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Hassler and colleagues published a similar study, with certain methodological differences, in 19692,3. Their aim was similar, namely the alerting of consciousness by activation of anatomically undamaged neurons in the unspecific thalamocortical system. McLardy et al.4 were also motivated by the same concept, but gave little detail of methodology and failed to produce a result. Several reports followed, but that by Schiff et al., though it concerns only a single case, is the most detailed and is strengthened by its internal statistical control.

Hassler’s subject2 is described as having a post-traumatic apallic state. This term derives from the original description by Kretschmer5 of a state of waking either without awareness (as seen in the vegetative state), or with minimal awareness (as in the minimally conscious state). Hassler stimulated pallidum on the basis that it feeds into the unspecific system as well as the specific system. This view was supported at the time by the elicitation of recruiting responses (incremental high-voltage synchronizing waves, usually, though not always, of long latency, carried over the unspecific thalamocortical system6) by stimulation of pallidum7. The dipole for such laminar field potentials is in the superficial layers of the cortex8. This is perhaps concordant with the later demonstration of the ubiquitously distributed matrix of calbindin-immunoreactive neurons, which project to the superficial layers of wide areas of cortex9,10. Hassler also chose the basal portion of, using his terminology, the latero–polar nucleus of the thalamus on the opposite side.

As a neurologist, a neuroanatomist who wrote the anatomy of the thalamus for the Schaltenbrand stereotactic atlas, and someone with a wide experience of stereotaxy, Hassler was well placed to make the foregoing contribution.