Midline thalamic neurons are differentially engaged during hippocampus network oscillations

Area of Science:

• Neuroscience
• Systems Neuroscience
• Computational Neuroscience

Background:

• The midline thalamus and medial temporal lobe are crucial for spatial navigation and memory.
• The dynamic relationship between midline thalamus and medial temporal lobe activity remains poorly understood.

Purpose of the Study:

• To investigate the functional heterogeneity of midline thalamic neurons.
• To explore how these neurons' activity is modulated by hippocampal rhythms.

Main Methods:

• Electrophysiological recordings in anesthetized mice.
• Identification of thalamic neurons based on calretinin and calbindin expression.
• Analysis of neuronal firing rates during hippocampal theta oscillations and sharp-wave ripples.

Main Results:

• Calretinin-positive midline thalamic neurons showed low firing rates, no change during theta, and inhibition during sharp-wave ripples.
• Calretinin-negative midline thalamic neurons exhibited higher firing rates, increased activity during theta, and no change during sharp-wave ripples.
• These findings reveal functional differentiation within the midline thalamus based on neuronal subtypes and hippocampal network states.

Conclusions:

• The midline thalamus contains at least two distinct projection neuron classes.
• Differential engagement by hippocampal pathways during network oscillations suggests roles in specific memory processing stages.
• This highlights the thalamus's pivotal role in coordinating cortical circuits for memory and navigation.