Markov chain Dotaz Zobrazit nápovědu
- MeSH
- pravděpodobnost MeSH
- učení MeSH
Applications of Mathematics ; 29
361 s.
- Konspekt
- Statistika
- NLK Obory
- statistika, zdravotnická statistika
1st ed. xvii, 486 s., grafy, tab.
- Konspekt
- Statistika
- NLK Obory
- statistika, zdravotnická statistika
The nature of neural codes is central to neuroscience. Do neurons encode information through relatively slow changes in the firing rates of individual spikes (rate code) or by the precise timing of every spike (temporal code)? Here we compare the loss of information due to correlations for these two possible neural codes. The essence of Shannon's definition of information is to combine information with uncertainty: the higher the uncertainty of a given event, the more information is conveyed by that event. Correlations can reduce uncertainty or the amount of information, but by how much? In this paper we address this question by a direct comparison of the information per symbol conveyed by the words coming from a binary Markov source (temporal code) with the information per symbol coming from the corresponding Bernoulli source (uncorrelated, rate code). In a previous paper we found that a crucial role in the relation between information transmission rates (ITRs) and firing rates is played by a parameter s, which is the sum of transition probabilities from the no-spike state to the spike state and vice versa. We found that in this case too a crucial role is played by the same parameter s. We calculated the maximal and minimal bounds of the quotient of ITRs for these sources. Next, making use of the entropy grouping axiom, we determined the loss of information in a Markov source compared with the information in the corresponding Bernoulli source for a given word length. Our results show that in the case of correlated signals the loss of information is relatively small, and thus temporal codes, which are more energetically efficient, can replace rate codes effectively. These results were confirmed by experiments.
- MeSH
- biomedicínské inženýrství metody přístrojové vybavení MeSH
- databáze faktografické využití MeSH
- koronární nemoc patofyziologie patologie MeSH
- lidé MeSH
- Markovovy řetězce MeSH
- neuronové sítě (počítačové) MeSH
- počítačové zpracování signálu MeSH
- srdeční ozvy fyziologie MeSH
- teoretické modely MeSH
- Check Tag
- lidé MeSH
The P2X4 receptor (P2X4R) is a member of a family of purinergic channels activated by extracellular ATP through three orthosteric binding sites and allosterically regulated by ivermectin (IVM), a broad-spectrum antiparasitic agent. Treatment with IVM increases the efficacy of ATP to activate P2X4R, slows both receptor desensitization during sustained ATP application and receptor deactivation after ATP washout, and makes the receptor pore permeable to NMDG+, a large organic cation. Previously, we developed a Markov model based on the presence of one IVM binding site, which described some effects of IVM on rat P2X4R. Here we present two novel models, both with three IVM binding sites. The simpler one-layer model can reproduce many of the observed time series of evoked currents, but does not capture well the short time scales of activation, desensitization, and deactivation. A more complex two-layer model can reproduce the transient changes in desensitization observed upon IVM application, the significant increase in ATP-induced current amplitudes at low IVM concentrations, and the modest increase in the unitary conductance. In addition, the two-layer model suggests that this receptor can exist in a deeply inactivated state, not responsive to ATP, and that its desensitization rate can be altered by each of the three IVM binding sites. In summary, this study provides a detailed analysis of P2X4R kinetics and elucidates the orthosteric and allosteric mechanisms regulating its channel gating.
- MeSH
- adenosintrifosfát metabolismus MeSH
- algoritmy MeSH
- gating iontového kanálu účinky léků fyziologie MeSH
- HEK293 buňky MeSH
- ivermektin metabolismus MeSH
- lidé MeSH
- Markovovy řetězce MeSH
- metoda terčíkového zámku MeSH
- purinergní receptory P2X4 účinky léků metabolismus fyziologie MeSH
- vazebná místa MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
