Overview:

The trisynaptic loop is a critical pathway within the hippocampus, a brain structure crucial for forming and processing new memories. It involves three main synapses (connections between neurons) and flows through specific hippocampal subregions: the dentate gyrus, CA3, and CA1.

Step-by-Step Breakdown:

1. Entorhinal Cortex → Dentate Gyrus

• Input comes from the entorhinal cortex (a part of the medial temporal lobe that receives information from many areas of the brain).
• This input is passed to granule cells in the dentate gyrus via a pathway called the perforant path.
• Purpose: The brain is bringing in information from the outside world to start processing.

2. Dentate Gyrus → CA3 (via Mossy Fibers)

• The granule cells in the dentate gyrus send axons to the CA3 region of the hippocampus.
• These axons are called mossy fibers.
• Purpose: Dentate gyrus starts refining the information and passes it deeper into the hippocampal circuit.

3. CA3 → CA1 (via Schaffer Collaterals)

• Neurons in the CA3 region send axons to the CA1 region using branches called Schaffer collaterals.
• Purpose: Further processing occurs here; CA1 integrates and refines the signal.

Then what?

• After CA1, the processed information can be sent back to the entorhinal cortex and also projected to other cortical areas for long-term memory storage.