Measuring Before Claiming: Electrode Mapping, Spontaneous Burst Dynamics, and Plasticity Testing on Two Commercial Human Brain Organoid Cultures

Commercial cloud platforms now provide remote access to living human brain organoid cultures, opening experimental neuroscience to researchers without laboratory affiliation. What such platforms do not provide is a characterization of the specific tissue a given user receives. This report documents a 12-day measurement campaign on two human neurosphere cultures accessed through the FinalSpark Neuroplatform, in which tissue characterization was treated as the primary object of study, ahead of any experimental protocol. Four properties were established. First, functional electrode coverage was sparse and culture-specific: of 32 available electrodes, 7 carried measurable activity in the first culture and 10 in the second, with partial but incomplete overlap between them. Second, both cultures produced spontaneous synchronized bursts with no stimulation applied; in the second culture, 39,031 consecutive readings across 5.5 hours yielded 404 discrete events at matched sampling rate, approximately twice the rate measured in the first culture under identical protocol. Third, event magnitudes were incompatible with a power-law distribution across five independent detection thresholds, tested against both exponential and lognormal alternatives, indicating that this tissue did not operate in the near-critical regime described for cortical preparations. Fourth, event timing was strongly clustered rather than Poisson-distributed, with a coefficient of variation between 2.35 and 2.67 depending on sampling resolution. Spike-timing-dependent plasticity was tested using an isolated single-pair protocol with millisecond-scale pairing intervals. Small-sample measurements produced a directionally symmetric effect consistent with the classical STDP curve. When the same protocol was repeated with larger samples and a drift-corrected measurement ratio, the effect did not reach statistical significance in either culture across three electrode pairs. The measurement pipeline developed to reach that conclusion (burst detection and rejection, ratio-based drift correction, and sampling-rate matching between cultures) is reported in full, along with two analysis errors identified and corrected during the work. All raw data, analysis code, and an independent verification script are released openly.