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Biomedical subjects

J A Freeman

Publications and source records attributed to J A Freeman.

At least 145 records · Page 8Linked to original sources
PubMed1975

Theory of current source-density analysis and determination of conductivity tensor for anuran cerebellum.

The theoretical basis of current source-density (CSD) analysis in the central nervous system is described. Equations relating CSD, the current flow vector, and the extracellular field potential are given. It is shown that the CSD provides superior resolution of neuronal events when compared to conventional field-potential analysis. Expressions for the CSD in rectangular Cartesian coordinates are derived, including the general case of anisotropic, inhomogeneous conductive tissue, and a coordinate system rotated with respect to the principal axes (APPENDIX). The minimum number of spatial dimensions for accurate CSD analysis is discussed. The conductivity tensor was experimentally measured in frog and toad cerebella. All three principal components of the tensor were evaluated and their spatial gradients determined to be negligible. It was also shown that the conductivity was independent of potential. Thus the anuran cerebellum is anisotropic, homogeneous, and ohmic. On the basis of these results the appropriate mathematical expression for the CSD was selected.

Animals↗
PubMed1975

Experimental optimization of current source-density technique for anuran cerebellum.

This paper represents a systematic, semirigorous attempt to optimize the technique of current source-density (CSD) analysis experimentally. We compared different spatial differentiation formulas in terms of accuracy, aliasing, and smoothing, and provide experimental and theoretical rationale for their use. Sources of error have also been investigated. Expressions were derived to enable one to estimate the relative magnitude of errors due to electrical noise, uncertainty in tip position of recording electrodes, and error in the conductivity tensor. Corresponding experiments illlustrating the validity of such estimates are also presented. Methods to determine the optimum interelectrode spacing are given, based on computations of spatial energy-density spectra in the anuran cerebellum. The application of the technique of CSD analysis developed in this, and the accompanying paper, to the vestibulocerebellar input in the toad cerebellum provided significantly better temporal and spatial resolution of neuronal events than conventional field-potential analysis. Considerations germane to the optimum application of this technique to other neural structures are also discussed.

Animals↗
PubMed1968

A role for the sodium pump in photoreception in Limulus.

The membranes of photoreceptor cells in Limulus have an electrogenic sodium pump which contributes directly to membrane potential and whose activity is changed by light. These light-induced changes in pump activity underlie the receptor potential.

Adenosine Triphosphatases↗
PubMed1968

Dendritic spikes and their inhibition in alligator Purkinje cells.

Alligator Purkinje cells generate action potentials in the peripheral dendritic tree, after synaptic depolarization via superficial parallel fibers. These action potentials are inhibited at the dendrite level by preceding parallel-fiber volleys at close intervals. We conclude that this inhibition is produced by the activation of the inhibitory interneurons of the molecular layer, the stellate cells, which establish synaptic contacts with the dendrites of the Purkinje cells.

Action Potentials↗