We have developed human stem cell derived brain organoid models that are capable of generating complex physiological activities. These activities include neural oscillations at the same frequencies as are recorded from in vivo human brain and single cell calcium transients that segregate into multiple, distinct, neural networks. To achieve this, we generate “fusion” brain organoids that contain excitatory neurons, inhibitory interneurons, as well as astrocytes. We will now leverage the methodologies we have developed in organoid generation and physiologic monitoring to dive deeper into the mechanisms of normal neural circuit development and how neurological disease perturbs circuit formation and function. 

Brain oscillations are believed to be critical for neural computation and can serve as a biomarker of excitatory- inhibitory (E/I) balance in neural circuits. Disruptions in oscillatory activity have been observed in patients with autism spectrum disease (ASD). Indeed, oscillatory dysregulation is thought to be a pathophysiological mechanism linking E/I imbalance with cognitive difficulties in ASD. In particular, a failure to generate gamma oscillations in early life is associated with language, cognitive, and attention deficits characteristic of ASDs. However, uncovering the basic mechanisms linking E/I imbalance to oscillatory changes is difficult given the structural differences between human brain and animal models of ASD, and the challenges of studying basic mechanisms in patients. Uncovering the downstream effects of E/I imbalance on gene and cell expression may also reveal novel therapeutic targets. We recently developed a novel brain organoid platform ideal for modeling the effect of E/I imbalance on downstream cellular plasticity and oscillatory activity. Specifically, we have generated an organoid system where we can consistently generate gamma oscillations. 

In preliminary studies, we have shown a loss of gamma oscillatory power in organoids generated from patient induced pluripotent stem cells (iPSCs) harboring autism risk genes. In this project we will use a combination of multiphoton calcium indicator imaging, confocal microscopy, and single cell RNA sequencing to identify the cellular etiology of this change.

Hippocampal sharp wave ripples (SWRs) are ~100-200Hz oscillations that are thought to be an interneuron-initiatedactivity that is critical to memory consolidation. Interestingly, we frequently observe SWRs in non-mutant hippocampal organoids suggesting that the cellular inputs necessary to generate these can be created in vitro in an organoid. Recently, we also generated hippocampal organoids from patient iPSCs containing a gain of function mutation in the SCN8A gene. As a result of this mutation, these patients typically have a devastating childhood epilepsy known as developmental epileptic encephalopathy 13 (DEE13). Unlike in the case of non-mutant hippocampus, the DEE13 hippocampus so far appears incapable of generating SWRs. In this project we will use chemogenetic, optogenetic, and pharmacological manipulations together with single cell recording, spike sorting, and immunolabeling approaches to identify the mechanisms of SWR generation in hippocampal organoids.