The Brain from Inside Out

by György Buzsáki

While a plot such as that in Figure 2.1 shows only the values of observations, we often wish to read much more from a static cloud of data points. For example, there are many empty areas without measured values on the graph. We can simply assume that those values exist so that, if we had more time and more funding to generate more data, those new points would fill in the blanks between the already-measured ones. This operation, performed intuitively or with mathematical rigor, is called interpolation (the arrow in Figure 2.1), but we can also call it explanation or deduction. Postdiction would be another possible term because interpolation is done based on data collected in the past. If we feel comfortable filling the graph with imagined data between the dots, perhaps it is not much of a jump to imagine more data that extend the cloud, again following the trend in the observations. This operation is called extrapolation or induction. Alternatively, we can call it prediction or guessing from the currently available data, an act of “logical inference.”5 It is an abstraction from the present, which amounts to predicting the future. How far can we go in our extrapolation of the graph? Just because two sets of variables correlate now, there is no guarantee that this correlation will continue into the future.