PubMed · 450985
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C B Oxby, K Brooks. 1979. A versatile variable anthropomorphic phantom.. https://doi.org/10.1088/0031-9155%2F24%2F2%2F021
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The magnetic field pattern over the temporal area of the scalp 100 ms following the onset of a tone burst stimulus provides evidence for neuronal activity in auditory primary and association cortices that overlap in time. Habituation studies indicate that onset and offset features of a tone produce activation traces in primary cortex that are at least partially common, but only the onset produces an appreciable trace in association cortex. The characteristic time constant for the decay of the latter's activation trace is several seconds longer than for the former.
At any template position, the decision to extend the transcript by one residue or to release the nascent RNA represents a kinetic competition between elongation and termination pathways. This competition is discussed in terms of alternative Eyring transition state barriers; changes in termination efficiency correspond to small changes in the relative heights of these barriers. Elongation complexes are stable at nonterminator positions; a model is presented to explain the destabilization of these complexes at intrinsic termination sites. Functionally analogous effects can operate at rho-dependent terminators. Mechanisms for modulation of termination efficiency by regulatory proteins are described.
Hypotheses having to do with the neurochemical basis for mental disease can be tested by noninvasive measurement of flow, metabolism and neuroreceptor concentrations in various parts of the brain. The capabilities of these technologies for accurate absolute quantitation are limited by the instrument resolution and the limited statistics associated with allowable radiation doses. Nevertheless, very important new information regarding the brain function in normal and diseased states can be gleaned from the techniques of positron emission tomography (PET) and single photon emission tomography (SPECT). This chapter presents the critical problems which face the clinical researcher who endeavors to test hypotheses regarding mental illnesses using PET or SPECT. First, the quantitative capabilities of emission tomography will be discussed; then the special requirements of SPECT for attenuation correction will be reviewed. Next, the physiological principles required for inter-institutional comparisons are presented.