Vulnerability of developing brain to undernutrition: claims of selective sensitivity of the cerebellum found to be misleading on theoretical and empirical grounds.

The growing rat brain acquires most of its weight, cells, and other material during the suckling period. Undernutrition at this stage can diminish brain growth. Nutritionally induced depressions of cerebellar growth may be smaller or larger than corresponding depressions in other brain regions, but when the resulting deficits are transformed to '% of age control values', the cerebellar deficits appear specially large. The ubiquitous '% transformation' and its misrepresentation of cerebellar deficits have nurtured the impression that cerebellum has a special sensitivity to insult. The sensitivities of cerebellum and forebrain growth in rats were compared empirically. Data came from a large set constructed, some years ago, from measurements made of regional DNA contents. The animals had been raised from birth to various ages in small (well-fed) or large (underfed) litters. Growth curves were fitted, from which rate curves were derived, and these showed the depression in rate of DNA accumulation to be the same for each region, throughout suckling. The widely held extra-sensitivity of cerebellum is explained as an artifact of the % transformation, the timing of cerebellar growth, and the timing of restriction which experimenters usually choose. Problems of inferring uniformity, or otherwise, of growth rate depressions from incomplete, noisy, and badly sampled growth data are discussed and illustrated with computer simulations.