Juveniles of the cooperatively-breeding cichlid fish Neolamprologus pulcher either consistently provide help in form of alloparental egg care ('cleaners') or consistently abstain from helping ('non-cleaners'). These phenotypes are not based on heritable genetic differences. Instead they arise during ontogeny, which should lead to differences in brain structure or physiology, a currently untested prediction. We compared brain gene expression profiles of cleaners and non-cleaners in two experimental conditions, a helping opportunity and a control condition. We aimed to identify (i) expression differences between cleaners and non-cleaners in the control, (ii) changes in gene expression induced by the opportunity, and (iii) differences in plasticity of gene expression between cleaners and non-cleaners. Control cleaners and non-cleaners differed in the expression of a single gene, irx2, which regulates neural differentiation. During the opportunity, cleaners and non-cleaners had three up-regulated genes in common, which were implicated in neuroplasticity, hormonal signalling, and cell proliferation. Thus, the stimulus in the opportunity was sufficiently salient. Cleaners also showed higher expression of seven additional genes that were unique to the opportunity. One of these cleaner-specific genes is implicated in neuropeptide metabolism, indicating that this process is associated with cleaning performance. This suggests that the two types employed different pathways to integrate social information, preparing them for accelerated reaction to future opportunities. Interestingly, three developmental genes were down-regulated between the control and the opportunity in cleaners only. Our results indicate that the two behavioural types responded differently to the helping opportunity, and that only cleaners responded by down-regulating developmental genes.