Measurement of reinforcement in depression: a pilot study

We tested whether performance on a progressive ratio schedule of reinforcement with increasing magnitudes of monetary reward could be used as a behavioral measure of response to reinforcement during depression. Performance on the task was recorded before, during and after treatment of depression in six melancholic patients. The amount of money earned and the number of responses to obtain money during the task increased in the three subjects who improved with treatment but did not increase in three subjects who did not improve. In addition, the degree to which responses increased with increasing monetary reward became greater in two of the three subjects who improved but in none of the subjects who did not improve. Methodological liabilities (e.g., the small sample size and absence of a control group) may limit the validity of our findings. Our results do suggest performance of the task may be an objective measure of response to reinforcement that could be used in both basic and clinical research on depression.