bradley Voytek is here on Quora.A θ-γ Oscillation Code for Neuronal Coordination during Motor Behavior, Journal of Neuroscience 2013Phase-amplitude cross-frequency coupling in the human nucleus accumbens tracks action monitoring during cognitive control, Frontiers in human neuroscience, 2013[Open]Cross-Frequency Phase-Phase Coupling between Theta and Gamma Oscillations in the Hippocampus, Journal of Neuroscience, 2013[Open]Neural syntax: cell assemblies, synapsembles and readers, Neuron 2010[Open]High-order synchronization, transitions, and competition among Arnold tongues in a rotor using harmonic forcing, Physical Review 2008 [Open] Discusses the possibility of two or more coupled oscillators becoming synchronized when their autonomous frequencies are different but close, where the synchronization occurs as adjustment of those frequencies due to coupling. This form of coupling is in contrast to weak coupling where the frequencies of the individual oscillators do not change but oscillations still emerge due to coupling.Memories-getting wired during sleep, Science 6, June 2014Sleep promotes branch-specific formation of dendritic spines after learning Science, 6 June 2014Updated additional referencesA recent video lecture (Feb 2017) on the neuroscience of consciousness. Has references embedded in video related to oscillations. One particular mention of a paper (after 30 mins) examines how the brain perhaps reduces it prediction errors by adjusting its prediction in concert with sensory input - all within a single oscillatory cycle. The paper mentioned in video Journal of Cognitive Neuroscience - 28(9):1318 - Full Text (not open access)30 Sept 2019An informative talk on how the brain computes. It offers an explanation of how different sensory inputs (vision, auditory) that occur simultaneously can form associations when the inputs are projected randomly to a downstream region. This can happen not just across inputs but within a sensory stream. For instance, an experiment of former President Obama’s face shown along with an Eiffel tower makes a neuron that only fired for Eiffel tower later fires when shown just the face of the former President. Even if only a model, it is biologically grounded (for the most part) and the primitives for computation are fairly simple. The paper https://ccneuro.org/2019/proceedings/0000998.pdf

Josh Gordon Fantasy Outlook: Can he contribute for Seahawks?What does the return of Seattle Seahawks wide receiver Josh Gordon mean for your fantasy football team as the playoffs near?What's in this article?The Flash is back. Jeremy Fowler of ESPN has confirmed that Seattle Seahawks wide receiver Josh Gordon has been officially reinstated by the NFL and will resume his career. Josh Gordon’s return to the Seahawks has potentially massive implications, not just for the Seattle Seahawks themselves, but also for fantasy football team owners across the nation.Seahawks WR Josh Gordon reinstated after months of waitingThe NFL has suspended Gordon five times throughout his NFL career for similar issues related to violating the league policy on performance-enhancing drugs and substances of abuse. Most recently, the NFL suspended Gordon indefinitely last December, after playing five games with the Seattle Seahawks.As a free agent, Gordon re-signed with the Seahawks amidst his ongoing suspension and first applied for reinstatement in mid-June. Gordon’s suspension lasted into the season, and the NFL notably reinstated Antonio Brown of the Tampa Bay Buccaneers before Gordon. But the Gordon suspension is now over as well, and while questions remain regarding his long-term outlook, the focus is now on his viability as a weapon for the Seahawks in the latter stages of the 2020 season.What is Josh Gordon’s availability as a fantasy threat?Now that Gordon has been officially reinstated, he can return to the Seahawks’ facilities as soon as he passes through team protocols. At that time, he can begin the process of rekindling his chemistry with the Seahawks’ offense, most notably quarterback Russell Wilson.With that being said, Gordon will not be able to hit the field in a Seahawks’ uniform for three more weeks; while the NFL’s intent to reinstate Gordon has been made public, Gordon’s actual reinstatement won’t occur until the Monday after Week 15. This means that Gordon can only be active for Week 16 and Week 17 in the 2020 season and will consequently only be available for the final week of the fantasy football playoffs for many.Latest Videos from PFNCan Josh Gordon help you win your fantasy football league?Josh Gordon won’t be on your starting lineup, or the Seahawks starting lineup, until Week 16 at the earliest, but