Here, we report about a remarkable intraoperative observation during stereotactic implantation of electrodes for deep brain stimulation in the internal globus pallidus of a 42-year old female suffering from therapy-resistant head tremor and cervical dystonia. The operation was performed in general anesthesia, and targeting of the posteroventrolateral internal pallidum instead of the ventrolateral thalamus was intended because of the concomitant cervical dystonia. Intraoperatively, the optic tract was mapped by photostimulation and simultaneous microelectrode-recordings on both hemispheres. During monopolar test-stimulation (2-4V, 60microsec, 130Hz) at the ventral pallidal border, an arousal effect was observed resembling the éWeckeffekt' originally described by Hassler upon stimulation of intralaminar thalamic nuclei. This resulted in bilateral eye opening elicited by stimulation alone or stimulation and addressing the patient. The arousal reaction was accompanied by an EEG-activation in the beta- and gamma-frequency range, respectively. We propose that the unspecific arousal mechanism may involve the projections from the internal pallidum to intralaminar thalamic nuclei, which in turn have projections to virtually all cortical areas. Its relevance with regard to target definition is unclear.