Interacting with our ever-changing environment requires constant adaptation of our movements to reduce movement errors, a process termed motor adaptation. How the human brain implements motor adaptation poses an important question in neuroscience, but changes in the adapting motor system are currently not well understood. In my work, I combine multimodal MR imaging with brain stimulation and state-space modelling to investigate changes in the motor system during adaptation. In this talk, I present data linking neurochemistry, functional connectivity and behaviour in human motor adaptation. Acquisition of motor adaptation is thought to rely predominantly on the cerebellum but not on the primary motor cortex (M1), while storage of the adapted state (retention) is thought to depend on M1. In Experiment 1, I probe the role of the neurotransmitter concentrations in M1 in storing adapted movements, with particular focus on the main inhibitory neurotransmitter GABA. I show that individual concentration levels of M1 GABA relate to changes in M1-Cerebellar connectivity, which in turn govern the retention of an adapted state. In Experiment 2, I characterise cerebellar GABA changes during human motor adaptation. I show that adaptation drives GABA changes in the deep cerebellar nuclei and that the extent of these changes is associated with increases in cerebellar connectivity and relevant for adaptation performance. Finally, in experiment 3, I investigate the effect of applying anodal transcranial direct current stimulation (an intervention shown to decrease local GABA concentration) to the cerebellum on the acquisition of an adapted state.