THE NEUROPHYSIOLGY OF SELECTIVE ATTENTION IN HUMAN SUBCORTICAL MOTOR NUCLEI

Abstract

Selective attention and working memory are fundamental cognitive processes traditionally attributed to cortical regions. Emerging evidence suggests that subcortical motor nuclei, such as the thalamus and basal ganglia, also play crucial roles in these functions, but the mechanism is still unclear. This thesis aimed to examine the neurophysiological mechanisms of selective attention and working memory in subcortical motor nuclei through intraoperative single-unit and local field potential (LFP) recordings in humans. In the first study, neuronal activity was recorded from the ventral intermediate nucleus (Vim) and ventral oral anterior/posterior nuclei of the motor thalamus in 25 patients with parkinsonian and non-parkinsonian tremors during an auditory oddball task. Results showed a significant decrease in neuronal firing rates and in beta-band (13–35 Hz) oscillations to the deviant tones, indicating the involvement of Vim in auditory selective attention. Parkinson’s disease (PD) patients off medication exhibited increased beta power but reduced modulation to attended tones, suggesting dopamine's role in modulating thalamic beta oscillations for selective attention. The second study focused on the centromedian nucleus (CM) of the thalamus in 11 epilepsy patients performing a similar auditory attention task. CM neurons demonstrated selective, multiphasic firing and beta/low gamma (13–45 Hz) modulations to deviant tones in 81% of neurons tested. These findings highlight the CM's participation in cognitive function, supporting its role under top-down control and implicating beta and gamma oscillatory activities in cognitive processing. The third study investigated neuronal activity in the subthalamic nucleus (STN) and Vim during a visual 1-back task in 16 patients with PD or essential tremor. Both nuclei exhibited selective firing rate changes and beta desynchronization in response to target stimuli. Vim beta desynchronization occurred earlier than in the STN, even preceding the stimulus, suggesting a role in stimulus prediction. Collectively, these studies provide evidence that subcortical motor nuclei are actively involved in selective attention and working memory and have significant implications for understanding the neural circuitry underlying cognitive functions and the pathophysiology of neurological disorders like Parkinson’s disease and epilepsy. Furthermore, they offer potential insights for developing deep brain stimulation therapies targeting cognitive symptoms associated with these conditions.