a, Horizontal view of a representative cell in the Allen Reference Atlas space. The abrupt termination is labelled with a purple square. n = 28 abruptly terminating cells. b, The abrupt termination of the example cell shown as a maximum z projection (left) and in the individual z sections (right). c, Two normal terminations of the same cell, shown as a maximum z projection (left) and in two colour-coded series of z sections (right). d, Distance of abrupt termination from cell body versus distance of furthest regular termination of the same cell. Dashed line indicates the unity line. e, The distribution of target numbers of all projection neurons without abrupt terminations (as shown in the main figures; left), of projection cells with abrupt terminations (middle) and of all projection neurons (no abrupt terminations and abrupt terminations; right). f, To test the effect of false negatives on our analyses, we simulated the random loss or gain of projections from the MAPseq dataset, while maintaining overall area projection probabilities. n = 553 neurons; 400 repeats. P values based on a binomial test for all six projection motifs determined as significantly over- or underrepresented in our dataset are plotted after removing (dropfraction <1) or adding (dropfraction >1) connections. Mean (black line) and s.d. (shaded area) are indicated.