is it a good idea to stash him until then, as a not-so-secret weapon for the playoffs?It’s tough to project Gordon’s impact for the Seahawks down the stretch. Last year, Gordon played five games for the Seahawks, and in those games, he only caught seven passes for 139 yards while exceeding 50% of the team’s offensive snaps only once. He averaged just over two targets a game in that stretch, and while he did enough to earn another contract from Seattle, he didn’t sell many on his ability to be a consistent threat.This time around, Gordon will have another chance to earn a greater target share, but the circumstances are different in 2020. While he won’t have to contend with Phillip Dorsett for snaps — Dorsett has been on injured reserve since the start of the season with a foot injury — he will have to contend with a more-established DK Metcalf and an ever-consistent Tyler Lockett.The situational factors surrounding Gordon’s return in 2020Both Metcalf and Lockett are easily on pace to eclipse their target numbers from 2019 and have established themselves as a reliable one-two punch for Russell Wilson. Metcalf is embarking on a defining campaign as a transcendent WR1 giving off shades of Calvin Johnson, while Lockett has complimented Metcalf well, already with 70 catches through 11 games.Josh Gordon likely isn’t going to siphon much work from Metcalf and Lockett in such a short span, but he can work toward taking reps from David Moore, the team’s third wide receiver. Moore has been a surprisingly consistent part of the Seahawks’ offense, logging at least three targets in all but two games so far this season, and he’s already matched his career-high touchdown total.While Moore has been solid, Gordon is a clearly superior talent who should be fresh after another extended absence. Gordon can’t match the volume of Metcalf and Lockett, but if he can take some of Moore’s touchdown production, it would be a good start.Gordon faces tough matchups when he returns to the field in Week 16 and 17Unfortunately for Gordon, the opposition faced in his two games in 2020 will not be ideal. In Week 16, the Seattle Seahawks take on the Los Angeles Rams, who have allowed the fewest fantasy points per game to wide receivers among NFL teams this season. Back in November, the Rams’ defense held Russell Wilson to under 250 yards passing and logged two interceptions, and that pressure will no doubt be heightened in Week 16, as these two teams presumably fight for NFL playoff real estate.In Week 17, Seattle gets a slight respite, but only that, as they’ll take on the San Francisco 49ers, a defense that has allowed the 10th-fewest fantasy points per game to opposing wide receivers. The 49ers game will be somewhat circumstantial; if Seattle wins in Week 16 in Los Angeles, one can assume they’ve likely locked up the NFC West, and at that point, they might cede more opportunities to a player like Gordon while keeping Metcalf and Lockett injury-free for the playoffs. However, for many leagues, Week 17 is too late to impact the outcome of fantasy championships.Gordon’s 2020 fantasy playoffs outlookThe context doesn’t bring a ringing endorsement for Josh Gordon, but sometimes it’s important not to be frozen by analysis paralysis. Gordon will have a tough time earning an increased role right from the start, and he will have challenging opposition on the other side of the ball, but let’s not forget who Gordon is. He’s a 6-foot-3, 225-pound receiver with 4.5 speed, excellent explosiveness, and big-play aptitude wherever he ends up. While he only caught seven passes last season, he averaged almost 20 yards per catch, and that boom-or-bust nature is something you may be inclined to bank on in the fantasy playoffs.Josh Gordon is far from a certainty, and it would be advisable to have other options available across your fantasy football roster. But at this point in the season, injuries have a way of thinning out those options. At the very least, teams may not be adequately prepared for Gordon. With enough attention already being diverted to Metcalf and Lockett, Gordon could be in a situation that frees him up to make plays in late December. It’s all speculative, but Gordon does have the physical capabilities to transcend the context and produce. Now, it’s up to you to decide whether you want to take that chance.Want more fantasy football analysis and news?Be sure to follow us on Twitter: @PFN365 to stay up to date with all things around the NFL and the 2020 fantasy football season. Also, continue to visit Pro Football Network for NFL news and in-depth analysis while also seeing our fantasy football section for more coverage and up-to-date rankings.

