50 Israeli Defense Forces (IDF) infantry soldiers, all male, aged 18 years, with Hebrew as the dominant language and no condition excluding an MRI scan.

50 Reserve Officer Training Corps (ROTC) undergraduate students at Tel-Aviv University, all male, aged 18-19, with Hebrew as the dominant language and no condition excluding an MRI scan.

Soldiers will be exposed to combat as part of their routine military service. The ROTC students will not be exposed to combat.

PCL is questionnaire assessing posttraumatic stress disorder symptoms. It contains 20 items on a severity scale of 0-4, measuring the existence and severity of post-traumatic symptoms. The minimal score, indicating no post-traumatic stress, is 0. The maximal score is 80, indicating extremely severe post-traumatic stress.

Gray matter volume, i.e. the density of brain cells in a particular region (outcome to be measured in cm3), to be derived from the MRI scans, and compared between the two groups across the various time points.

Functional connectivity, indicating the level of synchronous activity of certain brain regions during rest (temporal correlation is usually expressed as a Pearson's r); Also to be derived from the MRI scans, and compared between the two groups across the various time points.

Structural connectivity between regions of the brain (Diffusivity is measured as 10-3mm2.s-1) and the properties of the white matter (expressed with Diffusion tensor imaging (DTI) measures, mainly Fractional Anisotropy (FA) and Mean Diffusivity (MD)); Also be derived from the MRI scans, and compared between the two groups across the various time points.

Task activations, and specifically the areas activated during the dot-probe task, and how they change over time (expressed as the level of the BOLD signal strength change during the task). To be derived from the MRI scans, and compared between the two groups across the various time points.