gms | German Medical Science

Objective: Attentive monitoring of the environment is fundamental for efficient detection of relevant stimuli and is well investigated for cortical regions. However, subcortical network circuitry and the involvement of these structures in the context of detection of relevant stimuli, involuntary attention and distractibility is not well understood. The P300 component is frequently used in electroencephalographic (EEG) studies as a measure for attentional and cognitive functions and is supposed to give further insight into context-specific processes of subcortical structures.

Method: In this ongoing study, simultaneous recordings of local field potentials (LFPs) and event-related potentials (ERPs) from intracranial and scalp EEG were obtained in 16 patients (mean age= 55.9 ± SD 19.7 years) undergoing deep brain stimulation (DBS). These patients were implanted bilaterally with quadripolar electrodes in the subthalamic nucleus (STN; n=6; Parkinson disease (PD)), the thalamic ventral intermediate nucleus (VIM; n=6; essential tremor and cervical dystonia), or the globus pallidus internus (GPi; n=5; segmental dystonia, PD and Tourette syndrome). Within five days after surgery, patients performed an auditory three-class oddball paradigm with externalized DBS electrodes. ERPs from scalp and DBS electrodes were analyzed upon presentation of one frequent standard stimulus (900 Hz; 72%) and two infrequent stimuli (600 Hz and 1200 Hz), either being a relevant (14%) or a distractor (14%) stimulus. Stimuli were presented for 62 ms with an interstimulus interval of 800 to 1200 ms. Patients were asked to press a button to the relevant stimulus.

Results: Analysis reveals high accuracy in all patients (84.45% ± 14.6). Preliminary behavioral results show the shortest response times in STN patients when compared with the two other groups of DBS patients. First EEG results show a P300 component over parietal regions that was largest upon presentation of target stimuli compared with distractor and standard stimuli. A similar P300-like component was also found in depth recordings, suggesting stimulus-specific responses of subcortical structures. Here, STN showed shorter latencies and larger amplitudes compared to GPi or Vim.

Conclusions: The P300 reflects attentional processes that require stimulus detection and discrimination. The present results point to an association between short response times and high LFP amplitudes in the STN and suggest that the STN may play a pivotal role in context-specific processes.