Electrical activity of the cingulate cortex. I. Generating mechanisms and relations to behavior

Area of Science:

• Neuroscience
• Electrophysiology
• Comparative Neurology

Background:

• The posterior cingulate cortex (PCC) plays a role in cognitive functions.
• Understanding PCC's electrical activity is crucial for deciphering its function.
• Rats serve as a model organism for studying brain activity.

Purpose of the Study:

• To investigate spontaneous and evoked electrical activities in the rat PCC.
• To correlate distinct EEG wave patterns and MUA with specific behaviors and sleep stages.
• To explore the relationship between PCC and hippocampal electrical activity.

Main Methods:

• Chronic implantation of electrodes in PCC (area 29) and dorsal hippocampus of freely moving rats.
• Recording of spontaneous electroencephalogram (EEG) slow waves and multiple unit activity (MUA).
• Analysis of EEG patterns (irregular slow waves, theta rhythm, fast waves) and MUA during different behavioral states (Type I, Type II, SWS, REMS) and evoked potentials.

Main Results:

• Three distinct EEG wave patterns were identified in the PCC: irregular slow waves with EEG-spikes during Type II behavior and SWS, theta rhythm (6-10 Hz) during Type I behavior and REMS, and fast waves (>30 Hz) more prominent during Type I behavior.
• EEG-spikes showed polarity reversal in PCC and correlated with increased MUA, suggesting generation by deep PCC neurons.
• MUA was phase-locked to theta waves, indicating local generation, but hippocampal volume conduction likely contributed to PCC theta. High-amplitude MUA occurred during Type II behavior/SWS, absent during REMS.
• Evoked potentials following contralateral PCC stimulation showed behavior-dependent long-latency oscillations (25-40 Hz) during Type I behavior.

Conclusions:

• The PCC exhibits a complex repertoire of spontaneous electrical activities, including unique wave patterns and MUA, closely linked to behavioral states and sleep.
• EEG-spikes in PCC appear to originate from deep cortical layers.
• PCC theta rhythm is influenced by both local generation and hippocampal input.
• Evoked potentials reveal behavior-specific oscillatory responses in the PCC, highlighting its dynamic nature and functional similarity to the hippocampus.