Objective: The current study applied direct electrophysiological registration of the local field potential activity in the thalamus, subthalamic nucleus (STN) and the pedunculopontine nucleus (PPN) within the 1 week after DBS-implantation. This research aims to answer the question if the thalamus, STN and PPN are involved in phoneme discrimination and word recognition.

Background: Although the phonological effects of subcortical modulation have been well described, it is unclear if phonologically related local field potentials can be elicited in the main subcortical nuclei.

Methods: Patients: The current study included 20 right-handed Parkinson’s Disease (PD) patients with STN stimulation, 2 patients with thalamic stimulation and 1 male PD patient with PPN stimulation.

Procedure: The patients were evaluated in a condition with (ON) and without (OFF) dopaminergic medication.

The first experiment (a phoneme discrimination task) consisted of an auditory oddball paradigm both executed in pre-attentive (MMN) and attentive (P300) condition. The second experiment consisted of a word recognition task where pseudowords were implemented as deviant stimuli and real words as standard stimuli.

Analysis: Data were collected using a 32 channel SynAmp (Neuroscan) amplifier. Electro-encephalographic analysis (ERP-waveform and source localizing) was performed in all nuclei using BrainVision Analyzer 2.

Results: PPN and thalamus: Within the PPN mid-latency auditory potentials were present. Within the PPN and thalamus no phonologically related long-latency potential could be demonstrated.

STN: A pre-attentive ERP occurred on average in both ON and OFF at a time-window of 64.26 ms and 60.71 ms post stimulus for the left and right hemisphere respectively. In the attentive condition an ERP was elicited between 241.86 ms and 241.15 ms post stimulus for the left and right hemisphere respectively. For the word recognition task a  potential is elicited in the ON-condition on 200 ms. In the off-condition an attenuation of the amplitudes on the same timepoints was found.

Conclusions: These data suggest an important role of the PPN and STN in the spectrotemporal preparation of phonological input processing and a primary role for the STN in phonological input processing. This abstract has been previously presented for the Society of Neurobiology of Language (August 2016) and Science of Aphasia (September 2016).

References: Aerts, A., van Mierlo, P., Hartsuiker, R.J., Hallez, H., Santens, P., & De Letter, M. (2013). Neurophysiological investigation of phonological input: aging effects and development of normative data. Brain and Language, 125, 253-263.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/subcortical-involvement-in-phonological-input-processing-an-electrophysiological-registration-study/