Pupillary Dynamics Link Spontaneous and Task-Evoked Activations Recorded Directly from Human Insula

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Autonomic Nervous System Research

Background:

• Most human brain activation studies focus on "task-evoked" responses to external stimuli.
• Spontaneous brain activity is a significant area of research, particularly for developing disease biomarkers.
• The dorsal anterior insula is crucial for salience processing and alertness.

Purpose of the Study:

• To investigate if spontaneous neuronal activations in the human brain share functional and physiological properties with task-evoked activations.
• To explore the relationship between spontaneous insular cortex activations and autonomic responses, specifically pupillary dilation.
• To compare the neurophysiological profiles of spontaneous and task-evoked activations within the same neuronal populations.

Main Methods:

• Utilized intracranial electroencephalography (EEG) and concurrent pupillometry in three human subjects.
• Localized neuronal populations in the dorsal anterior insula exhibiting task-evoked activations.
• Detected spontaneous activations during a resting state within the same neuronal populations.

Main Results:

• Task-evoked insular activations positively correlated with pupil dilation magnitude, with a several hundred-millisecond lag.
• Spontaneous activations in the insula displayed comparable electrophysiological properties (magnitude, duration, spectral signature) to task-evoked activations.
• Both spontaneous and task-evoked insular activations systematically preceded phasic pupil dilations with similar temporal profiles.

Conclusions:

• Spontaneous and task-evoked neuronal activations in the human insula exhibit similar neurophysiological profiles.
• A clear link exists between insular activations (both spontaneous and task-evoked) and autonomic functions, as indicated by pupillary dilation dynamics.
• Spontaneous brain activity is relevant to ongoing physiological processes and potentially self-generated mental states.