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The Finlay/Darlington Model

Based on: Finlay BL, Darlington RB. Linked regularities in the development and evolution of mammalian brains. Science 1995;268(5217):1578-84.

The model includes three factors – a "species factor", a "neural events factor", and a "primate factor", the latter to adjust for a systematic variability in primate cortical and limbic systems. Standard regression methods are used in computing the primate interaction, which is discussed in detail in Clancy B, Darlington RB, Finlay BL. The course of human events: predicting the timing of primate neural development. (Developmental Science 2000;3:57-66). It accounts for the fact that limbic and cortical components of rodent and human brains mature at different rates. This third factor adds 0.248683 to the estimated Y-score of every primate cortical event, and subtracts 0.079280 from the estimated Y-score of every primate limbic event.

The model predicts post conception (PC) dates transformed to the mathematical term Y as “Y = ln (PC days – 4.34)”. The constant (4.34) accounts for the fact that early events (blastulation, differentiation of basic germinal layers) generally take the same amount of time in all eutherian mammals. Each neural event in the database is assigned an event score (with later events having higher scores), and each species assigned a species score (with slower-developing species having higher scores) consistent with the general linear model described previously (see also Clancy B, Darlington RB, Finlay BL. Translating developmental time across mammalian species. Neuroscience 2001;105(1):7-17; Darlington RB. Regression and linear models. New York: McGraw-Hill; 1990). Then Y is modeled as the sum of three terms: the event score, the species score, and the primate interaction where appropriate. This general linear model has been fitted simultaneously to all cells with data, but it also generates estimates for the cells with no empirical data.

Although we are confident the predictions and comparisons for the neural events that are included in our database will be of value, we must also caution against overeager interpretations until more data become available. The developmental predictions from these algorithms will only be as accurate as the data that they are based on. The user can enter a post conception date that falls within the range of data upon which the model is based for any of the ten species in the model; this range currently ends at eye-opening. However, as new data are added, the precision of the model will be improved and the applicability of our statistical algorithms will be broadened. (Please note that for the data in this model, the day of birth is considered postnatal day 0, PN0.)