PubMed · 9396514
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A M Katz. 1997-11-18. Electrical remodeling.. https://pubmed.ncbi.nlm.nih.gov/9396514/
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We study the impact of correlated neuronal firing rate variability on the accuracy with which an encoded quantity can be extracted from a population of neurons. Contrary to widespread belief, correlations in the variabilities of neuronal firing rates do not, in general, limit the increase in coding accuracy provided by using large populations of encoding neurons. Furthermore, in some cases, but not all, correlations improve the accuracy of a population code.
Constant electric fields and constant ion currents are often considered in theories of ion transport. Therefore, it is important to understand the validity of these helpful concepts. The constant field assumption requires that the charge density of permeant ions and flexible polar groups is virtually voltage independent. We present analytic relations that indicate the conditions under which the constant field approximation applies. Barrier models are frequently fitted to experimental current-voltage curves to describe ion transport. These models are based on three fundamental characteristics: a constant electric field, negligible concerted motions of ions inside the channel (an ion can enter only an empty site), and concentration-independent energy profiles. An analysis of those fundamental assumptions of barrier models shows that those approximations require large barriers because the electrostatic interaction is strong and has a long range. In the constant currents assumption, the current of each permeating ion species is considered to be constant throughout the channel; thus ion pairing is explicitly ignored. In inhomogeneous steady-state systems, the association rate constant determines the strength of ion pairing. Among permeable ions, however, the ion association rate constants are not small, according to modern diffusion-limited reaction rate theories. A mathematical formulation of a constant currents condition indicates that ion pairing very likely has an effect but does not dominate ion transport.
Vibrotactilometry with testing of the thresholds of the vibration sense at seven frequencies between 8-500 Hz in different intensities has been correlated with nerve conduction studies of the ulnar nerve to evaluate its diagnostic power in neuropathies at the elbow. Thirty-nine patients with entrapment symptoms were studied. Vibrotactilometry was abnormal in 33 patients (85%) and nerve conduction studies were abnormal in 19 (49%). The sensitivity of vibrotactilometry in relation to nerve conduction studies was 89%, and in relation to the patients' symptoms was 85%. We conclude that vibrotactilometry is a sensitive test that correlates well with the patients' symptoms, while nerve conduction studies are less sensitive (49%) in relation to the patients' symptoms. Vibrotactilometry in the frequency area of 8-500 Hz is recommended in the screening of ulnar nerve entrapment. Nerve conduction studies are recommended in clinically doubtful cases to localise the entrapment to the elbow region.