Changes in cerebral blood oxygenation induced by deep brain stimulation: study by near-infrared spectroscopy (NIRS).

Previous studies have demonstrated that neural activation causes changes in cerebral blood oxygenation (CBO), i.e. increases in tissue levels of oxy-Hb and total-Hb with a decrease in deoxy-Hb concentration. It is unclear, however, whether neural activation always induces the same pattern of CBO changes or not. In the present study, employing a near-infrared spectroscopy (NIRS), we investigated the CBO changes in the frontal lobe induced by direct stimulation of the thalamus (Vim) or globus pallidus (GPi) in patients with Parkinson's disease or essential tremor. The results indicated that under conditions of neural activation in the frontal lobe, oxy-Hb and total-Hb increased in all 6 cases. Deoxy-Hb decreased in 2 cases during GPi stimulation, and increased in 4 cases during low frequency stimulation of the Vim. The above findings suggest that neural activation induces various patterns of CBO change, especially in deoxy-Hb. This implies that functional MRI based on the BOLD contrast may not consistently detect the area of neural activation.