Neuronal Population Effects of Ketamine on Human Brain Organoids

Ketamine rapidly silences population bursting in human forebrain organoids by disconnecting a subset of 'backbone' neurons that normally drive network activity, while individual neuron firing continues mostly unchanged. Acute exposure to 20 μg/mL ketamine abolished population bursts, reduced mean firing rates, and decreased functional connectivity globally, with backbone units losing their normally elevated connectivity. Re-exposure after chronic treatment no longer silenced bursting, indicating tolerance, though the network remained less active and less connected with fewer backbone units. The organoid-microelectrode array platform offers a scalable human-relevant system for studying circuit-level drug effects.

Study at a glance

Abstract

Abstract Ketamine’s rapid neuropsychiatric actions emerge from interactions that span receptors, cells, and circuits, but their net effects on human neuronal population dynamics remain incompletely defined. Here we combine human dorsal forebrain organoids with high-density microelectrode arrays (MEAs) to quantify ketamine’s effects from spikes to networks. In 6-month-old organoids, acute ketamine (20□μg/mL) abolished population bursting while neuronal firing continued mostly unchanged. Spike sorting revealed that mean firing rates declined but not silenced after ketamine Reductions were concentrated within a subset of burst-driver units previously defined as “backbone”. Functional connectivity, estimated with the spike time tiling coefficient (STTC), decreased globally after ketamine. Backbone units displayed elevated connectivity at baseline but were functionally disconnected by ketamine. Graph construction from STTC uncovered widespread network reconfiguration, characterized by redistribution of edges from backbone to non-backbone units leading to loss of hubs and less-interconnected communities. Re-exposure after chronic ketamine treatment no longer silenced population bursting, indicating tolerance. Together, these results show that ketamine acutely silences human organoid networks by disconnecting backbone units, while chronic exposure induces tolerance to re-silencing while reducing the number of backbone units and leaving the network less active and less connected. The organoid-MEA platform provides a scalable, human-relevant system for dissecting circuit-level drug effects.