Locus coeruleus activity in monkey: phasic and tonic changes are associated with altered vigilance

Area of Science:

• Neuroscience
• Behavioral Neuroscience

Background:

• The locus coeruleus (LC) is a key brainstem nucleus involved in arousal and vigilance.
• Understanding LC neuronal activity in relation to behavioral states is crucial for comprehending attention and cognitive function.

Purpose of the Study:

• To investigate the relationship between locus coeruleus (LC) neuronal activity and behavioral states in unanesthetized monkeys.
• To examine the tonic and phasic responses of LC neurons to different stimuli and during cognitive tasks.

Main Methods:

• Recording impulse activity of individual neurons in the nucleus locus coeruleus (LC) of chair-restrained, unanesthetized cynomolgus monkeys.
• Observing LC activity during different behavioral states (alert waking, drowsiness, agitation).
• Utilizing a visual oddball discrimination task to assess LC responses to specific cues (CS+).

Main Results:

• LC neuronal activity correlated with behavioral state: continuous in alert waking, with pauses during drowsiness.
• LC activation preceded EEG changes and eye opening during awakening.
• LC neurons exhibited tonic activity variations related to alertness and agitation.
• Phasic LC responses were selectively triggered by unexpected, meaningful sounds and a visual oddball cue (CS+).
• The latency of CS+ evoked responses was significantly shorter than the behavioral response.

Conclusions:

• The locus coeruleus (LC) plays a dual role in vigilance, maintaining tonic alertness and modulating it phasically based on stimulus relevance.
• Stimulus-evoked LC responses may optimize behavioral reactions and enhance vigilance to subsequent stimuli.
• LC activity is integral to both sustained attention and rapid responses to salient environmental events.