Indian armoured is one of the biggest and powerful armoured corps in the world with around 4300 tanks and 8700 armoured vehicles. Tanks and armoured vehicles can play a vital role in land warfare it was the German tanks only which helped Hitler to capture Paris and the Battle of Asal Uttar which was a turning point in the 1965 Indo-Pak war. India currently holds 5th rank in total combat Tanks strength list. Indian army operates Russian made T-72 Ajeya, T-90S “Bhisma” and T-90M tanks followed by Indian Arjun Main Battle Tank (MBT).Graveyard of Pakistani Tanks: Battle of Asal Uttar 1965Indian Army currently uses 124 (1 regiment -62 Tanks) Arjun Mk 1 across two regiments and 118 new improved versions Mk 1A tanks will be procured by the Indian Army in near future. Arjun is widely criticized for its weight, logistic issues, low serviceability, and timeline. In 2016 Comptroller and Auditor General (CAG) of India report said that Arjun tanks have not been operational since 2013 due to a lack of spares.In 2017 it was reported that the DRDO had received the necessary imported spares to repair the faults that had grounded 75% of the fleet.The Arjun tank was fielded during the Ashwamedha exercise in the deserts of Rajasthan in 2007. The army highlighted several deficiencies that included “deficient fire control system”, “inaccuracy of its guns”, “low speeds in tactical areas” and persistent “inability to operate in temperatures over 50 degrees Celsius”. In the 2007 winter trials, the Indian army deemed Arjun’s performance unsatisfactory, including at least four engine failures leading the DRDO to suggest that the unsatisfactory performance of the engine during the winter trials was due to sabotage.All the above-mentioned problems gave this indigenous tank a tag of ‘failure’. But these problems have been rectified by DRDO and the tank improved within 2 years. This also eventually led to the development of Arjun Mk.1A and Mk2, an advanced version of the Arjun MBT.In spite of a proven, indigenous MBT and DRDO having created capabilities within the country for the fabrication of Hull and Turret for accelerated deliveries, the Cabinet Committee on Security in 2019 approved the procurement of 464 Russian made T-90MS main battle tanks in a Rs 13,400 Cr deal.VARIANTS –Arjun Mk1 the basic and first tank of this series.Arjun Mk1 A : A 68 tonne improved variant of Arjun Mark 1, specifically requested by the Indian Army for better firepower, protection, improved weight distribution and mobility. The number of foreign made imported components are also reduced from 63 to 59 percent with around 72 improvements and 14 major improvements.Arjun Mk2 – Arjun Mark II has a total of 93 upgrades, including 13 major improvements. The indigenous content was also increased to around 50%. This variant will be lighter than MK1A and will be less than 65 tonnes.Tank EX: Prototypes have been built for a new tank obtained by coupling a T-72 chassis and an Arjun turret.Challenges and CriticismWeightArjun Mk1 and Mk1 A are heavily criticized for their huge weight of 68 tonnes when compared to the Russian T-90 and T-72 which weight only 44-46 tonnes.The main reason for the increase in weight is the addition of one extra crew member. Russian based tanks consist crew of 3 members i.e – Commander, Driver and Gunner whereas Arjun Tank is based on the western design which has an extra crew for loading i.e Loader, Russian tanks are autoloader.Thus an increase in the crew count will definitely increase the overall weight of the tank. The weight of some of the most advance and proven western tanks also weights near Indian Arjun MBT :Eg – Challenger 2 -62.5 tonnes, with a combat-ready weight of 75.0 tonnes, Leopard 2A6M – 62.5 tonnes and Abrams M1A1 – 67.5 tonnes.Arjun is powered with a 1400 HP engine which gives it a high power to weight ratio and high mobility. The Arjun also features a hydro-pneumatic suspension. This coupled with the Arjun’s stabilization and fire control system allows the tank excellent first-hit probability against moving targets while on the move.LogisticsThis can be regarded as one of the biggest problems. Logistics refers to the overall process of managing how resources are acquired, stored, and transported to their final destination.The weight of Arjun restricts it for quick