EXAMINING THE ROLE OF THE SUBTHALAMIC NUCLEUS IN A STOP SIGNAL REACTION TIME TASK IN PARKINSONIAN PATIENTS
Panna Hegedüs1, 2, Tamás Laszlovszky1, 2, Gertrúd Tamás3, László Halász4, Virág Bokodi4, György Perczel4, András Széll1, István Ulbert4, 5, 6, Dániel Fabó4, Loránd Erőss4, Balázs Hangya1
Parkinson’s disease (PD) is one of the most common neurodegenerative disorders. While the symptoms are initially dominated by motor impairment, the overwhelming majority of PD patients develop cognitive impairment with the progression of the disease. The subthalamic nucleus (STN) is modulated by frontal cortex and thought to mediate motor responses during decision making. Therefore, during decision conflict, the precise timing of STN activation may be crucial for response inhibition. In our study, we investigated the role of STN neural activity in decision making, focusing on its proposed role on inhibitory control. PD patients performed a stop-signal reaction time task, in which two numbers were presented on a screen and the patients had to press the corresponding buttons on a button box as fast as possible. After a subset of the cues, a stop instruction was presented, indicating that the patient had to withhold the motor response. The patients performed this task before, during and after DBS implantation surgery. During surgery, extracellular unit recording from the STN and frontal EEG was co-registered. A subpopulation of STN neurons were suppressed during button presses, consistent with their role in the indirect basal ganglia pathway. Importantly, a subset of STN neurons showed differential activity upon cue presentation before successful and unsuccessful stops, thus predictive of successful inhibition. This activation pattern is consistent with the proposed role of the STN in inhibitory control during decision making. Simultaneous EEG recordings may reveal how STN coherence with frontal cortical population activity mediates successful and unsuccessful response inhibition.