Physics of Life (2022) / Chapter Skim
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Pages 160-171
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From page 160... ...
Adaptation to input statistics is predicted by theories of neural coding that maximize the information captured in a limited number of action potentials given that the natural sensory world has intermittent dynamics (Chapter 2) , and in some cases it has been possible to show that the form of adaptation really does optimize information transmission, quantitatively.
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From page 161... ...
(C) Modulation of the rate of action potentials in response to sinusoidal variations of current or current variance.
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From page 162... ...
For a generation, the focus of these explorations was on the regulation of single genes in bacteria, for example the gene for one crucial enzyme in the consumption of a particular sugar. This work provided the paradigms for how information encoded in regulatory sequences of DNA (Chapter 2)
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From page 163... ...
more slowly, so that the calcium concentration provides a record of electrical activity; this is what makes possible the use of calcium-sensitive fluorescent proteins to monitor the electrical activity of neurons, as in Figure 3.13. Of all the ions that contribute to electrical current across the cell membrane, calcium is special because it both car ries electrical current and serves as a signaling molecule for various biochemical processes inside the cell.
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From page 164... ...
Differences of maximum 164 conductances as indicators of the state of activity of a neuron. a, Activity of P hysics of L ife model neurons with similar frequency and action potentials per burst is gener ated with gmaxCa, gmaxA, and gmaxKCa currents that differ by 1.4-, 7.0-, and 7.0-fold, respectively (inset histograms)
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From page 165... ...
It has been suggested that systems with this sort of behavior form a well-defined class of "sloppy models," neither robust nor finely tuned but with a full spectrum of parameter sensitivities. There is a substantial effort underway to understand the origins of this behavior, its connections to other ideas in statistical physics, and its implications for the dynamics of adaptation.
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From page 166... ...
, (d) generic circadian rhythm [31]
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From page 167... ...
The biological physics community entered the subject through models for networks of neurons, as described in Chapter 3. Statistical Physics Approaches to Learning The functions that are accomplished by a neural network are determined by the strengths of connections or "synaptic weights," among all the neurons in the network.
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From page 168... ...
This sort of behavior is seen in many learning problems, and the songbird experiments agree quantitatively with experimental predictions. Rather than using theory to understand macroscopic learning behaviors, other groups in the biological physics community have tried to push down to the mo lecular events at real synapses to understand how learning rules are implemented.
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From page 169... ...
H o w D o L i v i n g S y s t e m s N av i g at e P a r a m e t e r S pa c e ? 169 FIGURE 4.4 Songbirds learning to shift pitch in response to altered auditory feedback.
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From page 170... ...
community is playing a key role in sharpening these questions, and it is reasonable small i values) to en The structure of the cascade to expect substantial progress over the coming decade.
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From page 171... ...
Correlated patterns of amino acid substitutions within a protein family can be a signature of natural selection to restore physical interactions between residues that are in contact in the three dimensional structure of the protein. As discussed in Chapter 3, researchers from the biological physics community have used methods from statistical physics to describe the distribution of sequences as being as variable as possible consistent with the observed correlations.
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