deployment, in recent times T-72 and T90 were deployed in Ladhak because of their low weight. The Arjun MBT is specially built for desert warfare in India’s western border, not for the Himalayas and hilly terrain. The Arjun tank is significantly heavier than the Soviet-legacy tanks used presently by the Indian Army, and required changes to the army’s logistics establishment, including new railroad cars to transport the bigger and heavier Arjuns this increased the cost of the whole project.Arjun has a cannon of 120mm whereas the T90 and T72 have 125mm guns this increases the requirement of different types of ammunition and explosive rounds.Change in the PhilosophyPositions of crewmembers in a Russian T-72B3 tank. The driver (3) is seated in the vehicles front, commander (1) and gunner (2) are positioned in the turret, directly above the carousel (4), which contains the ammunition for the autoloading mechanism. @WikiwandAs mentioned earlier Arjun Tank is based on western philosophy which consists of 4 crew members whereas T-72 and T-90 are based on 3 crew Russian philosophy. This change causes a major problem for the tank operators. The training for both the types of tank is different and for a country like India which uses 4000+ tanks based on Russian philosophy, it is difficult to switch to western philosophy overnight. This will surely take time for operators to adapt to the configuration of the Arjun tank but with time and proper training, this problem will be solved in the future.TimelineThe development of the Arjun tank began in 1972 by the Combat Vehicles Research and Development Establishment (CVRDE) a DRDO lab and the first batch of 16 production version Arjun tanks were received in 2004 to the 43 Armoured Regiment.Did it take around 30+ years to produce a tank that too based on different philosophies? It took time because India had no experience in this field as it was the first indigenous tank built by India. The continuous change in the requirements of the Tank with time and technology extended the aimed period for completion. The same issue was faced by the Tejas fighter jet.The False Claim Of IndigenousIn the phase of induction around 69% and most of the parts were imported which included the engine, transmission, gun barrel, tracks, and fire control system. Due to the delay in indigenizing the required components, the supply of spares has stopped. In the absence of spare support, MBT Arjun was not operational for some time during 2013.Later on, several parts were either replaced by indigenous systems or were co-developed with foreign firms. The tracks which were being supplied by German company Diehl are now being manufactured by L&T. 1400 HP engine is still provided by German company MTU as the setup and developing an engine for such a small number of the tank is not favored, with the increase in order an indigenous engine project can be started.ArmamentTank Ex firing ATGMThe allegations regarding the armament of Arjun MBT were recently collapsed when Tank Ex (chassis of the T-72M1 Ajeya and turret and weapon system of the Arjun) successfully test-fired the indigenously-developed Laser-Guided Anti Tank Guided Missile (ATGM) by DRDO on 22 September 2020 followed by successful trails of it from Arjun MBT on 1 October 2020 at KK Ranges.Trials of Israeli LAHAT missiles were successful on Arjun at a long-range but were not satisfactory when tested at a close range of 500m. DRDO’s CLGM SAMHO ( Canon launched Guided Missile – Semi-active missile homing) was fired at a range of around 3 km in the test and successfully took out a target. While the missile is currently being tested from the MBT Arjun, it has been designed so that it can be fired from other platforms too. DRDO scientists said the operability of the missile from a tank is a key feature in armored warfare. The missile has the capability of engaging with the target even if it is not in the line of sight.The questions on its rifled canons were also raised, as most of the modern tanks use a smoothbore gun. A rifled barrel has lands and grooves that cause the projectile to spin when it exits the muzzle (end of the barrel). A smooth bore has no lands and grooves. A smooth bore does not encourage the projectile to spin as a rifled barrel does.From @RiverValleyRiffled tank guns have better accuracy