Neurophysiological mechanisms involved in tonic immobility (TI).

Area of Science:

• Neurophysiology
• Animal Behavior
• Comparative Psychology

Background:

• Tonic immobility (TI) is a natural defensive behavior observed in many animal species.
• Understanding the neurophysiological underpinnings of TI is crucial for comprehending fear and stress responses.

Purpose of the Study:

• To summarize the key neurophysiological characteristics of tonic immobility.
• To investigate the role of different brain regions in TI.
• To explore the impact of TI on learning and memory.

Main Methods:

• Analysis of cortical EEG and hippocampal activity during TI.
• Assessment of reflex activity and brain metabolism (glycogen, glucose).
• Evaluation of learning and avoidance responses before, during, and after TI.
• Surgical lesion studies (decortication, decerebellation, telencephalic and ponto-mesencephalic sections).

Main Results:

• TI is characterized by high-voltage slow cortical EEG waves and specific hippocampal activity patterns predicting onset and termination.
• Reflexes are depressed independently of EEG activity, and brain metabolism indicates reduced neuronal activity.
• Learned behaviors can be extinguished and reacquired during TI, and animals can learn new avoidance responses.
• Ponto-mesencephalic sections abolish TI and righting reflexes, while other lesions do not significantly affect TI characteristics.

Conclusions:

• TI is a complex neurophysiological state regulated by specific brainstem pathways.
• TI influences cognitive functions like learning and memory, suggesting a role beyond a simple motor shutdown.
• The findings provide insights into the neural mechanisms of defensive behaviors and their impact on animal cognition.