Based on recent findings showing rapid neocortical memory formation when relying on existing schema, this study investigated whether learning entirely novel concepts can also rapidly engender a neocortical engram. Two groups of 40 participants encoded the same abstract visual stimuli during functional MRI by either categorizing them based on similar features (concept learners) or forming detailed item-context associations (detail learners). At baseline, 1h & 24h after encoding, diffusion-weighted imaging data was acquired to assess learning-related microstructural plasticity. 24h after encoding, memory performance was assessed in a categorization and an item-context recognition task. While concept learners performed better in categorizing novel stimuli (t78=6.91; p<0.001), detail learners preferentially remembered item-context combinations (t78=-6.31; p<0.001). While acquiring category knowledge during learning, the concept group showed increasing functional activity in early visual cortex (increase x concept>detail, tpeak=7.38, pFWE<0.05), indicating rapid concept learning-specific and experience-dependent changes in this early sensory area. Concept-related functional changes during encoding were relevant for 24h category retrieval (r=.39, p=0.01; between groups z=1.68, p=.046) and re-occurred 24h later when encountering the same visual stimuli (r=.42, p=0.008), indicating stability of the functional changes. Novel concept formation further induced learning-related microstructural plasticity after 24h in early visual cortex, indicated by a decrease in mean diffusivity (concept>detail × 24h>baseline, p<.001). In conclusion, we could show that, even without prior knowledge, the neocortex can acquire new memories rapidly. Remarkably, group-specific functional and microstructural changes occurred in early visual cortex, indicating that novel concept formation can induce changes much earlier in the visual-processing hierarchy than previously assumed.