Phineas Gage Information
Psychology
Within weeks of Phineas Gage's accident there were differences of opinion among those who examined him about the extent and location of the damage to his skull and brain. Over time these differences increased. The problems are of two kinds: first, whether the path of the tamping iron can be estimated accurately from the damage to Gage's skull, and, second, whether the damage to his brain can be inferred from that path. Here I discuss first the damage to his skull and then that to his brain.
The skull and the path of the tamping iron
There are three places where Gage's skull is damaged. There is a relatively small area under the zygomatic arch (or cheek bone) where the tamping iron first impacted. The second place is the orbital bone of the base of the skull behind the eye socket. After healing this area is about 1 inch wide by 2 inches in the anterior-posterior direction and must have been larger at the time of injury (upper left of a, below). The total area of bone damage caused by the tamping iron where it emerged is truly enormous. As can be seen in (b), there is an unhealed irregular, roughly triangular shaped area of total bone destruction at the top of the skull. Lying mainly to the left of the midline, it is about 2 inches wide and 4 inches in circumference, and there is another on the lower left side about 2.7 inches in circumference. Between them there is a flap of frontal bone about 2.5 inches long and about x 2 inches wide at the widest point (c). Behind the main area is a second flap of parietal bone about 2 wide and 0.75 to 1.5 inches long. Harlow replaced both flaps; the rear (parietal) reuniting so successfully that it is actually difficult to see from outside the skull. In (c) it has been copied from a photograph of the underside of the skull and ‘pasted' to the outside.
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Differences over the damage to the skull
Harlow and Williams, the two physicians to see Gage on the day of the accident, said nothing specific about the entry under the zygomatic arch or the damage at the base, but Harlow was definite that the tamping iron had emerged at the junction of the coronal and sagittal sutures, and in the midline. Phelps, who examined Gage six weeks later, thought the point was about 0.5 inches in front of the junction and 1 inch to the left of the mid line.
Bigelow apparently drew no conclusions from his examination of Gage late in 1849, about a year later, but when he drilled holes through a demonstration skull to show that the passage was possible, he may have arbitrarily placed the centre of the hole in the base 1 inch from its midline, and that of the exit to the front of the junction and to the right of the midline.
The differences were not resolved when Gage's skull was brought to Massachusetts in 1868. Harlow placed the entrance in the base of the skull 1.25 inches from the median line. He was now rather vague about where it emerged, saying only that it was to the front of the junction and in the midline. Eugene Dupuy used Jackson's 1870 description, and possibly the photographs, from the Catalogue of the Warren Museum to conclude it had emerged frontally and to the left of the midline. After later seeing the skull itself, he seemed to maintain the left sided point of emergence but now moved it to behind the junction. In developing his reply to Dupuy's criticism of his work on localisation, David Ferrier first judged Bigelow's placement of the entry in the base to be too far the left of the midline, and the exit too frontal and too far to the right. In an important later discussion he omitted mentioning an exit point; it was almost as if he had given up trying to determine one.
Cobb prepared a sketch in 1940 on the basis of a visual examination of the skull. He implied that the exit was between the frontal bones and that some right-sided damage had been caused.
The Tylers concluded from their 1982 CT study, the that only a range could be specified
within which the tamping iron could have emerged. As can be seen
on their scan below (d), it included the area of total destruction so that
the small area to the right of the midline marked one extreme limit of
that range.
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Ratiu and his colleagues compared computer-generated three-dimensional reconstructions of a thin-slice computed tomography scan (CAT) of Gage's skull with the actual skull. They paid especial attention to two aspects of the skull that had not been considered by previous workers. First, there was a continuous line of fracture that began from well behind the area of bone loss on the top of the skull and ran down to the lower left side of the jaw (e). Second, they noted that the area of bone loss at the entrance and in the eye-socket was about 50% smaller than the maximum diameter of the tamping iron. Consequently the skull must have hinged open to allow the iron to enter and then have been closed by the soft tissue of the head after it had emerged through the hole in the unhealed area at the top of the skull.
Differences over the damage to the brain
The different views over the passage of the tamping iron naturally led to different views about which parts of Gage's brain were damaged. Put simply, perhaps over simply, the further to the left of the midline of the base and the further to the right of the midline at the top, the more of the right lobe would be involved. Similarly, if the exit point is placed in front of the coronal and sagittal junction, the greater the frontal involvement; if behind it, the frontal damage is less.
Harlow concluded that only the left hemisphere had been
affected and that the right was ‘intact.' Bigelow was equally clear that
there was some right-sided damage. Dupuy accepted that the trajectory
was left sided but placed it less frontally, claiming that the more posterior
motor and language areas should have been destroyed. That Gage had
no motor impairment or aphasia was prime evidence for Dupuy's anti-localisation
arguments. In rebuttal, Ferrier showed fairly conclusively that the
passage was not as posterior and that both areas had been spared.
He also concluded that the only damage was to the left hemisphere, a conclusion
that seems not to have been disputed for about 70 years.
Cobb's diagram, the first of the ‘modern' reconstructions, showed damage rather like that supposed
by Bigelow: both hemispheres were involved with more damage on the
left than on the right. That conclusion, although less detailed,
is broadly congruent with that of the Tylers. When Hanna Damasio
and her colleagues simulated the passage of the iron along their five selected
trajectories through a three dimensional model of Gage's brain, they found
the damage to be even more frontal and right sided. Ratiu and his colleagues concluded that the damage was limited to the left frontal lobe, did not extend to the right side, and did not affect the ventricular system or vital blood vessels inside the skull -- conclusions that seem to provide the most likely reconstruction of the damage.
What to make of the differences?
The disagreements have a number of different bases, not
the least of which is what David Ferrier called "the inexactitude and distortion
... by men who have some pet theory to support." But, even were there no bias and it was
possible to determine the path of the tamping iron exactly, there was more damage
than that caused by its movement through Gage's brain. Haemorrhaging
and damage from it was massive, the iron pushed fragments of bone through
the brain that were not recovered (Gage was still vomiting some of them
several days after the accident), and a massive abscess took further toll.
Further, almost all the above methods, especially that used by Hanna Damasio
and her colleagues, make the unlikely assumption that Gage's brain and
its position within the skull can be estimated from the skull itself, and
that its functions were localised in an average way.
Suppose all these problems were overcome we would still
not be able to learn much more from Gage's case that that the massive injury
to his brain caused a massive change in his behaviour. Some 150 years
after the accident we know almost no more about Phineas' pre- and post-accident
behaviour than Harlow told us in 1868 and that is too little from which
to infer any detail about the relation between brain and behaviour.
Phineas Gage's case is important for what it pointed to, rather than what
we can learn in any detail from it about the relation between brain and behaviour.
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