Aperiodic components of local field potentials reflect inherent differences between cortical and subcortical activity

Area of Science:

• Neuroscience
• Computational Neuroscience
• Electrophysiology

Background:

• Local field potentials (LFPs) contain periodic and aperiodic components crucial for understanding brain function.
• The aperiodic component, characterized by a 1/fχ power spectrum, reflects arousal and physiological states.
• Previous research has primarily focused on cortical aperiodic activity, with limited exploration in subcortical structures.

Purpose of the Study:

• To investigate and characterize the aperiodic activity in the human thalamus and basal ganglia.
• To compare subcortical aperiodic parameters with simultaneously recorded cortical activity.
• To explore the potential of aperiodic features as electrophysiological biomarkers for neurological disorders.

Main Methods:

• Refined the specparam model for robust parameterization of aperiodic signals, including the 'knee' parameter.
• Analyzed intracranial LFPs from cohorts of patients with movement disorders (including Parkinson's disease) and epilepsy.
• Compared aperiodic parameters (exponent, offset, knee) across cortical, thalamic, pallidal, and subthalamic nucleus recordings.

Main Results:

• The cortical aperiodic exponent correlated with Parkinson's disease symptom severity.
• Subcortical regions (thalamus, pallidum, subthalamic nucleus) consistently showed a lower aperiodic exponent than the cortex.
• No aperiodic knee was detected in thalamic, pallidal, or subthalamic nucleus recordings, unlike in cortical signals.
• These subcortical-cortical differences were replicated in epilepsy patients.

Conclusions:

• Aperiodic activity in the brain exhibits distinct characteristics between cortical and subcortical regions.
• The aperiodic exponent may serve as a valuable electrophysiological biomarker for movement disorder symptoms.
• Differences in aperiodic parameters likely reflect underlying cytoarchitectonic or functional distinctions between brain regions.