Many brain disorders are hereditary diseases with a known genetic
cause, which allowed scientists to generate animal models to study disease progression, understand disease mechanisms, and perform therapeutic
intervention studies [1, 2]. However, (1) mice are different from humans, and it is difficult to translate results
from animal experiments into clinical application; (2) the genetic
cause of many diseases is not yet known; (3) many disease-causing genes are mainly expressed in the cells that are affected; (4) for many of them, there are no (humanized-)mouse
models available; (5) there is governmental and public pressure to advance the development of alternative model systems to replace animal studies. This emphasizes the need for patient-derived disease models that bridge the translational gap between animal models and human clinical trials. Progress in stem cell biology has made it possible to generate human induced pluripotent stem cells (hiPSCs)  that can be differentiated into the important cell types of the brain, neurons, and astrocytes [4, 5]. The disadvantage of these 2D models is that they are descriptive at a cellular level, but they fail to adequately provide the details that could be derived from a more complex, three-dimensional structure, where the cells are spatially organized . In 2013, Lancaster and colleagues developed a hiPSC-derived three-dimensional organoid
culture system, termed cerebral organoids, that develop various discrete, although interdependent, brain regions . These organoids recapitulate many features of human cortical development, including a progenitor zone organization with abundant outer radial glial stem cells .
Here we describe the generation of cerebral organoids using a modified version of the Lancaster protocol [7, 9]. In short, feeder-free cultured hiPSCs were dissociated and replated in neural induction medium in a non-adherent cell culture plate, and differentiated for 100 days (Fig. 1). Cryosections of these organoids can be used for immunofluorescence studies. Organoids can be used for many different purposes including disease modeling, studying disease mechanisms, or analyzing therapeutic
interventions (using for example antisense oligonucleotides) at any given time point.