than smoothbore tank guns. The use of HESH (High Explosive Squash Head) rounds which are more effective against buildings and infantry fighting vehicles as well as being able to damage other tanks without penetrating the amour is very useful in riffled guns.The use of APFSDS (Armoured Piercing Fin Stabilised Discarded Sabot) is not that effective in rifled guns, another Armour piercing discarded sabot can be used in rifled guns which is without fins and prevent overspin of ammunition, although laser-guided ATGM is more effective against ERA (Explosive Reaction Armour).APS MissingAn active protection system (APS) is a system (usually for a military application) designed to prevent line-of-sight guided anti-tank missiles/projectiles from acquiring and/or destroying a target.APS has two types of protection systemsSoft Kill – countermeasures consist of multispectral aerosol smoke grenades that can blind all missiles including fire and forget missiles, Electro-Optical/ Infrared (EO/IR) jammers can jam Semi-Active Command Line of Sight (SACLOS) missiles.Hard Kill – this measure in general physically affects the incoming warhead/missile using either blast and/or fragment action. But these systems comes at a price of an increase in weight and power constraints.Video showing the working of Israeli Rafael TROPHY APSCurrently, none of the Indian tanks have APS hard kill feature, new T-90MS being procured has a new APS, however, the variant India would receive will be without Arena APS. Indian tanks rely on ERA (explosive reactor armour) for their protection.Performance Of Arjun Against T90T-90 BhishmaIn March 2010 Arjun squadron (14 tanks) competed against the T-90 squadron. A Business Standard report stated that each squadron was given three tactical tasks; each involved driving across 50 kilometers of desert terrain and then shooting at a set of targets. Each tank had to fire at least ten rounds, stationary and on the move, with each hit being carefully logged. In total, each tank drove 150 km and fired between 30–50 rounds. The trials also checked the tanks’ ability to drive through water channels 5-6 deep. A Ministry of Defence press release reported that the Arjun demonstrated excellent performance under various circumstances, such as driving cross-country over rugged sand dunes, detecting, observing, and quickly engaging targets, accurately hitting targets – both stationary and moving, with pinpoint accuracy. It displayed accurate and quick target acquisition capability during day and night in all types of weather and shortest possible reaction time during combat engagements, which is about the same level as the Russian T-90, if not better.Via — Business StandardUpgradesAs part of improving the Arjun to the Mark 2 variant, DRDO is continuing to develop new technology systems for MBT Arjun, to improve performance in areas like automatic target locating, tracking, and destruction. The Arjun Mk.2 variant is being developed in coordination with and with the involvement of the Indian Army and will feature several modifications that are being sought by it.DRDO has developed the Tank Urban Survival Kit which is a series of improvements to the Arjun intended to improve fighting ability in urban environments which includes defensive aids like laser warning, IR jammer, and aerosol smoke grenade system.DRDO and Israeli Elbit Limited also developed a Laser Warning Control System (LWCS) for Arjun which will help in reducing the signatures of the tank in the battlefield and improve its survivability. Barracuda Camouflaging Limited a Gurgaon-based private sector with DRDO is also developing the Mobile Camouflaging System (MCS) technology to help the tank reduce the threat of interference from all types of sensors and smart munitions of the enemy in the tank’s systems.Mobile Camouflaging System (MCS) reducing the signature of TankThe upgrade also includes a new improved 1500 hp engine. An anti-helicopter round is under development as well.Indian Army Armoured Corps has cleared the upgraded Arjun Mk.1A after the successful completion of final integration tests conducted in 2019 in Rajasthan. It comes with 72 improvements over Arjun Mk.1 with 14 major upgrades. Arjun Mk.1A is ready to undergo mass production at Heavy Vehicle Factory and is waiting for orders from the Indian Army.