Phasic changes in motoneuron membrane potential during REM periods of active sleep

Area of Science:

• Neuroscience
• Sleep Science
• Motor Control

Background:

• Active sleep is characterized by rapid eye movements (REMs) and generally suppressed motor activity.
• However, muscular twitches and jerks can occur during some REM episodes, indicating complex motor control mechanisms.
• The underlying membrane potential changes in motoneurons during these events are not fully understood.

Purpose of the Study:

• To investigate the membrane potential changes in lumbar motoneurons during active sleep REM episodes in cats.
• To elucidate the neural mechanisms responsible for both motor suppression and occasional twitches during REM sleep.

Main Methods:

• Intracellular recordings were performed on lumbar motoneurons in undrugged, unanesthetized, and normally respiring cats.
• Membrane potential changes were analyzed during different phases of active sleep REMs.

Main Results:

• REM episodes were associated with summated hyperpolarizing potentials, decreasing motoneuron excitability.
• Other REM episodes showed summated depolarizing potentials, sometimes leading to action potentials.
• These depolarizing events were often preceded by a brief hyperpolarization.

Conclusions:

• Lumbar motoneurons receive inhibitory input during all REM periods of active sleep.
• Simultaneous excitatory input during some REM episodes causes depolarization and action potential generation, explaining observed twitches.
• This suggests a balance of inhibitory and excitatory inputs regulates motor activity during REM sleep.