In Drosophila melanogaster, the circadian cycle is a powerful tool to study neurons/network and how they control behaviours. Particularly, how the information is processed from molecular clocks within neurons to circadian behaviours. The neuronal network underlying the circadian clock is well described and the different neuronal clusters have begun to be hierarchically classified depending on their role in controlling the circadian locomotor behaviour. However, how neuronal activity affects the molecular phase of the circadian clock, and consequently the locomotor behaviour, remains an open question. By using optogenetic tools expressed in the so-called master pacemaker neurons, I could acutely modify the neuronal firing rate in L3 larvae. This alteration triggered a phase shift, which could be monitored during adulthood using behavioural assessment. Interestingly, not every timepoint throughout the day are equivalently sensitive to firing rate modification. Those results tend to show that the molecular clock could be modified by neuronal activity of the pacemaker neurons themselves. Moreover, the time of day dependency could imply an impossibility of pacemaker neurons and/or their targets to transduce/receive information.