Frequency-dependent information flow from the entorhinal cortex to the hippocampus

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Systems Neuroscience

Background:

• Information storage and retrieval in the hippocampus depend on input from the entorhinal cortex (EC).
• Two primary pathways, originating from EC layers II and III, transmit information to the hippocampus.
• Understanding how these pathways are selected for information transfer is crucial for comprehending hippocampal function.

Purpose of the Study:

• To investigate the differential activation of EC layer II and III projection cells during repetitive synaptic stimulation.
• To determine the frequency-dependent regulation of information transfer from the EC to the hippocampus.
• To identify potential mechanisms for pathway selection in entorhinal-hippocampal communication.

Main Methods:

• Intracellular recordings from EC layer II and III projection cells in combined EC-hippocampal slices.
• Analysis of synaptic responses to stimulation of deep layers or lateral EC at subthreshold intensities.
• Systematic variation of stimulus frequencies during repetitive synaptic stimulation.

Main Results:

• EC layer II cells were preferentially activated at stimulation frequencies above 5 Hz.
• EC layer III cells responded preferentially to frequencies below 10 Hz and were inhibited at higher frequencies (>10 Hz).
• Both layer II and III cells showed increased firing likelihood at stimulus frequencies between 5 and 10 Hz.

Conclusions:

• A frequency-dependent switch mechanism in the entorhinal cortex regulates the output of layer II and III cells.
• This frequency-dependent regulation represents a novel principle in neuronal information processing for controlling hippocampal information flow.
• The findings provide insights into how the brain dynamically modulates information transfer based on stimulation frequency.