Chaotic Signatures of Heart Rate Variability and Its Power Spectrum in Health, Aging and Heart Failure

A paradox regarding the classic power spectral analysis of heart rate variability (HRV) is whether the characteristic high- (HF) and low-frequency (LF) spectral peaks represent stochastic or chaotic phenomena. Resolution of this fundamental issue is key to unraveling the mechanisms of HRV, which is critical to its proper use as a noninvasive marker for cardiac mortality risk assessment and stratification in congestive heart failure (CHF) and other cardiac dysfunctions. However, conventional techniques of nonlinear time series analysis generally lack sufficient sensitivity, specificity and robustness to discriminate chaos from random noise, much less quantify the chaos level. Here, we apply a ‘litmus test’ for heartbeat chaos based on a novel noise titration assay which affords a robust, specific, time-resolved and quantitative measure of the relative chaos level. Noise titration of running short-segment Holter tachograms from healthy subjects revealed circadian-dependent (or sleep/wake-dependent) heartbeat chaos that was linked to the HF component (respiratory sinus arrhythmia). The relative ‘HF chaos’ levels were similar in young and elderly subjects despite proportional age-related decreases in HF and LF power. In contrast, the near-regular heartbeat in CHF patients was primarily nonchaotic except punctuated by undetected ectopic beats and other abnormal beats, causing transient chaos. Such profound circadian-, age- and CHF-dependent changes in the chaotic and spectral characteristics of HRV were accompanied by little changes in approximate entropy, a measure of signal irregularity. The salient chaotic signatures of HRV in these subject groups reveal distinct autonomic, cardiac, respiratory and circadian/sleep-wake mechanisms that distinguish health and aging from CHF

A biophysical model of endocannabinoid-mediated short term depression in hippocampal inhibition

Memories are believed to be represented in the synaptic pathways of vastly interconnected networks of neurons. The plasticity of synapses, that is, their strengthening and weakening depending on neuronal activity, is believed to be the basis of learning and establishing memories. An increasing number of studies indicate that endocannabinoids have a widespread action on brain function through modulation of synap–tic transmission and plasticity. Recent experimental studies have characterised the role of endocannabinoids in mediating both short- and long-term synaptic plasticity in various brain regions including the hippocampus, a brain region strongly associated with cognitive functions, such as learning and memory. Here, we present a biophysically plausible model of cannabinoid retrograde signalling at the synaptic level and investigate how this signalling mediates depolarisation induced suppression of inhibition (DSI), a prominent form of shortterm synaptic depression in inhibitory transmission in hippocampus. The model successfully captures many of the key characteristics of DSI in the hippocampus, as observed experimentally, with a minimal yet sufficient mathematical description of the major signalling molecules and cascades involved. More specifically, this model serves as a framework to test hypotheses on the factors determining the variability of DSI and investigate under which conditions it can be evoked. The model reveals the frequency and duration bands in which the post-synaptic cell can be sufficiently stimulated to elicit DSI. Moreover, the model provides key insights on how the state of the inhibitory cell modulates DSI according to its firing rate and relative timing to the post-synaptic activation. Thus, it provides concrete suggestions to further investigate experimentally how DSI modulates and is modulated by neuronal activity in the brain. Importantly, this model serves as a stepping stone for future deciphering of the role of endocannabinoids in synaptic transmission as a feedback mechanism both at synaptic and network level

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This mixed media piece was created by constructing a copper frame and adding different elements that were made up of library cards. The larger elements have a wood base to give them the weight that is needed to balance the piece with the cards collaged on top and painted or stained using acrylic paint. The smaller, round elements were constructed only of library cards built in a circular pattern and were later spattered with acrylic paint. The middle element, which was created to add a sense of playfulness to the piece, was constructed by using a copper frame and adding fishing line and library cards to help add length to the piece and tie it all together. This work, and a few of my other works, was inspired by Alexander Calder’s mobiles and his many sculptural works.https://csuepress.columbusstate.edu/card_catalog_artwork/1001/thumbnail.jp

Laughter and the Death of the Comic: Charlie Chaplin's The Circus and Limelight in Light of the Ethics of Emmanuel Levinas

Using the work of Emmanuel Levinas, this article sheds light on Charlie Chaplin's The Circus (1928), a piece that so far eluded the critics, despite its immense popularity with theater viewers. I show that it is not Chaplin's lack of inventiveness that makes the Tramp risk his life on the tightrope 'for nothing'. It is, on the contrary, Chaplin's intuitive sense that makes him believe, anticipating Levinas, that it is human and simple for a person to help another for no benefit. It is this point that cinema-goers understood more easily than we, scholars, may think. Starting with The Circus (1928) I demonstrate that this film, which critics have underestimated due to its 'pointless' ending, becomes meaningful once interpreted as promoting radical for-the-other ethics. My argument about The Circus is supported by close reading as well as Chaplin's own remarks and his later talkie Limelight (1952) in which similar ideas are expressed more openly through language and through the ending scene, with the protagonist dying on stage, to the sounds of roaring laughter of the audience

A CMOS Current-Mode Dynamic Programming Circuit

Dynamic programming (DP) is a fundamental algorithm for complex optimization and decision-making in many engineering and biomedical systems. However, conventional DP computation based on digital implementation of the Bellman–Ford recursive algorithm suffers from the “curse of dimensionality” and substantial iteration delays which hinder utility in real-time applications. Previously, an ordinary differential equation system was proposed that transforms the sequential DP iteration into a continuous-time parallel computational network. Here, the network is realized using a CMOS current-mode analog circuit, which provides a powerful computational platform for power-efficient, compact, and high-speed solution of the Bellman formula. Test results for the fabricated DP optimization chip demonstrate a proof of concept for this solution approach. We also propose an error compensation scheme to minimize the errors attributed to nonideal current sources and device mismatch.Croucher FoundationAmerican Society for Engineering Education. National Defense Science and Engineering Graduate FellowshipNational Institutes of Health (U.S) ( EB005460)National Institutes of Health (U.S) ( RR028241