Imprinting: correlations between behaviour and incorporation of (14-C) uracil into chick brain

On the first day after hatching 106 domestic chicks were injected with (14-C)uracil and exposed to a yellow or a red rotating flashing light for 72 min. Shortly before they were killed and 115 min after injection they were given a choice between the two lights. Incorporation of the (14-C)uracil into 4 regions of the brain was measured. Differences between batches and between training conditions were eliminated as sources of variation by standardising the behavioural and biochemical measures. Correlations between the measures were obtained. Chicks that were active from the early stages of training showed lower rates of incorporation in the midbrain, forebrain base and anterior of roof of the forebrain, than less responsive chicks. When the general lowering effect of behavioural activity on incorporation was eliminated as a source of variations, a striking positive correlation emerged between the preference for the familiar object and incorporation in the anterior of forebrain roof. Since preference for the familiar is a direct measure of imprinting and since no other behavioural measure is positively correlated with biochemical changes in anterior roof, it is concluded that these biochemical changes were closely linked with the learning process.