Recent anatomical and clinical evidence has shown that the cerebellum, primarily considered a motor control structure, is also involved in higher cognitive functions and behavioural changes. such as impulsive behaviour. Impulsive behaviour has been shown in several studies to be increased by lesions of the mediodorsal (MD) thalamic nucleus. We performed deep brain stimulation (DBS) of the mediodorsal and ventrolateral (VL) thalamic nuclei in rats, clinically mimicking such a lesion, and tested them for changes in impulsive behaviour in a choice reaction time test. We then analysed the effects of this stimulation on c-Fos expression in both the deep cerebellar nuclei (DCbN) and the prefrontal cortex (PFC), and correlated these outcomes to the measured changes in impulsive behaviour. DBS of the MD thalamic nucleus increased impulsive behaviour without changing motor parameters. This was accompanied by a decrease in the c-Fos expression in all cerebellar nuclei; with a corresponding increase in c-Fos expression in the PFC. DBS of the VL thalamic nucleus caused no significant change in behaviour or c-Fos expression in either region. The present study demonstrates that impulsive behaviour involves the cerebellar nuclei, possibly through a decreased selective attention caused by a disruption of the cerebello-thalamo-cortical pathways through the MD thalamic nucleus. (C) 2009 Elsevier B.V. All rights reserved.