Deep brain stimulation (DBS) is the functional surgery performed for Parkinson’s disease, dystonia, essential tremors, epilepsy, chronic pain, and psychiatric diseases (obsessive-compulsive disorder, refractory major depression). DBS is nondestructive, reversible, and adjustable surgical therapy performed based on the disease characteristic, treatment availability, and patient preferences .  DBS electrodes are placed bilaterally for Parkinson’s disease and unilaterally for essential tremors. DBS is known to improve the quality of life and reduce drug requirements. In Parkinson’s disease, the degeneration of the substantia nigra and the corresponding loss of dopamine production results in excessive GPi activity inhibiting the thalamus and reducing the thalamocortical activity resulting in akinesia and rigidity. High-frequency DBS suppresses the neuronal activity of GPi and activates the efferent fibre pathway.  

In DBS surgery, the correct placement of electrodes is guided by stereotactic frame-based imaging. Additional methods include localization (microelectrode recording MER and macrostimulation). Initially, the stimulation electrodes are placed, and electrical stimulation is passed to record the improvement in the motor activity in the patient to determine the most optimal electrode location. Side effects are also monitored at different stimulation strengths. After the location is determined, the stimulation electrodes are replaced with the permanent electrodes, which are activated after 1-2 weeks. Currently, preoperative levodopa responsiveness is the only predictor of postsurgical improvement after DBS. Neural activation induces an increase in regional cerebral blood flow (rCBF) and metabolism. Since the increase in regional cerebral blood flow exceeds the increase in tissue oxygen demands of activated brain tissue, the blood concentration of deoxy-Hb decreases while those of oxy-Hb and total-Hb increase.

Problem statement: There are many physiological changes described before and after activation of Insitu DBS electrodes - an increase in blood flow and changes in cerebral oxygenation corresponding with the improvement in motor activity. The changes during the placement and neurological testing are not studied due to limitations of surgical access, equipment and the confounding influence of anaesthetic agents. In this study, we will perform continuous regional cerebral oxygenation changes in the prefrontal area throughout the neurological testing and electrode placement. The observed changes and their impact on the postsurgical outcomes will be evaluated.

Hypothesis: We hypothesize that there will be improvement in the rSO2 values as early as during the neurological testing stimulation. The extent of the increase in rSO2 should correlate with the improvement in motor activity. This improvement in motor activity should also improve their pulmonary functions - either by improving muscle rigidity or improved coordination, resulting in a better test performance. There might be an improvement in cerebral blood flow velocities after DBS.