From Phineas Gage to H.M.: Revisiting Disconnection Syndromes
Speaker: Dr. Michel Thiebaut de Schotten, Brain and Spine Institute, Hôpital de la Salpêtrière, Paris
Tuesday 14th of April, 12:30-2pm
Seminar Room 5, main IoPPN
Click here to read the paper associated with this talk.
Fifty years have passed since Norman Geschwind published in Brain a seminal contribution to clinical neurology: “Disconnexion syndromes in animals and man.” In what would become the manifesto of behavioural neurology, Geschwind revitalised the network approach to disorders of the brain and his ideas have been long lasting. At the time of publication, however, neurologists were impeded by the limited tools available to apply the disconnection paradigm to their patients. As a consequence, neurology continued along a path chiefly dictated by case reports of patients with focal lesions where cortical and subcortical localisation was favoured to disconnection.
On the 50th anniversary of Geschwind’s seminal contribution we pay tribute to his ideas by applying contemporary tractography methods to understand the disconnections in three classical cases that made history in behavioural neurology. We first documented the locus and extent of the brain lesion from the skull CT scan of Phineas Gage and from the MRIs of Louis Victor Leborgne’s brain, Broca’s first patient, and Henry Gustave Molaison. We then applied the reconstructed lesions to an atlas of white matter connections obtained from diffusion tractography of 128 healthy adults. Our results showed that in all three patients, disruption extended to connections projecting to areas distant from the lesion. We confirmed that the damaged tracts link areas that in contemporary neuroscience are considered functionally engaged for tasks related to emotion and decision-making (Gage), language production (Leborgne) and declarative memory (Molaison). While these cases remain pivotal to our understanding of brain function, the localisation of the lesions and associated dysfunctions were heavily biased by a narrow localisationist interpretation. Our findings suggest that even historical cases should be reappraised within a disconnection framework whose principles were plainly established by Geschwind.