PTSD results from life-threatening fear. We use mouse as an experimental model to investigate acute and persistent fear responses, imaging brain activity by MEMRI, coupled with behavioral responses and histologic confirmation of activity with c-Fos staining. We imaged neural activity at multiple time points in mouse lacking the serotonin transporter, SERT, and with/without early life stress. This approach represents an unbiased comprehensive method to look at the dynamics of the brain’s response to fear over time, not possible by other imaging methods. We find altered activity and circuits in mice after fear dependent on genotype and environment.