The odds ratio: a useful tool in neurosciences.

The odds ratio is very useful; when used as a measure of association (or to describe the results of a randomised controlled treatment trial) it expresses both the strength and direction of the association (or size and direction of treatment effect). Its 95% confidence interval estimates the likely degree of sampling error and provides a test of significance at the 5% level. Authors, when reporting the results of descriptive studies, case-control studies and randomised controlled trials, should consider presenting their results this way rather than by simple significance testing with a chi squared test.

Methods for calculating the probabilities of finding patterns in sequences.

This paper describes the use of probability-generating functions for calculating the probabilities of finding motifs in nucleic acid and protein sequences. Equations and algorithms are given for calculating the probabilities associated with nine different ways of defining motifs. Comparisons are made with searches of random sequences. A higher level structure--the pattern--is defined as a list of motifs. A pattern also specifies the permitted ranges of spacing allowed between its constituent motifs. Equations for calculating the expected numbers of matches to patterns are given.

A quantitative anatomical study of the granule cell dendritic fields of the rat dentate gyrus using a novel probabilistic method.

The granule cell dendritic fields of the adult rat dentate gyrus were analyzed quantitatively using a probabilistic method developed to correct dendritic length and segment number for dendrites cut during sectioning. Golgi-impregnated, linearized hippocampi were sectioned serially in one of the three hippocampal planes. Three dendritic field parameters were quantified from camera lucida drawings of these dendritic fields: dendritic field spread, dendritic length, and the branching and termination patterns of dendritic segments. Granule cell dendritic fields resembled cones, their maximal extent occurring in the distal third of the molecular layer. The ratio of transverse to longitudinal dendritic field spread was greater than 1:1 for the dorsal leaf and crest regions, but close to or less than 1:1 for the ventral leaf. The probabilities of segment branching and termination were highly similar for transversely and longitudinally sectioned tissue. The probability of branching varied among dendritic orders and across the molecular layer for the same order. The probability of termination did not vary greatly across orders. Most nonbranching segments terminated adjacent to the hippocampal fissure. On the average, a granule cell had 2.23 first-order dendrites that branched into a dendritic field containing seventh-order dendrites. Total dendritic length, corrected for cut dendrites and projection errors, averaged 3,662 +/- 88 microns. The somatic layer and proximal third of the molecular layer contained approximately 35% of this total length. The remainder, ca. 60%, was restricted to the distal two-thirds of the molecular layer, the predominant termination zone of perforant path axons. These data provide a quantitative characterization of the rat granule cell dendritic fields. Implementation of the probabilistic correction method overcomes methodological problems common to quantitative Golgi studies. These data permit a more precise relationship to be drawn between dendritic architecture and granule cell physiology.