Key study: Damasio et al. (1994) the return of Phineas Gage

In 1848, Phineas Gage was a railway construction foreman in Vermont, USA. An explosion drove a tamping iron (an iron rod over a metre long) up through his left cheek and out of the top of his skull.
He survived, but his doctor, John Harlow, reported a personality change: he became impulsive, rude and unable to stick to plans. Friends said he was 'no longer Gage'.
Gage died in 1860. His skull and the tamping iron were kept in a museum at Harvard.

Aim: to identify which brain areas were damaged in Gage's injury, using modern neuroimaging techniques, and so explain his changed behaviour.
Procedure: the researchers photographed and took precise measurements of Gage's skull. They used computer modelling to build a 3D reconstruction of a skull matching Gage's, and tested possible trajectories of the rod, keeping only paths consistent with the entry and exit wounds and with him surviving.
Results: the damage was in the frontal lobes, affecting the ventromedial region of the prefrontal cortex in both hemispheres, while the dorsolateral region was spared. Areas for movement and language were spared.
Conclusion: damage to the ventromedial prefrontal cortex explains Gage's problems with rational decision-making and processing emotion. Modern patients with damage to the same area show similar problems.

Strengths: used objective, scientific technology (computer modelling and imaging) rather than guesswork; shows how psychology has changed over time. The findings match other patients with similar damage.
Weaknesses: based on a skull, not the brain itself, so the damage is an estimate. It is one case, so it is hard to generalise. Reports of Gage's personality change were second-hand and may have been exaggerated, and little is known about his personality before the accident.