6. 🚀 This is enabled by transcranial ultrasound stimulation (TUS)—a safe, reversible, precise method to non-invasively probe deep brain function, which finally makes the hippocampus accessible in healthy humans.

Here is me being stimulated to test the TUS effect myself.

5. 🌟Empirical evidence: Using TUS to temporarily modulate hippocampal activity in healthy humans, we primarily disrupted their ability to use relational knowledge for inference, confirming its causal necessity for relational structure learning.

4. ⏩Computational predictions: An RNN trained on our task developed hippocampus-like units encoding relational structure. Lesioning these units selectively disrupted inference — predicting the hippocampus’s causal role.

3. 🧠 Neural basis: using fMRI, we show that such relational knowledge is consistently represented in the hippocampus across diverse contexts, in a manner distinct from other brain regions.

Next, we asked: Is this representation causally necessary for structure-based inference?

2. 🤖 Our RL models show that only models with relational knowledge capture human behaviour, outperforming experience-only models.

1. 👥 When meeting new people, we don’t learn about them from scratch — in our “Goalkeeper Game”, participants showed structure-based inference by leveraging relational knowledge to rapidly learn new relationships in changing environments.

🚨We believe this is a major step forward in how we study hippocampus function in healthy humans.

Using novel behavioral tasks, fMRI, RL & RNN modeling, and transcranial ultrasound stimulation (TUS), we demonstrate the causal role of hippocampus in relational structure learning.