Several activities and functions of neurons are determined by intracellular signals generated by calcium ions, with calcium levels rapidly increasing during neuronal activity. Technological advances in calcium imaging techniques have allowed a large amount of data to be collected to study brain behavior at the neuronal level. We investigate the effects of different sensory stimuli on neuronal activity in the visual cortex of mice. The novel contribution of this work is the investigation of the relationship between visual stimuli and calcium concentration levels in terms of causal effects. Estimation and inference are carried out in a potential outcomes framework, where the dynamic behavior of calcium traces is managed by borrowing tools from the randomized experiments literature. Results show significant causal effects on the neuronal activity due to the smoothness and geometry of the stimuli.