The low-frequency resonome of the human brain, understood as the structured hierarchy of infra-slow, delta, and theta electromagnetic field organization across approximately 0.1–8 Hz, is central to large-scale neural coordination, state transitions, sleep-wake dynamics, predictive regulation, and conscious access. Existing theories explain many aspects of these phenomena through neuronal synchronization, structural connectivity, neural-field dynamics, and recurrent cortical loops. Yet the brain also appears to require slow, spatially extended control variables integrating activity across seconds, centimeters, metabolic regimes, and neuromodulatory states, while measurable fields are generated primarily by neuronal currents. This article proposes that astrocytic syncytia provide this substrate. I introduce glial syncytial control fields: effective mesoscale fields arising from astrocytic syncytial organization, gap-junction coupling, calcium/IP3 signaling, extracellular ionic regulation, metabolic support, and neuromodulator-sensitive astrocyte-neuron interactions. These fields are not proposed as dominant direct generators of EEG or MEG signals. Rather, they constrain the neuronal resonome by modulating excitability, gain, damping, local time constants, synaptic plasticity thresholds, and coherence persistence. The central claim is not that astrocytes replace neurons, but that neuronal field-organization is partly shaped by a slower glial control geometry. A compact mathematical formulation is developed. A glial control field ug(x, t) obeys an effective damped-field ansatz driven by neuronal forcing and physiological fluctuations. Its low spatial modes define persistent control components that can bias neuronal low-frequency field variables ψLF(x, t). A state-control formulation relates glial parameters to neuromodulatory variables, allowing the same anatomy to support different resonome geometries across arousal, sleep, attention, pathology, and development. The framework is related to neural-field and connectome models, predictive processing, active inference, electromagnetic and resonance theories of consciousness, and global workspace approaches. The hypothesis generates falsifiable predictions. Astrocyte-specific perturbations should alter slow cortical synchronization and traveling-wave persistence; gap-junction disruption should fragment long-range coherence; astrocyte-related disorders should change damping and low-dimensional geometry; and source-space phase analyses should reveal smoother, more persistent low-mode organization than phase-randomized or neuron-only null models predict. The low-frequency resonome should therefore be understood as a coupled glio-neural architecture: neurons generate primary measurable activity, while astrocytic syncytia may regulate the slow landscape within which large-scale resonance becomes stable, metastable, or pathological.